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Livingstone, Margaret Anne. "Timing young pulsars: challenges to standard pulsar spin-down models." Thesis, McGill University, 2010. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=94909.
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Pulsars are rapidly rotating neutron stars which are often noted for their very regular rotation rates. Young pulsars however, frequently exhibit two types of deviations from steady spin down, ``glitches'' - sudden jumps in spin frequency, which provide insight into pulsar interiors, and ``timing noise,'' a smooth stochastic wander of the pulse phase over long time periods. The youngest pulsars also offer a window into the physics that govern pulsar spin down via the measurement of the "braking index'' - a parameter that relates the observable spin frequency of the pulsar with the slowing down torque acting on the neutron star. This thesis discusses long-term timing observations of two young pulsars. First, we present observations of PSR J0205+6449, acquired with the Green Bank Telescope, the Jodrell Bank Observatory and the Rossi X-ray Timing Explorer. We present phase-coherent timing analyses showing timing noise and two spin-up glitches. We also present an X-ray pulse profile analysis showing that the pulsar is detected up to approximately 40 keV and does not vary appreciably over four years. We report the phase offset between the radio and X-ray pulse, showing that the radio pulse leads by 0.10+/-0.01 in phase. We compile measurements of phase offsets for this and other X-ray and gamma-ray pulsars and show that there is no relationship between pulse period and phase offset. Next, we present 10 years of monitoring of PSR J1846-0258 with the Rossi X-ray Timing Explorer. We report the first measurement of the braking index for this pulsar, n=2.65+/-0.01, only the sixth such measurement ever made, and show that the pulsar experienced a small glitch in 2001. In May 2006, PSR J1846-0258 was briefly transformed: it exhibited a series of X-ray bursts, a dramatic increase in the source flux, and significant softening of its X-ray spectrum - behaviours best explained in the context of the magnetar model. PSR J1846-0258 was thus identified as the first rotation-poLes pulsars, des étoiles à neutrons tournant rapidement sur elles-mêmes, sont reconnus pour leur vitesse de rotation très régulière. Les jeunes pulsars, par contre, présentent fréquemment des comportements qui dévient du ralentissement uniforme de leur vitesse de rotation: des glitchs, variations brutales de la fréquence de révolution qui nous aident à comprendre l'intérieur des plusars, et le bruit chronométrique, une variation stochastique de la phase de rotation sur une longue échelle de temps. Les pulsars les plus jeunes nous offrent aussi un aperçu de la physique qui gouverne le ralentissement de la vitesse de rotation par l'indice de freinage, un paramètre qui relie la fréquence de rotation d'un pulsar au torque qui agit sur lui, et dont la valeur diminue graduellement. Cette thèse discute du chronométrage à long terme de deux jeunes pulsars. Tout d'abord, nous présentons des observations de PSR J0205+6449 acquises avec l'Observatoire de Green Bank, l'Observatoire Jodrell Bank ainsi que le Rossi X-ray Timing Explorer. Nous présentons l'analyse du chronométrage à phase cohérente montrant du bruit chronométrique ainsi que deux glitchs. Nous présentons aussi une analyse du profil du pulse en rayons X montrant que le pulsar est détectable jusqu'à ~40 keV et ne varie pas significativement sur quatre ans. Nous rapportons une mesure de la différence de phase entre le pulse radio et le pulse en rayons X, montrant que le pulse radio précède le pulse en rayons X par 0.10+/-0.01. Une compilation des différences de phase pour ce pulsar et d'autres qui émettent en rayons X et en rayons gamma montre qu'il n'y a aucune relation entre la période de rotation et la différence de phase. Ensuite, nous présentons 10 années de suivi de PSR J1846-0258 avec le Rossi X-ray Timing Explorer. Nous rapportons la première mesure de l'indice de freinage pour ce pulsar, n=2.65+/-0.01, le sixième indice mesuré à ce jour, et montrons que ce pul
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Desvignes, Grégory. "L'observation des pulsars au Radiotélescope de Nançay : applications à la recherche de nouveaux objets, à l'étude des systèmes binaires relativistes et à la détection d'un fond d'ondes gravitationnelles." Phd thesis, Université d'Orléans, 2009. http://tel.archives-ouvertes.fr/tel-00496806.
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Un pulsar est une étoile à neutrons en rotation rapide et dotée d'un fort champ magnétique qui peut se manifester en émettant sur tout le spectre électromagnétique. Dans cette thèse, je m'intéresse au rayonnement radio produit par l'étoile. Je commence ainsi par décrire l'instrumentation de dédispersion cohérente à base de GPUs installée au Radiotélescope de Nançay avec deux autres modes d'observation que j'ai développés : un mode pour la recherche de nouveaux pulsar et un mode spectromètre. Une autre partie de ce travail détaille le retraitement en cours du sondage Foster fait à la fin des années 90 à Nançay ainsi que de nouvelles observations ciblées, sur des candidats HESS notamment. Je présente ensuite les résultats obtenus sur les pulsars relativistes J0737-3039A et J1906+0746 avec respectivement des tests de la Relativité Générale et la mesure de la précession géodétique. Des données de polarimétrie ont ainsi permis de déterminer la géométrie du système de PSR J1906+0746. Enfin, je termine par l'analyse des temps d'arrivées de 20 pulsars millisecondes observés à Nançay dans le cadre de l'EPTA, une collaboration européenne pour un réseau de chronométrage pulsar avec pour objectif la détection d'un fond d'ondes gravitationnelles, possible d'ici 5 à 10 ans.
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Octau, Franck. "Exploration d'un grand relevé à Nançay et diversité de la population de pulsars." Thesis, Orléans, 2017. http://www.theses.fr/2017ORLE2042/document.
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Depuis la découverte du premier pulsar en 1967, nous connaissons désormais plus de 2500 pulsars aujourd’hui. Les pulsars offrent un champ d’études considérable : depuis l’étude des propriétés du milieu interstellaire et l’étude de la magnétosphère des pulsars jusqu’aux tests de la gravité en champ fort et la caractérisation d’un fond d’ondes gravitationnelles d’origine cosmologique. Cela explique pourquoi nous continuons de chercher de nouveaux pulsars de nos jours. Après des découvertes de pulsars millisecondes dans les sources non identifiées du Fermi Large Area Telescope, un programme de recherche de nouveaux pulsars a été mené à partir de 2012 par G. Desvignes. Observant à 1.4 GHz avec une haute résolution temporelle et fréquentielle, le programme SPAN512 a été conçu pour la recherche de pulsars rapides et lointains situés dans le plan Galactique. Nous décrirons les méthodes d’analyse mises en place pour traiter les données afin de trouver de nouveaux pulsars, méthodes soit basées sur la stabilité de la période de rotation des pulsars soit sur leur émission d’impulsions individuelles. Nous présenterons aussi l’état actuel de l’analyse du programme SPAN512 et les découvertes effectuées, plus particulièrement du pulsar trouvé au cours de ce travail de thèse, PSR J2055+3829, un pulsar milliseconde de période de rotation de 2.08 ms appartenant à un système de type « Veuve Noire ». Ce sera l’occasion de présenter les études chronométriques réalisées pour trouver l’éphéméride de ce pulsar et, dans le même temps, j’en profiterai pour parler d’une analyse similaire faite sur le pulsar J1618-3921, un pulsar dans une orbite excentrique. Enfin, nous présenterons des études polarimétriques de pulsars réalisées à la lumière d’un nouveau modèle, le modèle du vecteur tournant décentré (DRVM). Nous montrerons qu’un champ magnétique hautement décentré peut expliquer les variations brusques de l’angle de polarisationSince the discovery of the first pulsar in 1967, we know over 2500 pulsars today. Pulsars offer a broad range of studies: from the study of the properties of interstellar medium and of pulsar magnetospheres up to test of gravity in the strong-field regime and the characterisation of the cosmological Gravitation Waves background. This explains why we keep searching pulsars nowadays. After successful detections of new millisecond pulsars in Fermi Large Area Telescope unassociated sources at Nançay, a blind pulsar survey was initiated in 2012 by G. Desvignes. Conducted at 1.4 GHz with short sampling time and narrow frequency channels, the SPAN512 was designed to find fast and distant pulsars within the Galactic plane. We describe the methods to analyse data in order to find new pulsars, thanks to their spin stability or tto their single pulses. We will also describe the current status of the survey and the discoveries, more especially the pulsar discovered during this thesis, PSR J2055+3829, a 2.08 ms pulsar in a black widow system. It will be the opportunity to present the radio timing analysis of this pulsar and, in the same time, we will describe similar studies conducted on the pulsar J1618-3921, a pulsar in an eccentric orbit. Finally, we present some polarisation studies of pulsars in light of a new model, the Decentred Rotating Vector Model (DRVM). We will show that a highly decentred dipole may explain abrupt variations of polarisation profiles
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Cameron, Andrew [Verfasser]. "Innovative Pulsar Searching Techniques : or Fantastic Pulsars and How to Find Them / Andrew Cameron." Bonn : Universitäts- und Landesbibliothek Bonn, 2018. http://d-nb.info/1162953063/34.
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Keane, Evan. "The transient radio sky." Thesis, University of Manchester, 2010. https://www.research.manchester.ac.uk/portal/en/theses/the-transient-radio-sky(37c08735-cd96-4598-a8b9-2d24ef9e871d).html.
