A detailed look at the thermal and nonthermal X-ray emission from the Vela supernova remnant with SRG/eROSITA

¹ Max-Planck Institut für extraterrestrische Physik, Giessenbachstrasse, 85748 Garching, Germany
e-mail: mmayer@mpe.mpg.de
² Max-Planck Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
³ Dr. Karl Remeis Observatory, Erlangen Centre for Astroparticle Physics, Friedrich-Alexander-Universität Erlangen-Nürnberg, Sternwartstrasse 7, 96049 Bamberg, Germany

Received: 18 April 2023
Accepted: 12 June 2023

Abstract

Context. The Vela supernova remnant (SNR) is one of the most nearby and extended objects in the X-ray sky. It constitutes a unique laboratory for studying the thermal and nonthermal X-ray emission from an evolved SNR and its central plerion at an unprecedented level of detail.

Aims. Our goal is to characterize the hot ejecta and shocked interstellar medium (ISM) associated with the Vela SNR, as well as the synchrotron-emitting relativistic electrons injected into the ambient medium by the central pulsar. To achieve this, we analyzed the dataset of Vela acquired by SRG/eROSITA during its first four all-sky surveys.

Methods. We present and analyze the energy-dependent morphology of Vela using X-ray images extracted in multiple energy bands. A quantitative view of the physical parameters affecting the observed thermal and nonthermal emission is obtained by performing spatially resolved X-ray spectroscopy of over 500 independent regions using multicomponent spectral models.

Results. Imaging demonstrates that the X-ray emission of the Vela SNR consists of at least three morphologically and energetically distinct components, with shell-like structures dominating below 0.6 keV, radial outward-directed features becoming apparent at medium energies, and the pulsar wind nebula (PWN) dominating the hard emission above 1.4 keV. Our spectroscopy reveals a highly structured distribution of X-ray absorption column densities, which intriguingly appears to lack any correlation with optical extinction measurements, possibly due to dust destruction or a clumpy ISM. The shock-heated plasma in Vela is found to be comparatively cool, with a median temperature of 0.19 keV, but exhibits several, often ejecta-rich, warmer regions. Within the observed ejecta clumps, we find an unexpectedly high concentration of neon and magnesium relative to oxygen, when compared to nucleosynthetic predictions. This includes the bright “shrapnel D”, in which we can separate shocked ISM in the soft bow-shock from a hot, ejecta-rich clump at its apex, based on the new data. Finally, we find an extremely extended, smoothly decreasing distribution of synchrotron emission from the PWN, which extends up to three degrees (14 pc) from the pulsar. The integrated X-ray luminosity of the PWN in the 0.5–8.0 keV energy band corresponds to 1.5 × 10⁻³ of the pulsar’s present-day spin-down power. The extended PWN emission likely traces the diffusion of a high-energy electron population in an ISM-level magnetic field, which requires the existence of a TeV counterpart powered by inverse Compton radiation.