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 (SNR_s)^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 (S_ν ˜ ν^α) 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.