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The high time-resolution radio sky represents unexplored astronomical territory where the discovery potential is high. In this thesis I have studied the transient radio sky, focusing on millisecond scales. As such, this work is concerned primarily with neutron stars, the most populous member of the radio transient parameter space. In particular, I have studied the well known radio pulsars and the recently identified group of neutron stars which show erratic radio emission, known as RRATs, which show radio bursts every few minutes to every few hours. When RRATs burst onto the scene in 2006, it was thought that they represented a previously unknown, distinct class of sporadically emitting sources. The difficulty in their identification implies a large underlying population, perhaps larger than the radio pulsars. The first question investigated in this thesis was whether the large projected population of RRATs posed a problem, i.e. could the observed supernova rate account for so many sources. In addition to pulsars and RRATs, the various other known neutron star manifestations were considered, leading to the conclusion that distinct populations would result in a 'birthrate problem'. Evolution between the classes could solve this problem - the RRATs are not a distinct population of neutron stars. Alternatively, perhaps the large projected population of RRATs is an overestimate. To obtain an improved estimate, the best approach is to find more sources. The Parkes Multi-beam Pulsar Survey, wherein the RRATs were initially identified, offered an opportunity to do just this. About half of the RRATs showing bursts during the survey were thought to have been missed, due to the deleterious effects of impulsive terrestrial interference signals. To remove these unwanted signals, so that we could identify the previously shrouded RRATs, we developed new interference mitigation software and processing techniques. Having done this, the survey was completely re-processed, resulting in the discovery of 19 new sources. Of these, 12 have been re-detected on multiple occasions, whereas the others have not been seen to re-emit since the initial discovery observations, and may be very low burst-rate RRATs, or, isolated burst events. These discoveries suggest that the initial population estimate was not over-estimated - RRATs, though not a distinct population, are indeed numerous. In addition to finding new sources, characterisation of their properties is vital. To this end, a campaign of regular radio observations of the newly discovered sources, was mounted, at the Parkes Observatory, in Australia. In addition, some of the initially identified RRATs were observed with the Lovell Telescope at Jodrell Bank. These have revealed glitches in J1819-1458, with anomalous post-glitch recovery of the spin-down rate. If such glitches were common, it would imply that the source was once a magnetar, neutron stars with the strongest known magnetic fields of up to 10¹⁵ gauss. The observations have also been used to perform 'timing' observations of RRATs, i.e. determination of their spin-down characteristics. At the beginning of this thesis, 3 of the original sources had 'timing solutions' determined. This has since risen to 7, and furthermore, 7 of the newly discovered sources now also have timing solutions. With this knowledge, we can see where RRATs lie in period-period derivative space. The Parkes RRATs seem to be roughly classifiable into three groupings, with high observed nulling fractions - normal pulsars, high magnetic field pulsars and old, 'dying' pulsars. It seems that RRATs and pulsars are one and the same. When a pulsar is more easily detected in searches for single bright pulses, as opposed to in periodicity searches, we label it a RRAT. Such searches impart a selection effect on the parameter space of possible sources, in both nulling fraction and rotation period. In this sense, an observational setup could be designed to make any pulsar appear as a RRAT. For realistic survey parameters however, this is not the case, and the groups mentioned above seem to be the most likely to appear as RRATs. In fact, we can utilise RRAT searches to identify neutron stars, difficult to find by other means, in particular high-magnetic field pulsars, and pulsars approaching the pulsar "death valley". Some of the RRATs are well explained as being distant/weak pulsars with a high modulation index, others seem to be nulling pulsars. This highlights the incomplete knowledge of nulling behaviour in the pulsar population. It seems that there may be a continuum of nulling durations, under a number of guises, from 'nulling pulsars' to 'RRATs' to 'intermittent pulsars'. In fact this nulling may fit into the emerging picture, whereby pulsar magnetospheres switch between stable configurations.
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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.
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Brook, Paul Richard. "The variability of radio pulsars." Thesis, University of Oxford, 2015. http://ora.ox.ac.uk/objects/uuid:65ae413c-cd12-408b-843c-60886cecf1b7.
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Neutron stars are amongst the most exotic objects known in the universe; more than a solar mass of material is squeezed into an object the size of a city, leading to a density comparable to that of an atomic nucleus. They have a surface magnetic field which is typically around a trillion times stronger than the magnetic field here on Earth, and we have observed them to spin up to around 700 times per second. The existence of neutron stars was first proposed by Baade and Zwicky in 1934 but later graduated from theory to fact in 1967 as the first pulses were detected by Jocelyn Bell-Burnell, a then graduate student at the University of Cambridge. There are now well over 2000 neutron stars whose radio emission beams point at, and have been detected on Earth. We call these objects pulsars. Because of their remarkable properties, pulsars are very useful to physicists, who can employ them as precision timing tools due to the unwavering nature of their emission and of their rotation. Having an array of ultra-accurate clocks scattered throughout our galaxy is very useful for performing astrophysical experiments. In particular, precise pulsar timing measurements and the models that explain them, will permit the direct detection of gravitational radiation; a stochastic background initially, and potentially the individual signals from supermassive black hole binaries. Our models of pulsar behaviour are so precise that we are now able to notice even slight departures from them; we are starting to see that unmodelled variability in pulsars occurs over a broad range of timescales, both in emission and in rotation. Any unmodelled variability is, of course, detrimental to the pulsar's utility as a precision timing tool, and presents a problem when looking for the faint effects of a passing gravitational wave. We are hoping that pulsar timing arrays will detect gravitational radiation in the coming decade, but this depends, in part, on our ability to understand and mitigate the effects of the unmodelled intrinsic instabilities that we are observing. One important clue as to the nature of the variability in pulsar emission and rotation, is the emerging relationship between the two; we sometimes observe correlation on timescales of months and years. We have been observing pulsars for almost fifty years and our expanding datasets now document decades of pulsar behaviour. This gives us the ability to investigate pulsar variability on a range of timescales and to gain an insight into the physical processes that govern these enigmatic objects. In this thesis I describe new techniques to detect and analyse the emission and rotational variability of radio pulsars. We have employed these techniques on a 24 year pulsar dataset to unearth a striking new example of a dramatic and simultaneous shift in a pulsar's emission and rotation. We hypothesise that this event was caused by an asteroid interaction, although other explanations are also possible. Our variability techniques have also been used to analyse data from 168 young, energetic pulsars. In this thesis we present results from the nine most interesting. Of these, we have found some level of correlated variability in seven, one of which displays it very strongly. We have also assessed the emission stability of the NANOGrav millisecond pulsars and have found differing degrees of variability, due to both instrumental and astrophysical causes. Finally, we propose a method of probing the relationship between emission and rotation on short-timescales and, using a simulation, we have shown the conditions under which this is possible. Throughout the work, we address the variability in pulsar emission, rotation and links between the two, with the aim of improving pulsar timing, attaining a consolidated understanding of the diverse variable phenomena observed and elucidating the evolutionary path taken by pulsars.
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Bondonneau, Louis. "Première caractérisation de la population de pulsars radio à basses fréquences avec NenuFAR." Thesis, Orléans, 2019. http://www.theses.fr/2019ORLE3032.
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Un pulsar est une étoile à neutrons en rotation rapide (typiquement un tour par seconde) dont le faisceau d’émission radio provenant des pôles magnétiques de l'étoile balaie l’univers. Quand le faisceau intercepte la Terre, le pulsar est détectable comme une série de pulsations régulières dans dans un vaste domaine de longueurs d'onde, de la radio jusqu'aux rayons gamma. Au cours de cette thèse j’ai utilisé, adapté et développé des méthodes d'analyses ainsi qu'un pipeline de traitement de signal en temps réel afin d’étudier les signaux radio des pulsars dans la gamme des basses fréquences utilisée par les radiotélescopes LOFAR(LOw Frequency Array) et NenuFAR (New Extension in Nançay Upgrading loFAR).NenuFAR est le nouvel instrument de la station de Radioastronomie de Nançay, construit pour observer le ciel entre 10 et 85 MHz de fréquence. C'est un réseau compact de nouvelle génération, constitué à terme de 1938 antennes phasées analogiquement et numériquement. Depuis le début de ma thèse, j'ai participé activement au développement, puis à la recette de ce nouvel instrument, jusqu'à son ouverture à la communauté scientifique le 1er juillet 2019 dans le cadre d’un appel à "Early Science".Le premier chapitre de ma thèse est consacré à la description du phénomène « pulsar », de l'émission du rayonnement dans la magnétosphère de l'étoile à neutrons jusqu'à l'observation du signal par le radiotélescope. Le second chapitre décrit l’instrumentation des radiotélescopes utilisés pendant la thèse, et en particulier, la conception du dédisperseur « pulsar » cohérent en temps réel de NenuFAR (LUPPI) et du « pipeline » de traitement des observations. Le troisième chapitre est réservé à l’étude d’une centaine de pulsars observés à basse fréquence avec LOFAR. Les données sont issues de deux relevés, l’un effectué avec le coeur de LOFAR (situé aux Pays-Bas) et l’autre avec la station LOFAR de Nançay. Finalement, le dernier chapitre est dédié à la mise en service de NenuFAR et aux premiers résultats scientifiques obtenus pour les observations des pulsars. Ce chapitre décrit en particulier les tests pour les différents modes d'observation (dédispersion cohérente, multi-beam, single pulse, enregistrement en forme d'onde) et le résultat du premier grand relevé du ciel Nord par NenuFAR, qui a permis à partir de l’observation de 500 pulsars la détection de 130 sources, dont plus de 50 pour la première fois à ces fréquences. J'y présente également le programme scientifique du projet clé pulsars de NenuFAR, que j'ai fortement contribué à mettre en placeA pulsar is a rapidly rotating neutron star (typically one revolution per second). As it rotates, the beamed radio emission from the star's magnetic poles scans the universe. When the beam intercepts the Earth, the pulsar is detectable as a series of regular pulses over a wide wavelength range, from radio to gamma rays. During this thesis I used, adapted and developed analysis methods and a real-time signal processing pipeline to study pulsar radio signals in the low frequency range used by the radio telescopes LOFAR (LOw Frequency Array) and NenuFAR (New Extension in Nançay Upgrading loFAR).NenuFAR is the new instrument of the Nançay Radio Astronomy Station, built to observe the sky at frequency between 10 and 85 MHz. It is a compact array of the last generation of radio telescopes. Ultimately it will be composed of 1938 antennas with analog and digital phasing. Since the beginning of my thesis, I have been actively involved in the development of this new instrument, until it was opened to the scientific community on July 1, 2019 as part of a call for "Early Science".The first chapter of my thesis is devoted to the description of the "pulsar" phenomenon, from the emission of radiation in the magnetosphere of the neutron star to the observation of the signal by a radio telescope. The second chapter describes the instrumentation of the radio telescopes used during the thesis, and in particular the design of the NenuFAR coherent real-time "pulsar" dedispersion system (LUPPI) and the pipeline for the processing of the observations. The third chapter presents the study of about 100 pulsars observed at low frequency with LOFAR. The data are based on two surveys, one with the LOFAR core (located in the Netherlands) and the other with the LOFAR station in Nançay. Finally, the last chapter is dedicated to the commissioning of NenuFAR and the first scientific results obtained from pulsars observations. This chapter describes in particular the tests for the different observation modes (coherent dedispersion, multi-beam, single pulse, waveform recording) and the result of the first major survey of the North sky by NenuFAR. Based on the observation of 500 pulsars, this survey allowed the detection of 130 sources, including more than 50 which had never been detected at these frequencies before. I also present the scientific program of the NenuFAR pulsar Key Project, to which I have strongly contributed
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Edwards, Russell T., and Russell Edwards@csiro au. "Pulsar searching." Swinburne University of Technology, 2001. http://adt.lib.swin.edu.au./public/adt-VSWT20050323.141044.
