Дисертації з теми "Gamma ray sources"
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1
Rogers, Martin John. "Gamma-ray evidence for cosmic-ray sources." Thesis, Durham University, 1988. http://etheses.dur.ac.uk/6343/.
Анотація:
The origin of cosmic-rays is one of the long-standing problems in astro physics. In recent years, strong evidence has been found that certain classes of object contain and are able to accelerate particles to high energies. In this thesis the origin problem is addressed in two different ways. Firstly, two different regions of the Galaxy are studied using γ-ray observations from the COSB satellite combined with atomic and molecular gas measurements. The Vela region contains a pulsar and a supernova remnant and is particularly valuable location for cosmic-ray studies because of its proximity, the association of the two objects, and the intensity of the γ -ray flux it produces. At greater longitudes, the region around the peculiar object η Carinae is also studied. It is rich in potential sources of cosmic rays including active stars and a spiral arm seen at a tangent at l ~ 282º .Analysis of the Vela region reveals strong evidence for cosmic ray production at all energies observed by COSB. The supernova remnant seems the most likely candidate, but the possibility of the pulsar itself producing some of the particles cannot be ruled out. The excess γ -ray emission from around η Carinae does not appear correlated with the active stars but seems to becoming predominantly from the spiral arm. This is the first time evidence has been presented for cosmic-ray acceleration by the spiral shock in a particular, known spiral arm which is observed as a feature in the gas. The γ -rays are produced in the gas clouds associated with this arm. The second approach to the cosmic-ray origin problem involves a model for cosmic-ray production in supernova remnants and is used in association with a Monte-Cailo simulation of their occurrence in the Galaxy. Unlike earlier models (Bhat et al 1987), the motion of the Sun is also taken into account and the supernova explosions occur mainly in spiral arms. The results are in the form of a time sequence of energy density values and tire compared in detail with (^10)Be results. It is found that the model accounts for the long-term rise in the concentration of this radioisotope and does not predict large excursions from the mean energy density that beset older models. Thus the cosmic ray production by supernova remnants seems to be consistent with the radioisotope data.
2
吳文謙 and Man-him Ng. "Searching for gamma-ray signals form pulsars and periodic signals fromthe galactic gamma-ray sources." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1996. http://hub.hku.hk/bib/B31213509.
3
Syson, Alexandra Jane. "Search for unidentified gamma-ray sources." Thesis, University of Leeds, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.493790.
Анотація:
This thesis shows how improvements can be made to two dimensional gamma - ray source analysis by using a probabilistic approach to describe the possible source location and likelihood of a candidate gamma-ray event. The mapping algorithm developed assesses the significance of source detection, and background subtraction is implemented both by a modified standard approach and by the development of a multivariate kernel analysis.
4
Ng, Man-him. "Searching for gamma-ray signals form pulsars and periodic signals from the galactic gamma-ray sources /." Hong Kong : University of Hong Kong, 1996. http://sunzi.lib.hku.hk/hkuto/record.jsp?B19667942.
5
Tsurusaki, Kazuma. "VERITAS observations of galactic gamma-ray sources." Diss., University of Iowa, 2012. https://ir.uiowa.edu/etd/3394.
Анотація:
The main topic of this thesis is analysis of an unidentified Galactic TeV gamma-ray source, MGRO J1908+06, discovered by Milagro instrument in 2007. We analyzed 54 hours of observational data from the Very Energetic Radiation Imaging Telescope Array System (VERITAS), a ground-based gamma-ray observatory in southern Arizona comprised of an array of four Cherenkov Telescopes that reconstructs the energy and direction of astrophysical gamma-rays by imaging Cherenkov light emitted by energetic particles in air showers produced by the primary gamma-rays. MGRO J1908+06 is located between a supernova remnant SNR G40.5-0.5 and a young, energetic pulsar PSR J1907+0602. We studied the energy dependent morphology of the TeV emission from the source and measured the source extent and spectrum. The source extends well past the boundary of the SNR and is not correlated with strong radio continuum or molecular line emission which likely excludes an origin for the emission as solely due to the SNR. While emission in the 0.5-1.25 TeV band was centered around the pulsar, higher energy emission was observed near the supernova remnant. This morphology is opposite that observed in other pulsar wind nebulae. We proposed two models for the high energy emission located well away from the pulsar but close to the SNR: (1) shock acceleration at the shock front created by an interaction between the pulsar wind and the dense gas at the edge of the SNR or (2) molecular clouds around the SNR provides seed photons with energies higher than those from Cosmic Microwave Backgrounds for inverse Compton scattering. The former model can be tested by looking for molecular emission lines that trace shocks and by measuring the pulsar velocity.
In addition, we investigated the gamma-ray emission from the nova explosion of V407 Cygni that occurred in March 2010. The Fermi-LAT observed this event in the energy range of E >100 MeV. The origins of the gamma-ray emission that the Fermi-LAT team proposed are either protons (hadronic model) or electrons (leptonic model), both of which were accelerated at the nova shock via the Fermi acceleration mechanism. We did not consider their leptonic model because no TeV gamma-ray emission is predicted. Their hadronic model can generate TeV gamma-rays with the modeled parameters. We found no evidence for TeV emission. We showed that with the flux upper limit calculated using the VERITAS data imposes constraints on the extension of the proton spectrum at high energies.
6
Edwards, Philip Gregory. "A search for ultra high energy gamma ray emission from binary X-ray systems." Title page, contents and summary only, 1988. http://web4.library.adelaide.edu.au/theses/09PH/09phe266.pdf.
7
Ciampa, Dominic. "A southern hemisphere search for ultra-high-energy gamma ray sources." Title page, contents and summary only, 1988. http://web4.library.adelaide.edu.au/theses/09PH/09phc565.pdf.
8
Graham, Lilian Joan. "Ultra high energy gamma ray point sources and cosmic ray anisotropy." Thesis, Durham University, 1994. http://etheses.dur.ac.uk/5594/.
Анотація:
The experimental set-up at the Baksan Air Shower Array, used to detect air showers above ~0.2xl0(^14)eV, is described. An estimation of the angular resolution using the cosmic ray shadow of the Sun and the Moon gives a value of ~2.5˚ which is consistent with previous estimates from Monte-Carlo simulations. Using data from this array covering 1985-1992, a search is made for 7-ray emission from 18 candidate sources. Upper limits to the flux from these sources are stated in all cases. A periodicity search is made on data for which the excess for a single transit of a particular source is above 3(7. The results of this periodicity analysis on such days points to 4 possible observations of pulsed emission at the 95% confidence level. These are 4U0115+63 on 19.03.89, PSR19534-29 on 12.02.85, 1E2259+586 on 01.08.91 and PSR0655+64 on 12.08.89. Without confirmation from other groups however the findings are not significant enough to stand alone. A harmonic analysis has been performed on the 8 years of data and after pressure corrections and a Farley & Storey analysis to eradicate any spurious sidereal variations we find negligible evidence of 2nd or 3rd harmonic but a 1st harmonic amplitude and phase of (12.7 ±1.2) x 10(^-4) at 23.1 ± 0.3hr right ascension. When one takes into account the cosϐ effect on the sidereal anisotropy this value becomes 17.4±1.6xl0(^-4).Future developments and improvements to be undertaken at BASA, including the building of a muon detector, are outlined.
9
余君岳 and Kwan-ngok Peter Yu. "The origin of extragalactic gamma rays." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1988. http://hub.hku.hk/bib/B31231469.
