The BAT Slew Survey (BATSS) is the first wide-field survey of the hard X-ray sky (15–150 keV) with a slewing coded aperture imaging telescope. Its fine time resolution, high sensitivity and large sky coverage make it particularly well-suited for detections of transient sources with variability timescales in the \(\sim 1 sec–1 hour\) range, such as Gamma-Ray Bursts (GRBs), flaring stars and Blazars. As implemented, BATSS observations are found to be consistently more sensitive than their BAT pointing-mode counterparts, by an average of 20% over the 10 sec–3 ksec exposure range, due to intrinsic systematic differences between them. The survey’s motivation, development and implementation are presented, including a description of the software and hardware infrastructure that made this effort possible. The analysis of BATSS science data concentrates on the results of the 4.8-year BATSS GRB survey, beginning with the discovery of GRB 070326 during its preliminary testing phase. A total of nineteen (19) GRBs were detected exclusively in BATSS slews over this period, making it the largest contribution to the Swift GRB catalog from all ground-based analysis. The timing and spectral properties of prompt emission from BATSS GRBs reveal their consistency with Swift long GRBs (L-GRBs), though with instances of GRBs with unusually soft spectra or X-Ray Flashes (XRFs), GRBs near the faint end of the fluence distribution accessible to Swift-BAT, and a probable short GRB with extended emission, all uncommon traits within the general Swift GRB population. In addition, the BATSS overall detection rate of 0.49 GRBs/day of instrument time is a significant increase (45%) above the BAT pointing detection rate. This result was confirmed by a GRB detection simulation model, which further showed the increased sky coverage of slews to be the dominant effect in enhancing GRB detection probabilities. A review of lessons learned is included, with specific proposals to broaden both the number and range of astrophysical sources found in future enhancements. The BATSS survey results provide solid empirical evidence in support of an all-slewing hard X-ray survey mission, a prospect that may be realized with the launch of the proposed MIRAX-HXI mission in 2017. / Physics

Astrophysical flows have an enormous dynamic range of relevant length scales. The physics occurring on the smallest scales often influences the physics of the largest scales, and vice versa. I present a detailed study of the multiscale and multidimensional behavior of three high-energy astrophysical flows: jet-driven supernovae, massive black hole accretion, and current-driven instabilities in gamma-ray burst external shocks. Both theory and observations of core-collapse supernovae indicate these events are not spherically-symmetric; however, the observations are often modeled assuming a spherically-symmetric explosion. I present an in-depth exploration of the effects of aspherical explosions on the observational characteristics of supernovae. This is accomplished in large part by high-resolution, multidimensional numerical simulations of jet-driven supernovae. The existence of supermassive black holes in the centers of most large galaxies is a well-established fact in observational astronomy. How such black holes came to be so massive, however, is not well established. In this work, I discuss the implications of radiative feedback and multidimensional behavior on black hole accretion. I show that the accretion rate is drastically reduced relative to the Eddington rate, making it unlikely that stellar mass black holes could grow to supermassive black holes in less than a Hubble time. Finally, I discuss a mechanism by which magnetic field strength could be enhanced behind a gamma-ray burst external shock. This mechanism relies on a current-driven instability that would cause reorganization of the pre-shock plasma into clumps. Once shocked, these clumps generate vorticity in the post-shock plasma and ultimately enhance the magnetic energy via a relativistic dynamo process. / text

Thesis (Ph.D.)--Tufts University, 2002. / Adviser: Alexander Vilenkin. Submitted to the Dept. of Physics. Includes bibliographical references (leaves 95-98). Access restricted to members of the Tufts University community. Also available via the World Wide Web;

Thesis (M. Phil.)--University of Hong Kong, 2007. / Title proper from title frame. Also available in printed format.

Gamma-ray bursts are still not fully understood events. However, their exploration could pro- vide a useful tool for a better understanding of the early Universe because they belong to the most distant and violent objects that astronomers know. This thesis tries to bring more information about a so-called group of intermediate-duration bursts claimed by different authors employing dif- ferent data samples. Firstly, duration and spectral hardness properties of bursts from the Reuven Ramaty High-Energy Solar Spectroscopic Imager are statistically analysed. The obtained results bring a suspicion that these intermediate bursts gather into a separate group. Secondly, these bursts are investigated in more detail with respect to their spectral lags, peak count rates, red- shifts, supernova observations, and so forth. Thirdly, long-duration bursts with known redshifts and with derived pseudo-redshifts detected by The Burst and Transient Source Experiment, Swift and Fermi bursts with known redshifts, are used to study the cosmological effects on the observed flux and fluence distributions.