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This thesis reports the results of two pulsar survey projects conducted at the Parkes 64-m radio telescope in New South Wales, Australia.
The first, the Swinburne Intermediate Latitude Pulsar Survey, covered a large region of the southern Galaxy flanking that of the ongoing Galactic plane survey. We used the 13-feed 20 cm
'multibeam' receiver package to achieve this broad sky coverage in a short observing campaign with 14 days� total integration time. The survey proved remarkably successful, detecting 170 pulsars, 69 of which were new discoveries. Eight of the new discoveries possess small periods and period derivatives indicative of 'recycling', an hypothesis supported by the fact that six of them are in circular orbits with probable white dwarf companions. Pulse timing measurements have revealed that two of the white dwarfs are massive CO or ONeMg dwarfs. The mass of one of them (the companion to PSR J1157�5112) exceeds 1.14 M, providing the most convincing evidence to date for the production of 'ultra-massive' ONeMg white dwarfs as the end result of stellar evolution on the asymptotic giant branch (albeit with mass transfer indicated). PSR J1757�5322 also possesses a heavy white dwarf companion, in a close 11-h orbit. The proximity of the massive companion leads to significant relativistic orbital evolution and the effects of this will be measurable by pulsar timing in the coming decades. Under general relativity, the gravitational wave power radiated from the system is sufficient to cause coalescence in an event which will have dramatic and unknown consequences. Such events are possible gamma-ray burst sources, and the remnants could include isolated millisecond pulsars, close eclipsing binaries or pulsar planetary systems. The remaining four pulsar binaries show some discrepancies with the bulk of previously known low mass binary pulsars (LMBPs). PSR J1618-39 is
in a 23-d orbit, filling what previously appeared to be a gap in the orbital period distribution. PSR J1745-0952 has a relatively long pulse period (19 ms) and along with PSR J1618-39 (12 ms) may have experienced a different evolutionary history
to the majority of previously known LMBPs. A ninth pulsar discovered in the survey may also be recycled. The mean pulse profile of PSR J1411�7404 is exceedingly narrow and lies in stark contrast to that of other pulsars of similar pulse period. In the past the only other pulsars
known with anomalously narrow profiles were believed (for other reasons) to have been recycled, and this fact in combination with the low period derivative measured in timing analysis of PSR J1411�7404 leads me to suggest that it, too, may have been recycled. If this is the case, it is possible that the recycling took place in a
system similar in configuration to the progenitors of the double neutron star systems,
but that sudden mass loss or an unfavourably oriented kick in the birth event of the second neutron star disrupted the system, leaving an isolated, mildly recycled pulsar. The second pulsar survey program conducted for this work was a targeted search of southern globular clusters. We used a baseband recording system to provide unprecedented time resolution (typically 25 �s). The large number of channels and short sampling interval achievable in software filterbanks, in combination with the ability to coherently remove most of the interstellar dispersion from clusters with previously known pulsars, made us the first to achieve a relatively flat sensitivity response to pulsars of ~10−3.5�10 s. This characteristic is vital if we are to constrain the true period distribution of millisecond pulsars, an important task in the evaluation of alternative equations of state for nuclear matter. We detected six millisecond pulsars and produced pulse profiles of higher resolution than were previously available. The basic sensitivity of the search was not high enough to detect any new pulsars, however the work demonstrates that the approach is feasible with the use of currently available high-performance computing resources (such as the Swinburne workstation cluster), and is capable of delivering excellent sensitivity characteristics.
It is expected that future searches of this kind, of which this is the first, will achieve the goal of sampling the true pulse period distribution within a few years.
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Edwards, Russell T. "Pulsar searching /." Australian Digital Theses Program, 2001. http://adt.lib.swin.edu.au/public/adt-VSWT20050323.141044.
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Thesis (Ph.d.) - Swinburne University of Technology, 2001.Submitted for the degree of Doctor of Philosophy, Swinburne University of Technology, 2001. Typescript. Includes bibliographical references (p. 122-131).
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Lassus, Antoine. "Méthode de détection de sources individuelles d'ondes gravitationnelles par chronométrie d'un réseau de pulsars : application aux données de l'EPTA." Phd thesis, Université d'Orléans, 2013. http://tel.archives-ouvertes.fr/tel-01017215.
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L'existence des ondes gravitationnelles, fluctuations de l'espace-temps lui-même, a été prédite sans, pour l'instant, qu'une détection directe n'ait été encore possible. A l'heure actuelle, des méthodes consistant en des détecteurs interférométriques de plusieurs kilomètres de long sont à l'oeuvre pour permettre une première détection. Nous proposons, dans cette thèse, d'étudier une autre méthode : la chronométrie d'un réseau de pulsars milliseconde. Elle consiste en l'observation régulière et la datation précise des impulsions radio en provenance de pulsars ultrastables. L'onde gravitationnelle produisant retards ou avances des impulsions sur Terre, nous recherchons sa présence sous forme d'un signal corrélé entre les observations faites des différents pulsars du réseau. Dans un premier temps, nous détaillons les processus d'observation et de chronométrie des pulsars, pour nous pencher sur un cas particulier avec le pulsar J1614-2230. Puis, nous présentons les ondes gravitationnelles et leurs sources ainsi que les différentes méthodes de détection. Nous décrivons tout particulièrement la méthode de chronométrie d'un réseau de pulsars appliquée à la recherche d'un signal en provenance d'un système binaire de tous noirs supermassifs. Ensuite, après avoir détaillé les outils statistiques et numériques utilisés, nous appliquons notre méthode à l'injection d'un tel signal dans les observations réelles faites dans le cadre de l'EPTA. Enfin, nous présentons les limites supérieures sur l'amplitude d'un signal en provenance d'un système binaire obtenues sur ces données sans injection grâce à notre méthode en fonction de la fréquence et de la position de la source.
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范改玲 and Gailing Fan. "Galaxy radio pulsar population modelling and magellanic clouds radio pulsar survey." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2002. http://hub.hku.hk/bib/B31243058.
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Fan, Gailing. "Galaxy radio pulsar population modelling and magellanic clouds radio pulsar survey /." Hong Kong : University of Hong Kong, 2002. http://sunzi.lib.hku.hk/hkuto/record.jsp?B25059294.
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Spir-Jacob, Marion. "Observation et détection de pulsars avec les télescopes gamma H.E.S.S. et phénoménologie d'une nouvelle composante spectrales pulsée atteignant 20 TeV." Thesis, Université de Paris (2019-....), 2019. http://www.theses.fr/2019UNIP7169.
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La thèse porte sur la recherche avec le réseau de télescopes H.E.S.S. de pulsations en rayons gamma en provenance de pulsars.Une première partie est dédiée à l’étude de tests statistiques de périodicité à base de simulations Monte Carlo, notamment dans un régime de basse statistique et/ou de faible rapport signal sur bruit. Dans une deuxième partie, ces tests sont utilisés dans l’analyse des données de H.E.S.S. du pulsar de Vela et de deux autres pulsars, PSR B1706-44 et PSR J1509-5850. Les pulsations de Vela ont un spectre très dur et sont observées aux énergies allant de 3 TeV jusqu’au-delà de 20 TeV. Il s’agit des rayons gamma les plus énergétiques jamais détectés en provenance d’un pulsar. C’est également la première découverte d’une composante spectrale pulsée en discontinuité avec celle déjà connue des pulsars à plus basse énergie, au GeV. Le pulsar B1706-44 est détecté dans l’intervalle 10-80 GeV depuis le sol, avec un indice et un flux compatibles avec ceux de l’instrument LAT embarqué à bord du satellite Fermi. Un autre pulsar, J1509-5850, présente une indication pour une émission au TeV mais celle-ci reste à confirmer avec plus de données.Dans une troisième partie, la phénoménologie de la composante spectrale 3-20 TeV de Vela est étudiée en détail. Une revue critique de deux modèles récents ayant proposé une interprétation possible est suivie par un travail de modélisation sur la base d’une autre catégorie de modèles plus récente. Celle-ci repose sur l’accélération par reconnexion magnétique dans la feuille de courant et sur un boost de Lorentz, a contrario des modèles précédents. Nous démontrons qu’il est possible de reproduire nos données dans ce cadre où l’émission est produite par une diffusion Compton inverse sur les photons thermiques provenant de la surface de l’étoile. Cette découverte ouvrant de nouveaux horizons, nous terminons avec l’étude des perspectives du domaine avec le futur observatoire gamma CTAThe thesis focuses on the search of gamma rays pulsations coming from pulsars with the H.E.S.S. telescopes.The first section is dedicated to the study of statistical tests of periodicity based on Monte Carlo simulations, in particular with scarce data and/or a small signal to noise ratio.In the second section, these tests are used in the analysis of H.E.S.S. observations of Vela and two other pulsars, PSR B1706-44 and PSR J1509-5850. The pulsations of Vela exhibit a very hard spectrum and are observed at energies ranging from 3 TeV to beyond 20 TeV. These are the most energetic gamma rays ever detected from a pulsar. It is also the first discovery of a pulsed spectral component in discontinuity with that already known at lower energies (GeV) from pulsars. The pulsar B1706-44 is detected from the ground in the 10-80 GeV range, with an index and a flux compatible with those of the LAT instrument onboard the Fermi satellite. Another pulsar, J1509-5850, shows a hint for a TeV emission but it still needs to be confirmed with further data.In the third part, the phenomenology of the spectral component between 3 and 20 TeV of Vela is studied in detail. After a critical review of two recent models suggesting possible interpretations, we explore another and more recent category of models. These rely on magnetic reconnection in the current sheet for the acceleration and on a Lorentz boost, as opposed to previous models. We demonstrate that it is possible to reproduce our data in this framework where the emission is due to an inverse Compton scattering of thermal photons from the neutron star surface.With this discovery opening new horizons, we conclude with the study of the perspectives of the field with the future gamma observatory CTA
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Zajczyk, Anna. "Studies of the influence of magnetospheric pulsar winds on the pulsar surroundings." Thesis, Montpellier 2, 2012. http://www.theses.fr/2012MON20065/document.
