Дисертації з теми "X-ray pulsars"
Щоб переглянути інші типи публікацій з цієї теми, перейдіть за посиланням: X-ray pulsars.
Оформте джерело за APA, MLA, Chicago, Harvard та іншими стилями
Ознайомтеся з топ-50 дисертацій для дослідження на тему "X-ray pulsars".
Біля кожної праці в переліку літератури доступна кнопка «Додати до бібліографії». Скористайтеся нею – і ми автоматично оформимо бібліографічне посилання на обрану працю в потрібному вам стилі цитування: APA, MLA, «Гарвард», «Чикаго», «Ванкувер» тощо.
Також ви можете завантажити повний текст наукової публікації у форматі «.pdf» та прочитати онлайн анотацію до роботи, якщо відповідні параметри наявні в метаданих.
Переглядайте дисертації для різних дисциплін та оформлюйте правильно вашу бібліографію.
1
Gavriil, Fotis Panagiotis. "Magnetar-like x-ray bursts from anomalous x-ray pulsars." Thesis, McGill University, 2006. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=100371.
Повний текст джерелаАнотація:
The leading model for understanding the energetics of anomalous X-ray pulsars (AXPs) is that they are "magnetars"---young, isolated neutron stars powered by the decay of their enormous magnetic fields. The identification of AXPs as magnetars is motivated by the similarity of AXPs to another enigmatic class of sources, the Soft Gamma Repeaters (SGRs). We report on long-term monitoring of AXPs using the Rossi X-ray Timing Explorer (RXTE). We monitor AXPs with RXTE to study their rotational stability, to search for variations in their pulsed flux and pulsed morphology. During our regular monitoring observations we discovered multiple bursts from two AXPs: this was the first time such behavior has been observed from these sources. Prior to our monitoring campaign, the detection of bursts solely from SGRs was the principle difference between AXPs and SGRs. The first detection of AXP bursts came in Fall 2001 when we discovered two SCR-like X-ray bursts from the direction of AXP 1E 1048.1--5937. Due to RXTE's large (1° x 1°) field-of-view we could not unambiguously identify the AXP as the burster. Recently, we detected a third burst from the direction of this source as well as a simultaneous increase in the pulsar's pulsed emission---this clearly identified the AXP as the burster. The most outstanding demonstration of AXP bursting behavior came on 2002 June 18 when AXP 1E 2259+586 underwent a major outburst involving 80 bursts and several changes in the persistent and pulsed emission, including a huge pulsed flux enhancement, a pulse morphology change and a rotational glitch. We also find variations in the persistent emission of AXPs in the absence of an obvious outburst. For example, we discovered two pulsed flux flares from AXP 1E 1048.1--5937. Both flares lasted several months and had well resolved few-week-long rises. The long rise tunes of the flares is a phenomenon not previously reported for this class of object, but has a clear explanation within the context of the magnetar model. All these results imply a close relationship between AXPs and SGRs, which we now believe are both magnetars, and have posed significant challenges to competing models.
2
Tang, Pui-shan Anisia, and 鄧佩姗. "Thermal X-ray pulses resulting from pulsar glitches." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1999. http://hub.hku.hk/bib/B29790992.
Повний текст джерела
3
Tang, Pui-shan Anisia. "Thermal X-ray pulses resulting from pulsar glitches /." Hong Kong : University of Hong Kong, 1999. http://sunzi.lib.hku.hk/hkuto/record.jsp?B2089675X.
Повний текст джерела
4
Inam, Sitki Cagdas. "X-ray Observations Of Accretion Powered Pulsars." Phd thesis, METU, 2004. http://etd.lib.metu.edu.tr/upload/12605552/index.pdf.
Повний текст джерелаАнотація:
In this thesis, X-ray observations of four accretion powered
pulsars are presented. Using RXTE
observations of 4U 1907+09, we found three new pulse periods of the source. We
found that the source spun-down almost at a constant rate of
$dot nu$ = (-3.54 $pm 0.02) times 10^{-14}$ Hz s$^{-1}$ for more than
15 years. Using RXTE
observations, X-ray flux
related spectral and timing features in 2S 1417-62 were, in general,
interpreted as a sign of a disc accretion with
a similar geometry with a varying mass accretion rate,
whereas spectral and timing features of the low X-ray flux regions were
interpreted as a sign of possible temporary accretion geometry change prior
to the next periastron. Using XMM-Newton and RXTE observations of SAX
J2103.5+4545, we discovered quasi periodic oscillations around 0.044 Hz
(22.7 sec) while the source was spinning-up with a rate of
$(7.4pm0.9)times10^{-13}$Hz s$^{-1}$. In the X-ray
spectrum, we also found a soft component consistent with a
blackbody emission with ${rm{kT}}sim1.9$keV. Using RXTE observations, we also
studied spectral evolution of Her X-1
5
吳國偉 and Kwok-wai Eddie Ng. "Neutrino production from accreting X-ray pulsars." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1993. http://hub.hku.hk/bib/B31211811.
Повний текст джерела
6
Ng, Kwok-wai Eddie. "Neutrino production from accreting X-ray pulsars /." [Hong Kong : University of Hong Kong], 1993. http://sunzi.lib.hku.hk/hkuto/record.jsp?B13745013.
Повний текст джерела
7
Icdem, Burcin. "Viscous Time Scale In Accreting Powered Pulsars And Anomalous X-ray Pulsars." Master's thesis, METU, 2011. http://etd.lib.metu.edu.tr/upload/12613373/index.pdf.
Повний текст джерелаАнотація:
In this thesis we analyse X-ray data of accretion powered low mass and high mass X-ray binaries to understand the nature of their accretion mechanisms by searching for some clues of viscous time-scales of their accretion discs, if they have, in their low frequency power density spectra created from their long-term X-ray observations, or by doing pulse timing analysis with much shorter X-ray data to detect the effects of torque fluctuations caused by the accreting material on the pulsar.
The low mass and high mass X-ray binaries we analysed have breaks in their power density spectra, which are attributed to the role of viscosity in the formation of accretion discs. Although, the time-scales corresponding to these break frequencies are smaller than the predictions of the Standard theory of accretion discs, the sources give consistent results among themselves by displaying the expected correlation between their break and orbital frequencies. The correlation curve of LMXBs implies thicker appearing accretion discs than those assumed by the theory. The dichotomy
of the HMXBs on this curve points out the different origins of accretion that these sources may have, and offers a way to distinguish the stellar-wind fed systems from the Roche-lobe overflow systems.
The timing and spectral analysis of Swift J1626.6-5156 reveal a correlation between the spin-up rate and the luminosity of the source implying that the pulsar is accretion-powered. This correlation together with the characteristics of the X-ray spectra enables us to estimate the magnetic field and the distance of the source.
The AXP 1E 2259+586 does not display any signs of viscous time-scale in its low frequency power density spectra, and its pulse timing analysis gives a much smaller torque noise value than that expected from accretion powered pulsars. In addition, the analysis results presented in this thesis reveal magnetar-like glitches which differ than those of radio pulsars, due to the presence of the strong magnetic field of the pulsar. These results eliminate the possibility that the AXP is an accretion-powered pulsar.
8
Dib, Rim. "RXTE monitoring of 5 anomalous x-ray pulsars." Thesis, McGill University, 2009. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=66730.
Повний текст джерелаАнотація:
Anomalous X-ray Pulsars (AXPs) are a group of neutron stars that share several common properties. They are dubbed "anomalous'' because their observed luminosity exceeds the rate of loss of their rotational kinetic energy. According to the magnetar model, they are young, isolated neutron stars, powered by a large magnetic energy reservoir. Five of these AXPs (1E 2259+586, 4U 0142+61, RXS J170849.0-400910, 1E 1841-045, 1E 1048.1-5937) have been monitored with the Rossi X-ray Timing Explorer (RXTE) since 1997 (1998 for two of the sources). The goal of the monitoring program is to study the timing behaviour of these sources including glitches, and the radiative variability in the soft X-ray band including pulsed flux changes, pulse profile changes, and bursts. The program provides a detailed description of the evolving properties of these objects, which can then be used to test AXP models, such as the magnetar model. In this thesis, I present some of my co-authored contributions to the AXP monitoring program. I first present a long-term (1998-2006) study of AXP 4U 0142+61 in which we show that from 2000 to 2006 the pulse profile of the pulsar slowly evolved, and the pulsed flux increased by 29+/-8%.
AXP 4U 0142+61 then entered an active phase in 2006 March that lasted several months and included several X-ray bursts. I present a study of the behaviour of AXP 4U 0142+61 during this active phase.
I then present a long-term (1998-2007) study of AXPs RXS J170849.0-400910 and 1E 1841-045 in which we report on four new glitches. We show that AXPs are very active glitchers and that some AXP glitch properties are challenging to interpret in standard glitch models. Furthermore, we note that AXP glitches appear to fall in two classes: radiatively loud and radiatively quiet.
Finally, I present a long-term (1997-2008) study of AXP 1E 1048.1-5937 in which we show that three timing events occurred cont
Les pulsars X anormaux (AXPs) sont des étoiles à neutrons qui partagent certaines propriétés spécifiques. Ils sont dits "anormaux'" car leur luminosité est supérieure au taux de perte de leur énergie de rotation. Selon le modèle des "magnétars'', ces pulsars sont des étoiles à neutrons jeunes, isolées, et dont la luminosité provient d'un grand réservoir d'énergie magnétique. Cinq de ces AXPs (1E 2259+586, 4U 0142+61, RXS J170849.0-400910, 1E 1841-045, 1E 1048.1-5937) sont sous observation depuis 1997 dans le cadre d'un programme de surveillance utilisant le Rossi X-ray Timing Explorer (RXTE). Le but de ce programme est d'étudier les propriétés temporelles de ces pulsars tels les changements soudains de fréquence, et d'étudier leurs propriétés radiatives tels les changements de flux pulsé, les changements de profil de pulse, et les sursauts d'énergie. Ce programme de surveillance aide à obtenir une description détaillée des propriétés de ces objets, qui servira à tester les modèles théoriques des AXPs, dont le modèle des "magnétars''. Dans cette thèse, je présente quelques-unes de mes contributions au programme de surveillance.
