Is the G18.95–1.1 radio source a shell-type supernova remnant with a central object?

Abstract

Fürst et al.¹ have reported that the nonthermal galactic radio source G18.95–1.1 shows arc-like structures pointing towards the radio peak near its centre, and that its morphology does not conform to any known class of supernova remnants (SNRs). They propose an accreting binary origin for the source, following the suggestion by Helfand and Becker² for the galactic nonthermal radio sources G5.3–1.0 and G357.7–0.1, which show filamentary structure and a compact feature along the axis of symmetry near the brightest edge of the extended emission^3,4. But recently these two sources have been shown to be SNRs^5,6. The compact feature in G537–0.1 is identified with a compact HII region, and there is no direct evidence for a binary in any of these sources. Although de Kool and van den Heuvel⁷ have modelled these sources as accreting binary systems, the details of conversion of energy into radio filamentary structure are not apparent. In view of the suggested peculiar morphology of G18.95–1.1, high-resolution (96x 36 arc s) low-frequency (327 MHz) observations were made using the Ooty Synthesis Radio Telescope (OSRT)⁸. This high-resolution map of G 18.95–1.1 is consistent with the conventional shell-type morphology around a central object.