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Cette thèse présente le travail réalisé par l'auteur consacréà l'étude de l'influence des vents magnétosphériques des pulsars sur leur environnement. Le problème du vent magnétosphérique des pulsars est étudié dans le contexte des pulsars classiques, qui forment des nébuleuses de pulsar. L'observation de ces nébuleuses fournit des informations importantes sur leurs conditions physiques et dynamiques. Le vent magnétosphérique des pulsars milliseconde est également étudié. La contribution des pulsars millisecondeà l'émission gamma des amas globulaires est étudiée par des simulations numériques.Dans la première partie, les résultats des observations infrarouge du vestige de supernova G21.5-0.9 sont présentées. Les données utilisées comprennent des observations du Very Large Telescope de l'ESO, du télescope Canada-France-Hawaï (CFHT) et du télescope spatial Spitzer. La détection de la nébuleuse compacte autour du pulsar PSR J1833-1034, avec l'instrument CFHT/AOB-KIR (bande K') et la caméra IRAC/Spitzer (toutes les bandes), est présentée. La valeur moyenne de la fraction de polarisation linéaire de l'émission détectée est estiméeà $P_{rm L}^{avg} simeq 0.47$. Une oscillation du vecteur champ électrique dans la nébuleuse compacte peut être observée. Le spectre infrarouge de la nébuleuse compacte est bien décrit par une loi de puissance d'indice $alpha_{rm IR} = 0.7 pm 0.3$, et suggère un aplatissement spectral entre les domaines infrarouge et X. La détection de la raie d'émission [Fe II] à 1.64 $mu$m est présentée. La spectroscopieà moyenne résolution permet d'estimer l'extinction par le milieu interstellaire de l'émission infrarouge de l'objet, ainsi que la vitesse d'expansion de la matière émettant la raie du [Fe II], ce qui conduità une estimation de la distanceà G21.5-0.9 de $3.9 pm 1.2$ kpc.La deuxième partie présente une étude de l'activité magnétosphérique des pulsars milliseconde dans le contexte de l'émission gamma des amas globulaires. Une base de données des caractéristiques d'émission des pulsars milliseconde et des spectres d'éjection des électrons est créée sur la base du modèle pair starved polar cap de la magnétosphère des pulsars. Le concept de facteur de biais est introduit et étudié. Des spectres synthétiques d'amas globulaires sont simulés dans la gamme d'énergie allant du GeV au TeV. Ils consistent en une composante d'émission magnétosphérique des pulsars milliseconde résidant dans l'amas, et une composante Compton inverse résultant de la diffusion des photons ambiants (le champ stellaire des photons provenant des étoiles de l'amas, et le fond diffus cosmologique) par les leptons relativistes diffusant dans l'amas. Enfin, les spectres synthétiques des amas globulaires sont comparés et contrastés avec les observationsà haute et très haute énergie des amas globulaires sélectionnés: Terzan 5 et 47 TucanaeThis PhD thesis presents the results of the studies on the influence of magnetospheric pulsar winds on the surroundings of these objects. The problem of the magnetospheric pulsar wind is studied in the context of classical pulsars, which power prominent pulsar wind nebulae. Observations of these nebulae yield important information on their physical and dynamical conditions. The magnetospheric winds of millisecond pulsars are also investigated. The contribution of millisecond pulsars to the gamma-ray emission of globular clusters is studied through numerical simulations. In the first part of the thesis, the results of infrared observations of the supernova remnant G21.5-0.9 are presented. The observational material includes data obtained with the ESO Very Large Telescope, the Canada-France-Hawaii Telescope and the Spitzer Space telescope. The detection of the compact nebula around the pulsar PSR J1833-1034, through imaging with both the CFHT/AOB-KIR instrument (K' band) and the IRAC/Spitzer camera (all bands), is reported. The average value of the linear polarisation fraction $P_{rm L}^{avg} simeq 0.47$ of the detected emission is estimated. A swing of the electric field vector across the compact nebula is observed. The infrared spectrum of the compact nebula is best described as a power law of index $alpha_{rm IR} = 0.7 pm 0.3$, and suggests its flattening between the infrared and X-ray bands. The detection of [Fe II] 1.64 $mu$m line emitting material is reported. Through medium resolution spectroscopy the infrared interstellar extinction to the object is estimated, and also the expansion velocity of the iron-line emitting material is determined, which in turn leads to estimating the distance of $d = 3.9 pm 1.2$ kpc to G21.5-0.9. The second part presents a study of the magnetospheric activity of millisecond pulsars in the context of the gamma-ray emission of globular clusters. Based on the pair starved polar cap model of the pulsar magnetosphere the database of the millisecond pulsar emission characteristics and the electron ejection spectra is created. The modelled electron ejection spectra are single-peaked for mildly inclined and fast rotating pulsars, while double-peaked for slowly rotating pulsars. The concept of the bias factor is introduced and studied. Synthetic spectra of globular clusters, stretching from MeV up to TeV energies, are simulated. They consist of the magnetospheric contribution from the millisecond pulsar population residing in the cluster, and an inverse Compton scattering (ICS) component resulting from up-scattering of the ambient photon fields (cosmic microwave background and optical photons from stellar population in the cluster) on the relativistic electrons diffusing through the cluster. The spectral characteristics of the ICS component depends on the composition of the ambient photon fields and also on the magnitude of the cluster magnetic field $B_{rm GC}$. For low $B_{rm GC} sim 1 mu$G the spectra are double-peaked. For the high $B_{rm GC} gtrsim 10 mu$G the ICS spectra are single-peaked. The level of ICS emission increases with the increase of $B_{rm GC}$, but it saturates for $B_{rm GC} sim 10 ~mu$G. Finally, the simulated synthetic spectra of globular clusters are confronted with the existing gamma-ray data for selected clusters: Terzan 5 and 47 Tucanae
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Jussila, Adam P. "Simulating Pulsar Signal Scattering in the Interstellar Medium with Two Distinct Scattering Phenomena." Oberlin College Honors Theses / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=oberlin1528814998720461.
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Chrétien, Mathieu. "Détection du pulsar de Vela et recherche de violation d'invariance de Lorentz avec le cinquième télescope de H.E.S.S." Thesis, Paris 6, 2015. http://www.theses.fr/2015PA066362/document.
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Le cinquième télescope (CT5) du réseau H.E.S.S. (High Energy Stereoscopic System) a été inauguré en 2012. H.E.S.S. est destiné à l’observation du ciel austral dans le domaine des rayons γ et CT5, dont le seuil est d’environ 30 GeV, a permis la détection du pulsar de Vela après 24 heures d’observations. Certains scénarios de gravitation quantique (QG) prédisent une violation d’invariance de Lorentz (LIV). Celle-ci se manifeste par l’ajout de termes ∝(E/EQG)n aux relations de dispersion du photon, où E est l’énergie du quanta de lumière, EQG l’énergie caractéristique des processus de QG et n l’ordre de la correction. Cette dépendance en énergie peut être testée par des mesures de temps de vol entre photons reçus de sources astrophysiques variables (noyaux actifs de galaxies), transitoires (sursauts γ) ou encore périodiques (pulsars). Cette thèse présente l’analyse des données recueillies par CT5 sur le pulsar de Vela. Une méthode de maximum de vraisemblance ayant déjà montré sa robustesse sur d’autres types de sources a été adaptée au cas du pulsar de Vela. Aucune déviation des relations de dispersion standard n’est observée, par conséquent des limites sont placées sur EQG. La plus contraignante est obtenue pour une correction linéaire superluminique aux relations de dispersion EQG > 7.0×1015 GeVThe fifth telescope (CT5) of the H.E.S.S. array (High Energy Stereoscopic System) was inaugurated in 2012. H.E.S.S. is designed to scrutinize the southern γ ray sky and CT5, whose threshold is about 30 GeV, allowed the Vela pulsar detection in 24 hours observation time. Some quantum gravity (QG) scenarios predict a violation of Lorentz invariance (LIV). This could manifest by additional terms ∝(E/EQG)n to the photon dispersion relations, where E is the light quantum energy, EQG the typical scale at which QG processes are expected to occur and n the order of the correction. This energy dependence could be tested by time of flight measurements between photons emitted from variable (active galactic nuclei), transient (gamma ray bursts) or periodical (pulsars) astrophysical sources. This thesis presents the analysis of the CT5 collected data from the Vela pulsar. A maximum likelihood method already successfully applied to other source species has been adapted here to the Vela pulsar. No deviation from standard photon dispersion relations is observed, therefore limits have been placed on EQG. The most restrictive result has been obtained for a superluminal linear correction to the dispersion relations EQG > 7.0×1015 GeV
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Guillemot, Lucas. "Détections de pulsars milliseconde avec le FERMI Large Area Telescope." Phd thesis, Bordeaux 1, 2009. http://tel.archives-ouvertes.fr/tel-00432706.
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Le satellite Fermi a été lancé le 11 juin 2008, avec à son bord le Large Area Telescope (LAT). Le LAT est un télescope sensible au rayonnement gamma de 20 MeV à plus de 300 GeV. Au début de l'activité de Fermi, neuf pulsars jeunes et énergétiques étaient connus dans le domaine gamma. Le nombre de détections de pulsars par le LAT prédit avant lancement était de plusieurs dizaines au moins. Le LAT permettait également l'étude des pulsars milliseconde (MSPs), jamais détectés avec certitude à très haute énergie jusqu'alors. Cette thèse aborde dans un premier temps la campagne de chronométrie des pulsars émetteurs radio et/ou X, candidats à la détection par le LAT, en collaboration avec les grands radiotélescopes et télescopes X. Cette campagne a permis la recherche de signaux gamma pulsés avec une grande sensibilité. En outre, la plupart des MSPs galactiques ont été suivis dans le cadre de cette campagne, sans biais de sélection a priori sur cette population d'étoiles. Pour la première fois, des pulsations ont été détectées pour huit MSPs galactiques au-dessus de 100 MeV. Quelques bons candidats à une détection prochaine apparaissent. Une recherche similaire a été conduite pour des MSPs d'amas globulaires, sans succès à présent. L'analyse des courbes de lumière et des propriétés spectrales des huit MSPs détectés révèle que leur rayonnement gamma est relativement similaire à celui des pulsars ordinaires, et est vraisemblablement produit dans la magnétosphère externe. Cette découverte suggère que certaines sources non identifiées sont des MSPs, pour l'instant inconnus.
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Kundu, Anu. "Contribution of multipolar electromagnetic fields to the radio and high energy emission of pulsars." Thesis, Strasbourg, 2018. http://www.theses.fr/2018STRAE014/document.
