P. N. Bhat

Spectral lags in Gamma-ray Bursts (GRBs), wherein low-energy photons arrive at later times than the high-energy photons, have been observed in a significant number of bursts. Spectral lags have been attributed to curvature effects in GRBs. In this scenario, the relativistic GRB jet is assumed to be a cone with a certain opening angle. Photons that are off-axis relative to the observer arrive at later times than on-axis photons. In this work, we test GRB data for spectral lags and other such curvature effects by invoking a relatively simple kinematic, two-shell collision model for a uniform jet profile. We have isolated single pulse structures in the Fermi-GBM, BATSE, and Swift-BAT GRB samples. We present the preliminary results of our analysis.

Gamma-ray bursts are the most luminous explosions in the Universe, and their origin as well as mechanism are the focus of intense research and debate. More than three decades since their serendipitous discovery, followed by several breakthroughs from space-borne and ground-based observations, they remain one of the most interesting astrophysical phenomena yet to be completely understood. Since the launch of Fermi with its unprecedented energy band width spanning seven decades, the study of gamma-ray burst research has entered a new phase. Here we review the current theoretical understanding and observational highlights of gamma-ray burst astronomy and point out some of the potential promises of multi-wavelength observations in view of the upcoming ground based observational facilities.

We report on the detailed analysis of the high-energy extended emission from the short gamma-ray burst (GRB) 081024B detected by the Fermi Gamma-ray Space Telescope. Historically, this represents the first clear detection of temporal extended emission from a short GRB. The light curve observed by the Fermi Gamma-ray Burst Monitor lasts approximately 0.8 s whereas the emission in the Fermi Large Area Telescope lasts for about 3 s. Evidence of longer lasting high-energy emission associated with long bursts has been already reported by previous experiments. Our observations, together with the earlier reported study of the bright short GRB 090510, indicate similarities in the high-energy emission of short and long GRBs and open the path to new interpretations.