Pulse spectral evolution of classical long GRBs

Classical long GRBs (LGRBs) come with variety of temporal structures, which are difficult to describe with a single law. This situation simplifies if we consider a GRB event to be made up of broad pulses, generated simultaneously in a wide energy range and which can be described by empirical models. The GRB pulse spectrum is generally fitted with empirical Band model. We  show, for a set of Fermi GRBs with known redshift, that a simultaneous spectral and timing description of a GRB pulse can be achieved from an empirical model of spectral evolution. One of the major outcomes of this pulse model is finding a very good correlation of a spectral parameter with the energy of that pulse. 
As pulses are the building blocks of a GRB, we analyze single/separable pulsed GRBs to realize the spectral evolution in terms of various models. We found that a blackbody (BB) along with a powerlaw (PL) can describe the instantaneous spectrum much as the same as Band model. Moreover, the evolution of BBPL model leads to a spectrum which can be described as a Band model. We also find a smooth temperature decrement at the later part of all bursts. But, the initial part shows unexplained behaviour. We investigate multiple component in this part of the pulse and found that the inclusion of a second BB makes the temperature variation smooth throughout. This findings can be used to achieve a comprehensive description of GRB pulses having known redshift. This can lead to an even better correlation and raises an enormous hope for using GRB pulses as standard candles.