To see the other types of publications on this topic, follow the link: Gamma rays.
Dissertations / Theses on the topic 'Gamma rays'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Gamma rays.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Richardson, K. M. "Gamma rays, cosmic rays and local molecular clouds." Thesis, Durham University, 1988. http://etheses.dur.ac.uk/942/.
Full text
2
battersby, Stephen Joseph Richard. "Gamma-rays and active galaxies." Thesis, Imperial College London, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.336471.
Full text
3
Latham, Ian James. "V.H.E. gamma rays from microquasars." Thesis, Durham University, 2006. http://etheses.dur.ac.uk/2946/.
Full textAbstract:
This thesis is concerned with the detection of very high energy (VHE) 7-rays from microquasars, a recently discovered subclass of x-ray binaries that display jets of relativistic particles. A general introduction to ground based 7-ray astronomy is presented, which discusses the production of Cherenkov radiation and how VHE 7-rays are detected via extended air showers in the atmosphere. The important processes involved in the production and absorption of 7-rays are detailed, before the design of The High Energy Stereoscopic System (H.E.S.S.) Phase I telescope array, based in Namibia, is briefly described. There follows a general section on microquasars, describing x-ray binaries and the morphological analogy between microquasars and active galactic nuclei (AGN). Some important properties of jets are detailed before the spectral states of x-ray binaries and their importance in relation to jets are discussed. A synchrotron self-Compton (SSC) model designed for AGN is reviewed in some detail and is applied to the blazar 3C 279, showing a good fit to data. This SSC model is then applied to the microquasars GRS 1915+105, V4641 Sgr and GX 339-4 using a scale-invariant method to investigate if the jets from microquasars can be considered simply as scaled down AGN jets. Conclusions are drawn from the results. Data taken with H.E.S.S. on four microquasars are presented. The techniques used to take and analyse this data are described in some detail using data taken on the Crab nebula as an example of a VHE 7-ray emitter, before the analysis results for observations of GRS 1915+105, Circinus X-1, GX 339-4 and V4641 Sgr are presented. A novel method for manufacturing aluminum mirrors suitable for use on ground based 7-ray telescopes is described in detail along with the testing techniques used. The next generation telescope, H.E.S.S. Phase II is then described briefly. The thesis concludes with a brief outline of future work to be conducted, based on the SSC model, as applied to microquasars. A proposal for observations of IGR J19140+0951, which was tentatively detected in the field of GRS 1915+105, is outlined.
4
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.
Full text
5
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.
Full text
6
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.
Full text
7
Kirkman, Ian W. "VHE gamma rays from celestial objects." Thesis, Durham University, 1985. http://etheses.dur.ac.uk/7850/.
Full textAbstract:
This Thesis describes and discusses the results obtained from observations of the astronomical objects Cygnus X-3 and the Crab Pulsar, made during 1981 and 1982 using the Very High Energy (VHE) Gamma Ray Astronomy Facility of the University of Durham. Following an introductory chapter, chapter two describes the observational technique used for the work (known as the 'Atmospheric Cerenkov Technique') and chapter three describes in some detail the design, construction and operation of the equipment. Chapter four summarises the data taken during the course of the observations, whilst chapter five describes the analysis techniques used in the examination of this data. Chapter six presents the results derived from these analyses and, finally, chapter seven discusses their implications, both for the objects themselves and for the field of Astrophysics generally. Unless otherwise stated, the Author has either been principally responsible for, or has played an important part in the production of, all the work reported in this Thesis.
8
Abdelrahman, Y. S. "Prompt gamma-rays from fission fragments." Thesis, University of Manchester, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.234192.
Full text
9
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.
Full text
10
Gabici, Stefano. "Gamma ray astronomy and the origin of galactic cosmic rays." Habilitation à diriger des recherches, Université Paris-Diderot - Paris VII, 2011. http://tel.archives-ouvertes.fr/tel-00719791.
Full textAbstract:
Diffusive shock acceleration operating at expanding supernova remnant shells is by far the most popular model for the origin of galactic cosmic rays. Despite the general consensus received by the model, an unambiguous and conclusive proof of the supernova remnant hypothesis is still missing. In this context, the recent developments in gamma ray astronomy provide us with precious insights into the problem of the origin of galactic cosmic rays, since production of gamma rays is expected both during the acceleration of cosmic rays at supernova remnant shocks and during their subsequent propagation in the interstellar medium. In particular, the recent detection of a number of supernova remnants at TeV energies nicely fits with the model, but it still does not constitute a conclusive proof of it, mainly due to the difficulty of disentangling the hadronic and leptonic contributions to the observed gamma ray emission. The main goal of my research is to search for an unambiguous and conclusive observational test for proving (or disproving) the idea that supernova remnants are the sources of galactic cosmic rays with energies up to (at least) the cosmic ray knee. Our present comprehension of the mechanisms of particle acceleration at shocks and of the propagation of cosmic rays in turbulent magnetic fields encourages beliefs that such a conclusive test might come from future observations of supernova remnants and of the Galaxy in the almost unexplored domain of multi-TeV gamma rays.
11
Esau, Andrew John. "Monte Carlo Simulations of Complex Germanium Escape Suppression Spectrometers with MCNPX a Case Study." Thesis, University of the Western Cape, 2009. http://etd.uwc.ac.za/index.php?module=etd&action=viewtitle&id=gen8Srv25Nme4_7899_1276453432.
Full textAbstract:
<p>Gamma ray spectroscopy has provided enormous amounts of information on the behaviour and structure of atomic nuclei [SHA88, BEA92, EBE08]. Most of the major discoveries in experimental nuclear physics over the last five decades are strongly associated with improvements in detector technologies. Inorganic scintilators led to the discovery in 1963 of the first excited states of a rotational band based on the ground state of 162Dy. Improvements in peak-to-background ratios and detector resolutions obtained with germanium led to the first evidence of backbending which is associated with a two quasi-particle excitation in 162Dy [SHA88]. More recently the development of composite and highly-segmented Ge detectors has significantly increased the performance and power of detection systems. The Clover detector is such a detector system and is in use at iThemba LABS. This study concerns the evaluation of the particle transport code MCNPX 2.5.0 as a tool to model complex composite detectors such as the Clover. Lanthanum silicate (LSO) and Lead tungstate (PbWO) are also evaluated as possible suppressor shield materials. It is shown that reasonable agreement between experiment and simulation is found when the experiment is accurately reproduced. However, when complex detection modes are implemented in the detector based on the number of elements that fire, MCNPX cannot be used to model the detector performance exactly. Differences between simulated and experimental results are found in suppressed add-back mode. It is proposed that the discrepancies are due to limitations in implementation of the pulse-height and special anti-coincidence tally in MCNPX. LSO and PbWO are compared to BGO as suppressor shield materials. It is found that LSO is not an ideal material for a suppression shield. PbWO is shown to give performance values similar to that of BGO. The back-plug is shown to have no effect on the Peak-to-Total ratio but is effective at reducing the background at lower energies.</p>
12
Calle, PeÌrez Ignacio de la. "Detection of high energy gamma rays from X-ray selected blazars." Thesis, University of Leeds, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.270857.
