The leading model for understanding the energetics of anomalous X-ray pulsars (AXPs) is that they are "magnetars"---young, isolated neutron stars powered by the decay of their enormous magnetic fields. The identification of AXPs as magnetars is motivated by the similarity of AXPs to another enigmatic class of sources, the Soft Gamma Repeaters (SGRs). We report on long-term monitoring of AXPs using the Rossi X-ray Timing Explorer (RXTE). We monitor AXPs with RXTE to study their rotational stability, to search for variations in their pulsed flux and pulsed morphology. During our regular monitoring observations we discovered multiple bursts from two AXPs: this was the first time such behavior has been observed from these sources. Prior to our monitoring campaign, the detection of bursts solely from SGRs was the principle difference between AXPs and SGRs. The first detection of AXP bursts came in Fall 2001 when we discovered two SCR-like X-ray bursts from the direction of AXP 1E 1048.1--5937. Due to RXTE's large (1° x 1°) field-of-view we could not unambiguously identify the AXP as the burster. Recently, we detected a third burst from the direction of this source as well as a simultaneous increase in the pulsar's pulsed emission---this clearly identified the AXP as the burster. The most outstanding demonstration of AXP bursting behavior came on 2002 June 18 when AXP 1E 2259+586 underwent a major outburst involving 80 bursts and several changes in the persistent and pulsed emission, including a huge pulsed flux enhancement, a pulse morphology change and a rotational glitch. We also find variations in the persistent emission of AXPs in the absence of an obvious outburst. For example, we discovered two pulsed flux flares from AXP 1E 1048.1--5937. Both flares lasted several months and had well resolved few-week-long rises. The long rise tunes of the flares is a phenomenon not previously reported for this class of object, but has a clear explanation within the context of the magnetar model. All these results imply a close relationship between AXPs and SGRs, which we now believe are both magnetars, and have posed significant challenges to competing models.

We present two examples of secondary effects on the large-scale polarization of the cosmic microwave background (CMB). We begin with a review of the standard model of cosmology, as well as the predictions of bulk flows by the linear theory of structure growth and the mathematical formalism of polarization. Following this review, we explore the impact of the epoch of reionization on the large-scale polarization of the CMB, paying particular attention to the effects of an alternate reionization history containing dark stars. Subsequently, we derive the CMB polarization signature of large-scale bulk flows and examine its potential for detection by future experiments. / Nous présentons deux exemples d'effets secondaires sur la polarisation du fond diffus cosmologique (CMB) à grande échelle. Nous débutons avec une revue du modèle standard de la cosmologie, une prédiction des mouvements d'ensemble des amas de galaxies par la théorie de la croissance linéaire des structures ainsi qu'une présentation du formalisme mathématique de la polarisation. Suivant cette revue, nous étudions l'impact de l'époque de réionisation sur la polarisation à grande échelle du CMB, en se concentrant sur les effets d'un modèle alternatif de réionisation incluant des étoiles sombres. Ensuite, nous dérivons la signature en polarisation dans le CMB engendrée par un mouvement d'ensemble à grande échelle et examinons la mesurabilité de ce signal par des expériences futures.

The advent of X-ray astronomy has turned the study of compact objects into one of the most active research fields in modern-day physics. Diverse luminosity phenomena have been remarked upon in neutron stars and it is believed that in many of them the neutron star crust plays a critical role. This work presents a steady-state model for the neutron star crust that describes, in particular, the profiles of temperature and flux along this region. It is divided as follows: First, a review of observational phenomena in neutron stars, where crust characteristics are thought to be crucial, are presented, alongside general aspects of the theoretical models applied. Second, the different elements that are needed to construct this model are considered. Third, the set of structure equations to be resolved and the calculations of the components of these equations are provided. Finally, the results are shown and discussed and the conclusion is presented. / L'avènement de l'astronomie des rayons X a transformé l'étude des objets compacts en un des champs de recherche des plus actifs en physique moderne. Divers phénomènes de luminosité ont été observés dans les étoiles neutron et on estime que la croûte de l'étoile neutron joue un rôle important dans beaucoup de ces phénomènes. Cet ouvrage présente un modèle d'équilibre stable pour la croûte de l'étoile neutron qui décrit, en particulier, les profiles de température et flux dans cette région. L'ouvrage est divisé comme suit: Premièrement, une révision des phénomènes observés dans les étoiles neutron, où les caractéristiques de la croûte sont supposées être cruciaux, est présentée, avec les aspects généraux des modèles théoriques utilisés. Deuxièmement, les différents éléments nécessaires pour construire ce modèle sont examinés. Troisièmement, l'ensemble des équations de structure à résoudre et les calculs des composantes de ces équations sont présentés. Finalement, les résultats sont montrés et discutés et la conclusion est présentée.

