  ASCA discovered an extended source in the Scutum constellation. The X-ray
morphology is an elliptical shape elongated from north to south with a mean
diameter of about 10'. The image center is located at RA = 18h43m53s, DEC =
03D52'55'' (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). The X-ray spectrum was fitted with a
model of either a thin thermal plasma in non-equilibrium ionization of a
temperature 5.4 keV or a power-law of photon index 2.1. The absorption column
is (2.4-4.0)E22 /cm2, which probably places this source in the Scutum arm. With
a reasonable distance assumption of about 7 kpc, we estimate the mean diameter
and X-ray luminosity to be ~20 pc and ~3E34 erg/s, 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 ~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.