D'abord, je présente une étude à long terme (1998-2006) du AXP 4U 0142+61 où nous montrons qu'entre 2000 et 2006, le profil de pulse du pulsar a lentement évolué, et que le flux pulsé a augmenté de 29+/-8%.
Le AXP 4U 0142+61 est ensuite entré dans une phase active en mars 2006, dans laquelle il a émis plusieurs sursauts d'énergie. Je présente une étude du comportement du AXP 4U 0142+61 pendant cette phase active.
Ensuite, je présente une étude à long terme (1998-2007) des AXPs RXS J170849.0-400910 et 1E 1841-045. Dans cette étude, nous avons détecté quatre nouveaux changements soudains de fréquence. Nous montrons que dans le contexte de changements soudains de fréquence, les AXPs sont très actifs. Nous montrons auss
9
Camero, Arranz Ascension. "Accreting X-Ray pulsars. The high energy picture." Doctoral thesis, Universitat de València, 2007. http://hdl.handle.net/10803/9484.
Повний текст джерелаАнотація:
El objetivo principal de esta tesis ha sido el estudio del comportamiento transitorio durante estallidos de distinto tipo, de una selección de pulsares acretores en rayos X, localizados en el plano galáctico.Con ello se pretende haber avanzado hacia una explicación más clara de la naturaleza de estas objetos binarios de alta masa (con estrella de neutrones como objeto compacto), así como de los mecanismos físicos que operan en este escenario. Para todo esto se han analizado datos de dos misiones espaciales:INTEGRA Y RXTE.El segundo objetivo ha sido el estudio de la zona del brazo galactico de Scutum. Al ser esta una región de fuerte absorción se cree de la existencia de sistemas del tipo anteriormente mencionado este todavía escondidos, y los cuales solo pueden ser descubiertos a altas energías. En esta tesis se han podido presentar resultados esperanzadores, con la detección de varios objetos posibles nuevos candidatos a pulsares acretores de rayos X.
10
Gavriil, Fotis P. "Long-term monitoring of anomalous X-ray pulsars with the rossi x-ray timing explorer." Thesis, McGill University, 2001. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=33763.
Повний текст джерелаАнотація:
We report on the long-term monitoring of five anomalous X-ray Pulsars (AXPs) using the Rossi X-ray Timing Explorer (RXTE ). We present a phase-coherent timing ephemeris for 4U 0142+61, and show that it has rotated with high stability over 4.4 yr, with RMS phase deviation of 7% of the pulse period from a simple fit including only n and n&d2; . We show that 1E 1048.1-5937 shows significant deviations from simple spin-down such that phase-coherent timing has not been possible over time spans longer than a few months. We find that the deviations from simple spin down are not consistent with single "glitch" type events, nor are they consistent with radiative precession. We suggest that 1E 1048.1-5937 may be a transition object between the soft gamma-ray repeater and AXP populations, and the AXP most likely to one day undergo an outburst. We also report on the continued timing stability of 1E 2259.1+586, for which phase coherence has now been maintained over 4.5 yr, as well as on the detection of a significant n&d3; in RXS J170849.0-400910, consistent with recovery following a glitch. We note a possible correlation in which timing stability decreases with increasing n&d2; . We find no large variability in pulse morphology as a function of time. We present high signal-to-noise ratio average pulse profiles for each AXP, and consider them as a function of energy. We find a variety of different behaviors, and consider possible trends in the data. We also find no large variations in pulsed flux, and set la upper limits of ∼20--30% of the mean.
11
Mannings, Vincent. "TeV gamma-ray emission from accreting binary pulsars." Thesis, Durham University, 1990. http://etheses.dur.ac.uk/6297/.
Повний текст джерелаАнотація:
The high-mass X-ray binary SMC X-1 has been observed during the interval 1986-1989 at a threshold γ-ray energy of 0.4 TeV using the University of Durham Mark III air Cerenkov telescope at Narrabri. The Cerenkov arrival time series recorded during these observations have been tested for periodicity at the contemporary pulse period of the SMC X-1 X-ray pulsar. This period analysis was performed using a new technique - introduced in the present work - which is designed for TeV γ-ray source candidates in binary systems and which simultaneously seeks evidence for pulsed TeV γ-ray emission and information on the location of the emission site within the binary. Results are also presented from the period analysis of data accumulated at Narrabri during observations of the low-mass X-ray binaries X0021.8-7221 (in the globular cluster 47 Tucanae) and GX 1+4. X-ray binaries as a class of TeV γ-ray source are considered and their properties compared. Previous models which invoke the interaction of beams of high-energy particles with material within the environment of a binary system are discussed. One of these models is adapted in the present work in order to propose a simple explanation of the narrow TeV 7-ray orbital light curve observed for the high-mass binary Centaurus X-3. The new model accounts for the γ-ray emission from Cen X-3 in terms of the collisions of ultrarelativistic protons with an accretion wake trailing the X-ray pulsar. This model, which incorporates the steering of charged particles in the magnetosphere of the massive primary star, is also applied to the Vela X-1 binary in order to investigate claims that TeV γ-ray outbursts observed during X-ray eclipse arise at particle collisions with the limb of the supergiant companion.
12
Chadwick, Mary Paula. "Very high energy cosmic gamma rays from radio and X-ray pulsars." Thesis, Durham University, 1987. http://etheses.dur.ac.uk/6720/.
Повний текст джерелаАнотація:
This thesis is concerned with the detection of very high energy cosmic gamma-rays from isolated pulsars and X-ray binary sources using the atmospheric Cerenkov technique. A general introduction to gamma ray detection techniques is followed by adscription of the properties of atmospheric Cerenkov radiation and a discussion of the principles of the atmospheric Cerenkov technique. The Mark I and Mark II gamma-ray telescopes operated in Dugway, Utah by the University of Durham between 1981 and 1984 are briefly described. There follows a discussion of the results from observations at many different wavelengths of Cygnus X-3. This object was observed by the Durham group between 1981 and 1983 in Dugway Utah and also in Durham during autumn 1985. The detection in the Dugway data of the 4.8 hr X-ray period and the possible detection of a19.2 day intensity variation are considered. The discovery of a 12.59 ms pulsar in data taken on Cygnus X-3 in 1983 is described. Evidence is presented which suggests this periodicity is also present at a weaker level in earlier data and also in the data taken in Durham in 1985.Results from observations of PSR1937+21 , PSR1953+29and six radio pulsars , are presented. The design and construction of the Mark III telescope, now operating in Narrabri , N.S.W. , is described in detail. Preliminary results from observations with the Mark III telescope of three objects, LMC X-4, the Vela pulsar and CentaurusX-3, are presented, with particular reference to periodicities inherent in the sources. An observation of the supernova in the Large Magellanic Cloud is discussed. A brief discussion of the mechanisms by which V.H.E. gamma-rays may be produced in isolated pulsars and X-ray binary pulsars is given, followed by a description of the future prospects for the Mark III and Mark IV telescopes.
13
高樹豐 and Shu-fung Ko. "Emission morphologies and phase-resolved spectrum of gamma ray pulsar." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2001. http://hub.hku.hk/bib/B31224489.
Повний текст джерела
14
Ko, Shu-fung. "Emission morphologies and phase-resolved spectrum of gamma ray pulsar /." Hong Kong : University of Hong Kong, 2001. http://sunzi.lib.hku.hk:8888/cgi-bin/hkuto%5Ftoc%5Fpdf?B23476370.
Повний текст джерела
15
RIGOSELLI, MICHELA. "X-ray emission from the magnetic polar caps of old rotation-powered pulsars." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2020. http://hdl.handle.net/10281/277373.
Повний текст джерелаАнотація:
Le stelle di neutroni sono il risultato dell'evoluzione di stelle massive dopo l'esplosione di supernova. Il progetto di questa Tesi di PhD consiste nello studio dell'emissione di raggi X da parte di stelle di neutroni isolate di età superiore a 100000 anni. Sono stati analizzati dati provenienti dal satellite XMM-Newton (ESA). Per estrarre la miglior informazione possibile dai dati, ho implementato un metodo di maximum likelihood (ML) e l'ho utilizzato per estrarre spettri e profili pulsati di pulsar vecchie in banda X, che poi sono stati analizzati con raffinati di emissione.
La Tesi è strutturata come segue: nei primi tre capitoli illustro le proprietà principali delle stelle di neutroni, con particolare attenzione ai processi termici e non termici che producono raggi X. I raggi X non termici sono prodotti da particelle relativistiche accelerate da campi elettromagnetici; una frazione di queste particelle viene accelerata verso la superficie della stella, e riscalda le zone delle calotte polari magnetiche. La componente termica, che può essere prodotta dall'intera superficie o da una parte, viene solitamente descritta come un corpo nero; tuttavia, la presenza di intensi campi magnetici superficiali influenza le proprietà della materia, e la radiazione emessa è ampiamente anisotropa.