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L'étude du champ électromagnétique autour des étoiles à neutrons est l'une des méthodes vitales pour comprendre la physique des pulsars. Alors que la plupart des publications utilisent l'hypothèse d'un champ électromagnétique dipolaire centré standard, des études récentes se sont concentrées sur l'inclusion de composantes de champ multipolaire plus élevées et ont présenté une image plus générale pour les pulsars dans lesquels le moment du dipôle magnétique est décalé du centre de l'étoile. Ce travail discute des conséquences d'un dipôle magnétique rotatif excentré dans le vide en montrant diverses caractéristiques des lignes de champ magnétique et de l'émission de pulsar. Une étude à large bande du spectre du rayonnement pulsar est également présentée par la création de cartes des différentes régions d'émission des pulsars distinguées sur la base de leur fréquence dans le but principal de rechercher l'évolution du profil d'impulsion avec la fréquence. La thèse présente tous les résultats ci-dessus accompagnés des discussions nécessaires pour comprendre les modèles théoriques utilisés et les détails des méthodes numériques appliquéesStudying the electromagnetic field around neutron stars is one of the vital methods to understand the physics of the pulsars. While major literature uses assumption of a standard centred dipolar electromagnetic field, recent studies have focused on including higher multipolar field components and have presented a more generalized picture for pulsars in which the magnetic dipole moment is shifted off from the centre of the star. This work discusses the consequences of an off centred rotating magnetic dipole in vacuum by showing various characteristic features of magnetic field lines and pulsar emission. A broadband spectrum study of pulsar radiation is also laid out by creating maps of different emission regions of pulsars distinguished on the basis of their frequency with the main aim of looking for the evolution of the pulse profile with frequency. The thesis presents all the above results accompanied by the necessary discussions to understand the theoretical models used and the details of the numerical methods applied
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Stark, Craig R. "Plasma processes in pulsar environments." Thesis, University of Glasgow, 2008. http://theses.gla.ac.uk/343/.
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The aim of this thesis is to study coherent plasma effects and collective plasma processes in pulsar environments. Pulsars are one of the most enigmatic objects in the universe. Formed in supernova explosions, pulsars are rapidly rotating neutron stars identified by their periodically pulsed electromagnetic emission. The source of the radiation is believed to be associated with the electron-positron (pair) plasma populating the pulsar magnetosphere. The theory of pulsar radiation is still in its infancy and there is lack of understanding about the energetic processes involved. The initial aim of this thesis is to study a possible emission mechanism in which electrostatic oscillations are coupled to propagating electromagnetic waves by a magnetic field inhomogeneity, thus creating a source of radiation in the pulsar magnetosphere. The full nonlinear equations in cylindrical geometry for a streaming cold pair plasma are solved numerically, together with Maxwell's equations, using a Finite-Difference Time Domain method. Electrostatic oscillations are induced in a streaming plasma in the presence of a non-uniform magnetic field, and the resulting electromagnetic waves are modelled self-consistently. Also presented is the linear perturbation analysis of these model equations perturbed from a dynamical equilibrium in order to probe the fundamental modes present in the system. These simulations successfully exhibit the coupling mechanism and the nonlinear interaction between electromagnetic waves and independent plasma oscillations, confirming the importance of coherent plasma effects and collective plasma processes in the pulsar magnetosphere. The observed electromagnetic signature is characterised by the nature of the emission mechanism and possibly by the menagerie of dust it encounters as it propagates through the surrounding supernova remnant. Supernova remnants are composed of multi-species electron-ion dusty plasmas. Conventional modelling of dust growth in this environment is based upon coagulation and nucleation of gas phase material. The second aim of this thesis is to study a possible spheroidal dust growth mechanism via plasma deposition. Dust grains immersed in a plasma acquire a net negative charge forming a plasma sheath. Ions are accelerated from the bulk plasma into the sheath and are deposited on the surface of the grain altering its shape and size. Grains with an elliptical geometry have a non-radial electric field and further anisotropic growth occurs if the deposited ions are non-inertial. In reality the extent of such growth depends upon the initial kinetic energy of the ions and the magnitude of the electric field in the sheath. Laplace's equation for the electric field for a range grain eccentricities is numerically solved using a bespoke finite difference method, the dynamics of the ions in the sheath are solved, showing how elliptical growth is related to the initial eccentricity and size of the seed relative to the sheath length.
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張益軍 and Yijun Zhang. "Pulsar statistics in our galaxy." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2000. http://hub.hku.hk/bib/B31225585.
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Clifton, T. R. "A galactic plane pulsar survey." Thesis, University of Manchester, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.374524.
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Van, Heerden Elmarie. "Data challenges in pulsar searches." Thesis, University of Oxford, 2017. https://ora.ox.ac.uk/objects/uuid:98b329d6-4dbf-4956-9277-4b52fa2971bd.
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Technological advances coupled with a decline in digital storage costs have resulted in a profusion of data being created, collected and consumed. These data give rise to new challenges and opportunities in many disciplines ranging from science and engineering to biology and finance. An example of a future project in radio astronomy that promises both Big Data and Big Discoveries is the Square Kilometre Array (SKA) radio telescope project. Astrophysicists are confident that the Big Data amassed by the SKA will not only answer fundamental questions regarding the Universe but also contain big discoveries not yet postulated. The transformational potential of the SKA and its ensuing data and algorithmic challenges, in particular for the discovery and study of pulsars, drive the research of this thesis. Discovering all pulsars beaming towards Earth is one of the key science goals of the SKA. However, in addition to low signal strengths, searching for pulsars is extremely difficult due to the intrinsic weakness of their signals, propagation effects and the presence of anthropogenic interferences. Numerous techniques have been developed to overcome some of these difficulties and to assist in the quest to find more pulsars. However, despite the success of these techniques, the number of pulsars discovered in recent surveys (Swiggum et al. 2014, Lazarus et al. 2015) has fallen well short of the number predicted by pulsar population synthesis models (Lorimer 2011). This shortfall in pulsar detections can be attributed to radio frequency interference (RFI), red noise and scintillation (Lazarus et al. 2015). For this thesis, and in order to investigate and quantify these claims, I first developed a new technique to simulate pulsar search data that contain different types of RFI and varying noise baselines (i.e. red noise). This surrogate modelling technique was then used in a framework that I developed to inexpensively explore the sensitivity of pulsar search pipelines for different noise and RFI settings. The results from this framework highlight the necessity to develop algorithms that are able to identify and remove non-stationary variations from the data before RFI excision and searching is performed in order to limit false positive detections. To address the shortcomings identified with the framework which assessed the performance of existing pulsar search pipelines, I developed a new real-time algorithm for excising RFI while simultaneously normalising the variability in time and frequency inherent to pulsar observations. Processing synthetic data with the algorithm resulted in an expansion of the noise/pulsar spin period parameter space for which we are able to successfully detect pulsars. Furthermore, the algorithm is shown to reduce the number of false positive detections. In conclusion, the insights gained from the work presented in this thesis and the improvements achieved will contribute to the development of a new realtime pulsar search pipeline adept at dealing with the challenges posed by the SKA.
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Ait, Allal Dalal. "Détection d’évènements impulsionnels en environnement radioélectrique perturbé : application à l’observation des pulsars intermittents avec un système temps réel de traitement du signal." Thesis, Orléans, 2012. http://www.theses.fr/2012ORLE2056/document.
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Les travaux présentés dans ce mémoire s’inscrivent dans le cadre de la détection d’évènements impulsionnels intermittents en provenance de pulsars. Ces objets astrophysiques sont des étoiles à neutrons hautement magnétisées en rotation rapide, qui émettent un faisceau radio balayant l’espace comme la lentille d’un phare. Ils sont détectables grâce à une instrumentation spécifique. Depuis quelques années, on a découvert de nouvelles catégories de ces pulsars, aux caractéristiques extrêmes, avec en particulier des impulsions individuelles plus intenses et irrégulières comparé à la moyenne. Il faut pouvoir les détecter en temps réel dans un environnement radio perturbé à cause des signaux de télécommunications. Cette étude propose des algorithmes de traitement d’interférences radio fréquence (RFI) adaptés à ce contexte. Plusieurs méthodes de traitement de RFI sont présentées et comparées. Parmi elles, deux ont été retenues et comparées au moyen de simulations Monte Carlo, avec un jeu de paramètres simulant le pulsar et un signal BPSK avec des puissances et des durées différentes. Pour la recherche de nouveaux pulsars, une méthode alternative est proposée (SIPSFAR), combinant capacité de recherche en temps réel et robustesse contre les RFI. Elle est basée sur la transformée de Fourier 2D et la transformée de Radon. Une étude comparative théorique a permis de confronter et comparer la sensibilité de cette nouvelle méthode avec celle communément utilisée par les radioastronomes. La méthode a été implantée sur un GPU GTX285 et testée sur un grand relevé du ciel effectué au radiotélescope de Nançay. Les résultats obtenus ont donné lieu à une comparaison statistique complémentaire à partir de données réellesThe work presented in this thesis is in the context of the intermittent impulsive event detection at Nançay Observatory. The pulsars are highly magnetized neutron stars in rapid rotation, which emit a radio beam scanning the space like a lighthouse. They are detectable with a specific instrumentation. In recent years, new classes of such pulsars were discovered. These pulsars with extreme features, especially with individual pulses more intense and irregular compared to the average, must be detected in real time in a disrupted radio environment because of telecommunication signals. This study presents some radio frequency interference (RFI) mitigation algorithms adapted to this context. Several methods are presented and compared. Among them, two were selected and compared using Monte Carlo simulations with a set of parameters to simulate the pulsar and a BPSK signal with power and different durations. In the case of researching new pulsars, an alternative method is proposed (SIPSFAR), combining research capacity in real time and robustness against RFI. It is based on 2D Fourier transform and the Radon transform. A theoretical comparative study has confronted and compared the sensitivity of this new method and the commonly method used by radio astronomers. SIPSFAR was implemented on a GPU GTX285 and tested on a large survey of the sky made at Nançay radio telescope. The results have led to a further statistical comparison from the actual data
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Jacoby, Bryan Anthony Hillenbrand Lynne A. "Recycled pulsars /." Diss., Pasadena, Calif. : California Institute of Technology, 2005. http://resolver.caltech.edu/CaltechETD:etd-01272005-015012.
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Martín, Rodríguez Jonatan. "Theory & observations of the PWN-SNR complex." Doctoral thesis, Universitat Autònoma de Barcelona, 2014. http://hdl.handle.net/10803/283894.
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In this work, we study theoretical and observational issues about pulsars (PSRs), pulsar
wind nebulae (PWNe) and supernova remnants (SNRs). In particular, the spectral modeling
of young PWNe and the X-ray analysis of SNRs with magnetars comparing their characteristics
with those remnants surrounding canonical pulsars.