10
Yu, Kwan-ngok Peter. "The origin of extragalactic gamma rays /." [Hong Kong : University of Hong Kong], 1988. http://sunzi.lib.hku.hk/hkuto/record.jsp?B12362827.
11
Meyhandan, Rishi. "Search for ultra high energy radiation from astrophysical sources." Title page, contents and summary only, 1994. http://web4.library.adelaide.edu.au/theses/09PH/09phm6137.pdf.
12
Elton, Stephen Dennis. "A search for celestial sources of very high energy gamma-ray emission using the atmospheric Cerenkov technique /." Title page, contents and summary only, 1989. http://web4.library.adelaide.edu.au/theses/09PH/09phe51.pdf.
13
Dazeley, Steven Ashton. "A search for very high energy gamma-ray emission from four galactic pulsars : a thesis submitted to the Department of Physics and Mathjematical Physics, University of Adelaide for the degree of Doctor of Philosophy." Title page, contents and abstract only, 1999. http://web4.library.adelaide.edu.au/theses/09PH/09phd277.pdf.
14
Mannings, Vincent. "TeV gamma-ray emission from accreting binary pulsars." Thesis, Durham University, 1990. http://etheses.dur.ac.uk/6297/.
Анотація:
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.
15
Dowthwaite, J. C. "Very energetic gamma rays from binary X-ray sources and other astronomical objects." Thesis, Durham University, 1987. http://etheses.dur.ac.uk/7064/.
Анотація:
This thesis describes the observation of a number of astronomical objects using the University of Durham Atmospheric Cerenkov light detectors. The array of telescopes was used to study the Very High Energy (V.H.E.) gamma-radiation from these objects from June 1981 until November 1984.The general features of Gamma-ray astronomy are briefly discussed, and a review of the main results of previous gamma-ray observations is given. The basic theory and general characteristics of Atmospheric Cerenkov Effect experiments are reviewed. Details of the design, operation and performance of the University of Durham facility are presented in addition to details of the improvements achieved in the development of a new telescope. In particular, the new optical system is described. The main analysis procedures are explained. The adaptation of statistical techniques used to analyse the intensity of the Cerenkov light flash is described in some detail. A discussion of the problems involved in conducting an extensive search for periodicity in the data collected from Cygnus X-3 is given. A procedure for testing for transient pulsed gamma-ray emission from the Crab Pulsar is also described. The results of the observations from several objects are presented., the binary X-ray sources, Cygnus X-3, Hercules X-l and 4U0115+63, the Crab pulsar and the Galactic Plane. In addition, the preliminary results from observations of seven radio pulsars and seven other objects are given. A review of the main production mechanisms of V.H.E. gamma-radiation is given with particular emphasis on the models proposed for the high energy processes in Cygnus X-3, other binary-ray sources and pulsars.
16
Rowell, Gavin Peter. "A search for very high energy gamma rays from PSR1706-44 using the Atmospheric Cerenkov Imaging Technique /." Title page, contents and abstract only, 1995. http://web4.library.adelaide.edu.au/theses/09PH/09phr8808.pdf.
17
Robinson, Sean M. "The multichromatic wavelet transformation as a source identification tool for GLAST /." Thesis, Connect to this title online; UW restricted, 2004. http://hdl.handle.net/1773/9748.
18
Kwok, Ping Wai. "Very high-energy gamma rays from the Crab nebula and pulsar." Diss., The University of Arizona, 1989. http://hdl.handle.net/10150/184863.
Анотація:
This project is to search for Very High Energy (VHE) (10¹¹ eV to 10¹⁴ eV) gamma rays from the Crab nebula and pulsar using the atmospheric Cherenkov imaging technique. The technique uses an array of 37 photomultiplier tubes to record the images of the Cherenkov light pulses generated by energetic particles in the air showers initiated by VHE gamma rays or charged cosmic rays. Gamma-ray-like events are selected from numerous cosmic-ray events based on the predicted properties of the image, such as the size, shape, and orientation with respect to the axis of the detector. A steady weak flux of VHE gamma rays from the Crab is detected at high statistical significance (9 sigma), which is not usually achieved in VHE gamma-ray astronomy. No strong evidence of pulsed emission is found when the same data is folded at the Crab pulsar's radio ephemeris. The angular resolution of the technique cannot separate the emission coming from the nebula from that from the pulsar. Although it is generally believed that the unpulsed emission is coming from the nebula, there may be an unpulsed component coming at only a couple of light cylinder radii away from the pulsar too. Using the outer gap model of pulsar, the spectrum is derived and is found to be compatible with the observations.
19
劉美楣 and Mei-mei Lau. "A study of the gamma ray production from extragalactic objects." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1987. http://hub.hku.hk/bib/B31207698.
20
Lau, Mei-mei. "A study of the gamma ray production from extragalactic objects /." [Hong Kong : University of Hong Kong], 1987. http://sunzi.lib.hku.hk/hkuto/record.jsp?B12335320.
21
Cipiccia, Silvia. "Compact gamma-ray sources based on laser-plasma wakefield accelerator." Thesis, University of Strathclyde, 2011. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=23936.
Анотація:
Laser-plasma wakefield accelerator (LWFA) is a promising novel technology that is introducing miniaturization to the accelerator world: the unprecedented gradient of acceleration shrinks the accelerator down to table-top size. Moreover, the LWFA comes with an embedded light source: electrons, while accelerating, undergo betatron oscillatory motion that results in synchrotron radiation emitted in a narrow cone along the direction of propagation. In this thesis we study theoretically and we prove experimentally a new regime of betatron oscillation that occurs when electrons experience the electromagnetic field of the laser during acceleration and oscillate resonantly at the laser frequency or its sub-harmonics. The signature of the harmonically resonant betatron (HRB) regime is a large oscillation amplitude and consequently prolific emission of high energy photons up to the MeV range. The HRB source has unique properties: very short pulse length (~10 fs), small source size (few microns), high peak brightness of the order of 1023 photons/s mm2 mrad2 0.1% B.W., which is comparable with a third generation light source. These properties make the source particularly appealing for the life sciences and medical and security applications. As a part of a future applications project, we give the scaling of the photon energy as a function of laser intensity and plasma density, which could extend toward tens of MeV. The thesis also investigates another gamma-ray source that utilises beams from the LWFA: bremsstrahlung radiation from high energy electrons interacting with metal targets. We study the electron beam and target parameters to optimize the emission process and the gamma-ray beam properties to match potential application requirements, such as radioisotope generation via photonuclear process. The results of a proof of concept experiment are presented and compared with simulations. Finally, we investigate numerically the possibility of generating a converging gamma ray beam based on the bremsstrahlung process. The results are encouraging, and the potential impact of a compact converging gamma-ray beam source is discussed with particular attention to medical applications in cancer treatment.
22
Stycz, Kornelia. "VHE Gamma-ray sources at the resolution limit of H.E.S.S." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät, 2016. http://dx.doi.org/10.18452/17517.