The role played by ultrahigh frequencies or ultrashort distances in the usual derivation of the Hawking effect is discussed. We demonstrate the robustness of Hawking's prediction of black-hole evaporation, by carrying out an explicit calculation, in which short-distance physics is explicitly regularized using the Pauli-Villars regularization scheme. We find that short-distance effects due to physics at small distance scales, 1/$ Lambda gg 1/T sb{H}$, where 1/$ Lambda$ is a covariantly chosen short-distance cutoff, can only contribute to the Hawking flux an amount that is exponentially suppressed by the large ratio $ Lambda$/$T sb{H}$. We argue further that this behavior is not specific to our choice of regularization, but is a generic feature of any covariant short-distance regularization. We do so by showing that no possible covariant and local counterterm exists which can contribute to the Hawking flux at late times far from the hole.

We have constrained the neutrino parameter space of Deltam 2-sin2 2thetav by considering the possibility of r-process nucleosynthesis occurring in the hot bubble region of a supernova. In addition, we have calculated the effects of density fluctuations and spin-flavor oscillations on these constraints. We also considered the delayed shock mechanism of a supernova explosion and calculated the shock heating rate with and without the Mikheyev-Smirnov-Wolfenstein (MSW) and Resonant spin-flavor precession (RSFP) effects. We have confirmed that both these phenomena can significantly affect the neutrino heating rate of the supernova causing shock wave.

Studies on the statistical properties of the large scale structure of the universe have often separated the problem into a spatial point distribution of galaxies and a functional variation of their luminosity independent of position. We consequently attempt to bridge these two approaches by defining a family of generalized luminosity fields which depends on both spatial resolution and luminosity intensity. From analysis of 3, 2, and 1-dimensional catalogues, we find that in 3d the galaxy luminosity field exhibits two signatures of multifractal behavior: multiscaling and divergent statistical moments. Furthermore, we find evidence suggesting that the statislics governing this multifractal behaviour are determined by the parameters (the degree of multifractalily of the field) and C$ sb{1,1}$ (the codimension of the mean luminosity) which we estimate as 1.2 $ pm$ 0.4 and 1.28 $ pm$ 0.06 respectively. We consequently suggest that the non-linear mechanisms responsible for the formation of galaxies may be of multifractal origin. As many of the analyses were performed on projected fields a theoretical framework for multifractal projections is also developed.

The possible polar wandering of the planet Mars is investigated by modeling some of the many surface magnetic anomalies discovered by Mars Global Surveyor (MGS). First I describe the physics of polar wandering by exposing the theory developed by Ricard et al. [1993] and Spada et al. [1996]. I derive the linear form of the equation of polar motion in the time domain valid for polar motion of up to 10 deg. The long-term polar motion of a non-rigid planet is also discussed via the rotational number first defined by Spada et al. [1996]. The main conclusion of Spada et al. [1996] can be reached by using the simpler linear equation of polar motion.

The effects of density fluctuations on supernova neutrinos have been studied. Using the formalism developed by Burgess & Michaud (BM) and stellar evolution progenitors by Woosley & Weaver, the expected neutrino flux from a future galactic super-nova have been computed taking into account possible density fluctuations for a 2ν system. It has been shown that within the most recent constraints of mass squared difference values and vacuum mixing angle, neutrino fluxes on earth could be affected depending on the fluctuation levels. / The formalism developed by BM has been extended to the case of three neutrino generations. Preliminary results using this model show that in this case as well, density fluctuations could affect the expected neutrino flux. / A new multidimensional, non-Riemann solver based, High resolution Shock Capturing (HRSC) scheme has been proposed using the semidiscrete central and Weighted Essentially Non-Oscillatory (WENO) data reconstruction methods. The novel aspect of this algorithm is that for robustness, elements of the Piecewise Parabolic Method (PPM) has been incorporated in this HRSC scheme. The algorithm has been applied to the multidimensional classical and Special Relativistic Hydrodynamics (SRHD) equations. The new HRSC algorithm and codes were verified by a number of benchmark tests in one and two dimensions.