The spectra of PWNe range from radio to γ-rays. They are the largest class of identified
Galactic in γ-rays increasing the number from 1 to ∼30 during the last years. We have developed
a detailed spectral code which reproduces the electromagnetic spectrum of PWNe in
free expansion (tage .10 kyr). We shed light and try to understand issues on time evolution
of the spectra, the synchrotron self-Compton dominance in the Crab Nebula, the particle
dominance in PWNe detected at TeV energies and how physical parameters constrain the
detectability of PWNe at TeV. We make a systematic study of all Galactic, TeV-detected,
young PWNe which allows to find correlations and trends between parameters. We also
discuss about the spectrum of those PWNe not detected at TeV and if models with low magnetized
nebulae can explain the lack of detection or, on the contrary, high-magnetization
models are more favorable.
Regarding the X-ray analysis of SNRs, we use X-ray spectroscopy in SNRs with magnetars
to discuss about the formation mechanism of such extremely magnetized PSRs. The
alpha-dynamo mechanism proposed in the 1990’s produces an energy release that should
have influence in the energy of the SN explosion. We extend the work done previously done
by Vink & Kuiper (2006) about the energetics of the SN explosion looking for this energy
release and we look for the element ionization and the X-ray luminosity and we compare
our results with other SNRs with an associated central source.
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Grondin, Marie-hélène. "Premières détections de nébuleuses avec le Fermi-Large Area Telescope et étude de leurs pulsars." Thesis, Bordeaux 1, 2010. http://www.theses.fr/2010BOR14039/document.
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Dédié à l’étude de l’astronomie gamma, le satellite Fermi a été lancé le 11 juin 2008. Il comporte à sonbord l’instrument Large Area Telescope (LAT), sensible au rayonnement gamma dans la gamme d’énergie de20 MeV à 300 GeV. Bien que la nébuleuse du Crabe ait été étudiée dans la gamme d’énergie 70 MeV à 30GeV couverte par son précédesseur, l’expérience CGRO-EGRET, aucune nébuleuse n’a jamais été clairementidentifiée dans le domaine des rayons gamma de haute énergie jusqu’au lancement de Fermi.Les pulsars alimentent les nébuleuses qui les entourent par l’injection permanente d’un vent d’électrons etpositrons relativistes qui, accélérés au niveau de l’onde de choc délimitant les nébuleuses de pulsars, émettentun rayonnement pouvant être observé dans les différents domaines du spectre électromagnétique, et notammentdans le domaine des rayons gamma de haute énergie.Les données recueillies par le Fermi-LAT au cours des deux premières années de mission ont désormaispermis la détection et l’identification de trois nébuleuses et de leurs pulsars associés (nébuleuses du Crabe, deVela-X et de MSH 15-52) ainsi que de la nébuleuse de pulsar HESS J1825-137 découverte par les instrumentsau sol dédiés à l’astronomie gamma de très haute énergie.Les résultats des analyses temporelle, spectrale et morphologique réalisées sur les systèmes pulsars/nébuleuses détectés par le LAT sont exposés dans ce manuscrit. La synthèse des études systématiquesréalisées (i) dans les régions comportant un pulsar émetteur en rayons gamma et (ii) dans les régions comportant une source émettrice de rayons gamma de très haute énergie étant identifiée en tant que nébuleuse depulsar ou candidate en tant que telle, sont également présentés dans cette thèse. Ces études apportent de nouvelles contraintes sur les propriétés physiques des sources ainsi que sur les mécanismes de rayonnement mis enjeu dans la magnétosphère des pulsars et au sein de leurs nébuleusesThe Fermi Gamma-ray Space Telescope was launched on 2008 June 11, carrying the Large Area Telescope(LAT), sensitive to gamma-rays in the 20 MeV – 300 GeV energy range. The Crab Nebula had been detectedand studied in the 70 MeV – 30 GeV band using the CGRO-EGRET experiment, but no pulsar wind nebula(PWN) had ever been firmly identified in the high energy gamma-ray domain.PWNe are powered by the constant injection of a relativistic wind of electrons and positrons from theircentral pulsars. These charged particles are accelerated at the shock front forming the PWN and emit photons which can be observed along the entire electromagnetic spectrum, including the high energy gamma-raydomain.Data provided by the Fermi-LAT during the first two years of the mission have allowed the detection andthe identification of three PWNe and their associated pulsars (Crab Nebula, Vela X and MSH 15-52) as well asthe PWN HESS J1825-137 discovered by ground-based experiments sensitive to very high energy gamma-rays.Results of temporal, spectral and morphological analyses of the pulsar/PWN systems detected by Fermi-LAT, as well as results of systematic studies performed (i) around every gamma-ray pulsar detected by the LATand (ii) around every very high energy source identified as a PWN or a PWN candidate are presented in thisdissertation. These studies bring new insights and constraints on the physical properties of the sources as wellas on emitting processes in pulsar magnetospheres and in PWNe
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Nodes, Christoph. "Particle Acceleration in Pulsar Wind Nebulae." Diss., lmu, 2008. http://nbn-resolving.de/urn:nbn:de:bvb:19-80683.
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Leung, Chun-kwan, and 梁晉堃. "Gamma-ray emissions from pulsar binaries." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2014. http://hdl.handle.net/10722/206456.
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The launch of the Fermi Gamma-ray Space Telescope marked a new era in observing gamma-rays from astrophysical sources. Fermi’s high sensitivity in the ~ 0.1−300GeV energy range opens an important window in the observation of the gamma-ray emissions from pulsar binaries, which emit most of their radiation energy in the gamma-ray range. We can now observe the gamma-ray emissions from pulsar binaries at an unprecedented accuracy, and investigate their origin in detail. In this thesis, we present the studies on two systems of pulsar binary of two distinct classes. The gamma-ray emissions from the high-mass gamma-ray binary LS 5039 were studied using the latest data from Fermi. The emission is modulated according to the 3.9 hr orbital period of the system. The results can be explained by the contribution of three components: the pulsar magnetospheric emission, the pulsar wind emission and the emissions from the shock formed from the interaction between the pulsar wind and companion’s stellar wind. The results were compared with observed data from Fermi and also in X-ray and TeV. In addition, the emissions from the millisecond pulsar PSR J1023+0038 and its low mass binary companion were also studied. This system recently went through a transition from the rotation-powered state to the accretion state, after going the opposite way in 2007. This state transition, discovered through the disappearance of radio pulsation, was accompanied by the brightening in GeV, X-ray and UV fluxes. A detailed Fermi observation was performed, supplemented by multi-wavelength observations. It was found that the emission from this system can also be described by the emissions from the pulsar magnetosphere, the pulsar wind and its shock. These two systems, although of distinct classes of pulsar binaries, provide complementary cases for the study of high-energy radiation processes in pulsar binaries.published_or_final_version
Physics
Master
Master of Philosophy
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Ford, John M. "Pulsar Search Using Supervised Machine Learning." NSUWorks, 2017. http://nsuworks.nova.edu/gscis_etd/1001.
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Pulsars are rapidly rotating neutron stars which emit a strong beam of energy through mechanisms that are not entirely clear to physicists. These very dense stars are used by astrophysicists to study many basic physical phenomena, such as the behavior of plasmas in extremely dense environments, behavior of pulsar-black hole pairs, and tests of general relativity. Many of these tasks require information to answer the scientific questions posed by physicists. In order to provide more pulsars to study, there are several large-scale pulsar surveys underway, which are generating a huge backlog of unprocessed data. Searching for pulsars is a very labor-intensive process, currently requiring skilled people to examine and interpret plots of data output by analysis programs. An automated system for screening the plots will speed up the search for pulsars by a very large factor. Research to date on using machine learning and pattern recognition has not yielded a completely satisfactory system, as systems with the desired near 100% recall have false positive rates that are higher than desired, causing more manual labor in the classification of pulsars. This work proposed to research, identify, propose and develop methods to overcome the barriers to building an improved classification system with a false positive rate of less than 1% and a recall of near 100% that will be useful for the current and next generation of large pulsar surveys. The results show that it is possible to generate classifiers that perform as needed from the available training data. While a false positive rate of 1% was not reached, recall of over 99% was achieved with a false positive rate of less than 2%. Methods of mitigating the imbalanced training and test data were explored and found to be highly effective in enhancing classification accuracy.
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Jaroenjittichai, Phrudth. "Pulsar polarisation as a diagnostic tool." Thesis, University of Manchester, 2013. https://www.research.manchester.ac.uk/portal/en/theses/pulsar-polarisation-as-a-diagnostic-tool(cbbef2d8-5779-4f5b-a48d-09eec413f247).html.
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The geometry of pulsar beams is one of the intrinsic properties of neutron stars, governing the pulse-profile phenomenon and other aspects of pulsar astron- omy. With a number of pulsars in our dataset, their beam geometry is derived from the polarisation position angle (PPA) using the simple polar cap emission and dipole field model. This includes the rotating vector model (RVM), for which the solutions can hardly be constrained or fail to be consistent because of the lim- itations of the model itself. The inconsistencies in the results suggest that the initial PPAs can be strongly perturbed by additional parameters above the emis- sion altitude, such as the plasma medium or rotational aberration effects, after which their characteristic shape is no longer related to the geometry via the RVM. We investigate further into the effects of wave propagation in the pulsar magne- tosphere, and find an indication that, in most cases, the RVM-calculated PPAs are likely to be altered by plasma effects.In recent years, there have been an increasing number of intermittent and mode-switching pulsars observed to have their radio pulse profiles correlated with the change in pulsar spin frequency (ν ̇) (e.g. Lorimer et al. 2012, Lyne et al. 2010). These two phenomena are understood to be related via the states of plasma in the magnetosphere. As one such pulsar, and also one with known geometry and other astonishing behaviour, PSR B1822–09 is studied in terms of the mode- switching properties, the hollow-cone model and the wave propagation in the magnetosphere. We also study the model for explaining the intermittent pulsars PSRs B1931+24, J1841+0500 and J1832+0029, and find it can be consistently applied for PSRs B1822–09 and B0943+10, and other profile-switching pulsars. However, aspects of the conclusions are limited because of the lack of understand- ing of the connection between the radio flux and the states of plasma. We are also able to use the difference in the PPAs between two states of PSR B0943+10 to predict the change in plasma states and ν ̇, which cannot be measured directly from timing analysis as its switching timescale is too short.
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Kunzl, Thomas. "Coherent and incoherent radiation processes in pulsars." [S.l.] : [s.n.], 2001. http://deposit.ddb.de/cgi-bin/dokserv?idn=963899430.