Nel Capitolo 4 descrivo come ho generato spettri e profili pulsati sintetici, utilizzando modelli di emissione che considerano calotte polari ricoperte di un'atmosfera di idrogeno magnetizzata. Mi sono basata su un software esistente che, dato un certo set di parametri relativi alle proprietà fisiche della stella, stima l'intensità della radiazione prodotta. Successivamente, esso somma i contributi degli elementi di superficie che sono visibili all'osservatore alle differenti fasi di rotazione. Quindi, nel Capitolo 5 descrivo come ho implementato un software di analisi che si basa sul metodo di ML. Dato un certo modello, esso stima i parametri più probabili che ricostruiscono i dati osservati, nella fattispecie il numero di conteggi relativo alla sorgente e al background. Ho validato il metodo e dimostrato che esso è particolarmente efficace per sorgenti deboli, quali sono la maggior parte delle pulsar vecchie.
Successivamente, ho applicato i metodi finora descritti ad alcune pulsar vecchie. Nel Capitolo 6 riporto l'analisi di PSR J0726-2612, una pulsar radio che ha alcune delle caratteristiche delle XDINSs: un periodo di rotazione lungo, un intenso campo magnetico, ed emissione X termica. Grazie ad un'analisi congiunta dello spettro e del profilo pulsato, ho mostrato che la presenza di impulsi radio in PSR J0726-2612, così come la loro assenza nelle XDINSs, potrebbe essere dovuta ad un'orientazione differente rispetto all'osservatore. Nel Capitolo 7 presento il caso di PSR B0943+10, una pulsar con emissione X sia termica sia non termica ma che, nonostante sia un rotatore allineato, ha una grande frazione pulsata. Sono riuscita a riappacificare i due diversi aspetti grazie ad un'attenta analisi di ML e all'intrinseca anisotropia dell'emissione termica prodotta da un'atmosfera magnetizzata. Nel Capitolo 8 ho invece applicato il metodo di ML su sette pulsar poco brillanti, delle quali quattro avevano diverse analisi già pubblicate in letteratura, ma con risultati discordanti, mentre le altre tre non erano ancora state rivelate in banda X. Ho trovato tracce evidenti di emissione termica solo in due oggetti, più un accenno nello spettro pulsato di un terzo oggetto.
Infine, ho considerato tutte le pulsar vecchie che emettono raggi X termici e ho confrontato le misure di temperatura, raggio e luminosità alle aspettative dei modelli teorici. In particolare, ho scoperto che le aree di emissione sono generalmente in accordo con quelle previste dal modello di dipolo magnetico rotante, purché vengano considerati anche effetti di proiezione geometrica e modelli di emissione realistici, quali appunto i modelli di atmosfera magnetizzata.Neutron stars are the remnants of massive stars whose cores collapse during the supernova explosions. The project of this PhD Thesis consisted in the study of the X-ray emission from isolated neutron stars older than about 100000 years. The work was based mainly on data obtained with the XMM-Newton satellite (ESA). To extract the best possible information from the data, I implemented a maximum likelihood (ML) technique and used it to derive the X-ray spectra and pulse profiles of several old pulsars, that were then studied with state-of-the-art models of X-ray emission. The Thesis is structured as follows: in the first three chapters I outline the main properties of neutron stars, with a major focus on the thermal and nonthermal processes that produce X-rays. The nonthermal X-rays are produced by relativistic particles accelerated by rotation-induced electric fields and moving along the magnetic field lines. A fraction of these particles is accelerated backward and returns on the stellar surface, heating the magnetic polar caps. The thermal component, that can be produced by the whole stellar surface or by small hot spots, can be described, in a first approximation, by a blackbody. However, the presence of intense surface magnetic fields strongly affects the properties of matter, and the emergent radiation is widely anisotropic. In Chapter 4, I describe how I generated synthetic spectra and pulse profiles using thermal emission models that consider polar caps covered by a magnetized hydrogen atmosphere or with a condensed iron surface. I relied on an existing software that, given a set of stellar parameters, evaluates the emerging intensity of the radiation. A second software, which I adapted on the sources I analyzed in the Thesis, collects the contribution of surface elements which are in view at different rotation phases from a stationary observer. Then, in Chapter 5, I describe how I implemented an analysis software that relies on the ML method. It estimates the most probable number of source and background counts by comparing the spatial distribution of the observed counts with the expected distribution for a point source plus an uniform background. I demonstrated that the ML method is particularly effective for dim sources, as most old pulsars are. Subsequently, I applied the methods described above to some old pulsars. In Chapter 6, I report the analysis of PSR J0726-2612, a radio pulsars that shares some properties with the radio-silent XDINSs, as the long period, the high magnetic field, and the thermal X-ray emission from the cooling surface. Thanks to an in-depth analysis of the combined spectrum and pulse profile, I showed that the presence of radio pulses from PSR J0726-2612, as well as the absence from the XDINSs, might simply be due to different viewing geometries. In Chapter 7, I present the case of PSR B0943+10, a pulsar with a nonthermal and thermal X-ray spectrum but that, despite being an aligned rotator, has a large pulsed fraction. I could reconcile the two opposite properties analyzing with the ML the spectrum and the pulse profile, and considering the magnetic beaming of a magnetized atmosphere model, that well fits the thermal component. In Chapter 8, I applied the ML method to seven old and dim pulsars, of which four had controversial published results, and three were so far undetected. I found convincing evidence of thermal emission only in the phase-averaged spectrum of two of them, plus a hint for a thermal pulsed spectrum in a third object. Finally, I considered all the old thermal emitters and I compared their observed temperatures, radii and luminosities to the expectations of the current theoretical models for these objects. In particular, I found that the emitting area are generally in agreement with the polar cap regions evaluated in a dipole approximation, if the combined effects of geometry projections plus realistic thermal models (as the magnetic atmosphere) are taken into account.
16
Wang, Yu, and 王禹. "Non-thermal X-ray and soft gamma-ray radiation from the young pulsars." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2013. http://hdl.handle.net/10722/196467.
Повний текст джерелаАнотація:
This thesis focuses on the radiation mechanisms of non-thermal X-rays and soft gamma-rays of two types of thousands year old spin-down powered pulsars. The thousands year old pulsars have distinct radiation behaviors from the middle-aged gamma-ray pulsars. In the magnetosphere of the pulsar, the particles are accelerated by the electric field resulting from the rotation of the neutron star. These accelerated particles move along the magnetic field lines and emit GeV gamma-ray curvature photons. For the middle-aged pulsars, most of the curvature photons, whose observed spectra are described well by power law with exponential cut-off, can escape out of the light cylinder. In X-ray band, the middle-aged pulsars usually have black body radiation with a weak non-thermal component described by power law. On the other hand, for the thousands-year-old pulsars, the curvature spectra in GeV band, which obey power law with exponential cut-off, are smeared out by the pair creation or missed by the line of sight. The secondary pairs generated by pair creation processes spiral around the magnetic field lines and emit synchrotron photons, and the young pulsars have stronger non-thermal X-ray and soft gamma-ray radiation than the middle-aged ones.
Seven young pulsars have been studied here, they are the Crab pulsar, PSRs B0540-69, B1509-58, J1846-0258, J1811-1925, J1617-5055 and J1930+1852. These seven fall into two categories: the Crab-like pulsars and soft gamma-ray pulsars. The Crab-like pulsars include the Crab pulsar and the Giant Crab PSR B0540-69, and the soft gamma-ray pulsars include the other five. The main difference between the two types of young pulsars is that the Crab-like pulsars’ spectra peak at E ≤ 1MeV while the soft gamma-ray pulsars’ spectra (in units of MeV/cm2/s) peak at E ∼ 10MeV. Their spectra also have different photon indices in X-ray band. The physics behind is two different pair creations, the photon-photon pair creation and the magnetic pair creation. The former happens when a high energy photon collides with a soft photon, and the latter happens when a high energy photon penetrates through strong perpendicular magnetic field. In the outer gap of the pulsar, a large mount of pairs are generated around the null charge surface via photon-photon pair creation, and the electric field separates the two charges to move in opposite directions. Therefore, there are outflow and inflow of particles in the magnetosphere, whose curvature photons are converted to pairs by photon-photon pair creation and magnetic pair creation respectively. For the Crab-like pulsar, the non-thermal X-rays and soft gamma-rays are emitted by the outgoing secondary pairs generated by photon-photon pair creation in the outer magnetosphere; for the soft gamma-ray pulsar, the radiating secondary pairs are generated below the null charge surface by the magnetic pair creation.published_or_final_version
Physics
Doctoral
Doctor of Philosophy
17
Huang, Hsiu-Hui. "X-ray and Optical observations of Globular Clusters and Pulsars." Diss., lmu, 2010. http://nbn-resolving.de/urn:nbn:de:bvb:19-123830.
Повний текст джерела
18
Albano, Alessandra. "Spectral and timing properties of transient anomalous x-ray pulsars." Doctoral thesis, Università degli studi di Padova, 2010. http://hdl.handle.net/11577/3427009.
Повний текст джерелаАнотація:
In the last years, thanks to new generation satellites (mostly Chandra and XMM-Newton), an increasing number of high resolution spectral and timing observations of X-ray emitting isolated neutron stars (INS)has become available.
Several new classes of X-ray emitting INSs have been discovered, all of them radio silent or with radio properties much at variance with those of Pulsar Radio (PSRs): X-ray Dim Isolated Neutron Stars (XDINSs), Anomalous X-ray Pulsars (AXPs) and Soft Gamma-ray Repeaters (SGRs), Central Compact Objects (CCOs), Rotating Radio Transient (RRATs, in one case).
AXPs and SGRs represent two peculiar groups of INSs, totalling 15 objects (6 SGRs and 9 AXPs plus one candidate). Although much less noumerous than PSRs, these objects have been extensively studied because of their peculiar and extreme properties.