Gamma-ray bursts (GRBs) are short, intense flashes of 0.1-1 MeV electromagnetic radiation that are routinely observed by Earth orbiting satellites. The sources of GRBs are known to be extragalacitic and located at cosmological distances. Due to the extremely high isotropic equivalent energies of GRBs, which are on the order of Eiso~1054 erg, the gamma-ray emission is believed to be collimated, making them observable only when they are directed towards Earth. The favored progenitor models of GRBs are also believed to emit gravitational waves that would be observable by the current generation of ground-based interferometric gravitational wave detectors. The LIGO (Laser Interferometer Gravitational-Wave Observatory) and Virgo instruments operated near design sensitivity and collected more than a year of triple coincident data during the S5/VSR1 science run, which spanned the two year interval between November 2005 and October 2007. During this time, GRB detections were being made by the NASA/Goddard Swift Burst Alert Telescope at a rate of approximately 0.3 per day, producing a collection of triggers that has since been used in a coincident GRB-GW burst search with data from the LIGO-Virgo interferometer network. This dissertation describes the search for gravitational waves using the times and locations of 123 below-threshold potential GRB triggers from Swift over the same time period. Although most of the below-threshold triggers are likely false alarms, there is reason to believe that some are the result of actual faintly-observed GRB events. Recent GRB observations indicate that the local rate of low-luminosity GRBs is much higher than previously believed. This result, combined with the possibility of discovering a rare nearby GRB event accompanied by gravitational waves, is what motivates this search. The analysis results indicate no evidence for gravitational waves associated with any of the below-threshold triggers. A median distance lower limit of ~16 Mpc was derived for a typical neutron star-black hole coalescence progenitor assumption.