Prior to ~20 years ago, only two kinds of pulsars were known: RPPs and accretion-powered pulsars. The rapid advance of X-ray astronomy in the past few decades has led to the discovery of magnetic-powered pulsars, namely "magnetars". Magnetars were first identified with the SGRs which exhibit sporadic soft gamma-ray bursts. More recently, another group of pulsars, the AXPs, characterised by their bright persistent X-ray emission that is more powerful than their spin-down luminosity, were also recognized as members of the magnetar family. Both SGRs and AXPs have very high (10¹⁴-10¹⁵ G) magnetic fields as inferred from their spin-down. Studying AXP behaviour might help us understand the physics of magnetars and their connections with normal pulsars. In Chapter 3, I present our work on the X-ray afterglow of the AXP 1E 2259+586. It is the first AXP to exhibit a SGR-like outburst. It went through a major outburst in 2002. We studied the X-ray afterglow of this outburst, using ten XMM observations taken before and after the outburst. We found that the AXP's flux decayed following a power-law of index -0.69±0.03, remarkably similar what was found from the afterglow of some SGR outbursts. We also found a strong correlation between spectral hardness and X-ray flux, as seen in other AXPs. In Chapter 4 I present our work on searching for X-ray variability from the glitching AXP 1E 1841-045. This is one of the most frequent glitchers among AXPs. Magnetar theories and observations suggest that there could be a connection between magnetar glitches and their X-ray variability. However, we found no evidence of glitch-related X-ray variability from archival X-ray data of 1E 1841-045 taken between 1993 and 2006. Our finding supports the existence of radiatively silent glitches in AXPs. Interestingly, there is also a group of RPPs that have spin-down magnetic fields close to those of the magnetars (~10¹³G). These high-magnetic-field RPPs may share some observational properties with the magnetars. In Chapter 5, I present the first X-ray detection of the high-magnetic-field RPP B1916+14. We found that the pulsar's emission is likely thermal, with a surface temperature in the range of 0.08-0.23 keV. We did not detect pulsations in the data, and set a 1σ upper limit on the pulsed fraction in the 0.1-2 keV band of ~0.7. The origin of the thermal emission is not well constrained. We cannot rule out initial cooling or return current heating for this pulsar. To look for evidence of magnetic-field-decay heating, a deeper observation is needed. In Chapter 6, I present our work on CHANDRA X-ray observations of the high-magnetic-field RPP J1718-3718. We detected X-ray pulsations at the pulsar's period with 52%±13% pulsed fraction in the 0.8-2 keV band. We found, from a merged spectrum of multiple observations, a blackbody temperature of 0.19±0.02 keV, slightly higher than predicted by standard cooling models. However, the best-fit neutron star atmosphere model is consistent with standard cooling. We also found that the pulsar's bolometric luminosity represents 0.3 of its spin-down power, assuming a distance of 4.5kpc. Finally, we compared the blackbody temperatures measured for the high-magnetic-field pulsars with those from low-magnetic field rotation-powered pulsars of the same age, and found evidence of the former being on average hotter than the latter, as predicted by magneto-thermal evolution models that attempt to unify high-magnetic-field RPPs with magnetars. / Dans le chapitre 3, je présente mon travail sur la lueur résiduelle de AXP 1E2259+586. Il s'agit du premier pulsar anormal à partir duquel des pulsations similaires à celles des SGR ont été détectées. Ce pulsar a eu un sursaut énergétique majeur en 2002. Nous avons étudié la lueur résiduelle de ce sursaut au travers 10 observations faites avec le télescope XMM prises avant et après le sursaut. Nous avons trouvé que le flux du pulsar a diminué en suivant une fonction de puissance dont l'indice, −0.69±0.03, est remarquablement similaire à celui trouvé dans le rayonnement résiduel des sursauts des SGR. Nous avons aussi trouvé une corrélation entrela dureté du spectre et le flux en rayons-X, une corrélation qui est aussi observée dans d'autres AXP. Dans le chapitre 4, je présente mon travail sur la recherche de variations dans la luminosité-X de AXP 1E 1841−045. Ce pulsar est parmi les AXP qui présentent le plus fréquemment des sauts de fréquences, ou glitchs. Plusieurs théories des magnétars suggèrent une connection entre les glitchs et la variation de la luminosité-X. Malgré celà, nous n'avons pas trouvé de preuve de l'éxistence de ces variations dans la luminosité-X de 1E 1841−045 dans des observations prises entre 1993 et 2006 avec des télescopes variés. Ceci démontre l'existence de glitchs silencieux. Il est intéressant de noter qu'il existe un groupe de pulsars normaux, dont la source de luminosité est leur énergie rotationelle, qui ont un champ magnétique élevé et proche de celui des magnétars ( 1013 G). Certaines caractéristiques de ces pulsars à champ magnétique élevé sont similaires à celles des magnétars. Dans le chapitre 5, je présente la première détection en rayons-X du pulsar à champs magnétique élevé B1916+14. Nous avons trouvé que le spectre d'émission de ce pulsar est probablement thermique, avec une température de surface entre 0.08–0.23 keV. Nous n'avons pas détecté de pulsations régulières dans les données, avec une limite supérieure (1)de 0.7 sur la fraction pulsée entre 0.1 et 2 keV. Il est aussi difficile de déterminer si le spectre d'émission thermique observé est dû à un refroidissement initial ou à un courant qui réchauffe la surface du pulsar en ce moment. C'est pourquoi plus d'observations sont requises afin de prouver que le réchauffement de la surface est dû à une diminution du champ magnétique. Dans le chapitre 6, je présente mon travail effectué sur des observations faites avec le télescope Chandra du pulsar a champ magnétique élevé RPP J1718−3718. Nous avons détecté des pulsations régulières en rayons-X à un interval égal à celui de la fréquence rotationelle de ce pulsar et avec une fraction pulsée de 52%±13% entre 0.8 et 2 keV. Nous avons trouvé, en étudiant le spectre combiné de plusieurs observations,une température de corps noir de 0.19±0.02 keV. C'est une température un peu plus élevée que celle prédite par les modèles standards de refroidissement. Par contre, les modèles numériques d'atmosphère des étoiles à neutrons est en accord avec les modèles standards de refroidissement. Nous avons aussi trouvé que la luminosité bolométrique représente 0.3 de la puissance due à la perte d'énergie rotationelle, si l'on suppose une distance de 4.5 kpc. Finalement, nous avons comparé les températures de corps noirs des pulsars normaux à champ magnétique élevé avec ceux de pulsars normaux du même âge ayant un champ magnétique faible, et nous avons trouvé que les premiers avaient des températures plus élevées, comme le prédisent les modèles magnéto-thermiques ayant comme but d'unifier les pulsars normaux à champs magnétiques élevés et les magnétars.

