Chandra Detection of SN 2010da Four Months After Outburst: Evidence for a Supergiant X-ray Binary in NGC 300

TL;DR

Four months after its outburst, SN 2010da exhibits X-ray characteristics consistent with a supergiant X-ray binary, showing a hard central source and diffuse emission suggestive of a supernova remnant, indicating a complex post-outburst environment.

Contribution

This study provides the first X-ray detection of SN 2010da post-outburst, supporting its classification as a supergiant X-ray binary rather than a single star outburst.

Findings

Detection of a hard X-ray point source at SN 2010da location

Diffuse emission consistent with a supernova remnant

Significant decrease in X-ray luminosity since outburst

Abstract

We present the results of a 63 ks {\it Chandra} observation of the "supernova impostor" SN 2010da four months after it was first observed on 25 May 2010. We detect an X-ray source at $\sim7\sigma$ confidence coincident with the optical location of the SN 2010da outburst. Our imaging analysis has revealed a hard central point source, surrounded by soft diffuse emission extending as far as $\sim$8\asn north of the central source. The diffuse emission has a hardness ratio, 0.35-2 keV luminosity ($\sim6\times10^{35}$ erg s$^{-1}$), and size ($\sim20$ pc) consistent with that of a supernova remnant, although the low number of counts prohibits detailed spectral modeling. Our best-fit spectral model for the hard central source is a black body ($kT = 1.79^{+0.66}_{-0.43}$ keV) with no evidence for intrinsic absorption beyond the Galactic column. We estimate the 0.3-10 keV luminosity to be 1.7$^{+0.2}_{-0.5}\times10^{37}$ erg s$^{-1}$, a factor of $\sim$25 decrease since the initial outburst four months previously. The high X-ray luminosity and slow fading rate is not consistent with this object being a single massive star undergoing an outburst; instead, we favor the scenario where the massive star powering the SN 2010da optical transient is part of a wind-fed supergiant X-ray binary system with a compact companion powering the observed X-ray emission.