Photon Acceleration at Shock Breakout of Trans-Relativistic Supernova

TL;DR

This paper proposes a photon acceleration mechanism during shock breakout in trans-relativistic supernovae, explaining observed thermal and nonthermal emissions and suggesting a new class of gamma-ray bursts with high-energy outflows.

Contribution

It introduces the concept of photon acceleration via bulk Compton scattering at TRSN shock breakout, linking it to gamma-ray production in low-luminosity GRBs.

Findings

Thermal X-ray emission indicates trans-relativistic shock with >1E49 erg energy.

Photon acceleration can produce nonthermal gamma/X-ray components.

TRSNe are characterized by high kinetic energy and relativistic ejecta.

Abstract

The predicted thermal flash from SN shock breakout might have been detected for the first time by Swift in GRB 060218/SN 2006aj. The detected thermal X-ray emission in this event implies emergence of a trans-relativistic (TR) SN shock with kinetic energy of E_k>1E49 erg. During TRSN shock breakout, the thermal photons could be "accelerated" by the shock through repeated bulk Compton scattering, forming a nonthermal gamma/X-ray component with dominant energy over thermal one. This mechanism of "photon acceleration" at TRSN shock breakout might also account for gamma-rays in the other similar low-luminosity GRBs, implying that they are atypical GRBs with only TR outflows. TRSNe form a peculiar type of SNe with large kinetic energy, >1E49 erg, in TR ejecta, \Gamma\beta ~2.