X-ray counterpart detection and γ-ray analysis of the supernova remnant G279.0+01.1 with eROSITA and Fermi-LAT

A thorough inspection of known Galactic supernova remnants (SNRs) along the Galactic plane with SRG/eROSITA yielded the detection of the X-ray counterpart of the SNR G279.0+01.1. The SNR is located just 1.5° above the Galactic plane. Its X-ray emission emerges as an incomplete, partial shell of ~3° angular extension. It is strongly correlated to the fragmented shell-type morphology of its radio continuum emission. The X-ray spatial morphology of the SNR seems to be linked to the presence of dust clouds in the surroundings. The majority of its X-ray emission is soft (exhibiting strong O, Ne, and Mg lines), and it occurs in a narrow range of energies between 0.3 and 1.5 keV. Above 2.0 keV the remnant remains undetected. The remnant's X-ray spectrum is purely of a thermal nature. Constraining the X-ray absorption column to values which are consistent with optical extinction data from the remnant's location favors nonequilibrium over equilibrium models. A nonequilibrium two-temperature plasma model of kT ~ 0.3 keV and kT ~ 0.6 keV, as well as an absorption column density of N_H ~ 0.3 cm⁻² describe the spectrum of the entire remnant well. Significant temperature variations across the remnant have been detected. Employing 14.5 yr of Fermi-LAT data, we carried out a comprehensive study of the extended giga-electronvolt source 4FGL J1000.0-5312e. By refining and properly modeling the giga-electronvolt excess originating from the location of the remnant, we conclude that the emission is likely related to the remnant itself rather than being colocated by chance. The remnant's properties as determined by the X-ray spectra are consistent with the ~2.5 kpc distance estimates from the literature, which implies a source diameter of ~140 pc and an old age of >7 × 10⁵ yr. However, if the source is associated with any of the pulsars previously considered to be associated with the SNR, then the updated nearby pulsar distance estimates from the YMW16 electron density model rather place the SNR at a distance of ~0.4 kpc. This would correspond to a ~20 pc linear size and a younger age of 10⁴− < 7 × 10⁵ yr, which would be more in line with the nonequilibrium state of the plasma.