SGRs exhibit bursts and flares with intensity between $\sim 10^2$ and $\sim 10^{11}$ times their quiescent X-ray luminosity ($10^{34} - 10^{36} \ {\rm erg/s})$. In the last decade transient phenomena have been observed from few AXPs, with luminosity increases between few 10 and few 100 times the X-ray quiescent values. The many similarities in the timing and spectral properties among SGRs and AXPs led to the suggestion that they could be two different manifestations of the same phenomenon.
These objects are believed to host a Magnetar, an ultra-magnetized neutron star with magnetic field $\sim 10^{14}-10^{15}$ G. In the Magnetar model emission from SGRs and AXPs comes to the expanse of the ultra strong magnetic field rather than of the rotational, gravitational or thermal energy. In Magnetars the external magnetic field can acquire a toroidal component as a consequence of the deformation of the star crust induced by the super-strong internal field. As a result the star magnetosphere twists up and the currents required to support the non-potential field may provide a large enough optical depth to resonant cyclotron scattering (RCS).
As a consequence a distortion in the thermal spectra emitting by the star surface is expected, because primary photons gain energy in the repeated scattering with the magnetospheric charges.
Spectra emerging from a twisted magnetosphere in presence of RCS has been investigated by several authors (Lyutikov and Gavriil, 2006, Fernandez and Thompson, 2007, Nobili Turolla and Zane, 2008) and applied to SGRs and AXPs spectra by Rea et al. 2008 and Zane et al., 2008.
The NTZ model 3D montecarlo simulation is the more advanced tool to compute both lightcurves and spectra. Resulting spectra are described in terms of 5 parameters: the twist angle $\Delta \phi$, the
electron bulk velocity $\beta$, the surface temperature $T$ and the two geometrical angles$\xi$ and $\chi$($\xi$ is the misalignement between spin and magnetic axis while $\chi$ is the line of sight inclination with respect to the spin axis).
In this thesis the application of NTZ model to two Transient AXPs XTE J1810-197 and CXOU J164710.2-455216 is discussed. XTE J1810-197 exhibited an outburst in late 2002 - early 2003, increasing its luminosity by two orders of magnitude. After the outburst onset the source has been monitored by XMM-Newton between September 2003 and September 2007, showing a decrease in flux until the pre-outburst value has been reached.
CXOU J164710.2-455216 exhibited an outburst on 21 September 2006, when it was observed at a luminosity 300 times greater than that measured just five days before. The source has been observed by XMM-Newton 6 times after the outburst onset, between September 2006 and August 2009.
In this work, adapted from Albano et al., 2010 paper, a comprehensive study of the pulse profile and spectral evolution of the two TAXPs
following their outbursts onsets is presented. By confronting timing data with synthetic lightcurves obtained from the twisted magnetosphere model (Nobili, Turolla and Zane, 2008), we were able to estimate how the physical parameters of the source (surface temperature and emitting area, electron energy, twist angle) evolve in time.
The fits of the pulse profiles also allowed us to infer the geometry of the two systems, i.e. the angles between the magnetic and rotational axes and the line of sight. Spectral models, obtained with the parameter values derived for the timing analysis, provide acceptable fits to XMM-Newton data.Negli ultimi anni, grazie alla nuova generazione di satelliti (in particolare Chandra e XMM-Newton), è divenuto possibile osservare, con alta risoluzione, un crescente numero di stelle di neutroni isolate (INSs) che emettono raggi X. Molte nuove classi di INSs che emettono raggi X sono state scoperte, nessuna delle quali emette nel radio, o con proprietà nel radio in disaccordo con quelle delle PSRs: X-ray Dim Isolated Neutron Stars (XDINSs), Anomalous X-ray Pulsars (AXPs) e Soft Gamma-ray Repeaters (SGRs), Central Compact Objects (CCOs), Rotating Radio Transient (RRATs, in un caso). AXPs e SGRs sono due gruppi di INSs con caratteristiche peculiari, formati in tutto da 15 oggetti (6 SGRs e 9 AXPs più una candidata). Anche se meno numerose delle PSRs, questi oggetti sono stati ampiamente studiati proprio in virtù delle loro proprietà peculiari ed estreme. Gli SGRs mostrano bursts e flares con intensità tra le $\sim 10^2$ e le $\sim 10^{11}$ volte la loro luminosit\`a quiescente in banda X ($10^{34} - 10^{36} \ {\rm erg/s}$). Nell'ultima decade fenomeni spettrali transienti sono stati osservati in alcune AXPs, con un aumento di luminosità compreso tra alcune decine e alcune centinaia di volte la luminosità di quiescenza. Le molte similarità nelle proprietà spettrali e di timing di SGRs e AXPs portano a suggerire che questi oggetti possano essere nient'altro che differenti manifestazioni dello stesso fenomeno. Si ritiene che queste sorgenti ospitino una Magnetar, una stella di neutroni ultra magnetizzata con campo magnetico pari a $\sim 10^{14}-10^{15}$ G. Nel modello Magnetar l'emissione da SGRs e AXPs proviene dall'espansione del campo magnetico ultra intenso piuttosto che ad energie di tipo rotazionale, gravitazionale o termico. Nelle Magnetars il campo magnetico esterno potrebbe acquisire una componente di tipo toroidale, come conseguenza della deformazione della crosta della stella indotta dall'intensissimo campo magnetico interno. Il risultato netto è un twist della magnetosfera della stella; inoltre le correnti richieste per supportare il campo non potenziale potrebbero dar luogo ad una profondità ottica sufficientemente spessa per il resonant cyclotron scattering (RCS). Di conseguenza ci si aspetta una distorsione negli spettri termici, dato che i fotoni primari guadagnano energia nei ripetuti urti con le particelle cariche presenti nella magnetosfera. Gli spettri all'uscita della magnetosfera twistata in presenza di RCS sono stati studiati da svariati autori (Lyutikov e Gavriil, 2006, Fernandez e Thompson, 2007, Nobili Turolla e Zane, 2008) e questo modello è stato applicato agli spettri di SGRs e AXPs da Rea et al. 2008 and Zane et al., 2008. Il codice montecarlo 3D creato da Nobili, Turolla e Zane (2008) è lo strumento più avanzato per calcolare curve di luce e spettri. Gli spettri così ottenuti possono essere descritti in termini di 5 parametri: l'angolo di twist $\Delta \phi$, la velocità di bulk degli elettroni $\beta$, la temperatura superficiale $T$ e i due angoli geometrici $\chi$ e $\xi$ ($\xi$ è il disassamento tra campo magnetico e asse di rotazione mentre $\chi$ è l'inclinazione della linea di vista rispetto all'asse di rotazione). In questo lavoro, riadattato dall'articolo Albano et al., 2010, viene presentato un ampio studio dei profili pulsati e dell'evoluzione spettrale delle due TAXPs a partire dall'inizio dell'outburst. Confrontando i dati di timing con le curve di luce sintentiche ottenute con il modello di magnetosfera twistata (Nobili, Turolla e Zane, 2008) siamo stati in grado di stimare l'evoluzione temporale del parametri fisici della sorgente (temperatura superficiale e area emittente, energia degli elettroni, angolo di twist). I fit del profilo pulsato ci permettono anche di asserire la eometria del sistema, e cioè l'angolo fra campo magnetico e asse di rotazione e quello tra asse di rotazione e linea di vista. I modelli spettrali, ottenuti dai valori dei parametri derivati dall'analisi di timing, danno dei fit accettabili dei dati di XMM-Newton.
19
Coburn, Wayne. "A study of magnetic fields of accreting x-ray pulsars with the Rossi x-ray timing explorer /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC IP addresses, 2001. http://wwwlib.umi.com/cr/ucsd/fullcit?p3015845.
Повний текст джерела
20
Beklen, Elif. "X-ray And Optical Observations Of High Mass X-ray Binaries." Phd thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12612636/index.pdf.
Повний текст джерелаАнотація:
In this thesis, X-ray and optical observations of accretion powered pulsars are presented.
By using archival RXTE observations we work on the X-ray spectral and pulse timing
analysis of 4U 1538-52, 4U 1907+09, SMC X-1 to have more detailed information about their orbital and spin parameters.
For 4U 1538-52 and SMC X-1, we determined new orbital epochs.
By using long term pulse history of 4U 1907+09, we were able to work spin-down trend of the system and also calculate the change in the spin-down rate.
Using Fermi/GBM observations we can monitor bright accreting pulsar systems. We are producing long term
histories of pulse frequency and
flux of 20 continuosly monitoring systems.
Adding Swift/BAT observations to GBM observations, for 4U 1626-67, we did reveal the characteristics belong to spin-down trend before and
spin-up behaviour after torque reversal seen in 2008 February.
Two newly discovered IGRJ06074+2205 and IGRJ01583+6713 sources are identified as X-ray binary systems and we found
parameters of them like distance, magnitudes, by using both optical photometric and spectroscopic observations.
21
Sasmaz, Mus Sinem. "X-ray And Timing Properties Of Anomalous X-ray Pulsar 1e 2259+586." Master's thesis, METU, 2007. http://etd.lib.metu.edu.tr/upload/3/12608625/index.pdf.
Повний текст джерелаАнотація:
In this thesis, we present the spectral and timing variabilities of anomalous X-ray pulsar 1E 2259+586 observed with European Photon Imaging PN Camera (EPIC PN) on board X-ray Multi Mirror Mission (XMM), Proportional Counter Array (PCA) on board Rossi X-ray Timing Explorer (RXTE) and Advanced CCD Imaging Spectrometer (ACIS) on board Chandra X-ray Observatory.
We presented the results of spectral analysis of 2000 January 11 ACIS observation. Pulse phase spectroscopy was performed on two XMM observations before and after the outburst. Pulse profiles of two XMM observations before the outburst and three XMM observations after the outburst were studied. Results are consistent with the those presented by Patel et al. (2001) and Woods et al. (2004).