Full text
13
Reesman, Rebecca R. "Gamma-Rays as Probes of the Universe." The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1406122854.
Full text
14
Chandler, Adam M. Prince Thomas A. "Pulsar searches : from radio to gamma-rays /." Diss., Pasadena, Calif. : California Institute of Technology, 2003. http://resolver.caltech.edu/CaltechETD:etd-01232003-213508.
Full text
15
Pinzke, Anders. "Gamma-Ray Emission from Galaxy Clusters : DARK MATTER AND COSMIC-RAYS." Doctoral thesis, Stockholms universitet, Fysikum, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-42453.
Full textAbstract:
The quest for the first detection of a galaxy cluster in the high energy gamma-ray regime is ongoing, and even though clusters are observed in several other wave-bands, there is still no firm detection in gamma-rays. To complement the observational efforts we estimate the gamma-ray contributions from both annihilating dark matter and cosmic-ray (CR) proton as well as CR electron induced emission. Using high-resolution simulations of galaxy clusters, we find a universal concave shaped CR proton spectrum independent of the simulated galaxy cluster. Specifically, the gamma-ray spectra from decaying neutral pions, which are produced by CR protons, dominate the cluster emission. Furthermore, based on our derived flux and luminosity functions, we identify the galaxy clusters with the brightest galaxy clusters in gamma-rays. While this emission is challenging to detect using the Fermi satellite, major observations with Cherenkov telescopes in the near future may put important constraints on the CR physics in clusters. To extend these predictions, we use a dark matter model that fits the recent electron and positron data from Fermi, PAMELA, and H.E.S.S. with remarkable precision, and make predictions about the expected gamma-ray flux from nearby clusters. In order to remain consistent with the EGRET upper limit on the gamma-ray emission from Virgo, we constrain the minimum mass of substructures for cold dark matter halos. In addition, we find comparable levels of gamma-ray emission from CR interactions and dark matter annihilations without Sommerfeld enhancement.<br>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Accepted.
16
Beckmann, Volker. "Unification of Active Galactic Nuclei at X-rays and soft gamma-rays." Habilitation à diriger des recherches, Université Paris-Diderot - Paris VII, 2010. http://tel.archives-ouvertes.fr/tel-00601042.
Full textAbstract:
Through the work on X-ray and gamma-ray data of AGN I contributed significantly to the progress in the unification of AGN since I finished my PhD in 2000. <p> The study of the evolutionary behaviour of X-ray selected blazars (Beckmann & Wolter 2001; Beckmann et al. 2002, 2003b; Beckmann 2003) shows that their evolution is not as strongly negative as indicated by previous studies. The overall luminosity function is consistent with no evolution in the 0.1−2.4 keV band as seen by ROSAT/PSPC. There is still a difference compared to the luminosity function of FSRQ and LBL, which seem to show a positive evolution, indicating that they have been more luminous and/or numerous at cosmological distances. We indicated a scenario in order to explain this discrepancy, in which the high luminous FSRQ develop into the fainter LBL and finally into the BL Lac objects with high frequency peaks in their spectral energy distribution but overall low bolometric luminosity. <p> Studying the variability pattern of hard X-ray selected Seyfert galaxies, we actually found differences between type 1 and type 2 objects, in the sense that type 2 seemed to be more variable (Beckmann et al. 2007a). This breaking of the unified model is caused by the different average luminosity of the absorbed and unabsorbed sources, as discussed in Sect. 4.7.3. This can be explained by a larger inner disk radius when the AGN core is most active (the so-called receding disc model). <p> The work on the sample characteristics of hard X-ray detected AGN also led to the proof that the average intrinsic spectra of type 1 and type 2 objects are the same when reflection processes are taken into account (Beckmann et al. 2009d). This also explains why in the past Seyfert 2 objects were seen to have harder X-ray spectra than Seyfert 1, as the stronger reflection hump in the type 2 objects makes the spectra appear to be flatter, although the underlying continuum is the same. <p> Further strong evidence for the unification scheme comes from the observation of a fundamental plane which connects type 1 and type 2 objects smoothly (Beckmann et al. 2009d). In addition, in the case of the Seyfert 1.9 galaxy MCG-05-23-016 I showed that the spectral energy distribution of this source and its accretion rate is similar to that of a Galactic binary (Beckmann et al. 2008a). <p> Throughout the studies I have shown that the intrinsic spectral shape appears to be very stable on weeks to year time scale (Beckmann et al. 2004d, 2005b, 2007b, 2008a). This implies that the overall geometry of the AGN over these time scales did not change dramatically. The variations in intensity can then be explained in two ways: either the amount of material emitting the hard X-rays varies, or the amount of plasma visible to the observer varied, e.g. through different orientation of the disk with respect to the observer. In an upcoming paper we will show though, that NGC 4151 indeed also shows different spectral states, similar to the low-hard versus high-soft spectra in Galactic black hole binaries (Lubinski et al. 2010). A similar result seems to emerge from our INTEGRAL studies on NGC 2110 (Beckmann & Do Cao 2011). For INTEGRAL's AO-8 I have submitted a proposal in order to study spectral states in the Seyfert 2 galaxy NGC 2992, which seems to show a state change over the past 5 years as seen in Swift/BAT longterm monitoring. <p> The work on the luminosity function of AGN at hardest X-rays (Beckmann et al. 2006d) had a large impact on our understanding of the cosmic X-ray background. As this was the first study of its kind, it showed for the first time that indeed the fraction of highly obscured Compton thick AGN is much lower than expected before the launch of INTEGRAL and Swift. The X-ray luminosity function we revealed is indeed not consistent with the source population seen by INTEGRAL (Beckmann et al. 2006a, 2009d; Sazonov et al. 2007) and Swift (Tueller et al. 2008) being the only contributors to the cosmic hard X-ray background. Thus other sources outside the parameter space observable by these missions have to contribute significantly to the cosmic X-ray background. Our work on the luminosity function triggered several other studies on this issue. The subsequent derived luminosity functions by other groups (Sazonov et al. 2007; Tueller et al. 2008; Paltani et al. 2008) are consistent with our findings. <p> This also