Les sursauts gamma se divisent entre sursauts courts, issus de la coalescence de deux objets compacts, et sursauts longs, issus de l'effondrement d'une étoile très massive de type Wolf-Rayet. Ce phénomène cataclysmique produit un jet ultra-relativiste. La dissipation de l'énergie au sein de ce jet est à l'origine d'une bouffée de photons gamma (keV-GeV) d'une durée moyenne de 10 s que l'on nomme émission prompte. Elle est suivie d'une phase d'émission rémanente détectable en X, en optique et en radio qui est visible de quelques secondes après le sursauts à quelques jours voir semaines et provient de la dissipation de l'énergie du jet dans le milieu environnant. Il s'agit des événements transitoires les plus lumineux que nous connaissons ce qui permet de les détecter jusqu'à des valeurs de décalage cosmologique (redshift) de l'ordre de 8-9. Cela permet l'exploration du diagramme de Hubble à grand redshift qui reste encore mal connu. Mais pour cela, il est nécessaire de standardiser ces sources astrophysiques afin de calibrer leur luminosité. Diverses relations, liant la luminosité des sursauts gamma à un paramètre indépendant de la cosmologie, ont été mises en évidence permettant de transformer les sursauts en " chandelles standards ". Au cours de cette thèse, nous avons étudié ces relations afin d'apporter un éclairage nouveau sur la façon dont elles sont affectées par divers effets de sélection instrumentaux. Les relations spectrales lient la luminosité isotropique ou l'énergie isotropique à l'énergie du maximum spectral de l'émission prompte. Nous avons montré que la combinaison de deux effets de sélection (détection puis mesure du redshift) permettait d'expliquer les contradictions entre les études reposant sur les sursauts avec redshift et celles incluant les sursauts sans redshift. Cela a conduit à la mise en évidence d'un lien entre l'émission prompte en gamma et l'émission rémanente en optique. Nous nous sommes également intéressé à l'une des relations temporelles, celle reliant Liso au délai spectral. Ce paramètre correspond à la différence entre le temps d'arrivée des photons de hautes et de basses énergies. Après avoir développé notre propre méthode de calcul de cette quantité, nous avons obtenu des résultats intéressants sur les distributions de ce paramètre et son lien avec l'évolution spectrale au sein des sursauts gamma. Nous avons également mis en évidence l'existence d'effets de sélection impactant cette relation et compromettant son usage pour la cosmologie. Plus généralement, cette thèse a permis de mettre en évidence la complexité de la standardisation des sursauts gamma qui ne peut être faites de manière aussi simple que celle utilisée jusqu'à présent. Nous avons montré qu'une étude détaillée des effets de sélection qui affectent ces relations de standardisation est un préalable indispensable avant toute utilisation de ces dernières à des fins cosmologiques. / GRBs are divided between short bursts, resulting from the coalescence of two compact objects, and long bursts, resulting from the collapse of a very massive star (Wolf-Rayet type). This cataclysmic phenomenon produces an ultra-relativistic jet. Energy dissipation in this jet produces flashes of gamma photons (keV-GeV) with an average duration of 10 seconds which is called prompt emission. It is followed by a detectable afterglow phase in X, optical and radio band which is visible from a few seconds after the bursts to several days or weeks and results from the dissipation of the energy contained in the jet into the surrounding medium. They are the most luminous transient events that we know, which can be detected up to redshifts of about 8-9. Being so bright, GRBs may allow the exploration of the Hubble diagram at high redshift, which is still poorly understood. To do this, it is however necessary to standardize these astrophysical sources and calibrate their brightness. Various relationships linking the intrinsic luminosity of GRBs with a parameter independent from cosmology have been highlighted allowing GRBs standardization. To achieve this goal, it is necessary to assess whether the observed correlations represent an intrinsic property of GRBs. In this thesis, we study selection effects to understand their impact on several relations which have been used to standardize GRBs. Spectral relationships connect the isotropic brightness or isotropic energy, and the peak energy of the prompt emission. We show that a combination of two selection effects, respectively associated with the GRB detection and the measure of their redshift, explains the contradiction between studies based on GRBs with a redshift and studies based on larger samples of GRBs without a redshift. Our study led us to discover a link between the prompt gamma emission and the optical afterglow that is a first step to understand the link between these two phases of the gamma-ray burst emission. Among the second category of relations, we focused on the relation between the luminosity and the spectral lag of the prompt emission. This parameter corresponds to the difference between the times of arrival of GRB photons at high and low energies. We developed our own method for the measure of the spectral lag, which led us to discuss the distribution of this parameter and its relationship to the spectral evolution within GRBs. We also confirmed the existence of selection effect affecting this relationship and compromising its use for cosmology. This thesis highlights the strong impact of observational selection effects on the relations which have been proposed for GRB standardization. We conclude that the study of selection effects is essential to understand if the relations proposed for the standardization of GRBs are intrinsic or due to selection effects, and if they can be used for cosmological purposes.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第22255号 / 理博第4569号 / 新制||理||1656(附属図書館) / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)准教授 前田 啓一, 講師 LEE Shiu Hang, 教授 長田 哲也 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

abstract: Several key, open questions in astrophysics can be tackled by searching for and mining large datasets for transient phenomena. The evolution of massive stars and compact objects can be studied over cosmic time by identifying supernovae (SNe) and gamma-ray bursts (GRBs) in other galaxies and determining their redshifts. Modeling GRBs and their afterglows to probe the jets of GRBs can shed light on the emission mechanism, rate, and energetics of these events. In Chapter 1, I discuss the current state of astronomical transient study, including sources of interest, instrumentation, and data reduction techniques, with a focus on work in the infrared. In Chapter 2, I present original work published in the Proceedings of the Astronomical Society of the Pacific, testing InGaAs infrared detectors for astronomical use (Strausbaugh, Jackson, and Butler 2018); highlights of this work include observing the exoplanet transit of HD189773B, and detecting the nearby supernova SN2016adj with an InGaAs detector mounted on a small telescope at ASU. In Chapter 3, I discuss my work on GRB jets published in the Astrophysical Journal Letters, highlighting the interesting case of GRB 160625B (Strausbaugh et al. 2019), where I interpret a late-time bump in the GRB afterglow lightcurve as evidence for a bright-edged jet. In Chapter 4, I present a look back at previous years of RATIR (Re-ionization And Transient Infra-Red Camera) data, with an emphasis on the efficiency of following up GRBs detected by the Fermi Space Telescope, before some final remarks and brief discussion of future work in Chapter 5. / Dissertation/Thesis / Doctoral Dissertation Physics 2019

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第18791号 / 理博第4049号 / 新制||理||1582(附属図書館) / 31742 / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)教授 中村 卓史, 教授 谷森 達, 教授 田中 貴浩 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM