Gamma-ray bursts and their afterglows

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.