gave rise to an increased interest in the exact shape of the Cosmic X-ray background around its peak at 30 keV, triggering several attempts to a new measurement. Background studies were presented based on a Earth-occultation observation by INTEGRAL (Churazov et al. 2007, 2008; Türler et al. 2010) and by Swift (Ajello et al. 2008). <p> The understanding of the emission processes in AGN requires knowledge over a wide range of the spectral energy distribution (SED). In studies using CGRO/EGRET and Fermi/LAT data I derived the SED for blazars and non-blazars towards the gamma-ray range (Beckmann 2003; Beckmann et al. 2004b, 2010b). The work on the LAT data not only presented the gamma-ray detection of five gamma-ray blazars (QSO B0836+710, RX J1111.5+3452, H 1426+428, RX J1924.8-2914, and PKS 2149-306) for the first time, but also showed the potential in the combination of INTEGRAL and Fermi data. In the case of Cen A I derived the total energy output of the inverse Compton component based on the combined LAT, ISGRI, and JEM-X data, showing evidence for a spectral break at several hundred keV (Beckmann et al. 2010b). <br> In addition I successfully showed that gamma-ray blazars can be predicted through the study of their synchrotron branch at energies below 2 keV (Beckmann 2003 and this work). <p> Contributions of mine to research in fields other than AGN include the study of INTEGRAL detected gamma-ray bursts (e.g. Beckmann et al. 2003a, 2004a, 2008b, 2009a). Here and in collaboration with other colleagues I showed the potential of INTEGRAL data on GRB research. In the field of Galactic X-ray binaries I published one of the first Swift results on a newly discovered highly absorbed HMXB, IGR J16283-4838 (Beckmann et al. 2005a, 2006b). I also contributed significantly to analysis of many other Galactic sources, as shown in Section 4.6.1.
17
Rengifo, Gonzáles Javier. "Disentangling atmospheric cascades started by gamma rays from cosmic rays with CORSIKA." Master's thesis, Pontificia Universidad Católica del Perú, 2017. http://tesis.pucp.edu.pe/repositorio/handle/123456789/8716.
Full textAbstract:
En este trabajo buscamos un método para diferenciar entre lluvias de partículas producidas por rayos cósmicos y por rayos gamma a energías de TeV, utilizando simulaciones CORSIKA. Este método intenta resolver el problema que existe en la búsqueda de señales de rayos gamma medidos por diversos experimentos frente a un fondo de flujo dominante de hadrones. Los resultados de este trabajo pueden aplicarse al estudio de Explosiones de Rayos Gamma (GRBs). Los GRBs emiten fotones muy energéticos, que al interactuar con la atmósfera terrestre, producen una gran cascada electromagnética de partículas secundarias, las cuales son detectables.
El procedimiento sería simular eventos producidos por fotones, la señal, y protones, el fondo, que son las partículas más abundantes de los rayos cósmicos. Extraemos varios parámetros de los perfiles longitudinales de las lluvias de partículas, caracterizando las lluvias simuladas. Algunos de los parámetros de ajuste más importantes son el m_aximo de lluvia (Xmax), el ancho de la lluvia FWHM, el parámetro de asimetría, el número máximo de partículas Nmax y el comienzo de lluvia XStart. Existen diferentes experimentos utilizando tanques Cherenkov de agua y detectores de fluorescencia que pueden medir estos parámetros de las lluvias.
Hemos probado dos métodos. El primero se basa en cortes simples, mientras que el segundo se basa en un análisis multivariado utilizando el paquete TMVA, que mejora los cortes individuales. El primer método se aplicó a las energías simuladas separadas de 102, 103, 104 y 105 GeV para encontrar cortes adecuados.
Encontramos que Xmax, FWHM, Xstart y Nmax dependen de la energía.
Posteriormente aplicamos estos cortes dependientes de la energía y otros cortes
fijos a una muestra realista, que consiste en 104 eventos de señales (fotones) y 106 eventos de fondo (protones) que cubren un rango de energía de 102 a 105 GeV con diferentes espectros. Además, se introdujo un error en la energía simulada para simular la eficiencia de reconstrucción de energía de un detector. El resultado obtenido deja 54% eventos de señal y 12% eventos de fondo. Aplicando el análisis multivariado TMVA, encontramos que el método Boosted Decision Trees (BDT) era el mejor para distinguir la señal del fondo. El resultado para una eficiencia de señal similar fue 0:7% de eventos de fondo.
Por último, utilizando cortes más estrictos en la BDT para mejorar la significancia, el resultado fue 1 evento de fotón por cada 1000 eventos de protón. Dada la proporción de flujo inicial, significa una capacidad de rechazo de fondo de 103.
Por lo tanto, la viabilidad de la separación gamma/hadrón requiere una mejora adicional.<br>In this work we search for a method to differentiate between particle showers produced by cosmic rays and by gamma rays at TeV energies, using CORSIKA simulations. This method tries to solve the dominant hadron flux background problem when looking for gamma-ray signals measured by different experiments. The results of this work can be applied to the study of Gamma-Ray Bursts (GRBs).
GRBs emit very energetic photons, which after interacting in the Earth's atmosphere, produce a large detectable electromagnetic cascade of secondary particles.
The procedure will be to simulate events produced by photons, the signal, and protons, the most abundant cosmic-ray background. We extract several parameters from fitting particle air-shower longitudinal profiles, characterizing the simulated showers. Some of the most important _t parameters are the shower maximum (Xmax), the width of the shower FWHM, the asymmetry parameter, the maximum number of particles Nmax and the shower start Xstart. There are different experiments using water Cherenkov tanks and fluorescence detectors which can measure these shower parameters.
We tested two methods. The first relies on simple cuts, while the second is based on a multivariate analysis using the TMVA package, which improves individual cuts. The first method was applied to single simulated energies of 102, 103, 104 and 105 GeV to find adequate cuts. We found that Xmax, FWHM, Xstart and Nmax depend on the energy. Later we applied these energy-dependent cuts and other fixed cuts to a realistic sample, which consists of 104 signal events (photons) and 106 background events (protons) covering an energy range from 102 to 105 GeV with different spectra. Moreover, we introduced an energy smearing to simulate a detector energy reconstruction efficiency. The obtained result leaves 54% signal events and 12% background events. Applying the multivariate analysis TMVA, we found that the Boosted Decision Trees (BDT) method was the best for distinguishing signal from background. The result for a similar signal efficiency was 0:7% of background events.
