A new non-thermal galactic radio source with a possible binary system

Abstract

Helfand and Becker1 recently discussed the unusual filamentary appearance of the galactic radio sources G357.7–0.1 and G5.3–1.0, both of which had originally been classified as supernova remnants (SNRs)2,3, and proposed that these sources belong to a new class of non-thermal radio sources that originate in accreting binary systems containing a neutron star or a black hole. Becker and Helfand4 have pointed out that other galactic sources may be identified as members of this class; we report here our claim that a new non-thermal galactic object (G18.95–1.1), detected in the recently published 2.695-GHz galactic plane survey5, is a possible candidate. That the integrated flux density spectral index α = −0.4 (Sν ˜ να) and the polarization is ≍ 2.5% at 4.75 GHz, proves the non-thermal nature of the new source; morphologically, a classification of this object as a SNR seems impossible. G18.95–1.1 consists of various arcs all pointing towards a central radio peak; we suggest that the object is a binary system containing a compact component, located at or close to this radio peak, accelerating electrons to relativistic energies—observed in the arcs by the synchrotron emission of the accelerating electrons.