Constraints on the local interstellar magnetic field from non-thermal emission of SN1006

Abstract

Context. The synchrotron radio morphology of bilateral supernova remnants depends on the mechanisms of particle acceleration and on the viewing geometry. However, unlike X-ray and γ-ray morphologies, the radio emission does not depend on the cut-off region of the parent electron population, making it a simpler and more straightforward tool to investigate the physics of cosmic ray production in supernova remnants (SNRs). Aims. We will use the radio morphology to derive tight constraints on the direction of the local magnetic field and its gradient, and on the obliquity dependence of the electron injection efficiency. Methods. We perform a set of 3D MHD simulations describing the expansion of a spherical SNR through a magnetized medium with a non-uniform magnetic field. From the simulations, we derive non-thermal radio maps and compare them with observations of the SN1006 remnant. Results. We find that the radio morphology of SN1006 at 1 GHz is best-fitted by a model with quasi-parallel injection efficiency, a magnetic field aspect angle of 38 • ± 4 • with the line of sight, and a gradient of the field strength toward the galactic plane, higher then the expected variations of the large scale field of the Galaxy. Conclusions. We conclude that the radio limbs of SN1006 are polar caps that do not lie in the plane of sky. The study of the synchrotron radio emission of SNRs is of crucial importance to derive information on the galactic magnetic field in the vicinity of the remnants, and to gather more hints on the actual injection efficiency scenario.

Radio polarization maps of shell-type supernova remnants – I. Effects of a random magnetic field component and thin-shell models

“…Orlando et al 2007;Fulbright & Reynolds 1990), or more specifically the case of SN 1006 ((e.g. Schneiter et al 2015;Bocchino et al 2011;Schneiter et al 2010).…”

The northwestern ejecta knot in SN 1006

“…Because of the low surrounding density, the ionisation age of SN 1006 is one of the lowest measured in the Galactic supernova remnants. We used C-statistic to fit the data, which for a progressively higher number of counts asymptotically approaches the χ 2 value (Cash 1979). The best-fit model to the EPIC spectrum of the knot is a single non-equilibrium ionisation (NEI) model and a basic absorption model.…”

“…The remnant has a particular morphology, in the sense that X-ray synchrotron radiation seems to be emitted only in the northeastern and southwestern part of the remnant, with very little synchrotron emission along the line of sight toward the centre. The most viable explanation is that these synchrotron limbs are polar caps of the remnant, and the axis of the ambient magnetic field lies SW-NE (Rothenflug et al 2004;Völk et al 2003;Berezhko et al 2009;Bocchino et al 2011). Such a magnetic field parallel to the shock A&A 552, A9 (2013) This study is part of a large observing project on SN 1006 (PI: Decourchelle), which consists of seven XMM-Newton pointings that, coupled with archival data, bring the total observing time to ≈900 ks.…”

Supernova of 1006 (G327.6+14.6)

“…This is also in favor of the polar cap model. Finally, Bocchino et al (2011) compared an observed radio morphology at 1 GHz with synthesized radio maps based on 3D magnetohydrodynamic (MHD) simulations, finding that a model assuming quasi-parallel injection efficiency better represents the data than the quasi-perpendicular model. Direct estimates of the magnetic-field orientation were performed through radio polarization measurements for the bright lobes (Kundu 1970).…”