Finally using tighter cuts on the BDT to improve the significance results in 1 photon event for every 1000 protons. Given the initial ux proportion, it means a 103 background rejection capability. Thus the feasibility of gamma/hadron separation requires further improvement.<br>Trabajo de investigación
18
James, Kory T. "High energry gamma-ray source search with SPASE-2." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 65 p, 2007. http://proquest.umi.com/pqdweb?did=1397914891&sid=16&Fmt=2&clientId=8331&RQT=309&VName=PQD.
Full text
19
Banik, Prabir. "Probing the sources of cosmic rays with high energy gamma rays and neutrinos." Thesis, University of North Bengal, 2017. http://hdl.handle.net/123456789/2711.
Full text
20
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.
Full text
21
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.
Full text
22
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/.
Full textAbstract:
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.
23
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/.
Full textAbstract:
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.
24
Seglar-Arroyo, Monica. "Studying the origin of cosmic-rays : Multi-messenger studies with very-high-energy gamma-ray instruments." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLS260.
Full textAbstract:
Les phénomènes explosifs qui se produisent dans l'Univers à haute énergie sont capables d'accélérer les particules jusqu'aux énergies les plus élevées. Ces processus produisent des particules secondaires de nature différente, c'est-à-dire des photons et des neutrinos. Dans des cas particuliers, ces événements induisent des perturbations sur l'espace-temps, c'est-à-dire des ondes gravitationnelles détectables par des interféromètres sur Terre. La combinaison des informations complémentaires fournies par ces messagers cosmiques peuvent permettre de répondre à des questions ouvertes en astrophysique. Parmi les événements les plus violents qui produisent de tels signaux figurent la fusion des deux objets les plus denses, comme les étoiles à neutrons et les trous noirs ou l'activité accréatrice dans les galaxies sur un trou noir supermassif. Dans ce travail, nous nous concentrons sur les photons à très haute énergie que produisent ces événements extrêmes, et sur la connexion avec les autres contreparties, afin de fournir une image globale multi-messagers qui permet l'étude des mécanismes physiques en place. Les défis inhérents à l'astronomie multi-messager dans le domaine temporel, ce qui implique un effort mondial coordonné et simultané entre les installations et les disciplines astronomiques, sont discutés et abordés. Une nouvelle stratégie d'observation optimisée du suivi de l'eau souterraine pour les petits et moyens instruments de FoV comme le H.E.S.S. et le futur CTA, capable d'apporter une réponse rapide aux alertes, qui prend en compte les risques caractéristiques de l'événement GW et maximise les chances de détecter la contrepartie électromagnétique, sera présentée. Cette stratégie s'est avérée fructueuse lors d'observations de suivi avec les télescopes H.E.S.S., et en particulier dans le cas de la première detection de la fusion d'une binaire d'étoiles à neutrons, GW170817. Dans le cadre du réseau AMON, une analyse multi-messagers qui combine des événements d'ondes gravitationnelles avec des données HAWC a été développée dans le but d'identifier les coïncidences astrophysiques à partir d'événements indépendants. De plus, la découverte par H.E.S.S. en très hautes énergies du noyau galactique actif OT 081, lors d'un état de flux élevé en juillet 2016, sera présentée<br>The explosive phenomena occurring in the high-energy Universe are able to accelerate particles up to the highest energies. These processes produce secondary particles of different nature, i.e. photons and neutrinos. In special cases, these events induce perturbations on the space-time, i.e. gravitational waves detectable by interferometers on Earth. The combination and the complementary information provided by these cosmic messengers may allow to answer open questions in astrophysics, as the origin of cosmic rays. Amongst the most violent events producing such signals are the merge of the two densest objects, as neutron stars and black holes or the accretion activity in galaxies onto a supermassive black hole. In this work, we focus on the very-high energy photons that these extreme events produce, and the connection with the other counterparts, in order to provide a broad multi-messenger picture which enables the study of the physical mechanisms in place. The challenges inherent to time-domain multi-messenger astronomy are discussed and tackled, which involves simultaneous coordinated worldwide effort across facilities and astronomical disciplines. A novel, optimized GW follow-up observation strategy for small/mid- FoV instruments as H.E.S.S. and the future CTA, able to perform a rapid response to alerts, which considers the characteristics of the GW event and maximizes the chances to detect the electromagnetic counterpart will be presented. This strategy was proven successful in follow-up observations with the H.E.S.S. telescopes and in particular in the case of the first ever detected binary neutron star merger, GW170817. In the context of the AMON network, a multi-messenger analysis that combines gravitational wave events with HAWC data, with the aim to identify astrophysical coincidences out of independent events, has been developed. In addition, the discovery by H.E.S.S. in very-high energies of the active galactic nucleus OT 081, during a flaring episode in July 2016, will be presented
25
Cardwell, David A. "Compton scattering with gamma-rays and synchrotron radiation." Thesis, University of Warwick, 1987. http://wrap.warwick.ac.uk/99433/.
Full textAbstract:
Directional Compton profile measurements of aluminium and chromium have been performed with 60 keV and 412 keV γ-radiation to assess the complementarity of the 241Am and 198Au spectrometer systems in common use by experimentalists. Revision of the data reduction procedure has yielded symmetrical Compton profiles within experimental error for the first time. The effects of exchange and correlation on theoretical Compton profiles calculated within the local density approximation have been evaluated via the Lam-Platzman correction and applied to existing transition metal results. Novel experiments using circularly polarised synchrotron radiation to detect the magnetic Compton profiles of iron and nickel have been performed successfully.
26
Dickinson, Hugh John. "Very high energy gamma-rays from binary systems." Thesis, Durham University, 2010. http://etheses.dur.ac.uk/290/.
