Spontaneously quenched gamma-ray spectra from compact sources

TL;DR

This paper investigates a mechanism called automatic photon quenching that can produce intrinsic broken power-law gamma-ray spectra in compact astrophysical sources, explaining observed spectral features.

Contribution

It derives analytical expressions for the critical gamma-ray compactness and emergent spectra, demonstrating how spontaneous photon quenching can produce large spectral breaks.

Findings

Spontaneous photon quenching leads to a photon index of 3Γ/2 in the gamma-ray spectrum.

Large spectral breaks (ΔΓ ≥ 1) can be explained by this mechanism.

Application to a blazar spectrum suggests the mechanism can account for observed spectral features.

Abstract

We study a mechanism for producing intrinsic broken power-law gamma-ray spectra in compact sources. This is based on the principles of automatic photon quenching, according to which, gamma-rays are being absorbed on spontaneously produced soft photons, whenever the injected luminosity in gamma-rays lies above a certain critical value. We derive an analytical expression for the critical gamma-ray compactness in the case of power-law injection. For the case where automatic photon quenching is relevant, we calculate analytically the emergent steady-state gamma-ray spectra. We perform also numerical calculations in order to back up our analytical results. We show that a spontaneously quenched power-law gamma-ray spectrum obtains a photon index 3{\Gamma}/2, where {\Gamma} is the photon index of the power-law at injection. Thus, large spectral breaks of the gamma-ray photon spectrum, e.g. $\Delta \Gamma \gtrsim 1$, can be obtained by this mechanism. We also discuss additional features of this mechanism that can be tested observationally. Finally, we fit the multiwavelength spectrum of a newly discovered blazar (PKS 0447-439) by using such parameters, as to explain the break in the gamma-ray spectrum by means of spontaneous photon quenching, under the assumption that its redshift lies in the range 0.1<z<0.24.