iPTF15dtg is a supernova (SN) Type Ic (lacking hydrogen and helium in its spectrum) with a light curve indicating that it is the result of a massive star explosion. Taddia et al. (2016) suggested that the progenitor star was a Wolf-Rayet (WR) star that previously suffered strong mass loss. More recent observations show that the SN light curve did not decline as expected, indicating the existence of an additional power source. One possibility is a magnetar, a hyper-magnetic neutron star capable of injecting its rotational energy into the light curve during relevant time scales. This bachelor thesis adds previously unpublished data to the iPTF15dtg light curve and compares simple semi-analytical models to rule out a radioactive scenario and discuss the possibility of a magnetar as the primary source of luminosity.

<p>This article-based dissertation provides a review on the broad subject of magnetars-their characteristics, giant flares (GFs) and associated observations of X-ray, gamma-ray, and radio emissions and their proposed physical mechanisms. The primary purpose of this dissertation is to provide an extensive description of the two research projects I undertook during my tenure as a Graduate Research Assistant, under the guidance of my advisor. Broadly, my research was focused on building analytical models and running three-dimensional (3-D), high-resolution magnetohydrodynamic (MHD) simulations using the astrophysical PLUTO code to investigate the physical mechanisms behind high-energy (X-ray and gamma-ray) and radio emissions associated with magnetar GFs using observational constraints. This, in turn, aided in either validating or disfavoring existing theories behind such energetic explosions.</p><p>Chapter 1 provides a review on magnetars, their GFs and associated high-energy and radio emissions, largely based on excellent reviews by [1]–[5]. I summarize interesting observational features of magnetars, specifically those of soft gamma-ray repeaters (SGRs) and anomalous X-ray pulsars (AXPs), along with known aspects of their X-ray and gamma-ray activity. I focus on the December 27, 2004 GF emitted by SGR 1806-20, the most energetic GF out of the three that occurred to date, describe its energetics and summarize existing theories behind the physical mechanisms that give rise to two emission characteristics associated with the GF - (i) quasi-periodic oscillations (QPOs) seen in the tail, and (ii) a radio afterglow detected a week after the GF. Lastly, I describe the methods I used to hypothesize the physical mechanisms behind QPOs and the radio emission and compare and contrast them with those suggested previously.</p><p>In chapter 2, I present a version of the research article in preparation and pending publication in the Monthly Notices of the Royal Astronomical Society. The work titled “Radio afterglow of magnetars’ giant flares”, undertaken under the supervision of Dr. Maxim Lyutikov and in collaboration with Dr. Maxim Barkov, explores the possible physical mechanisms behind the radio afterglow associated with the SGR 1806-20 GF using high-resolution 3-D MHD simulations.</p><p>In chapter 3, I present a version of the research article previously published by the Journal of Plasma Physics. The work titled “Tilting instability of magnetically confined spheromaks”, undertaken under the supervision of Dr. Maxim Lyutikov, in collaboration with Dr. Lorenzo Sironi and Dr. Maxim Barkov, investigates the tilting instability of a magnetically confined spheromak using 3-D MHD and relativistic particle-in-cell (PIC) simulations with an application to astrophysical plasmas, specifically to explain the QPOs arising in the tail of the SGR 1806-20 GF.</p><p>I summarize the main results and conclusions of the two research projects and describe future prospects in chapter 4, followed by appendices A and B which describe additional theoretical concepts and simulation results for a better understanding of the nature of radio afterglows associated with GFs, and structure of spheromaks. References are compiled after the appendices in order that they are first cited, followed by a brief autobiographical sketch, and a list of publications.<br></p>

No description available.

Esta tesis doctoral por compendio de artículos está formada por tres análisis en los que estudiamos observaciones tomadas con el telescopio XMM-Newton de tres fuentes diferentes: La fuente 4U0114+65 es uno de los púlsares más lentos conocidos hasta el momento. Está formado por una donante de alta masa de tipo espectral B1Ia y una NS que la orbita con un periodo de 11.6 d. La NS gira sobre su eje con un periodo de ~ 9350 s. Esta fuente podría ser un magnetar (NS con un campo magnético muy intenso, incluso para una NS). En este trabajo presentamos el análisis de una observación en periodo propietario realizada con el satélite XMM-Newton durante 49 ks, donde hemos estudiado el proceso de acreción, las propiedades del viento estelar y la naturaleza de los pulsos de rayos X. Cen X-3 es un sistema binario compacto de rayos X de alta masa. La acreción sobre el objeto compacto, una NS en este caso, tiene lugar mediante disco de acreción. En este trabajo hemos analizado dos observaciones llevadas a cabo con el telescopio XMM-Newton. Una de ellas tuvo lugar en el año 2001, durante las fases orbitales ∅= 0.0 − 0.37. Esta observación fue tomada durante la salida del eclipse del objeto compacto, cuando la fuente se encontraba en un estado súper-orbital hard-low, hard porque la emisión de rayos X es muy energética y low porque la intensidad es baja. La segunda observación tuvo lugar en el año 2006, durante las fases orbitales ∅= 0.35 − 0.8. En este caso la fuente se encontraba en un estado súper-orbital soft-high, es decir, la luz emitida no es tan energética como en la primera observación pero su intensidad es mayor. Por último, presentamos un análisis de la primera observación tomada con el observatorio XMM-Newton del sistema eclipsante HMXRB XTE J1855−026. La observación tuvo lugar totalmente durante el eclipse de la NS, cubriendo las fases orbitales ∅= 0.00 − 0.11. Hemos comparado nuestro análisis de la fuente en eclipse con uno previo realizado con Suzaku en las fases orbitales previas al eclipse y hemos estudiado el viento estelar retroiluminado de la donante tipo B0I.