We searched for the spectral variations versus spin rate during the outburst. Long-term spectral, frequency and spin-down rate variations are presented between 1996 and 2006 including 98 RXTE and 4 XMM observations. However, except outburst region (Woods et al. 2004) no significant spectral and spin rate variabilities were seen. Around the outburst region we confirmed the spectral hardening with increasing spin rate and flux.
22
González, Galán Ana. "Fundamental properties of High Mass X-ray Binaries." Doctoral thesis, Universidad de Alicante, 2014. http://hdl.handle.net/10045/41723.
Повний текст джерелаАнотація:
The aim of this thesis is to characterise a sample of High Mass X-ray Binaries (HMXBs) formed by: IGR J00370+6122, XTE J1855-026, AX J1841.0-0535 and AX J1845.0-0433. These objects are composed of pulsars (rotating neutron stars) accreting material from the wind of their supergiant companions. The X-rays are produced in the interaction of the accreted material with the strong gravitational field of the neutron star that accelerates this material and heats it up to ~ 107 K. The study of HMXBs has strong implications in several areas of Physics and Astrophysics. They contain neutron stars whose study is essential to constrain the equation of state of nuclear dense matter, and provides insights on the astrophysical models of core collapse and Supernovae explosions. HMXBs considered as a population give information on the properties of the galaxy. In addition they are excellent test-beds to study accretion physics and outflows. The X-ray behaviour of these systems determines the class of system (classical HMXBs, Supergiant Fast X-ray Transients, Be/X-ray Binaries). The differences in the X-ray emission are supposed to be due to the different properties of the binary systems, such as the orbital properties, the magnetic field of the neutron star or the spectral type of the donor star. HMXBs in this thesis are wind-fed systems, therefore, the properties of the wind (which depend on the spectral type) and the interaction of this wind with the gravitational field of the compact object are key elements to understand the X-ray emission. Therefore, in this thesis an orbital solution for each target of study has been determined using optical spectra of the donor star. Moreover, to check if wind variability is related to the orbit of the binary system, analysis of Ha variations have been carried out. Furthermore, in the case of IGR J00370+6122 and XTE J1855-026 we have obtained an atmosphere model for each of the donor stars allowing us to characterise the atmospheres of these stars, and consequently to determine physical parameters such as the Teff or the log g. Finally publicly available X-ray light curves have been analysed to study the X-ray emission of the different sources against their orbital periods. As a general conclusion, it seems there is a continuum of properties of these systems more than a strict classification. A combination of factors, of which some of them could be unknown, might be the cause of their different X-ray flux behaviours. The outline of this thesis is as follows: the scientific context is given in Chapter 1 an overview of the analysis performed for each of the sources of study is presented in Chapter 2; Chapter 3 is dedicated to the description of a pipeline optimised for the reduction of FRODOSpec spectra of obscured red sources (donor stars of the targets of study); Chapters (4, 5 and 6) present the characterization of the four sources in this thesis, which are different kind of wind-fed systems; and finally general conclusions and future work are given in Chapter 7.
23
Chakrabarty, Deepto Prince Thomas A. Prince Thomas A. "Hard X-ray detection and timing of accretion-powered pulsars with BATSE /." Diss., Pasadena, Calif. : California Institute of Technology, 1996. http://resolver.caltech.edu/CaltechETD:etd-09022008-132322.
Повний текст джерела
24
Kumar, Harsha Sanjeev. "X-ray studies of highly magnetized neutron stars and their environs." Astrophysical Journal Letters, 2008. http://hdl.handle.net/1993/22091.
Повний текст джерелаАнотація:
Supernova explosions are among the most energetic events known in the universe, leaving supernova remnants (SNRs) as their relics. The cores of massive stars collapse to form neutron stars, among the most compact and strongest magnets in the cosmos. The thesis studies a sample of such magnetic "beauties" in X-rays, the magnetars and high-magnetic field pulsars (HBPs), with the motivation to understand their evolutionary links. We also address the connection between these sources by investigating their environs through their securely associated SNRs. Magnetars have ultra-high magnetic fields B ~ 10^{14} - 10^{15} Gauss (G) and include the soft-gamma repeaters (SGRs) and anomalous X-ray pulsars (AXPs). The HBPs have magnetic fields B ~ 10^{13} - 10^{14} G, intermediate between the classical rotation-powered pulsars (B ~ 10^{12} G) and magnetars.
We focussed on two HBPs: J1119-6127 and J1846-0258, with similar spin-properties and associated with the SNRs G292.2-0.5 and Kes 75, respectively. In our studies, magnetar-like behavior was discovered from the Crab-like pulsar J1846-0258, clearly establishing a connection between the HBPs and magnetars for the first time, while no such behavior has been observed from PSR J1119-6127 so far. J1119-6127's overall X-ray properties together with its compact pulsar wind nebula resemble more the classical rotation-powered pulsars. We studied two magnetars, one from each sub-class: SGR 0501+4516 and AXP 1E 1841-045. The spectral and statistical analysis of the bursts and the persistent X-ray emission properties observed from them were found consistent with the magnetar model predictions as well as those seen in other SGRs. Finally, we probed the environment of these stellar magnets by performing a detailed X-ray imaging and spatially resolved spectroscopic study of two SNRs: G292.2-0.5 and Kes 73 associated with J1119-6127 and 1E 1841-045, respectively. We found that both SNRs point to very massive progenitors (>~25 solar masses), further supporting the growing evidence for magnetars originating from massive progenitors using other multiwavelength studies.
25
Sahiner, Seyda. "X-ray Spectral And Timing Studies Of The High Mass X-ray Binary Pulsar 4u 1907+09." Master's thesis, METU, 2009. http://etd.lib.metu.edu.tr/upload/12610941/index.pdf.
Повний текст джерелаАнотація:
In this thesis, X-ray spectral and pulse timing analysis of the high mass X-ray binary pulsar 4U 1907+09, based on the observations with Rossi X-ray Timing Explorer (RXTE) and International Gamma-Ray Astrophysics Laboratory (INTEGRAL), are presented. INTEGRAL (October 2005 - November 2007) and RXTE (June 2007 - December 2008) observations confirm that the luminosity of the source is highly variable such that, flaring and dipping activities are observed.
The results of time-averaged energy spectra of RXTE and INTEGRAL observations are consistent with the previous studies. Orbital phase resolved spectroscopy with RXTE data, reveals that the Hydrogen column density varies through the orbit reaching to its maximum value just after periastron. This variation approves that the location of the absorbing material is the accretion flow. A slight spectral softening with increasing luminosity is aslo observed.
4U 1907+09 had been steadily spinning down for more than ~15 years with a rate of -3.54x10-14 Hz s-1. RXTE observations of the source in 2001 showed a ~60% decrease in the spin-down rate and INTEGRAL observations in 2003 showed a reversal to spin-up. The timing analysis presented in this thesis reveals a new spin-down episode with a rate of -3.59x10-14 Hz s-1, which is close to the previous steady spin-down rate. This result implies that a recent torque reversal before June 2007 has taken place. The reversal is a rare event for 4U 1907+09 and it indicates the variations in the mass accretion rate and/or geometry.
Using RXTE observations, 24 new pulse periods are measured to demonstrate the period evolution. Energy resolved pulse profiles confirm that the profile has a double peak sinusoidal shape at energies below 20 keV, whereas the leading peak significantly loses its intensity above 20 keV. This energy dependence indicates that the physical circumstances of the two polar caps are different.
26
Beklen, Elif. "Timing Observations From Rossi X-ray Timing Explorer (rxte)." Master's thesis, METU, 2004. http://etd.lib.metu.edu.tr/upload/1260199/index.pdf.
Повний текст джерелаАнотація:
In this thesis, RXTE observations of 4U 1907+09 are presented. Timing
analysis of these data sets have yielded quasi periodic oscillations
(QPOs) at orbital phases corresponding to the two flares in every orbital
period. Known continuous spin down trend and QPO behaviour at the
flares strongly suggest that a transient accretion disk occurs at the
flares. Our
findings strongly suggested that neutron star passes through the
equatorial wind of Be companion star. During these passages a
transient disk forms around Be neutron star.
27
Marini, Bettolo Cecilia. "Performance Studies and Star Tracking for PoGOLite." Doctoral thesis, KTH, Partikel- och astropartikelfysik, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-13015.
Повний текст джерелаАнотація:
PoGOLite is a balloon-borne experiment, which will study polarized soft γ-ray emissionfrom astrophysical targets in the 25-80 keV energy range by applying well-typephoswich detector technology. Polarized γ-rays are expected from a wide variety of sources including rotation-powered pulsars, accreting black holes and neutron stars,and jet-dominated active galaxies. Polarization measurements provide a powerfulprobe of the γ-ray emission mechanism and the distribution of magnetic and radiation fields around the source. The polarization is determined using Compton scattering and photoelectric absorption in an array of 217 plastic scintillators. The sensitive detector is surrounded by a segmented Bismuth Germanium Oxide (BGO) anticoincidence shield. The function of this shield is to reduce backgrounds from charged cosmic rays, primary and atmospheric γ-rays, and atmospheric and instrumenta lneutrons. The anticoincidence shield consists of 427 BGO crystals with three different geometries. The characteristics of the BGO crystals of the bottom anticoincidence shield have been studied with particular focus on the light yield.The maiden flight of PoGOLite will be with a reduced detector volume “pathfinder” instrument. The flight, lasting about 24 hours, is foreseen from Esrange, Sweden in August 2010. The performance of the pathfinder has been studied using computer simulations. The effect of atmospheric attenuation, both on the signal of theastronomical target and on the background, are studied. These allow an observationstrategy to be developed for the forthcoming flight. A polarization analysis method is described and applied to an observation example. The method sets anupper limit on the accuracy with which the polarimeter will be able to detect polarization the angle and degree. The PoGOLite polarimeter has a relatively small field of view (2.4◦×2.4◦) which must be kept aligned to objects of interest on the sky. A star tracker forms part of the attitude control system. The star trackersystem comprises a CCD camera, a lens, and a baffle system. Preliminary studiesof the star identification performance are presented and are found to be compatible with the environment around the Crab, which is the main observational target for the first flight.QC20100629
28
Pivovaroff, Michael James 1971. "X-ray astronomy with CCDs : calibration of the advanced CCD imaging spectrometer and observations of rotation-powered pulsars." Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/9026.