Full textAbstract:
This thesis presents a study of the very high energy (VHE) gamma-ray emission from X-ray binary systems using the H.E.S.S. imaging atmospheric Cherenkov array. The historical background and basic principles of ground-based gamma-ray astronomy are briefly reviewed and an overview of the design and capabilities of the H.E.S.S. telescope system is presented. The broadband observational properties of X-ray binary systems and their relevance in a broader astrophysical context is also discussed. A review of the radiative emission mechanisms which relate to VHE gamma-ray emission in X-ray binaries is presented, with emphasis given to the leptonic emission processes of synchrotron radiation and inverse-Compton scattering. Intrinsic absorption processes which act to attenuate the emitted flux of VHE gamma-rays are also discussed. Three computer models are introduced which simulate aspects of the gamma-ray emission and absorption in X-ray binary systems. A detailed analysis of the VHE gamma-ray emission from the X-ray binary LS 5039 is presented and the relevant procedures for data selection, gamma-hadron separation and background estimation are discussed in some detail. Methods for the determination of detection significance and the calculation of gamma-ray fluxes are also reviewed and results are derived which apply specifically to LS 5039. A detailed temporal analysis of the gamma-ray signal from LS 5039 is presented, applying tests for secular, excess and periodic variability. Strong evidence is found for modulation of the observed gamma-ray flux on the orbital period of ~3.9 days. Following a brief discussion of the procedures required for spectral analysis of VHE gamma-ray data, results are presented for LS 5039 which reveal evidence for spectral variability which is correlated with the observed gamma-ray flux and therefore, the orbital phase of the binary system. The spectral and temporal characteristics of LS 5039 are then compared with the predictions of theoretical models in an attempt to explain the observed behaviour. Contemporaneous X-ray and VHE gamma-ray observations of three galactic microquasars using the Rossi X-ray Timing Explorer and H.E.S.S. are presented. Although no gamma-ray detections are reported, the observations permit the derivation of upper limits to the VHE gamma-ray flux which correspond to episodes of known X-ray behaviour. The X-ray characteristics of each target are compared with pre-existing observational data to infer the presence or otherwise of relativistic outflows at the H.E.S.S. observation epochs. The implications of the gamma-ray non-detections are then discussed in the context of these inferred system properties. The results of a survey of the VHE gamma-ray emission associated with the positions of 125 known X-ray binaries are presented. Although no conclusive detections were obtained, tentative indications were found for a population of faint, spectrally hard gamma-ray sources associated with high-mass X-ray binary systems. The inferred characteristics of the indicated population show broad agreement with the measured properties of known gamma-ray-emitting X-ray binary systems like LS 5039.
27
Cheung, Wai-man, and 張惠民. "Unpulsed gamma rays from the Crab pulsar and nebula." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1994. http://hub.hku.hk/bib/B31211306.
Full text
28
吳子皎 and Tze-kau Ng. "A study of diffuse galactic gamma radiation." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1989. http://hub.hku.hk/bib/B31209397.
Full text
29
Ng, Tze-kau. "A study of diffuse galactic gamma radiation /." [Hong Kong : University of Hong Kong], 1989. http://sunzi.lib.hku.hk/hkuto/record.jsp?B12584289.
Full text
30
Li, Chung-chuen. "Radiation exposure due to radon and gamma rays in Hong Kong /." Hong Kong : University of Hong Kong, 1991. http://sunzi.lib.hku.hk/hkuto/record.jsp?B13148400.
Full text
31
Giller, Graham L. "The construction and analysis of a whole-sky map using underground muons." Thesis, University of Oxford, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.386589.
Full text
32
DICHIARA, Simone. "A multiwavelength view of the transient sky: gamma-ray bursts and other fast transients from optical to gamma-rays." Doctoral thesis, Università degli studi di Ferrara, 2015. http://hdl.handle.net/11392/2389002.
Full text
33
Pracilio, Gabriella. "The utilisation of gamma ray spectrometry, a soil mapping technology, to improve dryland crop production /." Connect to this title, 2007. http://theses.library.uwa.edu.au/adt-WU2007.0099.
Full text
34
Ödmark, Fredrik. "Model based pulse shaping for detection of gamma rays." Thesis, Luleå tekniska universitet, Institutionen för system- och rymdteknik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-66637.
Full textAbstract:
To analyse drill samples in a mine, a scanner that uses a gamma ray detector can be used. The scanner can analyse the drill sample to quickly see the elements present in the sample without destroying it. To improve the performance of the scanner, the electric signal from the detector needs to be less noisy, and different pulse shaping methods, filters and smoothers can be used on the sampled data to achieve an improved performance. In this master thesis, the electric noise model of the electronics around the detector was modeled, and analysed. Different pulse shaping method, filters and smoothers was also tested to see which method gave the best performance in FWHM sense. The Full Width at Half Maximum (FWHM) is the energy resolution of a detector, and is defined as the full width of a photopeak at the half maximum. The noise model of the schematic for the preamplifier was made by hand with support from MATLAB. The resulting noise model was compared between MATLAB and LTspice, and the conclusion is that the JFET is the main contributor of the significant noise, contributing to 98 % of the total noise at 10 GHz. The adopted filters and pulse shaping method are, matched filter, custom filter, CR-RC shaping, mean filter, median filter and clustering. The results from the tests indicated that custom filter with a FWHM of 1.96 keV and CR-RC with a FWHM of 1.67 keV shaping were more accurate than the matched filter with the FWHM of 5.1 keV. But the results also showed that it is important to take into account the waveform variance, due to inherent properties in the detector, with this consideration the FWHM of CR-RC shaper was improved from 2.29 keV to 1.67 keV. The clustering method was the most promising method but due to time constraints this method was never fully tested and no FWHM value was achieved.
35
Saunders, Jessica. "Secondary prompt gamma-rays to improve proton range verification." Diss., Georgia Institute of Technology, 2016. http://hdl.handle.net/1853/55003.
Full textAbstract:
The goal of this research is to evaluate the secondary prompt gamma (PG) yield from proton therapy at high characteristic energies from MC model simulations and experimental data. Recent studies indicate that target composition influences PG characteristic energy and yield, and the quantification of PG may be used to offer real-time dose verification for proton therapy. In this study PG analysis was performed for MC simulations to evaluate the characteristic measurements and total yield of secondary PG emitted from a target in the 0-8 MeV range from a proton therapy beam over a range of four different beam energies (70 MeV, 160 MeV, 200 MeV, 220 MeV). This was repeated in several target materials (carbon, calcium oxide, calcium fluoride, PMMA, and HDPE) in order to evaluate the influence of the incident energy and the target material on the PG yield and energy spectra. PG energy spectra determined from the specified target materials indicated that the 3.74 MeV energy peak shows a linear correlation between PG intensity and calcium mass fraction of the target material. 6.13 MeV and 4.44 MeV energy peak are not unique to the respective, oxygen and combined oxygen and carbon, mass fraction of the target material. This relationship is complicated by the addition of calcium within the target. Experimental data was collected in order to validate the computational model based on comparison of relative characteristic energy peek intensities. The relative peak ratio determined from experimental data is in good agreement with model prediction, the combined peak ratio is within 0.2%.
