Comptonization of photons near the photosphere of relativistic outflows

Abstract

We consider the formation of photon spectrum at the photosphere of ultrarelativistically expanding outflow. We use the Fokker-Planck approximation to the Boltzmann equation, and obtain the generalized Kompaneets equation which takes into account anisotropic distribution of photons developed near the photosphere. This equation is solved numerically for relativistic steady wind and the observed spectrum is found in agreement with previous studies. We also study the photospheric emission for different temperature dependences on radius in such outflows. In particular, we found that for $T\propto r^{-2}$ the Band low energy photon index of the observed spectrum is $\alpha \simeq -1$, as typically observed in Gamma Ray Bursts.

Accepted by MNRAS Letters

References in corpus (5)

• Temporal Evolution Of Thermal Emission From Relativistically Expanding Plasma
• A new method of determining the initial size and Lorentz factor of gamma-ray burst fireballs using a thermal emission component
• Prompt emission spectra from the photosphere of a GRB
• Variable jet properties in GRB110721A: Time resolved observations of the jet photosphere
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• "Double-tracking" Characteristic of the Spectral Evolution of GRB 131231A: Synchrotron Origin?
• Photospheric Emission in Gamma-Ray Bursts
• On the role of a cavity in the hypernova ejecta of GRB 190114C
• Physics of non-dissipative ultrarelativistic photospheres
• Transparency of an instantaneously created electron-positron-photon plasma
• Plasmas in Gamma-Ray Bursts: particle acceleration, magnetic fields, radiative Processes and environments
• Modeling of the Gamma Ray Burst photospheric emission: Monte Carlo simulation of the GRB prompt emission, numerical results and discussion