Повний текст джерелаАнотація:
Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Physics, 2000.Includes bibliographical references.
This dissertation concerns the use of charge coupled devices (CCDs) for X-ray astronomy. Part I of this thesis focuses on the calibration of the Advanced CCD Imaging Spectrometer (ACIS), one of the two primary focal plane instruments on the Chandra X-ray Observatory. I begin by presenting a series of measurements made using undispersed synchrotron radiation. I analyzed the results of these experiments to extract parameters necessary to model the absolute detection efficiency of CCDs used as reference standards for ACIS characterization. I also discuss a novel "mesh" technique I pioneered to non-destructively measure the sub-pixel structure of CCDs, including the channel stops and gates. This work also provided a valuable tool for understanding the way charge is collected inside certain regions of the ACIS detectors. Guided by the results of the mesh experiments, I performed additional measurements to constrain recombination effects in the channel stops. Part II of this thesis concerns the X-ray properties of rotation-powered (radio) pulsars. High energy observations serve as a powerful diagnostic of the energetics and emission mechanisms of neutron stars. Associations between pulsars and the remnants of their supernovae provide independent measures of the distance and age of neutron stars, as well as constraints on their initial velocities, magnetic fields, and spin periods. I analyze ASCA and ROSAT observations of three young pulsars which are particularly well-suited for addressing these issues. I also present observations of the rotation-powered pulsar with the highest known magnetic field, and describe how the results relate to anomalous X-ray pulsars, another type of neutron star. Finally, I analyze Chandra observations of the supernova remnant Cas A. These data fully demonstrate the capabilities of ACIS and reveal a previously unknown point source at the center of the remnant.
by Michael James Pivovaroff.
Ph.D.
29
Falkner, Sebastian [Verfasser], Jörn [Akademischer Betreuer] Wilms, Silas Gutachter] Laycock, and Jörn [Gutachter] [Wilms. "Modeling X-ray pulsars in curved space-time / Sebastian Falkner ; Gutachter: Silas Laycock, Jörn Wilms ; Betreuer: Jörn Wilms." Erlangen : Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 2018. http://d-nb.info/116380682X/34.
Повний текст джерела
30
Falkner, Sebastian Verfasser], Jörn [Akademischer Betreuer] [Wilms, Silas Gutachter] Laycock, and Jörn [Gutachter] [Wilms. "Modeling X-ray pulsars in curved space-time / Sebastian Falkner ; Gutachter: Silas Laycock, Jörn Wilms ; Betreuer: Jörn Wilms." Erlangen : Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 2018. http://d-nb.info/116380682X/34.
Повний текст джерела
31
Vybornov, Vadim [Verfasser], and Andrea [Akademischer Betreuer] Santangelo. "Changes in X-ray spectra of accreting pulsars on short and long time scales / Vadim Vybornov ; Betreuer: Andrea Santangelo." Tübingen : Universitätsbibliothek Tübingen, 2019. http://d-nb.info/1179180968/34.
Повний текст джерела
32
Yukita, M., A. Ptak, A. E. Hornschemeier, D. Wik, T. J. Maccarone, K. Pottschmidt, A. Zezas, et al. "Identification of the Hard X-Ray Source Dominating the E > 25 keV Emission of the Nearby Galaxy M31." IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/623858.
Повний текст джерелаАнотація:
We report the identification of a bright hard X-ray source dominating the M31 bulge above 25 keV from a simultaneous NuSTAR-Swift observation. We find that this source is the counterpart to Swift J0042.6+4112, which was previously detected in the Swift BAT All-sky Hard X-ray Survey. This Swift BAT source had been suggested to be the combined emission from a number of point sources; our new observations have identified a single X-ray source from 0.5 to 50 keV as the counterpart for the first time. In the 0.5-10 keV band, the source had been classified as an X-ray Binary candidate in various Chandra and XMM-Newton studies; however, since it was not clearly associated with Swift J0042.6+4112, the previous E < 10 keV observations did not generate much attention. This source has a spectrum with a soft X-ray excess (kT similar to 0.2 keV) plus a hard spectrum with a power law of Gamma similar to 1 and a cutoff around 15-20 keV, typical of the spectral characteristics of accreting pulsars. Unfortunately, any potential pulsation was undetected in the NuSTAR data, possibly due to insufficient photon statistics. The existing deep HST images exclude high-mass (> 3 M-circle dot) donors at the location of this source. The best interpretation for the nature of this source is an X-ray pulsar with an intermediate-mass (< 3 M-circle dot) companion or a symbiotic X-ray binary. We discuss other possibilities in more detail.
33
CUOFANO, Carmine. "Magnetic fields generated by r-modes in accreting millisecond pulsars." Doctoral thesis, Università degli studi di Ferrara, 2010. http://hdl.handle.net/11392/2389313.
Повний текст джерелаАнотація:
In rotating neutron stars the existence of the Coriolis force allows the presence of the so-called
Rossby oscillations (r-modes) which are known to be unstable to emission of gravitational waves.
In the Thesis, for the first time, we introduce the magnetic damping rate in the evolution equations of r-modes. We show that r-modes can generate very strong toroidal fields in the core of accreting
millisecond pulsars by inducing differential rotation. We shortly discuss the instabilities of the
generated magnetic field and its long time-scale evolution in order to clarify how the generated
magnetic field can stabilize the star. Finally we discuss the possible astrophysical scenarios.
34
Kulebi, Baybars. "The Broad-band Noise Characteristics Of Selected Cataclysmic Variables (cvs), Anomalous X-ray Pulsars (axps) And Soft Gamma Repeaters (sgrs)." Master's thesis, METU, 2007. http://etd.lib.metu.edu.tr/upload/12608117/index.pdf.
Повний текст джерелаАнотація:
In this work present the broad-band noise structure in the 2-60 keV data of Cataclysmic Variables (CVs) with Anomalous X-Ray Pulsars (AXPs) and Soft Gamma Repeaters (SGRs). We analyzed Rossi X-ray Timing Explorer (RXTE) PCA data and derived time series from 27 CVs, 4 AXPs and 1 SGR using the RXTE archive. In general, CVs of different types all show broad band noise which can be fitted with power laws, using exponentional cut-offs, and Lorentzians in a similar way to power spectral (noise) characteristics of X-ray Binaries (XRBs). In general terms the power spectra show a power law index of (-)1.2-2. A rather large scale flattening of the power spectra exits in nonmagnetic systems in the low to very low frequency range. We observe that in low and high states/outbursts the noise in the high frequency range and low frequency range is changed. CVs show considerably low frequency noise. In addition, we recovered several possible QPOs in the X-ray wavelengths from CVs mainly from Intermediate Polar systems. AXP and SGR sources which are thought to be powered by either magnetic decay or accretion show band limited noise in their low frequencies.
We also correlated their equal time interval noise characteristic with their burst states and discovered that in the two AXPs (1E 2259+586, 1E 1048.1-5937) noise correlates with their bursts.
35
Farrell, Sean Adam Physical Environmental & Mathematical Sciences Australian Defence Force Academy UNSW. "The multi-coloured universe of 2S 0114+650." Awarded by:University of New South Wales - Australian Defence Force Academy. School of Physical, Environmental and Mathematical Sciences, 2007. http://handle.unsw.edu.au/1959.4/38692.
Повний текст джерелаАнотація:
This thesis presents the results of a comprehensive multi-wavelength study of the high mass X-ray binary 2S 0114+650. This enigmatic source has previously been proposed to be the first in a new class of super-slow X-ray pulsars, containing a neutron star revolving once every 2.7 h. The 11.6 d orbital period of this system has been well established in both X-ray and optical wavelengths. During the initial stages of the research presented in this thesis we discovered an additional 30.7 d ???super-orbital??? modulation in the X-ray emission from this source. While similar periodicities seen in other X-ray binaries are commonly attributed to the precession of a warped accretion disc, the observational evidence suggests the absence of such a disc in 2S 0114+650. The purpose of this project is thus to determine the nature of the super-orbital modulation and to better constrain the astrophysical parameters of this system. To investigate the long-term variability we analysed ~8.5 yr of archived data from the Rossi X-ray Timing Explorer space telescope. The problem of the spurious ~24 h periods in this data was solved as a by-product of these studies. Follow-up pointed observations were obtained with this satellite in order to examine the spectral and temporal behaviour over the spin, orbital and super-orbital timescales. Independent confirmation of the super-orbital modulation was performed using ~2 yr of data from the INTEGRAL satellite obtained during a long-term monitoring campaign of the Cassiopeia region. The evolution of the spin, orbital and super-orbital periods over ~10 yr was examined using archived data from the Rossi X-ray Timing Explorer satellite. Radio observations were performed with the Giant Meterwave Radio Telescope to search for any radio emission associated with this source and to determine whether it is variable over the known periodicities. Near infrared observations were performed with the Mt Abu telescope to determine whether a Be star nature can be ruled out for the optical component. Finally, a statistical analysis of the properties of the confirmed super-orbital X-ray binaries was performed in order to search for commonalities between these systems.
