Photons’ scattering in a relativistic plasma with velocity shear: generation of high energy power-law spectra

by Dr. Mukesh Vyas

at Astrophysics and Cosmology Seminar

Wed, 16 Nov 2022, 11:10
Sacta-Rashi Building for Physics (54), room 207


A high energy power law is a common feature in the spectra of many astrophysical objects. In this talk I will show that the photons in an unmagnetized relativistic plasma composed of electrons and protons with a variable Lorentz factor (or a velocity shear) go through repeated scattering with electrons to gain energy. The escaped population of photons naturally produces a power-law-shaped spectrum making it a photons’ analogue to the conventional Fermi acceleration mechanism for charged particles. We theoretically investigate this phenomena for the first time and show that this mechanism provides a natural alternative to current explanations of high energy power-law spectra via synchrotron or thermal Comptonization. The model is applicable to any relativistic plasma beam with an arbitrary Lorentz factor profile. We implement the theory to GRB prompt phase and show that the obtained range of the photon indices is compatible with the observed values and the results of Monte Carlo simulations that we carry out independently. Therefore, the observed high energy spectral indices provide a unique indicator of the jet structure. At the end, I will discuss the possible extension of this work in several cases of astrophysical importance for the future.

Created on 12-11-2022 by Zitrin, Adi (zitrin)
Updaded on 12-11-2022 by Zitrin, Adi (zitrin)