Detection of a Prompt Fast-variable Thermal Component in the Multipulse Short Gamma-Ray Burst 170206A

Abstract

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 the same as that of the accompanying nonthermal component. The values of the time-resolved low-energy photon index in the nonthermal component are between about −0.79 and −0.16, most of which are harder than the −2/3 expected in the synchrotron emission process. In addition, we found a common evolution between the thermal component and the nonthermal component, E p , CPL ∝ kT BB 0.95 ± 0.28 and F CPL ∝ F BB 0.67 ± 0.18 , where E p,CPL and F CPL are the peak photon energy and corresponding flux of the nonthermal component, and kT 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.