Detection of Prompt Fast-Variable Thermal Component in Multi-Pulse Short Gamma-Ray Burst 170206A

TL;DR

This paper reports the detection of a strong, fast-variable thermal component in the short gamma-ray burst 170206A, revealing correlated evolution with the non-thermal component and suggesting photospheric emission and Comptonization as underlying mechanisms.

Contribution

First detection of a fast-variable thermal component in a short GRB with detailed spectral evolution analysis and proposed emission mechanisms.

Findings

Thermal component exhibits rapid flux variability matching non-thermal component.

Thermal and non-thermal components show correlated spectral evolution.

Thermal emission likely originates from photospheric processes with Comptonization effects.

Abstract

We report the detection of a strong thermal component in the short Gamma-Ray Burst 170206A with three intense pulses in its light curves, throughout which the fluxes of this thermal component exhibit fast temporal variability same as that of the accompanying non-thermal component. The values of the time-resolved low-energy photon index in the non-thermal component are between about -0.79 and -0.16, most of which are harder than -2/3 excepted in the synchrotron emission process. In addition, we found a common evolution between the thermal component and the non-thermal component, $E_{\rm p,CPL} \propto kT_{\rm BB}^{0.95\pm0.28}$, and $F_{\rm CPL} \propto F_{\rm BB}^{0.67\pm0.18}$, where $E_{\rm p,CPL}$ and $F_{\rm CPL}$ are the peak photon energy and corresponding flux of the non-thermal component, and $ kT_{\rm BB}$ and $F_{BB}$ are the temperature and corresponding flux of the thermal component, respectively. Finally, we proposed that the photospheric thermal emission and the Comptonization of thermal photons may be responsible for the observational features of GRB 170206A.