36
Müller, Sebastian [Verfasser], and Jörn [Akademischer Betreuer] Wilms. "Observations of the X-ray Pulsars XTE J1946+274, 4U 0115+634, and GX 304-1 / Sebastian Müller. Gutachter: Jörn Wilms." Erlangen : Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 2013. http://d-nb.info/1065380526/34.
Повний текст джерела
37
Müller, Sebastian Verfasser], and Jörn [Akademischer Betreuer] [Wilms. "Observations of the X-ray Pulsars XTE J1946+274, 4U 0115+634, and GX 304-1 / Sebastian Müller. Gutachter: Jörn Wilms." Erlangen : Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 2013. http://d-nb.info/1065380526/34.
Повний текст джерела
38
Taskin, Ozgur Mustafa. "Analysis Of The Physical Properties Of Different Types Of Neutron Stars." Phd thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/12606665/index.pdf.
Повний текст джерелаАнотація:
This thesis is composed of three published articles. Each chapter is devoted to an article. In the first part the origin of some of the single radio pulsars with relatively low magnetic fields (B <1e12 G) and with characteristic ages (tau) less than 1e7 years is questioned. We proposed that such pulsars might occur as a result of the disruption of high-mass X-ray binary systems after a second supernova explosion. In these binaries, mass accretion on to the surface of X-ray pulsars may lead to the decrease in the magnetic field from its value at birth (B similar to 1e12 &ndash
1e13 G) down to B <
1e12 G similar to the processes in low-mass X-ray binaries. In the second part we put together many observational data of SGRs and AXPs and analyzed them with the main purpose of the removal of contradiction between the real age (t) of these objects and their characteristic times of period change (tau). SGRs and AXPs are neutron stars that undergo star-quakes. Magnetic activity increases from time to time. We suggest that as a result of these processes plasma is ejected from the NS and propeller mechanism starts to work. Due to propeller effect dP/dt increases, tau decreases. Indeed, high dP/dt values are observed in SGRs and in half of the AXPs. Then, for a long time NS looses its activity, its dP/dt decreases, tau increases and rapid cooling begins. It seems that there is a possible transition between each NS stage (AXP,SGR,dim). This transient cycle may be repeated once or several times until the spin period of the neutron star becomes P >
10 - 12 s. Observational data and mainly the data of AXP 1E 1048-5937 and DRQNS RX J1308.8+2127 support this idea. In the third part dependence of the X-ray luminosity (Lx) of young single pulsars, due to ejection of relativistic particles, on electric field intensity, rate of rotational energy loss (dE/dt), magnetic field, period and some other parameters of neutron stars are discussed. Influence of the magnetic field and effects of some other parameters of neutron stars on the Lx - dE/dt and the Lx - tau(characteristic time) relations are considered. Evolutionary factors also play an important role in our considerations. Only the pulsars whose X-ray luminosity in the 2 &ndash
10 keV energy band is greater than 1033 erg/s have pulsar wind nebula around them. The pulsars from which gamma-ray radiation has been observed have low X-ray luminosity in general.
39
Serim, Muhammed Mirac. "Timing Properties Of Recently Discovered Soft Gamma Repeaters." Master's thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12614803/index.pdf.
Повний текст джерелаАнотація:
In this thesis, the recently discovered Soft Gamma Ray Repeaters SGR
J1833-0832, SWIFT J1822.3-1606 and SWIFT J1834.9-0846 are analysed
using the archival Swift, RXTE, Chandra and XMM-Newton observations.
The period fluctuations and timing noise properties of these sources are
investigated. Spectral characteristics and long term frequency evolution
of these sources are presented. Investigation for timing noise structure of
these magnetars has shown a correlation between first frequency derivative
of the spin frequency and torque noise strength.
40
Caballero, Doménech Isabel. "X-ray observations of the accreting Be, X-ray binary pulsar A 0535+26 in outburst." Tübingen, Neue Str. 16 : I. Caballero Doménech, 2009. http://d-nb.info/995113327/34.
Повний текст джерела
41
Matheson, Heather. "X-ray observations of the young pulsar wind nebula G21.5–0.9 and the evolved pulsar wind nebulae CTB 87 (G74.9+1.2) and G63.7+1.1." IOP Publishing Ltd. for The American Astronomical Society, 2010. http://hdl.handle.net/1993/30163.
Повний текст джерелаАнотація:
Pulsar wind nebulae (PWNe), nebulae harbouring a rotation-powered neutron star that was born in a supernova, provide opportunities to study highly relativistic pulsar winds and their interaction with the surrounding medium. Particularly interesting are PWNe that do not show any sign of the expected surrounding SNR shell and were thought to be born in subenergetic explosions or with unusual progenitors. The detection of a shell around one such PWN suggested that shells are indeed produced but may be faint due to unseen shocked ejecta, a low density environment, and/or a young age that has not yet allowed the shell to brighten and become visible.
Here, by using observational X-ray data from modern telescopes with excellent spatial and energy resolution (Chandra and XMM-Newton), we target PWNe that do not have prominent SNR shells, and are known to be in varied environments, to further explore the characteristics of this growing, but poorly explored, class of PWNe. By combining imaging and spectroscopic results, we study the morphology of the PWNe, search for thermal emission from shock-heated material, investigate the energetics of the nebulae, and search for candidates for the neutron stars powering the nebulae.
We find that while the faint shell surrounding G21.5–0.9 can be explained as a young PWN evolving in a low density medium, CTB 87 (G74.9+1.2) appears to be in an advanced stage of evolution, and G63.7+1.1 appears to be both in an advanced stage of evolution and in a dense environment. By performing spatially resolved spectroscopy, we have shown how the spectral characteristics vary across the PWNe, and note that more data will place better constraints on possible thermal emission in these remnants. The imaging portion of these studies has revealed intriguing large-scale morphologies for CTB 87 and G63.7+1.1, as well as a torus-jet structure in CTB 87 and neutron star candidates in both CTB 87 and G63.7+1.1. We conclude that both CTB 87 and G63.7+1.1 are likely interacting with the supernova remnant reverse shock, and CTB 87 may be additionally influenced by the motion of its neutron star.
42
Bergh, Magnus. "Interaction of Ultrashort X-ray Pulses with Material." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis Acta Universitatis Upsaliensis, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-8274.
Повний текст джерела
43
Hartman, Jacob M. Ph D. Massachusetts Institute of Technology. "X-ray timing of the accreting millisecond pulsar SAX J1808.4-3658." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/45413.
Повний текст джерелаАнотація:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2007.Includes bibliographical references (p. 105-114).
We present a 7 yr timing study of the 2.5 ms X-ray pulsar SAX J1808.4-3658, an X-ray transient with a recurrence time of =2 yr, using data from the Rossi X-ray Timing Explorer covering 4 transient outbursts (1998-2005). Substantial pulse shape variability, both stochastic and systematic, was observed during each outburst. Analysis of the systematic pulse shape changes suggests that, as an outburst dims, the X-ray "hot spot" on the pulsar surface drifts longitudinally and a second hot spot may appear. The overall pulse shape variability limits the ability to measure spin frequency evolution within a given X-ray outburst (and calls previous zi measurements of this source into question), with typical upper limits of Jil < 2.5 x 10-14 Hz s-1 (2a). However, combining data from all the outbursts shows with high (6 a) significance that the pulsar is undergoing long-term spin down at a rate /i = (-5.6 ± 2.0) x 10-16 Hz s-1, with most of the spin evolution occurring during X-ray quiescence. We discuss the possible contributions of magnetic propeller torques, magnetic dipole radiation, and gravitational radiation to the measured spin down, setting an upper limit of B < 1.5 x 108 G for the pulsar's surface dipole magnetic field and Q < 4.4 x 1036 g cm2 for the mass quadrupole moment. We also measured an orbital period derivative of Porb = (3.5 + 0.2) x 10-12 s s-1 We identify a strong anti-correlation between the fractional amplitude of the harmonic (r2) and the X-ray flux (fx) in the persistent pulsations of four sources: SAX J1808.4-3658, IGR J00291+5934, and XTE J1751-305, XTE J1807-294. These sources exhibit a powerlaw relationship r2 x( fx7 with slopes ranging from y = -0.47 to -0.70. The three other accreting millisecond pulsars that we analyzed, XTE J0929-314, XTE J1814-338, and HETE J1900.1-2455, do not as fully explore a wide range of fluxes, but they too seem to obey a similar relation. We argue that these trends may be evidence of the recession of the accretion disk as the outbursts dim. We examine the energy dependence of the persistent pulsations and thermonuclear burst oscillations from SAX J1808.4-3658.
We confirm the soft phase lags previously discovered from this source, and we discover that these phase lags increase as the source flux decays slowly following its peak flux. When the source decay becomes rapid and the outburst enters its flaring tail stage, this relationship reverses, and the phase lags diminish as the flux dims further. This result, along with the pulse profile changes observed at the beginning of the flairing tail stage, suggests an abrupt change in the geometry of the accretion disk and column at this time in the outburst. In contrast, the thermonuclear burst oscillation timing does not show appreciable lags, and the burst oscillation phases and fractional amplitudes appear to be relatively independent of energy.
by Jacob M. Hartman.
Ph.D.
44
Davies, Simon Robert. "The supernova remnant G109.1-1.0 and the X-ray pulsar 1E2259+586." Thesis, University of Southampton, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.252711.
Повний текст джерела
45
Caballero, Doménech Isabel [Verfasser]. "X-ray observations of the accreting Be, X-ray binary pulsar A 0535+26 in outburst / vorgelegt von Isabel Caballero Doménech." Tübingen, Neue Str. 16 : I. Caballero Doménech, 2009. http://d-nb.info/995113327/34.
