VLA structure of variable radio sources in the Galactic plane

VLA observations of 17 new variable and three nonvariable radio sources from the Galactic Patrol Survey of Gregory and Taylor (1981) are presented. The variable-source morphologies range from unresolved point sources to doubles and triples with jet-lobe structures. No optical counterparts were found for the variable sources to the plate limits of the Palomar Sky Survey, but a 15th-magnitude stellar-like object was found for the nonvariable source GT 0007 + 635. The new observations are combined with previous data to study the collective properties of 28 variable sources. Their spectra, morphologies, and variability characteristics suggest that they fall into two broad categories. The first category consists of 15 unresolved point sources which are characterized by flat inverted spectra between 6 and 20 cm and strong variability. The second category consists of a heterogeneous mixture of resolved sources having varying degrees of structure. The bimodal distribution of variability properties of the patrol sources, reported by Gregory and Taylor, can, in part, be explained by these results. The presence or absence of nonvariable extended emission, resolved in the VLA observations but not in the Patrol observations, appears to regulate the variabilities of these sources. (Author)