Анотація:
Die bodengebundene Gammaastronomie beschäftigt sich mit der Detektion von Photonen mit Energien >10GeV mittels der abbildenden Cherenkov-Technik. Dabei wird die Atmosphäre als Detektor verwendet: Photonen in diesem Energiebereich produzieren in ihr Teilchenschauer, die Cherenkov-Licht aussenden. Das Licht wird von Teleskopen gesammelt um Abbildungen der Schauer zu erhalten, aus denen Eigenschaften der Gammaquanten abgeleitet werden können. Da die Schauer statistischen Prozessen unterliegen, ist die Rekonstruktion der Richtung des Gammaquants durch Fluktuationen begrenzt. Die Qualität der Rekonstruktion hängt von der Energie des Quants, Beobachtungsbedingungen, Teleskop-Eigenschaften und der Rekonstruktionsmethode ab. Die Präzision der Richtungsrekonstruktion einzelner Gammaquanten wird als Winkelauflösung bezeichnet. Diese Arbeit beschäftigt sich mit der Winkelauflösung der vier Teleskope von HESS, die für bodengebundene Gammaastronomie im Energiebereich >100GeV verwendet werden. Es werden systematische Fehler der Winkelauflösungsfunktion und ihre Abhängigkeiten von Beobachtungsparametern mit Beobachtungsdaten und Simulationen abgeschätzt. Abweichungen der simulierten Auflösung von der mit HESS an Hand von Punktquellen gemessenen werden in dieser Arbeit identifiziert und quantifiziert, um mit einer korrigierten Funktion zwei Phänomene zu studieren: Erstens wird die Ausdehnung des Krebsnebels im TeV-Bereich untersucht, für die Werte bis ca. 0.03º vorausgesagt werden. Es werden die Beobachtungen des Nebels selektiert, die eine gute Auflösung und Kontrolle des systematischen Fehlers versprechen. Auf einem Konfidenzniveau von 95% wird die Obergrenze der Ausdehnung des Nebels damit zu 0.034º bestimmt. Zweitens wird nach ausgedehnter Emission um Aktive Galaxienkerne (AGN) gesucht. Verschiedene Modell-Vorhersagen werden mit den HESS-Daten dreier AGN verglichen - die so erzielten Obergrenzen auf den Fluss sind die niedrigsten bisher veröffentlichten im TeV-Bereich.Very-high-energy (VHE) gamma-ray astronomy deals with the ground-based detection of photons with energies of tens of GeV to few 100 TeV by employing the Imaging Air Cherenkov Technique (IACT). This method uses the atmosphere as a detector for VHE gamma-rays, exploiting that photons in that energy range produce particle showers in it. The showers emit Cherenkov light, which is collected by telescopes to image single showers. Properties of the gamma-rays can be deduced from the shower images. However, the interactions in the atmosphere are statistical processes, imposing a limit on the direction reconstruction. The quality of the reconstruction depends on the energy of the primary particle, telescope properties, observational conditions and reconstruction algorithm. The precision of the direction reconstruction of single photons is called the angular resolution. In this work, the angular resolution function of the IACT experiment HESS is studied in detail. HESS consists of five telescopes, four of which were built for the energy range >100 GeV. For this sub-array, the systematic errors on the angular resolution and their dependence on observation parameters are estimated from known point sources in HESS data and Monte-Carlo simulations. A mismatch between HESS data and simulations is quantified and corrected to assess two phenomena: First, the size of the the Crab Nebula at VHE is investigated. Some models predict a size of the emission region of more than 0.03º. Including a detailed accounting of the systematic errors, an upper limit on the size of emission region of the nebula is given by 0.034º at a 95% confidence level. Second, extended emission around Active Galactiv Nuclei is searched for. Various models are probed with HESS data and the most constraining upper limits on the so-called pair halo scenario are found. Assuming a different model, extra-galactic magnetic field strengths in the range of (0.1 - 10)* 10^{-15} G are excluded at a 99% confidence level.
23
Xu, Jiaxin. "Development of analysis tools for gamma-ray spectrometry." Electronic Thesis or Diss., université Paris-Saclay, 2020. http://www.theses.fr/2020UPASG030.
Анотація:
La spectrométrie gamma est une des techniques principales pour la mesure de la radioactivité, qui permet d'identifier et quantifier les radionucléides. L'objectif de la thèse est de développer de nouvelles méthodes d’analyse des spectres gamma afin d'améliorer les limites de détection. Dans ce contexte, la première contribution est la proposition de nouvelle approches statistiques pour l'estimation des activités en spectrométrie gamma par le démélange spectral, qui consiste à décomposer un spectre gamma mesuré en spectres individuels des radionucléides. Contrairement aux méthodes standard, cette approche permet de traiter un spectre gamma dans sa globalité et prendre en compte la statistique Poisson du processus de détection. En modélisant l'estimation des activités comme un problème inverse sous la contrainte de non-négativité, le démélange spectral parcimonieuse est étudié pour estimer conjointement l'ensemble des radionucléides actifs et leurs activités. La deuxième contribution est l'utilisation métrologique du démélange spectral étudié, qui nécessite en plus l'évaluation des limites caractéristiques pour la prise de décision et l'étalonnage des instruments pour l'analyse quantitativeGamma-ray spectrometry is one of the main techniques used for the measurement of radioactivity, which allows identifying and quantifying radionuclides. The objective of this thesis is to develop new spectrum analysis methods to improve the detection limits. In this context, the first contribution is investigating the activity estimation in gamma-ray spectrometry with spectral unmixing, which decomposes a measured spectrum into individual radionuclides' spectra. Contrary to standard methods, this approach allows accounting for the full spectrum analysis of a gamma-ray spectrum and the Poisson statistics underlying the detection process. By formulating the activity estimation as an inverse problem under non-negativity constraint, the sparse spectral unmixing is investigated to estimate the subset of active radionuclides and their activities jointly. The second contribution is the metrological use of the investigated spectral unmixing method, which further necessitates the evaluation of characteristic limits for decision making purposes and the instruments' calibration for quantitative analysis
24
Xie, Zhaohua, and 謝照華. "The study of phase-resolved spectra of gamma-ray pulsars." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2003. http://hub.hku.hk/bib/B26665633.
25
Fegan, Stephen. "A very high energy gamma-ray survey of unidentified EGRET sources." Diss., The University of Arizona, 2004. http://hdl.handle.net/10150/280605.
Анотація:
A survey of unidentified 100 MeV γ-ray sources is undertaken, with the Whipple 10m telescope, with the objective of detecting very high energy (>350 GeV) γ-ray emission. The survey consists of nineteen sets of observations of sources detected by the EGRET instrument on the Compton Gamma-Ray Observatory between 1991 and 1995. Results for 21 EGRET sources are reported; in some cases two EGRET sources are close enough to be viewed in a single observation. For each EGRET source, candidate associations are listed and the implications of each candidate for VHE emission discussed. Finally, a study of the performance of a next-generation ground based instrument, VERITAS, using simulations is presented. The implications of the increased sensitivity of such an instrument for suture gamma-ray surveys is briefly discussed.
26
Baring, Matthew Geoffrey. "Pair plasmas in astrophysics." Thesis, University of Cambridge, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.279144.
27
Poon, Alan Wing Pok. "Energy calibration of the Sudbury Neutrino Observatory using monoenergetic gamma-ray sources." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape15/PQDD_0028/NQ34610.pdf.
28
Bradbury, Stella Marie. "Atmospheric Cerenkov astronomy of cataclysmic variables & other potential gamma ray sources." Thesis, Durham University, 1993. http://etheses.dur.ac.uk/5632/.
