A Brief Introduction to the Study of Afterglows of Gamma Ray Bursts

Abstract

Gamma Ray Burst or GRB for short, is the term used to describe intense pulse of astronomical gamma rays of mean energy ~ 1 MeV, and such events were discovered in the late 1960’s by American satellites (VELA) serendipitously. In the last 30 odd years since their discovery more than 3000 papers have been written about them (including my own unpublished work with Richard Lingenfelter even before the formal discovery) and yet it is only in the last few years there has been any real progress in their understanding. This recent progress was made possible by the observations made with the Wide Field Camera (WFC) aboard the Italian-Dutch Satellite BeppoSAX, which operating in the soft X-ray band of 2–30 keV is capable of providing speedily the direction of the sources of the GRBs to within a few arcminutes. With the availability of such accurate positions optical and radio telescopes could be pointed in the direction, the source could be identified and the afterglow of the burst at these longer wavelengths could be observed continuously, upto several weeks after the burst. Detailed measurements in the 7-ray window were made with the BATSE instrument aboard the Compton Gamma Ray Observatory (CGRO) — we will review these before describing the measurements of the afterglow and some of the theoretical models that help us understand the phenomena that underline the GRBs which undoubtedly are at cosmological distances and constitute the most energetic events in the Universe.