36
Dutson, Kate Louise. "Gamma rays from galaxy clusters and their dominant members." Thesis, University of Leicester, 2014. http://hdl.handle.net/2381/29035.
Full textAbstract:
Clusters of galaxies are a long-expected source class of diffuse γ-ray emission, but a detection of such is yet to be made. Point-like signals from their dominant mem- bers are observed, and provide fresh insight into the processes involved in feedback from active galaxies, which suppress cooling in cluster cores, and inject non-thermal particles into the intracluster medium. The case for multi-scale γ-ray emission via leptonic and hadronic channels subse- quent to cosmic-ray acceleration, dark matter annihilation, and processes driven by the active nuclei of brightest cluster galaxies (BCGs), motivates the work. A temporal analysis of the source associated with the BCG NGC1275 is carried out; the high-energy (HE) emission (observed with Fermi) is compared with 1.3mm SMA data. No correlation is found on short timescales, however a gradual rising trend is common in both light curves, in agreement with the historical activity of the source, and suggestive of long-term variation in the fuelling of the black hole. Very-high-energy emission recorded with H.E.S.S. over the past decade from the BCG M87 is analysed spectrally, and compared with the HE activity of the source, and with NGC1275. Three samples of candidate HE sources are constructed: 114 galaxy clusters con- taining a radio-bright BCG (motivated by the detection of NGC1275 and M87), 105 hosting diffuse radio synchrotron emission, and the 90 most promising targets for dark matter annihilation signatures. Samplewise, candidate fields output from standard Fermi analyses are stacked. The upper limit on the emission within the stacked target region is at least an order-of-magnitude more constraining than lim- its on individual clusters in each case. A subset of local clusters are investigated as potential extended sources, yielding hints of diffuse emission from Perseus, and several individual fields are found to contain significant emission.
37
Cheung, Wai-man. "Unpulsed gamma rays from the Crab pulsar and nebula /." [Hong Kong : University of Hong Kong], 1994. http://sunzi.lib.hku.hk/hkuto/record.jsp?B13544536.
Full text
38
Wild, Walter James. "Gamma-ray imaging probes." Diss., The University of Arizona, 1988. http://hdl.handle.net/10150/184331.
Full textAbstract:
External nuclear medicine diagnostic imaging of early primary and metastatic lung cancer tumors is difficult due to the poor sensitivity and resolution of existing gamma cameras. Nonimaging counting detectors used for internal tumor detection give ambiguous results because distant background variations are difficult to discriminate from neighboring tumor sites. This suggests that an internal imaging nuclear medicine probe, particularly an esophageal probe, may be advantageously used to detect small tumors because of the ability to discriminate against background variations and the capability to get close to sites neighboring the esophagus. The design, theory of operation, preliminary bench tests, characterization of noise behavior and optimization of such an imaging probe is the central theme of this work. The central concept lies in the representation of the aperture shell by a sequence of binary digits. This, coupled with the mode of operation which is data encoding within an axial slice of space, leads to the fundamental imaging equation in which the coding operation is conveniently described by a circulant matrix operator. The coding/decoding process is a classic coded-aperture problem, and various estimators to achieve decoding are discussed. Some estimators require a priori information about the object (or object class) being imaged; the only unbiased estimator that does not impose this requirement is the simple inverse-matrix operator. The effects of noise on the estimate (or reconstruction) is discussed for general noise models and various codes/decoding operators. The choice of an optimal aperture for detector count times of clinical relevance is examined using a statistical class-separability formalism.
39
Guberman, Daniel Alberto. "MAGIC observations with bright Moon and their application to measuring the VHE gamma-ray spectral cut-off of the PeVatron candidate Cassiopeia A." Doctoral thesis, Universitat Autònoma de Barcelona, 2018. http://hdl.handle.net/10803/664122.
Full textAbstract:
Los rayos cósmicos son núcleos atómicos que constantemente bombardean la Tierra. Está largamente aceptado que estos núcleos con energías de hasta ~3 PeV son de origen Galáctico. Pero aún no se sabe dónde en la Galaxia ni cómo son acelerados. Durante muchos años la hipótesis más popular ha sido que son acelerados en remanentes de supernova. En esta tesis presento los detalles de una serie de observaciones de la joven remanente de supernova Cassiopeia A, uno de los candidatos más prometedores a ser un Pevatrón, un sistema capaz de acelerar rayos cósmicos hasta energías de PeV. Las observaciones fueron realizadas con los telescopios MAGIC, que observan rayos gamma de muy alta energía (VHE, E > 50 GeV), entre Diciembre de 2014 y Octubre de 2016, adquiriendo 191 horas de datos buena calidad. Acumular una gran cantidad de horas de observación era indispensable para obtener una medida precisa del espectro y fue posible gracias a la posibilidad de extender el tiempo activo de MAGIC operando los telescopios bajo una luminosidad lunar intensa. Trabajé en la optimización de las observaciones con Luna en MAGIC, tanto en el momento de operar los telescopios como en la etapa del análisis de los datos. Abordo los detalles de este desarrollo y evaluó su rendimiento. Con más del 70 % de las horas obtenidas con la Luna presente en el cielo, he podido obtener el espectro más preciso hasta ahora de Cassiopeia A en VHE. Por primera vez se encuentra evidencia de un corte a E = 3,5 (+1,6\—1,0) stat (+0,8\−0,9) sys TeV en el espectro. El
modelado de dicho espectro sugiere que la mayoría de los rayos gamma emitidos
pueden ser atribuidos a una población de protones de muy alta energía con un
índice espectral de ~2.2 y un corte a ~10 TeV. Esto implica que, asumiendo que no hay una difusión significativa d elos rayos cósmicos en el entorno de la supernova, Cassiopeia A no puede ser un PeVatrón en este momento.<br>Cosmic rays are atomic nuclei that are constantly bombarding the Earth. It is widely accepted that these nuclei with energies up to ~3 PeV are of Galactic origin. But the question about where in the Galaxy and how they are accelerated still remains unanswered. For several years the most popular hypothesis has been that they are accelerated in supernova remnants. In this thesis I present the details of a deep observation campaign on the young supernova remnant Cassiopeia A, one of the most promising candidates to be a PeVatron, a system capable of accelerating cosmic rays up to PeV energies. The observations were performed with the MAGIC telescopes, that observe very high energy (VHE, E > 50 GeV) gamma rays, between December 2014 and October 2016, acquiring 191 hours of good-quality data. Accumulating a large amount of observation
hours was indispensable to obtain a precise measurement of the spectrum and it was possible thanks to the possibility of extending the MAGIC duty cycle by operating the telescopes under bright moonlight. I worked in the optimization of moonlight observations with MAGIC, both during the operation of the telescopes and at the data analysis stage. I discuss the details of these developments and the resulting performance. With more than 70% of the data obtained under moonlight, I was able to obtain the most precise spectrum of Cassiopeia A to date at VHE. The obtained spectrum shows for the rst time 4:9 evidence of a cut-o at E = 3,5 (+1,6\—1,0) stat (+0,8\−0,9) sys TeV. The modelling of the spectrum suggests that the bulk of the gamma-rays emitted can be attributed to a population of high-energy protons with spectral index ~2.2 and
energy cuto at ~10 TeV. This implies that, assuming there is no signicant cosmic-ray diusion, Cassiopeia A cannot be a PeVatron at its present age.
