Photospheric emission from long duration gamma-ray bursts powered by variable engines

Abstract

We present the results of a set of numerical simulations of long-duration gamma-ray burst jets aimed at studying the effect of a variable engine on the peak frequency of the photospheric emission. Our simulations follow the propagation of the jet inside the progenitor star, its break-out, and the subsequent expansion in the environment out to the photospheric radius. A constant and two step-function models are considered for the engine luminosity. We show that our synthetic light-curves follow a luminosity-peak frequency correlation analogous to the Golenetskii correlation found in long-duration gamma-ray burst observations. Within the parameter space explored, it appears that the central engine luminosity profile does not have a significant effect on the location of a gamma-ray burst in the Luminosity-peak frequency plane, bursts from different central engines being indistinguishable from each other.

The photospheric origin of the Yonetoku relation in gamma-ray bursts

“…These problems arise from the fundamental physics of synchrotron emission and so cannot be explained within this framework. The above difficulties have led recent theoretical and observational studies to consider photospheric emission (photons released from a relativistic jet during the transition from optically thick to thin states) as a promising alternative scenario [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] . This model predicts the emergence of quasi-thermal radiation and can reproduce those spectral shapes that are incompatible with synchrotron theory.…”

“…However, these analyses adopted oversimplified jet dynamics (e.g. steady spherical flow) 12,13 and/or crude assumptions for radiation processes 14,15 . More sophisticated study is necessary to firmly connect photospheric emission to the Yonetoku relation.…”

Monte Carlo Simulations of Photospheric Emission in Gamma Ray Bursts

“…Models that rely on synchrotron emission are able to account for the non-thermal characteristics of GRB spectra 4,16 but are unable to fully account for various GRB observational relationships such as the Amati 17 and Yonetoku 18 relations 1 . The photospheric model on the other hand is able to reproduce the Amati and Yonetoku relations 10,12,13,15,19,20 but has issues with reproducing typical GRB spectral parameters 12,13 . In order to fully distinguish between these models additional data at different wavelengths is needed.…”