Анотація:
Recent developments in the application of the atmospheric Cerenkov technique to 7-ray astronomy are reviewed here. These include new methods of signal to noise enhancement and the increasing diversity of stellar systems positively identified as Very High Energy 7-ray sources. Four Cataclysmic Variable systems were observed using the University of Durham Atmospheric Cerenkov telescopes during the course of 1990 and 1991. The statistical analysis performed in the search for a 7-ray signal, above a threshold energy of approximately 0-4 TeV, from three of these objects, H0253+193, EF Eridani and VW Hydri, is described here. The results of this brief survey are discussed in the context of current ideas as to the mechanisms by which Very High Energy 7-rays may be emitted from accreting binary star systems of this type. The analysis techniques applied to Cataclysmic Variable data were extended to an x-ray binary system, Sgr X-7. For comparison, the analysis of data recorded on two radio pulsars, PSR 1855+09 and PSR 1509-58, having more accurately known pulse signatures than the accreting systems is also described here, together with that of the globular cluster 47 Tucanae, which may emit a steady 7-ray flux; an upper limit is placed upon the level of Very High Energy 7-ray emission from this object. Extension of the Very High Energy 7-ray source catalogue will require a further improvement beyond the current signal to noise ratios of atmospheric Cerenkov telescopes. Some features characteristic of the atmospheric Cerenkov emission triggered by Very High Energy 7-rays as opposed to other cosmic ray particles, which could be exploited in an attempt to reduce interference from the latter, are reviewed. The first attempt to obtain directional information from the relative time of arrival of a Cerenkov flash at the telescopes at the University of Durham Southern Hemisphere site, and thus isolate an anisotropic 7-ray flux is reported here.
29
Skole, Christian. "Search for extremely short transient gamma-ray sources with the VERITAS observatory." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät, 2016. http://dx.doi.org/10.18452/17608.
Анотація:
In der Astronomie zeigen viele Quellen ein veränderliches Verhalten, das in manchen Fällen sehr kurz sein und im Bereich von Sekunden bis Minuten liegen kann. Beispiele dafür sind Gammablitze (GB) und aktive Galaxienkerne (AGK). Um die zugrundeliegenden physikalischen Prozesse besser zu verstehen, ist eine Messung der Photonenflussänderung notwendig. Allerdings kann die Entdeckung sehr kurzzeitiger Ausbrüche im sehr hochenergetischen Bereich des Spektrums, für welche Cherenkov Teleskope, wie VERITAS, zum Einsatz kommen, schwierig sein. Die Ursache dafür ist der hohe Untergrund und die relativ niedrige Signalrate. Diese Arbeit behandelt die Implementierung fortschrittlicher und für die Entdeckung signifikanter Ratenänderung optimierter, statistischer Methoden (exp-test and Bayesian-Blocks) innerhalb der VERITAS-Analyse. Das Verhalten dieser Methoden wird anhand von Daten minutenlanger Ausbrüche, die mittels Monte-Carlo-Technik für zwei unterschiedliche VERITAS Stadien simuliert wurden (vor und nach der Hardware-Aufrüstung), bewertet und miteinander verglichen. Die fortschrittlichen Methoden verbessern die Empfindlichkeit bei der Entdeckung von kurzzeitigen Ausbrüchen, wenn deren Fluss den des Krebsnebels übersteigt (Krebsnebel-Einheit = K.E.). Es sind nun Ausbrüche von 2 K.E. selbst dann nachweisbar, wenn deren Dauer nur 100 Sek. beträgt. Dies ist mit der Standardmethode nicht möglich. Im darauffolgenden Schritt dieser Arbeit werden das Nachglühen von 6 GB sowie die 450, ebenfalls mit VERITAS erzeugten, Aufnahmen von AGK-Quellen mittels der fortschrittlichen Methoden analysiert. In keiner der AGK-Aufnahmen wird eine signifikante Entdeckung kurzzeitiger Variabilität gemacht, was mit den anerkannten AGK-Modellen übereinstimmt. Auch die Untersuchung des Nachglühens der 6 GB offenbart keine kurzen Ausbrüche im GeV-TeV Bereich. Jedoch ist es für 2 von ihnen möglich, ein oberes Flusslimit von 1.25 K.E. (3,7 · 10^(−10) erg/(cm^2*s) [0,1;10 TeV]) abzuschätzen.In astronomy, many of the observed sources show a transient behavior. Examples are gamma-ray bursts (GRBs) and active galactic nuclei (AGN). For those source types the variability can be very short, in the order of seconds to minutes. Measuring the flux variations is necessary to understand the underlying physical processes responsible for the emission. However, the detection of very short flares can be difficult in the very high-energy range, in which imaging atmospheric Cherenkov telescopes like VERITAS are operating. This is due to the large background and the comparable low signal rates. This thesis discusses the implementation of advanced statistical methods (exp-test and Bayesian-Blocks) into the VERITAS analysis framework, that are optimized for the detection of significant variations in the event rate. The performance of these methods is evaluated and compared by using Monte Carlo simulations of minute scale flares for two different VERITAS states, pre- and post-hardware-upgrade. It is shown that the advanced methods can improve the detection sensitivity for short flares with high fluxes of more than the Crab flux (Crab unit = C.U.). For example, flares at 2 C.U. with short durations down to 100 sec are now detectable, which is not possible with the standard method. In the next step of this thesis, 6 GRB afterglows and 450 runs of AGN data, observed by VERITAS, are analyzed with the advanced methods. In none of the AGN runs a significant detection of short time variability is made, which is in consistence with the canonical AGN models. The investigation of the 6 GRB afterglows also did not reveal any short flares in the GeV-TeV range. However, for two of them it was possible to estimate an upper flux limit of 1.25 C.U. (3,7 * 10^(−10) erg/(s*cm^2) [0,1;10 TeV]).
30
Bhadra, Arunava. "New studies on high energy cosmic-ray extensive air showers detected at sea-level with emphasis on the observation of celestial ultra high energy Gamma-ray sources." Thesis, University of North Bengal, 1996. http://hdl.handle.net/123456789/698.
31
Smith, Nigel James Telfer. "A search for ultra high energy gamma ray sources from the South Pole." Thesis, University of Leeds, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.291023.
32
Qi, Liqiang. "Measurements of Prompt Gamma Rays Emitted in Fission of ²³⁸U and ²³⁹ Pu Induced by Fast Neutrons from the LICORNE Neutron Source." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLS320/document.