40
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.
Full textAbstract:
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.
41
Reuschle, Christian Andreas. "A neural network based on background supression [i.e. suppression] technique applied to VHE gamma ray data coming from the Crab pulsar." Connect to this title, 2008. http://scholarworks.umass.edu/theses/145/.
Full text
42
Lacki, Brian Cameron. "Cosmic Rays in Star-Forming Galaxies." The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1313437011.
Full text
43
Peters, Chris (Christopher Joseph) Carleton University Dissertation Engineering Electrical. "MOSFET based gamma radiation detector." Ottawa, 1992.
Find full text
44
Venter, Christo. "Millisecond pulsars and pulsar wind nebulae as sources of gamma rays and cosmic rays / C. Venter." Thesis, North-West University, 2008. http://hdl.handle.net/10394/2067.
Full text
45
Federici, Simone. "Gamma-ray studies of the young shell-type SNR RX J1713.7-3946." Phd thesis, Universität Potsdam, 2014. http://opus.kobv.de/ubp/volltexte/2014/7173/.
Full textAbstract:
One of the most significant current discussions in Astrophysics relates to the origin of high-energy cosmic rays. According to our current knowledge, the abundance distribution of the elements in cosmic rays at their point of origin indicates, within plausible error limits, that they were initially formed by nuclear processes in the interiors of stars. It is also believed that their energy distribution up to 1018 eV has Galactic origins. But even though the knowledge about potential sources of cosmic rays is quite poor above „ 1015 eV, that is the “knee” of the cosmic-ray spectrum, up to the knee there seems to be a wide consensus that supernova remnants are the most likely candidates. Evidence of this comes from observations of non-thermal X-ray radiation, requiring synchrotron electrons with energies up to 1014 eV, exactly in the remnant of supernovae. To date, however, there is not conclusive evidence that they produce nuclei, the dominant component of cosmic rays, in addition to electrons.
In light of this dearth of evidence, γ-ray observations from supernova remnants can offer the most promising direct way to confirm whether or not these astrophysical objects are indeed the main source of cosmic-ray nuclei below the knee. Recent observations with space- and ground-based observatories have established shell-type supernova remnants as GeV-to- TeV γ-ray sources. The interpretation of these observations is however complicated by the different radiation processes, leptonic and hadronic, that can produce similar fluxes in this energy band rendering ambiguous the nature of the emission itself.
The aim of this work is to develop a deeper understanding of these radiation processes from a particular shell-type supernova remnant, namely RX J1713.7–3946, using observations of the LAT instrument onboard the Fermi Gamma-Ray Space Telescope. Furthermore, to obtain accurate spectra and morphology maps of the emission associated with this supernova remnant, an improved model of the diffuse Galactic γ-ray emission background is developed. The analyses of RX J1713.7–3946 carried out with this improved background show that the hard Fermi-LAT spectrum cannot be ascribed to the hadronic emission, leading thus to the conclusion that the leptonic scenario is instead the most natural picture for the high-energy γ-ray emission of RX J1713.7–3946. The leptonic scenario however does not rule out the possibility that cosmic-ray nuclei are accelerated in this supernova remnant, but it suggests that the ambient density may not be high enough to produce a significant hadronic γ-ray emission.
Further investigations involving other supernova remnants using the improved back- ground developed in this work could allow compelling population studies, and hence prove or disprove the origin of Galactic cosmic-ray nuclei in these astrophysical objects. A break- through regarding the identification of the radiation mechanisms could be lastly achieved with a new generation of instruments such as CTA.<br>Eine der gegenwärtigen bedeutendsten geführten Diskussionen in der Astrophysik bezieht sich auf den Ursprung der hochenergetischen Kosmischen Strahlung. Nach unserem heutigen Verständnis weist die am Ort des Ursprungs elementare Zusam- mensetzung der Kosmischen Strahlung darauf hin, dass diese zu Beginn mittels nuklearer Prozesse im Inneren von Sternen gebildet wurde. Weiterhin wird ange- nommen, dass die Kosmische Strahlung bis 1018 eV galaktischen Ursprungs ist. Auch wenn das Verständnis über die potentiellen Quellen der Kosmischen Strahlung ober- halb von 1015 eV, dem sogenannten „Knie“ des Spektrums der Kosmischen Strah- lung, lückenhaft ist, so liegt doch der Konsens vor, dass Supernovaüberreste (SNR) die wahrscheinlichsten Quellen für Energien bis 1015 eV sind. Unterstützt wird die- ser Sachverhalt durch Beobachtungen von nichtthermischer Röntgenstrahlung von SNR, deren Emission Elektronen mit Energien bis zu 1014 eV erfordern. Jedoch gibt es bis heute keinen überzeugenden Beweis, dass SNR zusätzlich zu den Elektronen auch Atomkerne, die den dominierenden Anteil in der Kosmischen Strahlung bilden, beschleunigen.
Trotz fehlender überzeugender Beweise ermöglichen nun Beobachtungen von SNR im γ-Strahlungsbereich einen vielversprechenden Weg zur Aufklärung der Fra- ge, ob diese astrophysikalischen Objekte in der Tat die Hauptquelle der Kosmischen Strahlung unterhalb des Knies sind. Kürzlich durchgeführte Beobachtungen im Welt- raum und auf der Erdoberfläche haben zu der Erkenntnis geführt, dass schalenartige SNR γ-Strahlung im GeV- und TeV-Bereich emittieren. Die Interpretation dieser Beobachtungen ist jedoch schwierig, da sowohl Atomkerne als auch Elektronen im betrachteten Energiebereich zu ähnlichen γ-Emissionen führen. Dadurch wird die eindeutige Identifizierung der Emission als das Resultat hadronischer oder leptoni- scher Emissionsprozesse erschwert.