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Straubmeier, Christian Michael. "OPTIMA Entwicklung und erste astronomische Messungen eines optischen Hochgeschwindigkeitsphotometers /." [S.l. : s.n.], 2000. http://deposit.ddb.de/cgi-bin/dokserv?idn=962132578.
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Lazarus, Patrick [Verfasser]. "Pulsar Discoveries and their Exploitation / Patrick Lazarus." Bonn : Universitäts- und Landesbibliothek Bonn, 2016. http://d-nb.info/1124540199/34.
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Camus, Nicholas Francois. "Relativistic magnetohydrodynamical models of pulsar wind nebulae." Thesis, University of Leeds, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.509036.
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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.
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Mingarelli, Chiara Maria Francesca. "Gravitational wave astrophysics with pulsar timing arrays." Thesis, University of Birmingham, 2014. http://etheses.bham.ac.uk//id/eprint/5117/.
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This thesis focuses on gravitational wave (GW) astrophysics with Pulsar Timing Arrays (PTAs). Firstly it is shown that anisotropy in the GW background may be present, and that its characterization at different angular scales carries important information. The standard analysis for isotropic backgrounds is then generalized by decomposing the angular distribution of the GW energy density into multipole moments. Generalized overlap reduction functions (ORFs) are computed for a generic level of anisotropy and PTA configuration. A rigorous analysis is then done of the assumptions made when calculating ORFs. It is shown that correlated phase changes introduce previously unmodeled effects for pulsars pairs separated by less than a radiation wavelength. The research then turns to the study of continuous GW sources from supermassive black hole binaries (SMBHBs). Here it shown that the detection of GWs from SMBHB systems can yield direct information about the masses and spins of the black holes, provided that the GW-induced timing fluctuations both at the pulsar and at Earth are detected. This in turn provides a map of the nonlinear dynamics of the gravitational field and a new avenue to tackle open problems in astrophysics connected to the formation and evolution of SMBHs.
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Antonucci, Federica <1976>. "Search for gravitational waves from known pulsar." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2009. http://amsdottorato.unibo.it/2061/.
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Geyer, Marisa. "Pulsar scattering and the ionized interstellar medium." Thesis, University of Oxford, 2017. http://ora.ox.ac.uk/objects/uuid:d20b2f33-f1ed-4c56-9227-cb12affb06d0.
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Fifty years after the discovery of the first pulsating neutron star, the field of pulsar science has grown into a multidisciplinary research field, working to address a wide range of problems in astrophysics - from stellar evolution models to high precision tests of General Relativity to analysing the detailed structure of the Interstellar Medium in the Milky Way. Over 2500 Galactic pulsars have been discovered. The next generation telescopes, such as the Square Kilometre Array, promise to discover the complete observable Milky Way population, of several tens of thousands, over the next decade. These point sources in the sky have extreme properties, with matter densities comparable to that of an atomic nucleus, and surface magnetic fields a trillion times stronger than Earth's magnetic field. Observationally, the most valuable property is their rotational stability - allowing us to anticipate and sum their beamed radio emission, as the pulsar spins around its axis, on millisecond to second timescales. The detected radio wave signals carry with them information of the ionised interstellar medium (IISM) paths they traveled along. The imprints reveal that the pulsar signals we detect travel along multiple paths. While the bulk of the emitted signal propagates along a straight line, we also receive delayed emission scattered through small angles, back into our line of sight. This scattering is caused by fluctuations in the free electron densities of the IISM. The impact of these inhomogeneities is exaggerated at low observing frequencies, where averaged pulsar profiles are observed to be broadened, and showcase exponential scattering tails characterised by a scattering timescale г. Simple theoretical models predict a power law dependence of г on frequency, with a spectral index α = 4. Despite these predictions, my analysis of pulsar data in this thesis, reveal a more complex frequency dependence on г. I investigate the scattering characteristics of a set of pulsars observed by the Low Frequency Array (LOFAR), at 110~MHz to 190~MHz. These data are ideal datasets for accurate studies of pulsar scattering, providing broad frequency bands at low frequencies. I find anomalously low power law spectral indices, α, describing the frequency dependence of г. These indices are likely due to anisotropic scattering mechanisms or small scattering clouds in the IISM. To conduct effective data analysis, I develop scattering fitting techniques by first analysing IISM effects on simulated pulsar data. I investigate the effects of two different types of scattering mechanisms, isotropic and anisotropic scattering, and consider each of their particular frequency-dependent impacts on pulsar data. The work on simulated data provides a robust fitting technique for extracting scattering parameters and a framework for the interpretation of the LOFAR data used in this study. The fitting technique simultaneously models scattering effects and standard frequency-dependent pulse profile evolution. I present results for 13 pulsars with simple pulse shapes, and find that г, associated with scattering by a single thin screen, has a power law dependence on frequency with α ranging from 1.50 to 4.0. My results show that extremely anisotropic scattering can cause low α measurements. The anomalous scattering properties can also be caused by the presence of small scattering clumps in the IISM, as opposed to the conventionally modelled large scattering screens. Evidence for both anisotropic scattering and small scattering clouds with high electron densities come from other areas of research. Indications of the anisotropic nature of the local IISM mostly come from high resolution pulsar scintillation analyses, while evidence for high density scattering clouds is often based on extreme scattering events measured through quasar observations. My results suggest that these anomalous scattering properties are more prevalent than formerly thought, prompting us to reconsider the physical conditions of the IISM, where traditionally high electron densities are reserved for HII regions and anisotropy is not modelled. High quality, low frequency pulsar data, where anomalous propagation effects become measurable, are a valuable addition in assisting us to distinguish between the different physical mechanisms that can be at play. The more complex these IISM characteristics reveal themselves to be, the harder it will be to disentangle intrinsic profile emission from IISM propagation imprints. Successfully separating these effects, however, promises to improve our understanding of the intrinsic pulsar radio emission - a process that is still poorly understood.
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Hemberger, Daniel. "Improving Pulsar Timing through Interstellar Scatter Correction." Oberlin College Honors Theses / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=oberlin1207521228.
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Gralla, Samuel E., Alexandru Lupsasca, and Alexander Philippov. "PULSAR MAGNETOSPHERES: BEYOND THE FLAT SPACETIME DIPOLE." IOP PUBLISHING LTD, 2016. http://hdl.handle.net/10150/622675.
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Most studies of the pulsar magnetosphere have assumed a pure magnetic dipole in flat spacetime. However, recent work suggests that the effects of general relativity are in fact of vital importance and that realistic pulsar magnetic fields will have a significant nondipolar component. We introduce a general analytical method for studying the axisymmetric force-free magnetosphere of a slowly rotating star of arbitrary magnetic field, mass, radius, and moment of inertia, including all the effects of general relativity. We confirm that spacelike current is generically present in the polar caps (suggesting a pair production region), irrespective of the stellar magnetic field. We show that general relativity introduces a similar to 60% correction to the formula for the dipolar component of the surface magnetic field inferred from spindown. Finally, we show that the location and shape of the polar caps can be modified dramatically by even modestly strong higher moments. This can affect emission processes occurring near the star and may help explain the modified beam characteristics of millisecond pulsars.
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Voisin, Guillaume. "Simulation numérique de la magnétosphère des pulsars : étude détaillée de processus radiatifs." Thesis, Paris Sciences et Lettres (ComUE), 2017. http://www.theses.fr/2017PSLEO015/document.
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Les pulsars sont des étoiles à neutron hautement magnétisées en rotation rapide produisant un rayonnement pulsé. Cette thèse est dédiée à leur magnétosphère, c'est à dire la zone proche de l'étoile à neutron, remplie d'un plasma entraîné par la rotation rapide de celle-ci. Il a été montré dès 1969 que la magnétosphère doit avoir des zones très peu denses arborant des champs électriques intenses capables d'accélérer le plasma raréfié de ces régions à des énergies très élevée le long du champ magnétique. La courbure des lignes de champ, couplé avec la rotation d'une particule autour du champ, cause un rayonnement dit de « synchro-courbure ». L'énergie est rayonnée essentiellement en photons gamma (g). Ces photons peuvent ensuite être convertis par interaction quantique photon γ-champ magnétique ou γ-γ en une paire électron-positron e+e- dont chaque composante rayonne à son tour, résultant en une cascade qui alimente la magnétosphère en plasma. Cette thèse traite particulièrement de deux phénomènes clefs de ces cascades : le rayonnement de synchro-courbure et la création de paires par interaction γγ.La théorie quantique du rayonnement de synchro-courbure est développée pour la première fois à partir des principes de base de l'électrodynamique quantique. Les paramètres compatibles avec les approximations du calcul correspondent à une large gamme de conditions physiques typiques des magnétosphères de pulsars. Les transitions quantiques sont considérées dans l'approximation continue lorsqu'elles impliquent un saut de l'impulsion de la particule dans la direction parallèle au champ, et discrète dans la direction perpendiculaire. Il en résulte un spectre tendant asymptotiquement vers les descriptions classiques des rayonnement de courbure et de synchro-courbure mais présentant des déviations très importantes lorsque les transitions discrètes dominent le rayonnement.L’interaction γγ→e+e- a été étudiée dans le cas où un gamma réagit sur un fond de photons de basse énergie. Ce mécanisme est considéré comme potentiellement important lorsque le champ magnétique n'est pas assez fort pour produire des paires par le mécanisme γ-champ magnétique. Tout indique que le fond est anisotrope, c'est pourquoi nous avons développé un formalisme permettant de prendre en compte arbitrairement les anisotropies et de produire les spectres des particules produites. Appliqué à un modèle simple d'étoile rayonnant thermiquement en X, il en résulte une dépendance forte du taux de réaction sur la direction du photon gamma.Cette thèse comprend également un modèle de chronométrage du pulsar milliseconde dans un système triple J0337+1715. Ce pulsar orbite avec deux étoiles naines blanches dont les interactions mutuelles ne sont pas négligeables. Une intégration numérique, à l'ordre newtonien et post-newtonien, a été développée pour déterminer les orbites. Un modèle complet incluant le calcul des retards du système du pulsars au télescope a été réalisé. Le modèle s'ajuste aux données de chronométrage provenant du radiotélescope de Nançay avec des résidus d'écart-type inférieur à 2 µs. Un tel système permet en principe le test du principe d'équivalence fort gravitationnel par une technique similaire à celle employée lors des expériences de laser-lune, mais avec une précision sans précédent en régime de champ fort. Ce test requiert une évaluation rigoureuse des incertitudes sur chaque paramètre, échantillonnées grâce à un code MCMC. La validation du code et l'évaluation des incertitudes sont en coursPulsars are highly magnetized fast rotating neutron stars producing a pulsed radiation. This thesis is dedicated to their magnetosphere, namely the zone surrounding the star and filled with a plasma dragged by the rotation of the star. It was shown as soon as 1969 that the magnetosphere must have vacuum gaps, where intense electric fields develop that are capable of accelerating the rarefied plasma to very high energies along the magnetic field. The curvature of the field lines, together with the rotation around the magnetic field, results in the so-called « synchrocurvature » radiation. The energy is mostly radiated in gamma photons (γ). These photons may then be converted by the quantum processes γ photon-magnetic field or γ-γ in an electron-positron pair e+e-, each component of which then radiates at its turn which results in a cascade that provides plasma to the magnetosphere. This thesis particularly deals with two key phenomena of these cascades : synchrocurvature radiation and γγ pairs.The quantum theory of synchrocurvature radiation is developed for the first time from the first principles of quantum electrodynamics. The range of parameters compatible with the approximations of the derivation covers a wide range of physical conditions typical of pulsar magnetospheres. Quantum transitions are considered in the continuous limit when they imply a jump of the particle impulsion parallel to the magnetic field, and discrete when the jump is in the perpendicular direction. It results in a spectrum that asymptotically tends to the classical descriptions of curvature and synchrocurvature radiations but that presents very important deviations when the discrete transitions dominate the radiation.The γγ→e+e- process was studied in the case of the reaction of a gamma photon on a soft photon background. This mechanism is considered as potentially important when the magnetic field is nopt strong enough for the γ-magnetic field process to efficiently produce pairs. The soft background is most likely anisotropic, and that is why we developed a formalism allowing to arbitrarily take into account anisotropies, as well as produce the spectra of the outgoing particles so as to be able to feed the subsequent cascade consistently. Applied to a simple model of a star radiating thermal X rays, it results in a strong dependence of the reaction rate on the direction of the gamma photon.This thesis also includes a timing model of the millisecond pulsar in a triple system J0337+1715. This pulsar orbits with two white-dwarf stars, and their mutual interactions are not negligible. It follows that a numerical integration of the orbits was developed at Newtonian and first post-Newtonian orders. A complete model including the computation of delays from the star to the telescope was realized. This model is able to fit the timing data from the Nançay (France) radiotelecope with a standard deviation of less than 2µs. In principle, such a system allows to test the strong equivalence principle by a technique similar to that employed in Lunar-laser-ranging experiments, but with an unprecedented accuracy in the strong-field regime. This test demands a careful estimate of the uncertainties on each parameter, which we sample using a MCMC code. The validation of the code and the evaluation of the uncertainties are ongoing
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Van, Straten Willem Herman Bernadus, and straten@astron nl. "High-Precision timing and polarimeter of PSR JO437-4715." Swinburne University of Technology. School of Biophysical Sciences and electrical Engineering, 2003. http://adt.lib.swin.edu.au./public/adt-VSWT20040311.123754.