Анотація:
Les spectres des rayons γ prompt de fission sont des données nucléaires importantes pour la physique des réacteurs, en tant qu'entrée pour les calculs de chauffage gamma, puisque l'effet de chauffage gamma peut être sous-estimé jusqu'à ~28% avec les données nucléaires actuelles. De plus, les nouvelles informations sur les rayons γ prompts de fission seront utiles du point de vue de la physique fondamentale, où les résultats peuvent être comparés à de nombreuses prédictions théoriques concurrentes pour affiner les modèles du processus de fission. Les spectres des rayons γ prompts de fission ont été mesurés pour la fission induite par neutrons rapides de ²³⁸U et de ²³⁹Pu, en utilisant des neutrons rapides générés à partir de la source LICORNE. Le dispositif expérimental se composait d'une chambre d'ionisation et de différents types de détecteurs à scintillation, dont les détecteurs LaBr₃ et PARIS phoswich. Une procédure d'analyse, comprenant le unfolding et la simulation de la réponse aux rayons γ dans les détecteurs à scintillation, est mise au point pour extraire le spectre des rayons γ prompts de fission et les caractéristiques spectrales correspondantes. Les résultats expérimentaux sont comparés aux codes de modélisation de fission GEF et FREYA. Cette comparaison révèle que les caractéristiques spectrales sont liées aux conditions énergétiques, aux rendements isotopiques et au moment angulaire des fragments de fission. La dépendance énergétique des caractéristiques spectrales montre que l'émission des rayons γ est tout à fait insensible à l'énergie neutronique incidente. Toutefois, on observe une forte dépendance à l'égard du système fissionnant particulierPrompt fission γ-ray spectra are important nuclear data for reactor physics, as an input for gamma heating calculations, since the gamma heating effect can be under-estimated by up to ~28% with present nuclear data. Furthermore the new prompt fission γ-ray information will be useful from a fundamental physics point of view, where results can be compared with many competing theoretical predictions to refine models of fission process. Prompt fission γ-ray spectra have been measured for the fast-neutron-induced fission of ²³⁸U and ²³⁹PuPu, using fast neutrons generated from the LICORNE source. The experimental setup consisted of an ionization chamber and different types of scintillation detectors, including LaBr₃ and PARIS phoswich detectors. An analysis procedure, including unfolding and recovering the γ-ray response in the scintillation detectors, is developed to extract the prompt fission γ-ray spectrum and corresponding spectral characteristics. The experimental results are compared to the fission modeling codes GEF and FREYA. This comparison reveals that the spectral characteristics are related to the energetic conditions, isotopic yields and angular momentum of the fission fragments. The energy dependence of the spectral characteristics shows that the prompt γ-rays emission is quite insensitive to the incident neutron energy. However, a strong dependence on the particular fissioning system is observed
33
Picquenot, Adrien. "Introduction and application of a new blind source separation method for extended sources in X-ray astronomy." Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPASP028.
Анотація:
Certaines sources étendues, telles que les vestiges de supernovae, présentent en rayons X une remarquable diversité de morphologie que les téléscopes de spectro-imagerie actuels parviennent à détecter avec un exceptionnel niveau de précision. Cependant, les outils d’analyse actuellement utilisés dans l’étude des phénomènes astrophysiques à haute énergie peinent à exploiter pleinement le potentiel de ces données : les méthodes d’analyse standard se concentrent sur l’information spectrale sans exploiter la multiplicité des morphologies ni les corrélations existant entre les dimensions spatiales et spectrales ; pour cette raison, leurs capacités sont souvent limitées, et les mesures de paramètres physiques peuvent être largement contaminées par d’autres composantes.Dans cette thèse, nous explorerons une nouvelle méthode de séparation de source exploitant pleinement les informations spatiales et spectrales contenues dans les données X, et leur corrélation. Nous commencerons par présenter son fonctionnement et les principes mathématiques sur lesquels il repose, puis nous étudierons ses performances sur des modèles de vestiges de supernovae. Nous nous pencherons ensuite sur la vaste question de la quantification des erreurs, domaine encore largement inexploré dans le milieu bouillonnant de l’analyse de données. Enfin, nous appliquerons notre méthode à l’étude de trois problèmes physiques : les asymétries dans la distribution des éléments lourds du vestige Cassiopeia A, les structures filamentaires dans l’émission synchrotron du même vestige, et la contrepartie X des structures filamentaires visibles en optique dans l’amas de galaxies PerseusSome extended sources, among which we find the supernovae remnants, present an outstanding diversity of morphologies that the current generation of spectro-imaging telescopes can detect with an unprecedented level of details. However, the data analysis tools currently in use in the high energy astrophysics community fail to take full advantage of these data : most of them only focus on the spectral information without using the many spatial specificities or the correlation between the spectral and spatial dimensions. For that reason, the physical parameters that are retrieved are often widely contaminated by other components. In this thesis, we will explore a new blind source separation method exploiting fully both spatial and spectral information with X-ray data, and their correlations. We will begin with an exposition of the mathematical concepts on which the algorithm rely, and particularly on the wavelet transforms. Then, we will benchmark its performances on supernovae remnants models, and we will investigate the vast question of the error bars on non-linear estimators, still largely unanswered yet essential for data analysis and machine learning methods. Finally, we will apply our method to the study of three physical problems : the asymmetries in the heavy elements distribution in the supernova remnant Cassiopeia A, the filamentary structures in the synchrotron of the same remnant and the X-ray counterpart to optical filamentary structures in the Perseus galaxy cluster
34
Zhou, Hao. "Search for TeV gamma-ray sources in the galactic plane with the HAWC observatory." Thesis, Michigan Technological University, 2016. http://pqdtopen.proquest.com/#viewpdf?dispub=10004778.
Анотація:
Cosmic rays, with an energy density of ∼ 1eVcm–3, play an important role in the evolution of our Galaxy. Very high energy (TeV) gamma rays provide unique information about the acceleration sites of Galactic cosmic rays. The High Altitude Water Cherenkov (HAWC) Gamma-Ray Observatory is an all-sky surveying instrument sensitive to gamma rays from 100,GeV to 100,TeV with a 2steradian instantaneous field of view and a duty cycle of >95%. The array is located in Sierra Negra, Mexico at an elevation of 4,100m and was inaugurated in March 2015. Thanks to its modular design, science operation began in Summer 2013 with one third of the array. Using this data, a survey of the inner Galaxy region of Galactic longitude l ∈ [+15°, +50°] and latitude b ∈ [–4°, +4°] is performed. To address the ambiguities arising from unresolved sources in the data, a maximum likelihood technique is used to identify point source candidates. Ten sources and candidate sources are identified in this analysis. Eight of these are associated with known TeV sources but not all have differential fluxes compatible with previous measurements. Three sources are detected with significances >5σ after accounting for statistical trials, and are associated with known TeV sources. With data taken with the full array and improved reconstruction algorithms, the significance on the Crab nebula increases from 3.1σ√day to 5.5σ√day, which allows more sensitive sky surveys and more precise spectral and morphological analyses on individual sources.
35
Houston, Brian P. "The role of gamma-ray sources in relation to the observed diffuse emission and the cosmic ray origin problem." Thesis, Durham University, 1985. http://etheses.dur.ac.uk/7236/.
Анотація:
Interpretation of the present gamma-ray data above 100 MeV is discussed in relation to cosmic ray interactions with the atomic and molecular hydrogen in the Galactic plane. The SAS II gamma-ray data are analysed for supportive evidence on the 2CG candidate sources identified from the COS B observations. The strongest sources are confirmed. There is good evidence to suggest that many of the weaker sources are not truly discrete. A Monte-Carlo analysis of the discrete source detection efficiencies suggests that many 2CG sources are unresolved giant molecular clouds, irradiated by the ambient cosmic ray flux. An attempt is made to define a genuine source catalogue. Taking account of the detection efficiencies the net source flux (from both resolved and unresolved sources) is estimated to be 11-23% of the Galactic plane emission. Cosmic ray interactions with the Orion molecular cloud complex are investigated through an analysis of the gamma-ray emission above 100 MeV. There is no evidence for cosmic ray exclusion from the clouds. A new derivation of the CO/H (_2) ratio is obtained. N (_H2) / T ((^12) CO) dv = (3.7 ± 0.6) x 10(^20) at cm (^-2) (K kms (^-1)) (^-1) Contributions to the extragalactic gamma-ray flux from radio galaxies and rich clusters are estimated. The flux may be dominated by emission from these objects. With the estimate of the discrete Galactic source flux and the CO→H (_2) ratio, the radial gamma-ray emissivity is compared to the HI, inferred H (_2) and possible cosmic ray radial densities in the inner Galaxy. It is shown that a moderate cosmic ray gradient overestimates the gamma-ray flux, unless the metal abundance gradient reduces the inferred H (_2) mass.
