SRG/eROSITA discovery of a radio faint X-ray candidate supernova remnant SRGe J003602.3+605421=G121.1-1.9

Abstract

We report the discovery of a candidate X-ray supernova remnant SRGe J003602.3+605421=G121.1-1.9 in the course of \textit{SRG}/eROSITA all-sky survey. The object is located at (l,b)=(121.1$^\circ$,-1.9$^\circ$), is $\approx36$ arcmin in angular size and has a nearly circular shape. Clear variations in spectral shape of the X-ray emission across the object are detected, with the emission from the inner (within 9') and outer (9'-18') parts dominated by iron and oxygen/neon lines, respectively. The non-equilibrium plasma emission model is capable of describing the spectrum of the outer part with the initial gas temperature 0.1 keV, final temperature 0.5 keV and the ionization age $\sim 2\times10^{10}$ cm$^{-3}$ s. The observed spectrum of the inner region is more complicated (plausibly due to the contribution of the outer shell) and requires substantial overabundance of iron for all models we have tried. The derived X-ray absorption equals to $(4-6)\times10^{21}$ cm$^{-2}$, locating the object at the distance beyond 1.5 kpc, and implying its age $\sim(5-30)\times1000$ yrs. No bright radio, infrared, H$_α$ or gamma-ray counterpart of this object have been found in the publicly-available archival data. A model invoking a canonical $10^{51}$ erg explosion (either SN Ia or core collapse) in the hot and tenuous medium in the outer region of the Galaxy $\sim$9 kpc away might explain the bulk of the observed features. This scenario can be tested with future deep X-ray and radio observations.