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This thesis reports on the recent results of a continuing, high-precision pulsar timing project, currently focused on the nearby, binary millisecond pulsar, PSR J0437_4715. Pulse arrival time analysis has yielded a remarkable series of constraints on the physical parameters of this system and evidence for the distortion of space-time as predicted by the General Theory of Relativity.
Owing to the proximity of the PSR J0437_4715 system, relative changes in the positions of the Earth and pulsar result in both annual and secular evolution of the line of sight to the pulsar. Although the changes are miniscule, the effects on the projected orbital parameters are detectable in our data at a high level of significance, necessitating the implementation of an improved timing model.
In addition to producing estimates of astrometric parameters with unparalleled precision, the study has also yielded the first three-dimensional orbital geometry of a binary pulsar. This achievement includes the first classical determination of the orbital inclination, thereby providing the unique opportunity to verify the shape of the Shapiro delay and independently confirm a general relativistic prediction.
With a current post-fit arrival time residual RMS of 130 ns over four years, the unrivaled quality of the timing data presented herein may eventually contribute to the most stringent limit on the energy density of the proposed stochastic gravitational wave background. Continuing the quest for even greater timing precision, a detailed study of the polarimetry of PSR J0437_4715 was undertaken. This effort culminated in the development of a new, phase-coherent technique for calibrating the instrumental response of the observing system.
Observations were conducted at the Parkes 64-m radio telescope in New South Wales, Australia, using baseband recorder technologies developed at York University, Toronto, and at the California Institute of Technology. Data were processed off-line at Swinburne University using a beowulf-style cluster of high-performance workstations and custom software developed by the candidate as part of this thesis.
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Icdem, Burcin. "Viscous Time Scale In Accreting Powered Pulsars And Anomalous X-ray Pulsars." Master's thesis, METU, 2011. http://etd.lib.metu.edu.tr/upload/12613373/index.pdf.
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In this thesis we analyse X-ray data of accretion powered low mass and high mass X-ray binaries to understand the nature of their accretion mechanisms by searching for some clues of viscous time-scales of their accretion discs, if they have, in their low frequency power density spectra created from their long-term X-ray observations, or by doing pulse timing analysis with much shorter X-ray data to detect the effects of torque fluctuations caused by the accreting material on the pulsar.
The low mass and high mass X-ray binaries we analysed have breaks in their power density spectra, which are attributed to the role of viscosity in the formation of accretion discs. Although, the time-scales corresponding to these break frequencies are smaller than the predictions of the Standard theory of accretion discs, the sources give consistent results among themselves by displaying the expected correlation between their break and orbital frequencies. The correlation curve of LMXBs implies thicker appearing accretion discs than those assumed by the theory. The dichotomy
of the HMXBs on this curve points out the different origins of accretion that these sources may have, and offers a way to distinguish the stellar-wind fed systems from the Roche-lobe overflow systems.
The timing and spectral analysis of Swift J1626.6-5156 reveal a correlation between the spin-up rate and the luminosity of the source implying that the pulsar is accretion-powered. This correlation together with the characteristics of the X-ray spectra enables us to estimate the magnetic field and the distance of the source.
The AXP 1E 2259+586 does not display any signs of viscous time-scale in its low frequency power density spectra, and its pulse timing analysis gives a much smaller torque noise value than that expected from accretion powered pulsars. In addition, the analysis results presented in this thesis reveal magnetar-like glitches which differ than those of radio pulsars, due to the presence of the strong magnetic field of the pulsar. These results eliminate the possibility that the AXP is an accretion-powered pulsar.
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Sanwal, Divas. "Optical study of pulsars /." Digital version accessible at:, 1999. http://wwwlib.umi.com/cr/utexas/main.
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Herfindal, Jeffrey. "Nulling Periodicities in Pulsars." ScholarWorks @ UVM, 2008. http://scholarworks.uvm.edu/graddis/108.
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Numerous studies of conal pulsars, e.g. B1133+16, have revealed fluctuation features and a steady null fraction. Sensitive Arecibo observations provide an unprecedented ability to detect nulls and confirm previously found fluctuation features. By replacing each pulse with a scaled version of the average profile, we were able to quench all subpulse modulation, dubbed pulse-modulation quelling (PMQ). It was surprising to note that the low-frequency feature observed in the natural longitude resolved fluctuation spectra (LRF) persisted in the PMQ LRFs! It appears that we can conclude, then, that the nulls themselves reflect whatever underlying periodicity is responsible for the low-frequency feature. Conversely, the aggregate fluctuation power of the low frequency feature changes little whether the pulse modulation is quelled or not, implying that the feature fluctuations are produced by the nulls! These conclusions are perplexing because (with very unusual exceptions) no obvious or regular periodicities have heretofore been attributed to null occurrence.
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Hassall, Tom. "Observing pulsars with LOFAR." Thesis, University of Manchester, 2012. https://www.research.manchester.ac.uk/portal/en/theses/observing-pulsars-with-lofar(1860a120-1c7a-4d64-a281-f482f3f53614).html.
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The LOw Frequency ARray (LOFAR) is the first of a new generation of telescopes which, instead of using a single large dish, will combine the signals from thousands of antennas. Combining these signals creates a virtual beam, which can be 'pointed' like traditional (dish-like) telescopes, but with significantly improved angular resolution and sensitivity at low frequencies. This unique configuration also allows LOFAR to observe in several modes which are not possible with other telescopes, including forming multiple beams, and simultaneously taking imaging and beam-formed data. In this thesis we present some of the early science and commissioning work which has been undertaken with LOFAR. Wide-band simultaneous observations of four pulsars using LOFAR, the Lovell Telescope and the Effelsberg 100-m Telescope are used to constrain emission heights and examine the evolution of the average pulse pulse profile between 50~MHz and 8~GHz. We find that the radio emission from all of the pulsars observed comes from a region not larger than 400~km in size, and also see pulse profile evolution that deviates significantly from what is expected from radius-to-frequency mapping. The same observations are also used to probe the interstellar medium (ISM). The ISM imparts a frequency-dependent dispersive delay on pulses propagating through it. This delay is well understood, and well measured but there are many second-order effects of the ISM, like refraction and anomalous dispersion, which have not yet been detected, and which are expected to scale steeply with frequency. These effects are potentially only observable at low frequencies, and if measured, can be used to determine the distribution of electrons and other charged particles along the line-of-sight. We find no evidence of these effects, instead finding that that the cold dispersion law is accurate to better than 1 part in 100,000 between ~40 and ~180 MHz. The absence of any of these effects in our data was used to place upper limits on some of the properties of the ISM. From these upper limits, we also show that delays from the ISM are <50 ns at normal pulsar timing frequencies (1400 MHz).We also present an investigation in to the behaviour of the single pulses of PSR B0809+74 at low-frequencies. We show that the drift rate of PSR B0809+74 is extremely constant on timescales of a few hours and a few years and compare the shape of driftbands at low frequencies to their high frequency counterparts. We identify a slowly evolving microstructure, which is persistent for several pulse periods, allowing us to solve the aliasing problem and determine the speed of the carousel. We also find evidence for 'partial nulls', in which one subpulse is extinguished without interrupting the emission of the others.
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Kirsten, Franz [Verfasser]. "Pulsar astrometry with VLBI and beyond / Franz Kirsten." Bonn : Universitäts- und Landesbibliothek Bonn, 2014. http://d-nb.info/1060787172/34.
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Jia, Jianjun. "The phase-resolved spectra of the crab pulsar." Click to view the E-thesis via HKUTO, 2005. http://sunzi.lib.hku.hk/hkuto/record/B36379918.
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Gomez, Julio D. "Pulse timings for binary black hole-pulsar systems." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape15/PQDD_0024/MQ31349.pdf.
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