36
Bultena, Sandra Lyn. "Direction measurement capabilities of the LEDA cosmic ray detector." Thesis, McGill University, 1988. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=63930.
37
Schirber, Michael Robert. "Sources, sinks and scatterers of the ultra-violet background." The Ohio State University, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=osu1072842778.
38
Lambert, Alyn. "Gamma-ray emission above 10sup(15)eV from Cygnus X-3 and other galactic sources." Thesis, University of Leeds, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.371051.
39
Hillert, Andreas [Verfasser], and Werner [Akademischer Betreuer] Hofmann. "GRASP - Development of an event reconstruction method using a Gamma Ray Air Shower Parameterisation and application to gamma-ray sources with H.E.S.S. / Andreas Hillert ; Betreuer: Werner Hofmann." Heidelberg : Universitätsbibliothek Heidelberg, 2014. http://d-nb.info/1180031768/34.
40
Hoffmann, Agnes Irene Dorothee [Verfasser]. "Analysis of hard X-ray emission from selected very high energy γ-ray [gamma-ray] sources observed with INTEGRAL / vorgelegt von Agnes Irene Dorothee Hoffmann". Reutlingen, Bruno-Matzke-Str.15 : A. Hoffmann, 2009. http://d-nb.info/999640429/34.
41
Idenden, David William. "Development of novel analytical techniques for use in searches for ultra high energy gamma ray sources." Thesis, University of Leeds, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.305705.
42
Satalecka, Konstancja. "Multimessenger studies of point-sources using the IceCube neutrino telescope and the MAGIC gamma-ray telescope." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2010. http://dx.doi.org/10.18452/16222.
Анотація:
Drei Botenteilchen koennen benutzt werden, um Informationen ueber Quellen der Kosmischer Strahlung zu erhalten: Photonen, geladene Teilchen und Neutrinos. In dieser Arbeit wird anhand von Beobachtungsdaten und theoretischen Modellen der Zusammenhang zwischen extrem hochenergetischer Gammastrahlung und Neutrinos untersucht. Um die Wahrscheinlichkeit fuer die Entdeckung einer Neutrino-Punktquelle zu erhoehen, wurden neue Ansaetze entwickelt. Zum einen wurde fuer 7 Objekte eine Suche nach Zeit- und Richtungskorrelationen zwischen Neutrinoereignissen, registriert vom AMANDA-II Teleskop am Suedpol, und den von IACT-Teleskopen im Zeitraum 2004-2006 beobachteten Gammastrahlungsausbruechen durchgefuehrt. Zum anderen wurde das selbe AMANDA-II Datensatz analysiert, unter Verwendung eines neuen Algorithmus zur Suche nach Strukturen in der zeitlichen Verteilung von Neutrino-Ereignissen aus einer vordefinierten Richtungen. Keine der Analysen fuehrte zur Entdeckung einer Neutrino-Punktquelle. Die zeitlich lueckenhafte Aufzeichnung von TeV Gammastrahlungs Daten, stellt eine der schwerwiegendste Einschraenkung bei Korrelationsstudien dar. Dieses Problem wurde in der vorliegenden Arbeit durch die Analyse historischer IACT Daten und neuer Ergebnisse des MAGIC AGN Beobachtungsprogramms beruecksichtigt. Anhand dieser Daten konnte eine statistische Analyse der verschiedenen Emissionszustaende zweier extragalaktischer Gammastrahlungsquellen durchgefuehrt werden. Aufgrund einer zu geringen Statistik der Messungen konnten jedoch keine endgueltigen Schluesse ueber die Wahrscheinlichkeit, diese Quellen in einem Emmisionszustand oberhalb eines gewissen Schwellenwertes anzufinden, gezogen werden. Fuer die zwei Quellen, Mrk501 und 1ES1959+650, werden hier die Ergebnisse des MAGIC AGN Beobachtungsprogramms von 2007 bis 2008 vorgestellt. Beide Quellen wurden in einem aehnlich niedrigen Zustand vorgefunden und wiesen maessige Variabilitaet und keine auffaelligen Ausbrueche auf.Three messengers can be used to extract information about the sources of cosmic rays: photons, charged particles and neutrinos. In this work the connection between the TeV gamma-rays and neutrinos is investigated in the context of recent observations and theoretical models. In order to increase the probability of detecting a neutrino point source two new approaches were developed. First, a correlation study of possible time and directional coincidences of neutrino events, detected by the AMANDA-II telescope at the South Pole, and gamma-ray flares, observed by the Imaging Atmospheric Cherenkov Telescopes in the years 2004-2006, was performed for 7 objects. Secondly, the same AMANDA-II data set was analyzed using a new algorithm which looks for structures in the time distribution of the neutrino events from pre-defined directions. None of the analysis resulted in a detection of a neutrino point source. The sparse time and flux state coverage of the TeV gamma-ray data is one of the most serious issues connected with any correlation study involving photons from the high energy range. This problem was addressed in this work by an analysis of historical gamma-ray data and of the recently obtained results from the MAGIC AGN monitoring program. Based on this data a statistical analysis of different emission states of two extragalactic TeV gamma-ray sources, was performed. Due to still low flux statistics, no final conclusions concerning the probability of finding those sources in a flux state above a certain threshold can be made. The results of the MAGIC AGN monitoring program from the observational season 2007/2008 are presented here, for two sources: Mrk501 and 1ES1959+650. Both sources were found in a similarly low state and show moderate variability with no prominent flares. Since a part of the 2008 monitoring data of Mrk501 was collected during a multiwavelength campaign a modeling of its broad-band Spectral Energy Distribution is also discussed.
43
Damon, Raphael Wesley. "Determination of the photopeak detection efficiency of a HPGe detector, for volume sources, via Monte Carlo simulations." Thesis, University of the Western Cape, 2005. http://etd.uwc.ac.za/index.php?module=etd&.
Анотація:
The Environmental Radioactivity Laboratory (ERL) at iThemba LABS undertakes experimental work using a high purity germanium (HPGe) detector for laboratory measurements. In this study the Monte Carlo transport code, MCNPX, which is a general-purpose Monte Carlo N &minusParticle code that extends the capabilities of the MCNP code, developed at the Los Alamos National Laboratory in New Mexico, was used. The study considers how various parameters such as (1) coincidence summing, (2) volume, (3) atomic number (Z) and (4) density, affects the absolute photopeak efficiency of the ERL&rsquo
s HPGe detector in a close geometry (Marinelli beaker) for soil, sand, KCl and liquid samples. The results from these simulations are presented here, together with an intercomparison exercise of two MC codes (MCNPX and a C++ program developed for this study) that determine the energy deposition of a point source in germanium spheres of radii 1 cm and 5 cm.
