Gamma-ray bursts and their afterglows

伽马射线暴(GRB)是一种短暂、强烈的伽马射线闪光，伴随着X射线向射电波长发出更持久的辐射。伽马射线发射的持续时间可能短至几毫秒，也可能长达几百秒，在此期间，伽马射线暴让已知宇宙中的所有物体都黯然失色。伽玛射线暴根据其伽马射线发射的持续时间被分为两类，分别与大质量恒星的坍塌或两个致密天体(两个中子星或一个中子星和黑洞)的合并有关。在他的博士学位中，山姆将研究伽玛暴的多波长余辉，以及他们能告诉我们什么关于伽玛暴爆炸的环境、它们的中央引擎和它们的喷气式飞机的结构。他将首先关注在光学、X射线和GeV波长光曲线中发现的相关性。这种关联将这些波长的伽玛暴余辉的早期固有亮度与它们的平均衰减率联系在一起，因此最亮的余辉比较暗的余辉衰减得更快。这种关联可能是控制能量释放的内在属性的结果，较亮的余辉的能量比较弱的余辉释放得更快。或者，这种相关性可能是由于视角引起的几何效应，与更亮、更快的衰减余辉相比，较弱、较慢衰减的余辉更多地偏离轴线观看。萨姆将通过确定射电光曲线中是否也存在这种相关性来开始这项调查。萨姆将主要研究由NASA Swift卫星观测到的伽玛暴，英国参与了船上三台仪器中的两台-紫外线和光学望远镜以及X射线望远镜。萨姆将作为UVOT团队的一员直接参与SWIFT。他将通过SWIFT和STARGATE团队的成员资格，利用UVOT和ESO望远镜参与伽玛暴的实时观测和后续行动。他还将通过雕刻社的成员身份参与寻找引力波的电磁对应物。

Gamma-ray bursts (GRBs) are brief, intense flashes of gamma-rays that are accompanied by longer lasting emission in the X-ray to radio wavelengths. The duration of the gamma-ray emission may be as short as a few milliseconds or may last for as long as a few hundred seconds, during which the GRB 'out-shines' all objects in the known universe. GRBs are divided, based on the duration of their gamma-ray emission, into two classes 'long' and 'short', which are associated, respectively, with the collapse of massive stars or the mergers of two compact objects (either two neutron stars or a neutron star and black hole). For his PhD, Sam will investigate the multi-wavelength afterglows of GRBs and what they can tell us about the environments GRBs explode in to, their central engines and the structure of their jets. He will initially begin by focusing on a correlation found in the optical, X-ray and GeV wavelength light curves. This correlation connects the early intrinsic brightness of GRB afterglows in these wavelengths with their average rate of decay, such that the brightest afterglows decay more quickly than the fainter ones. This correlation may be a result of an intrinsic property which regulates the energy release, with the energy of brighter afterglows being released more quickly than the fainter ones. Alternatively, this correlation may be due to a geometric effect caused by viewing angle, with the fainter slower decaying afterglows viewed more off-axis compared to their brighter and faster decaying counterparts. Sam will begin this investigation by determining whether the correlation exists also in the radio light curves.Sam will primarily work on GRBs observed by the NASA Swift satellite, the UK has key involvement in two of the three instruments onboard - the Ultra-violet and optical telescope and the X-ray telescope. Sam will be directly involved in Swift as a member of the UVOT team. He will participate in real time observation and follow-up of GRBs with UVOT and ESO telescopes through membership of the Swift and STARGATE teams. He will also participate in the search for the electromagnetic counterpart of gravitational waves through membership of ENGRAVE collaboration.