京都大学 / 新制・課程博士 / 博士(理学) / 甲第23703号 / 理博第4793号 / 新制||理||1686(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)教授 井岡 邦仁, 教授 萩野 浩一, 教授 田中 貴浩 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

With energy outputs &gt;~10^51 erg in 0.1-1000 seconds, Gamma-ray Bursts (GRBs) are the most powerful events yet observed in the Universe. As such they are potential probes of the very early Universe, back to the era of re-ionisation and the first stars, but at the same time they have been observed to span a wide range in luminosity and redshift from the relatively local Universe (z~0.0085) out to z~6.29. GRBs divide into two classes based primarily on their duration as measured by T90 (the time taken to observe 90% of the total burst fluence). Long bursts (L-GRBs) have T90&gt;~2 seconds, and shorts (S-GRBs) T90&lt;~2 seconds. Though much has been learned regarding long duration GRBs since the first afterglow discovery in 1997 (including their likely association with massive core collapse supernovae), much remains unknown regarding short duration GRBs. In this work, after a brief historical introduction and review, we present analyses of the angular cross-correlation on the sky of short GRBs from the BATSE catalogue with galaxies in the local Universe sampled from the PSCz Redshift Survey and the Third Reference Catalogue of Bright Galaxies (RC3). In particular we show that 20%+/-8% (1 sigma) of all BATSE short duration bursts (localised to 10 degrees or better) show correlation with galaxy samples (morphological T-type&lt;=4) within ~112 Mpc. Our statistics thus provide evidence that a substantial fraction of BATSE short GRBs show a tendency to be associated with large scale structure on the sky traced by a variety of galaxy types. Short GRBs are believed to be produced in the final merger of compact object (neutron star-neutron star or neutron star-black hole) binaries, though other possible progenitors are known to exist. The short initial spike of a giant flare from a Soft Gamma Repeater (SGR) such as the December 27th 2004 event from SGR1806-20 would have been detectable by BATSE as a short GRB if it occurred in a galaxy within ~30-50 Mpc (assuming a distance to SGR1806-20 of 15 kpc). Using the observed luminosities and rates of Galactic SGR giant flares, as well as theoretical predictions for the rate of binary mergers, we investigate the ability of plausible Luminosity Functions (LF), singly and in combination, to reproduce our observed correlations and a cosmological S-GRB population. We find the correlations are best explained by a separate population of lower luminosity S-GRBs, with properties consistent with them being due to giant flares from extra-galactic SGRs. Overall predicted number counts are a good fit to the observed BATSE number counts, and furthermore, the wider redshift distribution is consistent with the early Swift S-GRB redshift distribution. The three closest GRBs which have been observed to date were all long duration bursts, and we have therefore also searched for cross-correlation signals between the BATSE long GRBs and local galaxies. The three nearby bursts shared several similar properties such as being under-luminous, spectrally soft and of low variability. We have therefore also investigated a subset of L-GRBs with light curve properties similar to these known nearby bursts. The whole sample is found to exhibit a correlation level consistent with zero (1 sigma upper limit=10%, equivalent to 144 bursts) out to a radius of ~155 Mpc, but a spectrally soft, low observed fluence and low variability subset shows a correlation level of 28%+/-16% (=50+/-28 bursts) within 155 Mpc. These results are consistent with low-luminosity, low-variability bursts being a separate sub-class of L-GRBs which may be much more prevalent in the local Universe than their high-luminosity, cosmologically distant counterparts. To investigate this further, we once again examined plausible luminosity functions for single and dual high and low luminosity populations, based on observed intrinsic rates from the literature. The local population was once again found only to be produced to a sufficient level (while maintaining consistency with the observed overall number counts) by a separate low luminosity population with intrinsic rates several hundred times greater than their cosmological counterparts. Constraining the models via the Swift overall redshift distribution instead of threshold-adjusted BATSE number counts showed that the dual LF models were able to produce excellent fits to the entire redshift distribution while adequately reproducing a local population. Finally, suggestions are made as to the direction future work may follow in order to build on these initial investigations, as well as to how observations with future missions and detectors such as Fermi (formerly GLAST), Advanced LIGO and LOFAR may shed further light on nearby GRBs.