A Diffuse X-Ray Source, AX J1843.80352: Association with the Radio Complex G28.6-0.1 and Identification of a New Supernova Remnant

ASCA discovered an extended source in the constellation Scutum. The X-ray morphology is an elliptical shape elongated from north to south with a mean diameter of about $$ {10{}^{\mathrm {\prime }}}$$. The image center is located at $$ \mathrm{RA}_{2000}$$ = $$ {18{}^{\mathrm {h}}43{}^{\mathrm {m}}53{}^{\mathrm {s}}}$$, $$ \mathrm{DEC}_{2000}$$ = $$ - {03{}^{\mathrm {\circ }}52{}^{\mathrm {\prime }}55{}^{\mathrm {\prime \prime }}}$$ (hereafter, AX J1843.8–0352). The north and south rims of AX J1843.8–0352 are associated with non-thermal radio sources C and F of the G28.6–0.1 complex (Helfand et al. 1989, AAA $$ 49.125.029$$). The X-ray spectrum was fitted with a model of either a thin thermal plasma in non-equilibrium ionization of a temperature 5.4keV or a power-law of photon index 2.1. The absorption column is $$ (2.4$$-$$ 4.0)\times 10^{22}\mathrm{cm}^{-2}$$, which probably places this source in the Scutum arm. With a reasonable distance assumption of about 7kpc, we estimate the mean diameter and X-ray luminosity to be $$ \sim 20 \,\mathrm{pc}$$ and $$ \sim 3 \times 10^{34}\,\mathrm{erg} \,\mathrm{s}^{-1}$$, respectively. Although a Sedov solution for a thin thermal plasma model gives parameters of a young shell-like SNR, no strong emission lines are found with the metal abundances being $$ \sim$$ solar. Thus, a more likely scenario for both the radio and X-ray spectra and the morphologies is that AX J1843.8–0352 is a shell-like SNR which predominantly emits synchrotron X-rays.