A sensitivity analysis on the effect of the detector dimensions (dead layer and core of detector crystal) on the photopeak detection efficiency in a liquid sample and the effect of moisture content on the photopeak detection efficiency in sand and soil samples, was also carried out. This study has shown evidence that the dead layer of the ERL HPGe detector may be larger than stated by the manufacturer, possibly due to warming up of the detector crystal. This would result in a decrease in the photopeak efficiency of up to 8 % if the dead layer of the crystal were doubled from its original size of 0.05 cm. This study shows the need for coincidence summing correction factors for the gamma lines (911.1 keV and 968.1 keV) in the 232Th series for determining accurate activity concentrations in environmental samples. For the liquid source the gamma lines, 121.8 keV, 244.7 keV, 444.1 keV and 1085.5 keV of the 152Eu series, together with the 1173.2 keV and 1332.5 keV gamma lines of the 60Co, are particularly prone to coincidence summing. In the investigation into the effects of density and volume on the photopeak efficiency for the KCl samples, it has been found that the simulated results are in good agreement with experimental data. For the range of sample densities that are dealt with by the ERL it has been found that the drop in photopeak efficiency is less than 5 %. This study shows that the uncertainty of the KCl sample activity measurement due to the effect of different filling volumes in a Marinelli beaker is estimated in the range of 0.6 % per mm and is not expected to vary appreciably with photon energy. In the case of the effect of filling height on the efficiency for the soil sample, it was found that there is a large discrepancy in the trends of the simulated and experimental curves. This discrepancy could be a result of the use of only one sand sample in this study and therefore the homogeneity of the sample has to be investigated. The effect of atomic number has been found to be negligible for the soil and sand compositions for energies above 400 keV, however if the composition of the heavy elements is not properly considered when simulating soil and sand samples, the effect of atomic number on the absolute photopeak efficiency in the low energy (<
400 keV) region can make a 14 % difference.
44
Majumdar, Jhilik [Verfasser], and Dieter [Akademischer Betreuer] Horns. "Gamma-ray spectral modulations of astrophysical sources caused by photon-ALPs mixing / Jhilik Majumdar ; Betreuer: Dieter Horns." Hamburg : Staats- und Universitätsbibliothek Hamburg, 2018. http://d-nb.info/1163013609/34.
45
Al, Samarai Imen. "Search for neutrinos from transient sources with the ANTARES neutrino telescope and optical follow-up observations : Development of hemispheric hybrid Photomultipliers for astroparticle experiments." Thesis, Aix-Marseille 2, 2011. http://www.theses.fr/2011AIX22116.
Анотація:
Les expériences d’astroparticules n’ont cessé de fleurir ces dix dernières années dans le but de connaître l’origine des rayons cosmiques et les procédés mis en œuvre dans leur accélération à des ultra-hautes énergies. Les télescopes Cherenkov tels que ANTARES détectent la lumière Cherenkov issue des muons se propageant dans l’eau de mer méditerranée. Les muons sont les produits d’interaction de neutrinos cosmiques (signal) ou atmosphériques (bruit) avec les noyaux de la terre. Pour offrir les meilleures conditions de détection de la lumière Cherenkov, et par conséquent bien reconstruire les traces des muons détectés, les détecteurs de lumière i.e les photomultiplicateurs doivent satisfaire plusieurs conditions. Le premier volet de cette thèse porte sur le développement de photomultiplicateurs utilisant le cristal comme préamplificateur de signal optique. L’avantage d’un tel procédé est la possibilité de séparer plusieurs pics photo-électrons et d’améliorer la résolution tem- porelle grâce à un fort champ électrique. La conception d’un tel prototype et la possibilité de son industrialisation à grande échelle sont développés pour la première fois dans cette thèse. Le deuxième volet s’inscrit dans la nouvelle thématique multi-messagers d’ANTARES.Un suivi avec six télescopes optiques répartis sur chaque hémisphère est déclenché lorsque ANTARES détecte un neutrino de haute énergie ou un ensemble de neutrinos coïncidents en temps et en direction. Un tel système permet d’augmenter la sensibilité de détection de neutrinos provenant de sources transitoires tels que les sursauts gamma et les Supernovæ à effondrement de cœur. Un système d’alertes neutrino est maintenant implémenté et fonctionne continument et de manière autonome sur ANTARES. Le système offre de bonnes performances; le suivi optique se déclenche dans la minute suivant la détection neutrino et l’incertitude sur la reconstruction de la trajectoire du neutrino est de 0.4◦ (valeur médiane). Une fois l’alerte reu çe par un des télescopes, celui-ci se repositionne sur la direction du neutrino et entame une série d’observations réparties sur le mois suivant l’alerte. Cette thèse a porté dans un premier temps sur l’aspect neutrino en développant le filtre sélectionnant les évènements haute énergie et multi-neutrinos. Des outils d’analyse d’images optiques ont ensuite été implémentés pour la recherche de sources transitoires. Les premiers résultats de recherche de contreparties optiques de sursauts gamma en corrélation avec un signal neutrino sont présentésAstroparticle experiments are being developed with the aim of resolving the mystery of cosmic rays. Questions like from where cosmic rays originate or how do they get accelerated up to ultra high energies are still unresolved. Cherenkov telescopes like ANTARES detect the Cherenkov light emitted by muons propagating in the sea water. Muons are produced by the interaction of cosmic neutrinos (signal) or atmospheric neutrinos (noise) with the Earth nuclei.In order to offer the best detection conditions of Cherenkov light, and subsequently ensure a good reconstruction quality of the muons trajectory, the light sensors i.e the photomultipliers must satisfy various conditions.The first part of this thesis focuses on the development of photomultipliers using crystals as a preamplifier of the light signal. The advantage of such a method is the possibility to separate individual photo-electrons and to enhance the temporal resolution by applying a high electric field.The design and conception as well as the possibility to produce such devices at large industrial scales is for the first time developed in this thesis.The second part of the thesis is inspired from the new multi-messenger approach in ANTARES. An optical follow-up with six telescopes spread over the two hemispheres is triggered by the detection of a high energy neutrino or a set of neutrinos coincident in time and direction. Such a system enhances the sensitivity to transient sources such as Gamma Rays Bursts (GRB) or Core Collapse Supernovae. The neutrino alert system is now fully operational. The system offers good performances; the optical follow-up starts within one minute from the neutrino detection and the median angular accuracy of the reconstructed neutrinos is 0.4$^circ$.Upon the reception of an alert, the telescopes point at the neutrino direction and start the acquisition of image series almost each night of the month following the neutrino alert. Image analysis tools have been implemented to search for optical transients; First results on the search of GRB optical counterparts correlated with a neutrino signal are presented
46
Couturier, Camille. "Invariance de Lorentz et Gravité Quantique : contraintes avec des sources extragalactiques variables observées par H.E.S.S. et Fermi-LAT." Thesis, Paris 6, 2014. http://www.theses.fr/2014PA066555/document.
