PREPRINT
1D2ABB32-F226-47A3-970D-9647DC499CE4

# SRG/eROSITA discovery of an extremely radio-faint iron-rich X-ray candidate supernova remnant SRGe J003602.3+605421 = G121.1-1.9

I. I. Khabibullin, E. M. Churazov, A. M. Bykov, N. N. Chugai, R. A. Sunyaev
arXiv:2207.00064

Submitted on 30 June 2022

## 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 $\approx 36$ arcmin in angular size and features 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 $\sim 2×{10}^{10}$ 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 $\left(4-6\right)×{10}^{21}$ cm${}^{-2}$, locating the object at the distance beyond 1.5 kpc, and implying its the age $\sim \left(5-30\right)×1000$ yrs. No bright radio, infrared, H${}_{\alpha }$ or gamma-ray counterpart of this object have been found in the publicly-available archival data. A model invoking a canonical ${10}^{51}$ erg SN Ia explosion in the hot and tenuous medium in outer region of the Galaxy $\sim$9 kpc away might explain the bulk of the observed features.This object might be a rare example of an old SN Ia remnant in our Galaxy still bearing signatures of the ejecta enrichment and probing the thermal and non-thermal properties of the hot phase of the ISM above the cold disc. This scenario can be tested with future deep X-ray and radio observations.

## Preprint

Comment: 18 pages, 20 figures, submitted to MNRAS

Subjects: Astrophysics - High Energy Astrophysical Phenomena; Astrophysics - Astrophysics of Galaxies