Das Ziel dieser Arbeit ist es, am Beispiel des schalenartigen SNR RX J1713.7- 3946 ein tieferes Verständnis über die Strahlungsprozesse zu erhalten, indem vom γ-Weltraumteleskop Fermi durchgeführte Beobachtungen analysiert werden. Um ge- naue Spektren und die Ausdehnung der Region der Emission zu erhalten, wird ein verbessertes Modell für die diffuse galaktische γ-Hintergrundstrahlung entwickelt. Die mit diesem verbesserten Hintergrund durchgeführte Analyse von RX J1713.7- 3946 zeigt, dass das vom Fermi-Satelliten beobachtete Spektrum nicht dem hadro- nischen Szenario zugeschrieben werden kann, sodass das leptonische Szenario für die γ-Emissionen von diesem SNR verantwortlich ist. Das leptonische Szenario schließt jedoch nicht die Möglichkeit aus, dass auch Atomkerne in diesem SNR beschleu- nigt werden. Aber es deutet darauf hin, dass die umgebende Teilchendichte nicht ausreichend hoch genug ist, um zu einer signifikanten hadronischen γ-Emission zu führen.
Weitere Untersuchungen, die andere SNR in Kombination mit dem hier ent- wickelten verbesserten Modell der Hintergrundstrahlung beinhalten, können Popu- lationsstudien erlauben. Dies könnte klären, ob die SNR tatsächlich die Quellen der galaktischen Kosmischen Strahlung sind. Ein Durchbruch bezüglich der Identi- fikation des Strahlungsmechanismus könnte auch durch eine neue Generation von Beobachtungsinstrumenten, wie das Cherenkov Telescope Array, erreicht werden.
46
Schilling, Klaus-Dieter, and Horst Märten. "High-resolution spectroscopy of fission fragments, neutrons and gamma-rays." Forschungszentrum Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-32739.
Full text
47
Schilling, Klaus-Dieter, and Horst Märten. "High-resolution spectroscopy of fission fragments, neutrons and gamma-rays." Forschungszentrum Rossendorf, 1993. https://hzdr.qucosa.de/id/qucosa%3A22100.
Full text
48
Slabbert, Jacobus Petrus. "Inactivation synergy between high energy neutrons and ⁶⁰Co gamma rays." Doctoral thesis, University of Cape Town, 1993. http://hdl.handle.net/11427/27129.
Full textAbstract:
The interaction between sublesions produced by neutrons [p(66)/Be and d(16)/Be] and ⁶⁰Co γ-rays was investigated using mammalian cells, meristematic cells and human lymphocytes. The quality of each radiation source was quantified in terms of molecular yield per unit dose absorbed in a ferrous sulphate xylenol orange solution and was found to vary inversely with the mean LET of the radiation field. Inactivation parameters determined for mammalian and meristematic cells were not significantly different following simultaneous or sequential exposures to d(16)/Be neutrons and ⁶⁰Co γ-rays. Synergistic interaction was observed to be most pronounced in a radiation mixture consisting of about one part neutrons and three parts photons and appeared to be optimal at approximately 5 Gy. This phenomenon led to dose enhancement ratios that increase with radioresistance. Multi-target parameters indicated that on a per gray basis, priming doses of p(66)/Be neutrons and ⁶⁰Co γ-rays induce comparative levels of sublethal damage. However, non-parametric analysis of the survival data showed that mammalian cells regard a priming dose of neutrons as somewhat less effective than an iso-effective photon dose. A greater measure of synergy was observed between photons and priming doses of neutrons with less build-up. This is however mainly due to higher levels of biological damage induced with a more potent configuration of secondary charged particles. Interaction factors compared at levels of iso-effect tend to be smaller when the LET of the priming dose was increased. Split-doses of neutrons in the absence of build-up resulted in "negative" repair. The validity of proposed biophysical models was tested using meristematic cells, as the response of these cells show an apparent absence of intertrack damage. Contrary to expectations, synergistic interaction was observed for both growth delay measurements and micronuclear formations. Chromosome aberrations showed synergy between neutron and photon damage in human lymphocytes, as predicted by interaction functi ons. However, the synergistic interaction noted with micronuclear formation in binucleate cells was at variance with predictions based on biophysical models.
49
Kandlakunta, Praneeth. "Gamma Rays Rejection in a Gadolinium based Semiconductor Neutron Detector." The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1386883923.
Full text
50
CATALDO, MADDALENA. "High-Energy Neutrinos and Gamma-rays from the Milky Way." Doctoral thesis, Università degli Studi dell'Aquila, 2021. http://hdl.handle.net/11697/169000.
Full textAbstract:
Hadronic interactions of high energy protons (or nuclei) with ambient medium
represent one of the main processes that produce high-energy neutrinos and TeV
gamma-rays in our Galaxy. They occur both within the sources where cosmic rays
(CR) are accelerated and/or in the interstellar gas contained in our Galaxy. Being
gamma and neutrino production strictly related, it is natural to adopt a multimessenger approach in which their observations are explained within the same framework.
We present updated calculations of the diffuse emission produced by the interaction of CR with the gas contained in the Galactic disk considering also the possibility
of CR spectral hardening in the inner Galaxy, recently emerged from the analysis of
Fermi-LAT data at lower energies. Above TeV energies diffuse and source components are expected to provide comparable contributions and it is difficult to separate
them on observational grounds. Hence we compare our estimates with the total
(diffuse + sources) observed fluxes: IceCube HESE signal for neutrinos, and fluxes
from the Galactic plane measured by Argo-YBJ, H.E.S.S., HAWC and Milagro for the
gamma counterpart. We provide a limit to the fraction of the high energy neutrino
signal observed by IceCube that can be ascribed to a Galactic origin. We demonstrate
that the TeV gamma-ray sky can be used to probe the distribution of Galactic cosmic rays. We state that a potential tension exists between the CR spectral hardening
hypothesis and observational results.
The constraints can be strengthened if the contribution of sources not resolved by
H.E.S.S. is taken into account. The analysis of H.E.S.S. Galactic Plane Survey allows
to infer the properties of Galactic TeV source population. Evaluating the cumulative
flux expected at Earth by the considered population, we show that the H.E.S.S. unresolved sources provide a relevant contribution to the diffuse Galactic emission. By
the population study we infer general information on the total Milky Way such as
its high-energy gamma-ray luminosity and total flux. Finally, in the hypothesis that
the majority of bright sources detected by H.E.S.S. are powered by pulsar activity,
like e.g. pulsar wind nebulae or TeV halos, we estimate the main properties of the
pulsar population.