Following the lone detection of the Galactic supernova remnant Cas A by gamma-ray detectors aboard CGRO and hard X-ray detectors aboard INTEGRAL in the nuclear lines of the 44Ti decay chain, The et al, 2006, argued that these surveys should have detected several sources, given models for the yield of 44Ti and an estimate of the Galactic supernova rate. In this thesis, this result is revisited by exploring the effect of various newer yield models of Type II supernovae, which include yields that differ by approximately an order of magnitude. We also consider several estimates of the Galactic supernova rate, which also differ by an order of magnitude, and various models for the Galactic distribution of massive stars. We find that the lone detection of Cas A is in fact consistent with a large number of reasonable models. We find that in order to detect a significant number of previously unknown remnants in a survey for 44Ti and thus constrain supernova models, a sensitivity to fluxes of less than 1E-7 photon per square cm per second within an absolute Galactic latitude of less than 5 degrees is required. / Suivant la seule détection dans les lignes de désintégration nucléaires du 44Ti de Cassiopeia A avec les détecteurs à bord de CGRO et d'INTEGRAL, The et al, 2006 ont présenté une analyse de la distribution de jeunes restants de supernova dans la Galaxie dont la conclusion est que ces missions auraient dû detecter plusieurs sources. Ce mémoire vise a reproduire et raffiner ce résultat en prenant compte de différents modèles pour la production du 44Ti (qui sont incertains par approximativement un ordre de grandeur), de différents modèles de la répartition des étoiles massives dans la Galaxie et de différents taux de supernovae dans la Galaxie (également incertain par un ordre de grandeur). Nous concluons que la detection de Cassiopeia A est consistante avec une large gamme de modèles raisonnables. Finalement, nous extrapolons qu'il serait nécessaire qu'un futur relevé ait une limite de détection de moins de 1E-7 photon par cm carré par seconde dans le plan Galactique (ie. a une latitude Galactique absolue de moins de 5 degrés) afin de déctecter une quantité non-nulle de jeunes restants de supernova jusqu'ici inconnus dans le but de contraindre les modèles de supernova.