부산대학교 도서관

Simeis 147 (S147, G180.0-01.7, ``Spaghetti nebula'') is a supernova remnant (SNR) extensively studied across the entire electromagnetic spectrum, from radio to GeV $\gamma$-rays, except in X-rays. In this study, we report the first detection of significant X-ray emission from the entire SNR. Here, and in a companion paper, we present studies of X-ray emission from the S147 nebula using the data of the extended ROentgen Survey Imaging Telescope Array (eROSITA) onboard the Russian-German Spektrum Roentgen Gamma (SRG). The object is located at the Galactic anti-center, and its 3 deg size classifies it among the largest SNRs ever detected in X-rays. Overall, the X-ray emission morphology as observed with eROSITA is fully confined within the boundaries of both radio synchrotron and H$\alpha$ emission, except for the Western edge of the remnant where radio and H$\alpha$ emission appears to extend further to the West compared to X-rays. The X-ray emission is predominantly soft with a strong detection between 0.5-1.0 keV, leaving S147 undetected above 2.3 keV. The X-ray emission is purely thermal, exhibiting strong O, Ne, and Mg lines, whereas it lacks heavier-Z elements. A model of non-equilibrium collisional plasma, with a gas temperature of $kT=0.22^{-0.03}_{+0.02}$~keV, and an absorption column density of $N_\mathrm{{H}}=0.30_{-0.03}^{+0.04}\cdot10^{22}~\mathrm{cm^{-2}}$ ($\tau=4.27^{+1.87}_{-0.99}~\mathrm{\cdot10^{10}s~ cm^{-3}}$), is preferred over a collisional plasma model in equilibrium with $kT=0.11\pm0.01$~keV and with $N_\mathrm{{H}}=0.51\pm0.02\cdot10^{22}~\mathrm{cm^{-2}}$. By employing $\sim$14.5 years of Fermi-LAT data, our study confirms the association of the remnant with a spatially coincident diffuse GeV excess, namely 4FGL J0540.3+2756e or FGES J0537.6+2751. Age and distance estimates of the remnant are also reported based on the eROSITA data.