Повний текст джерела
46
Carstairs, Ian Ruthven. "Kernel density estimators applied to hard X-ray observations of the Crab Pulsar." Thesis, University of Southampton, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.315292.
Повний текст джерела
47
Barszczak, Sardinha Anna Luiza. "Coherent imaging of nano-objects with ultra-short X-ray pulses." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLX006/document.
Повний текст джерелаАнотація:
L'utilisation des rayons X est indispensable pour obtenir la résolution spatiale de la dizaine de nanomètres. La durée de ces flashs va de la dizaine de femtosecondes (1 fs =10-15 s) à la centaine d'attosecondes (1as=10-18 s). Durant ce laps de temps, les nano-objets n'ont pas le temps d'évoluer, assurant l'obtention d'une image précise. En excitant les nano-objets entre deux flashs de rayons X, il est alors possible de suivre sont évolution temporelle et ainsi de réaliser un « film » de son évolution suite à une excitation. Cette information est extrêmement importante car elle permettra d'identifier les états structuraux intermédiaires des nano-objets qui sont connus comme étant les plus importants pour comprendre leur pouvoir réactionnel.Ce genre d'études vient uniquement de débuter dans le monde en raison de l'apparition très récente des sources de rayons X suffisamment brèves et intenses pour réaliser ce genre d'images. La source de référence est un laser dit à « électrons libres » (LEL) dont il existe trois exemplaires au monde, en Allemagne, aux USA et au Japon. Le faible nombre d'exemplaires provient du coût extrêmement élevé de cette machine. Depuis plusieurs années, nous avons montré au LOA que les lasers pouvaient produire un rayonnement X femtoseconde et suffisamment intense pour réaliser des images de nano-objets avec des résolutions spatiales et temporelles équivalentes à celles obtenues sur LEL.La présente thèse a etait construite autour de trois phases : réalisation d'une source de rayons X polarisés circulairement, réalisation d'un nouveau système plus performant d'imagerie, et test sur des échantillons possédants des nano-structures dont la vitesse d'évolution après excitation est prévue aux environs de 100 fs. Ces études ont eu lieu ao LOA, LCLS, Laboratoire de Chimie-Physique, Matière et Rayonnement (LCPMR) et le CEA de Saclay et BESSY-II en Alemagne. Ils ont permis de acquérir une forte expertise en imagerie nanométrique basée sur la nouvelle technique que nous avons développéThe use of X-rays is fundamental to obtain a spatial resolution in the order of the dozen of nanometers. The duration of the flashes of radiation is placed between the dozen of femtoseconds (1 fs =10-15 s) to the hundreds of attoseconds (1as=10-18 s). During this time frame nano-objects are static in time, image wise it translates as a precise image. Exciting these nano-objects with flashes of X-ray beams it is possible to follow its temporal evolution and record a "movie" of the evolution due to excitation. This type of information is extremely important since it can allow the identification of intermediary structural states and therefore attaining a better understanding of their reactional power.This type of studies it is making its debut in the scientific community due to the recent development of ultra-fast and intense X-ray sources needed to perform this type of imaging. The referenced source is a free electron laser (FEL) and there are only tree of them in the world nowadays. One in Germany, one in the USA and one in Japan. The small amount of FELs is mainly due to its elevated costs. From some years the LOA has shown that lasers can also provide an X-ray beam in the femtosecond region and intense enough to produce images of nano-objects with equivalent temporal and spatial resolutions.This present thesis was built in tree phases: realization of an X-ray laser source, circularly polarized; realization of a new improved imaging system and testing of the nano-samples possessing nano-structures. These nano-structures have a velocity of evolution after excitation in the range of 100 fs. These studies have had place at LOA, LCLS, Laboratoire de Chimie-Physique, Matière et Rayonnement (LCPMR), the CEA de Saclay, BESSY-II in Germany. These cooperations have insured a specific training and expertise in the world of nanometric imaging based on the new technique developed during this work
48
Yu, Wayne Hong. "Application of X-ray pulsar navigation| A characterization of the Earth orbit trade space." Thesis, University of Maryland, College Park, 2016. http://pqdtopen.proquest.com/#viewpdf?dispub=10012594.
Повний текст джерелаАнотація:
The potential for pulsars as a navigation source has been studied since their discovery in 1967. X-ray pulsar navigation (XNAV) is a celestial navigation system that uses the consistent timing nature of X-ray photons from milli-second pulsars (MSP) to perform space navigation. Much of the challenge of XNAV comes from the faint signal, availability, and distant nature of pulsars. This thesis is the study of pulsar XNAV measurements for extended Kalman filter (EKF) tracking performance within a wide trade space of bounded Earth orbits, using a simulation of existing X-ray detector space hardware. An example of an X-ray detector for XNAV is the NASA Station Explorer for X-ray Timing and Navigation (SEXTANT) mission, a technology demonstration of XNAV set to perform on the International Space Station (ISS) in 2016.
The study shows that the closed Earth orbit for XNAV performance is reliant on the orbit semi-major axis and eccentricity as well as orbit inclination. These parameters are the primary drivers of pulsar measurement availability and significantly influence the natural spacecraft orbit dynamics. Sensitivity to initial orbit determination error growth due to the scarcity of XNAV measurements within an orbital period require appropriate timing of initial XNAV measurements. The orbit angles of argument of perigee and right ascension of the ascending node, alongside the other orbit parameters, complete the initial cadence of XNAV measurements. The performance of initial XNAV measurements then propagates throughout the experimental period.
49
Camacho, Garibay Abraham. "Dynamics of Highly Charged Finite Systems Induced by Intense X-ray Pulses." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-212203.
Повний текст джерелаАнотація:
The recent availability of X-ray Free Electron Lasers (XFELs) has opened a completely new and unexplored regime for the study of light-matter interactions. The extremely bright intensities delivered by XFELs can couple many photons into the target, turning well known interactions such as photoionization and scattering into new, non-linear, complex many-body phenomena. This thesis reports theoretical investigations aiming to improve the understanding of the fundamental processes and dynamics triggered by intense X-ray pulses, with a special focus in finite systems such as molecules and clusters.
Sequential multiple photoionization in atomic clusters was investigated, where previous observations were extended for higher charge states where direct photoionization is frustrated. Through a rate equation study and subsequent molecular dynamics simulations, it was found that frustrated ionization is partially responsible for the low-energy peak observed in the electron energy spectrum. The influence of plasma evaporation over the formation of the sequential low-energy peak was also investigated, identifying the effects of the system size and photon energy.
Multiple channel ionization was also investigated for the case of fullerenes. This is done through a series of studies, starting from a simplified rate equation scheme, and culminating with full molecular dynamics simulations. From these results, a good insight was obtained over the origin, physical meaning, and relevant parameters that give rise to the complicated features observed in the electronic spectra. The mechanisms responsible of all these features are expected to be present in other systems, making these results quite general.
Diffractive imaging of biomolecules was studied in a final step, with a particular focus on the influence of intramolecular charge transfer mechanisms. To this end a conformer of T4 Lysozyme was used, a representative enzyme with well known structure. Charge migration is found to allow for additional processes such as proton ejection, a mechanism which enables an efficient release of energy from the system. This mechanism considerably suppresses structural damage for heavy ions, improving the quality of the measured diffraction patterns.
50
Fabris, Nicola. "Instrumentation for Photon Handling of XUV and Soft X-ray Ultrafast Pulses." Doctoral thesis, Università degli studi di Padova, 2019. http://hdl.handle.net/11577/3425791.
Повний текст джерелаАнотація:
The recent availability of ultrafast coherent sources in the extreme ultraviolet (XUV) and soft X-ray spectral regions, such as high-order laser harmonics and free-electron lasers made possible time-resolved studies of electron and molecules dynamics on sub-femtosecond time scales. Simultaneously, the increasing demand of optical technologies suitable for photon handling and conditioning of this type of sources is a field where a strong collaboration between research and industry is required, in order to reach new results. This thesis concerns the design, realization and characterization of different monochromators dedicated to the selection of a portion of the spectrum generated by ultrafast sources.
The first contribution regards the comparison in terms of overall efficiency between two widely adopted single diffraction grating monochromators geometries, specifically the classical (CDM) and off-plane (OPM) mounts. A subsequent comparison with AFM-based simulations has been performed in order to validate the experimental results. Remarkably, the OPM diffraction efficiency is measured to about 2 times and 7 times higher than the CDM at the XUV energies of 100 eV and 310 eV. Efficiencies as high as 45 % at 100 eV and 35 % at 310 eV have been measured for OPM gratings.
The second contribution consists in the software and optical setup of a double grating time-delay compensated monochromator. This monochromator will be soon inserted and ready for the alignment at the Extreme Light Infrastructure - Attosecond Light Pulse Source, ELI-ALPS, European ultra-high brightness laser facility (Hungary). The chosen parameters of the monochromator, in order to obtain the requested spectral bandwidth and temporal performances are analyzed in detail. The XUV monochromator simulated temporal resolution is lower than 15 fs at low energy resolution mode and lower than 30 fs at high energy resolution.
The third contribution consists in the characterization results achieved in terms of aberrations minimization, resolution and efficiency by designing a novel monochromator with a new three-optical-elements layout. The measured spectral resolving power is in the 3700-5200 range (output bandwidth <10 meV) over the spectral region of 12-50 eV. This is comparable to spectral resolving powers achieved on synchrotron beamlines. Excellent XUV monochromator performances has been obtained throughout by using simple optical components, which are available off the shelf on the market with high optical quality; although at modest prices.