Some properties of synchrotron radio and inverse-Compton gamma-ray images of supernova remnants

TL;DR

This paper analyzes synchrotron radio and inverse-Compton gamma-ray images of supernova remnants, exploring how injection efficiency and magnetic field variations influence limb brightness and coincidence across wavelengths.

Contribution

It introduces models considering obliquity-dependent injection and maximum electron energy to explain observed limb coincidences in SNRs.

Findings

Radio and gamma-ray limbs can coincide under certain injection and energy variation conditions.

Limb position and coincidence alone do not conclusively determine obliquity dependence.

Magnetic field and injection effects are complex and require careful interpretation.

Abstract

The synchrotron radio maps of supernova remnants (SNRs) in uniform interstellar medium and interstellar magnetic field (ISMF) are analyzed, allowing different `sensitivity' of injection efficiency to the shock obliquity. The very-high energy gamma-ray maps due to inverse Compton process are also synthesized. The properties of images in these different wavelength bands are compared, with particular emphasis on the location of the bright limbs in bilateral SNRs. Recent H.E.S.S. observations of SN 1006 show that the radio and IC gamma-ray limbs coincide, and we found that this may happen if: i) injection is isotropic but the variation of the maximum energy of electrons is rather quick to compensate for differences in magnetic field; ii) obliquity dependence of injection (either quasi-parallel or quasi-perpendicular) and the electron maximum energy is strong enough to dominate magnetic field variation. In the latter case, the obliquity dependence of the injection and the maximum energy should not be opposite. We argue that the position of the limbs alone and even their coincidence in radio, X-rays and gamma-rays, as it is discovered by H.E.S.S. in SN 1006, cannot be conclusive about the dependence of the electron injection efficiency, the compression/amplification of ISMF and the electron maximum energy on the obliquity angle.