Effects of non-uniform interstellar magnetic field on synchrotron X-ray and inverse-Compton gamma-ray morphology of SNRs

摘要

Observations of SNRs in X-ray and gamma-ray bands promise to contribute withimportant information in our understanding on the nature of galactic cosmicrays. The analysis of SNRs images collected in different energy bands requiresthe support of theoretical modeling of synchrotron and inverse Compton (IC)emission. We develop a numerical code (REMLIGHT) to synthesize, from MHDsimulations, the synchrotron radio, X-ray and IC gamma-ray emission from SNRsexpanding in non-uniform interstellar medium (ISM) and/or non-uniforminterstellar magnetic field (ISMF). As a first application, the code is used toinvestigate the effects of non-uniform ISMF on the SNR morphology in thenon-thermal X-ray and gamma-ray bands. We perform 3D MHD simulations of aspherical SNR shock expanding through a magnetized ISM with a gradient ofambient magnetic field strength. The model includes an approximate treatment ofupstream magnetic field amplification and the effect of shock modification dueto back reaction of accelerated cosmic rays. From the simulations, wesynthesize the synchrotron radio, X-ray and IC gamma-ray emission withREMLIGHT, making different assumptions about the details of acceleration andinjection of relativistic electrons. A gradient of the ambient magnetic fieldstrength induces asymmetric morphologies in radio, X-ray and gamma-ray bandsindependently from the model of electron injection if the gradient has acomponent perpendicular to the line-of-sight. The degree of asymmetry of theremnant morphology depends on the details of the electron injection andacceleration and is different in the radio, X-ray, and gamma-ray bands. Thenon-thermal X-ray morphology is the most sensitive to the gradient, showing thehighest degree of asymmetry. The IC gamma-ray emission is weakly sensitive tothe non-uniform ISMF, the degree of asymmetry of the SNR morphology being thelowest in this band.