The Gamma-Ray Emission from the Supernova Remnant RX J1713.7-3946 Interacting with Two-phase Medium

TL;DR

This paper models gamma-ray emission from SNR RX J1713.7-3946 interacting with a two-phase ISM, explaining observed spectra and surface brightness correlations through cosmic ray interactions and ISM inhomogeneity.

Contribution

It introduces an analytical model accounting for two-phase ISM interaction and cosmic ray penetration, explaining gamma-ray spectra and surface brightness correlations in SNR RX J1713.7-3946.

Findings

Pi^0-decay gamma rays reproduce observed TeV spectrum.

The planar relation among ISM density, X-ray, and gamma-ray brightness is naturally explained.

Variations in ISM density or CR electron-to-proton ratio can be identified through data shifts.

Abstract

We study the origin of gamma rays from the supernova remnant (SNR) RX J1713.7-3946. Using an analytical model, we calculate the distribution of cosmic rays (CRs) around the SNRs. Motivated by the results of previous studies, we assume that the SNR is interacting with two-phase interstellar medium (ISM), where dense clumps are surrounded by tenuous interclump medium. We also assume that only higher-energy protons (~> TeV) can penetrate the dense clumps. We find that pi^0-decay gamma rays produced by protons reproduce the observed gamma-ray spectrum peaked at ~TeV. On the other hand, it has recently been indicated that the observed ISM column density (N_p), the X-ray surface brightness (I_X), and the gamma-ray surface brightness (I_g) at grid points across the SNR form a plane in the three-dimensional (3D) space of (N_p, I_X, I_g). We find that the planar configuration is naturally reproduced if the ISM or the CR electron-to-proton ratio is not spherically uniform. We show that the shift of the observed data in the 3D space could be used to identify which of the quantities, the ISM density, the CR electron-to-proton ratio, or the magnetic field, varies in the azimuthal direction of the SNR.