MG14 - Talk detail

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Abstract

Gamma-ray bursts (GRBs) are cosmological explosions which carry valuable information from the distant past of the expanding universe. One of the greatest discoveries in modern cosmology is the finding of the accelerated expansion of the universe using Type Ia supernovae (SN Ia) as standard candles. However, due to the interstellar extinction SN Ia can be seen only up to a redshift $z\sim 1.5$. GRBs are considered as the potential alternative to push this limit to as high as $z\sim 10$, a redshift regime when the universe just started to form the first structures. There exist several correlations between the energy and an observable of a GRB which can be used to derive luminosity distance (e.g., Amati et al. 2002). In recent works (Basak \& Rao 2012, 2013), we have studied such correlations in the sub-burst (pulses), and obtained the highest coefficient (Pearson correlation coefficient, r = 0.96) among all GRB correlations. In this talk, we shall present our results of the pulse-wise GRB correlation study. It is worth mentioning that the all GRB correlations are still empirical, and we cannot use them in cosmology unless we understand the basic physics of GRBs. To this end, we need to investigate the prompt emission spectrum which is so far described by the empirical Band function. We shall discuss our current understanding of the radiation process particularly the finding of two blackbodies and a power-law (the 2BBPL model) as the generic spectral model and its implication (Basak \& Rao 2014, 2015). This is a work in progress and we expect to obtain the most fundamental GRB correlation based on our improved spectral model.

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