Анотація:
Des modèles de Gravité Quantique (QG) prédisent une violation de l'invariance de Lorentz (LIV), se manifestant par une dispersion de la lumière dans le vide. Si un tel effet existe, des photons d'énergies différentes émis en même temps par une source distante sont détectés sur Terre à des moments différents. Les émissions transitoires à (très) hautes énergies provenant de sources astrophysiques lointaines, comme les sursauts gamma (GRBs) et les blazars sont utilisées pour contraindre cet effet LIV. Cet ouvrage présente les études menées avec deux télescopes gamma majeurs : H.E.S.S. -- pour lequel une étude de la qualité des données étalonnées a été réalisée -- et Fermi-LAT. Les énergies et les temps d'arrivée de photons individuels ont été utilisés pour contraindre le paramètre de dispersion dans le vide ainsi que l'échelle d'énergie E_QG à laquelle des effets LIV peuvent apparaitre. La méthode de maximum de vraisemblance est décrite, avec une étude détaillée des systématiques. Une modification dans le cas de fond non négligeable est appliquée aux données de l'éruption d'un blazar observé par H.E.S.S. : les limites obtenues sur E_QG sont moins contraignantes que les meilleures limites précédentes, mais elles se trouvent à un redshift non couvert à ce jour. Quatre GRBs observés par Fermi-LAT ont aussi été analysés, en déterminant la courbe de lumière de deux manières : ajustements gaussiens et estimation par densité de noyaux. Les meilleures limites sur E_QG pour le cas linéaire/subluminal sont obtenus avec GRB090510 : E_QG,1 > 7,6 E_Planck. Des limites plus robustes, tenant compte des effets intrinsèques à la source, ont également été produitesSome Quantum Gravity (QG) theories allow for a violation of Lorentz invariance (LIV), manifesting as a dependence on the velocity of light in vacuum on its energy. If such a dependence exists, then photons of different energies emitted together by a distant source will arrive at the Earth at different times. (Very) high energy transient emissions from distant astrophysical sources such as Gamma-ray Bursts (GRBs) and blazars can be used to search for and constrain LIV. This work presents the studies obtained with two leading Gamma-ray telescopes: H.E.S.S. -- for which a study of the quality of the calibrated data was performed -- and Fermi-LAT. The energies and arrival times of individual photons were used to constrain the vacuum dispersion parameter and the energy scale EQG at which QG effects causing LIV may arise. The maximum likelihood method is described, with detailed studies of the systematics. A modification for a non-negligible background is provided and applied to the data of an AGN flare observed by H.E.S.S.: the obtained limits on the QG energy scale are less constraining than the previous best limits obtained with blazars; yet, the new limits lie a redshift range not covered this far. Four bright and quasi background-free GRBs observed by the Fermi-LAT were also analysed, with two different template light curve determinations -- Gaussian fits and Kernel Density Estimates. The best limits on the E_QG scale for the linear/subluminal case are from the shortest burst, GRB090510: E_QG,1 > 7.6 E_Planck. More robust limits, considering the intrinsic effects possibly occurring at the source, were also derived
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Lyons, Karl. "The sensitivity of the Durham Mk6 ground-based atmospheric Cherenkov telescope to very high energy gamma-ray sources." Thesis, Durham University, 2001. http://etheses.dur.ac.uk/3843/.
Анотація:
The subject of this thesis is a determination of the sensitivity of the Durham Mk6 ground based Imaging Atmospheric Cherenkov Telescope (lACT), an instrument which uses the imaging atmospheric Cherenkov technique to detect Very High Energy (VHE) gamma-rays. The first three chapters are introductory: Chapter 1 describes the basics of Very High Energy (VHE) gamma ray astronomy. Chapter 2 describes the properties of Extensive Ak Showers (EAS). Chapter 3 describes the detection of these EAS on the ground by lACTs, Chapter 4 details the Durham Mk6 lACT and includes a description of the Cherenkov imaging technique for background discrimination. Chapter 5 describes the MOCCA and SOLMK simulation codes. Chapter 6 contains a description of the details of the simulations produced for this diesis. This chapter continues to its logical conclusion and presents a revised VHE gamma-ray flux of 2.5 ± 0.7(_stat) [+0.5 or -1.6](_syst x lO(_7) photons m(^-2) s(^-1) for a sub set of a previously published data set which gave a 6.8σ detection of the close X-ray selected BL Lac PKS 2155-304. Chapter 7 discusses the importance of PKS 2155- 304 and presents 3σ flux limits for another seven Southern hemisphere AGN observed between 1996 and 1999 using the Durham Mk6 IACT. Finally there is a short discussion on the future of VHE gamma-ray astronomy.
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Chin, Michael Raymond. "The design of a mobile synthetic aperture collimated gamma detector for passive HEU sources." Thesis, Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/50214.
Анотація:
This thesis covers the individual work of Michael Chin as part of the sponsored research project funded by the U.S. State Department in support of a computational design of a "Mobile Pit Verification System" (MPVS), a mobile “drive by” passive radiation detection system to be applied in special nuclear materials (SNM) storage facilities for validation and compliance purposes. The MPVS system is intended to enable a comprehensive, rapid verification and validation of stored nuclear weapon core physics packages containing SNM, or so-called “weapon pits,” in weapon materials and stockpile storage facilities. The MPVS platform is designed to move at a constant speed and accumulate a signal for each stored weapon pit container. The gamma detector was selected to be a 4 × 4 × 8 cubic inch CsI detector while the neutron detector array designed for the “Transport Simulation and Validation of a Synthetic Aperture SNM Detection System (“T-SADS”) project was used in conjunction with this work; T-SADS was a 3 year project funded by DOE-NNSA which was completed on May 2013.
The computational design effort for this project was completed in April 2013, and leveraged novel computational radiation transport methods, algorithms, and SNM identification methods, including a synthetic aperture collection approach, and a new gamma ratio methodology for distinguishing between naturally occurring radiation materials and weapon class SNM materials. Both forward and adjoint transport methods were utilized to characterize the adjoint reaction rate as a function of inter-source spacing, collimation thickness, linear and angular field of view, source age, source type, source geometry, and mobile platform speed. The integrated count was then compared with background radiation and the associated probabilities of detection and false alarm were then computed.
Publications resulting from this research were published in PHYSOR 2012, presented at the 53rd annual Proceedings of the INMM, and at the Mathematics & Computation 2013 Conference.
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Allyson, Julian David. "Environmental gamma-ray spectrometry : simulation of absolute calibration of in-situ and airborne spectrometers for natural and anthropogenic sources." Thesis, University of Glasgow, 1994. http://theses.gla.ac.uk/2028/.
Анотація:
The purpose of this work is to investigate experimentally and theoretically a range of problems encountered in calibration of -ray spectrometers (converting count rates to radioelement ground concentrations), for the natural and manmade radionuclides. For in-situ and aerial survey measurements, the form of radionuclide deposition with soil depth, aerial survey altitude, and detector spectral responses are important considerations when calibrating detector systems. A modification of spectral shape is apparent, owing to scattering and attenuation in the soil and air path between source and detector. A variety of depth profiles and detector configurations have therefore been considered, which are usually encountered in practice. It has been shown for the first time, that it is possible to reconstruct the full spectral response of a detector to calibrate a spectrometer from absolutely theoretical first principles. In doing so, one can avoid some of the problems inherent in experimental approaches. After overcoming technical and methodological problems, the work has been successful in all of its objectives. Experimental investigations of in-situ and aerial survey detectors serve as useful validation studies for theoretical models of the same detector types. The research therefore began with laboratory based measurements using point sources of radionuclides of interest. The acquisition of doped concrete calibration pads has enabled comparisons to be made with other facilities and spectrometers found world-wide. Small scale experimental simulations of detector responses at different altitudes have been made using the calibration pads and perspex absorbers. This extends and improves upon previous work done elsewhere, and uses more suitable absorber types. For the consideration of full energy responses only, analytical methods can be conveniently applied.
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Stycz, Kornelia [Verfasser], Thomas [Gutachter] Lohse, Marek [Gutachter] Kowalski, and Mathieu de [Gutachter] Naurois. "VHE Gamma-ray sources at the resolution limit of H.E.S.S / Kornelia Stycz. Gutachter: Thomas Lohse ; Marek Kowalski ; Mathieu de Naurois." Berlin : Mathematisch-Naturwissenschaftliche Fakultät, 2016. http://d-nb.info/1102992917/34.