Monte Carlo Simulations of the Photospheric Process

Abstract

We present a Monte Carlo (MC) code we wrote to simulate the photospheric process and to study the photospheric spectrum above the peak energy. Our simulations were performed with a photon to electron ratio $N_{\gamma }/N_e=10^5$, as determined by observations of the GRB prompt emission. We searched an exhaustive parameter space to determine if the photospheric process can match the observed high-energy spectrum of the prompt emission. If we do not consider electron re-heating, we determined that the best conditions to produce the observed high-energy spectrum are low photon temperatures and high optical depths. However, for these simulations, the spectrum peaks at an energy below 300 keV by a factor $\sim 10$. For the cases we consider with higher photon temperatures and lower optical depths, we demonstrate that additional energy in the electrons is required to produce a power-law spectrum above the peak-energy. By considering electron re-heating near the photosphere, the spectrum for these simulations have a peak-energy $\sim \mbox{300 keV}$ and a power-law spectrum extending to at least 10 MeV with a spectral index consistent with the prompt emission observations. We also performed simulations for different values of $N_{\gamma }/N_e$ and determined that the simulation results are very sensitive to $N_{\gamma }/N_e$. Lastly, in addition to Comptonizing a Blackbody spectrum, we also simulate the Comptonization of a $f_{\nu }\propto {\nu }^{-1/2}$ fast cooled synchrotron spectrum. The spectrum for these simulations peaks at $\sim 10^{4} \mbox{ keV}$, with a flat spectrum $f_{\nu }\propto {\nu }^0$ below the peak energy.

arXiv commentAccepted to MNRAS, 18 Pages, 8 Figures

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• Photospheric Emission in Gamma-Ray Bursts
• Monte Carlo radiation transfer simulations of photospheric emission in long-duration Gamma-Ray Bursts
• X-Ray and Gamma-Ray Emission From Core-collapse Supernovae: Comparison of Three-dimensional Neutrino-driven Explosions With SN 1987A
• Swift J1644+57: an Ideal Test Bed of Radiation Mechanisms in a Relativistic Super-Eddington Jet
• Diffusive photospheres in gamma-ray bursts
• Monte Carlo simulations of Photospheric emission in relativistic outflows