VLA Structure of Variable Sources in the Galactic Plane.II.
Abstract
We present first epoch VLA observations for 12 variable radio sources selected from the 300 ft Galactic Patrol Survey of Gregory and Taylor, as well as second and third epoch observations for another 7 and 2, respectively. Six of the 21 sources in the sample are unresolved at the 0.1 arcsec level, and the remainder exhibit a variety of morphologies. Results from multiepoch observations indicate that the integrated source variability properties from single dish measurements alone can be very misleading with respect to the degree of variability present in extended objects, in particular for lobe-dominated sources. In one case, GT 1945+241 (triple source), the core was observed to be brighter by a factor of 5 at the second epoch (at λ = 20 cm) but the corresponding change in integrated source flux density was only 2%. For two other triples, GT 0545+265 and GT 2129+492, the single dish (integrated) variability combined with the VLA morphology implies that at times the nuclei of these objects must brighten by factor of ~> 30. Consequently time-dependent activity in the nuclei of lobe-dominated radio sources may be much greater than previously suspected. If these sources are really extragalactic, the observed variability in the cores is difficult to reconcile with the unification theory of the beaming models. Although interstellar scintillation may play a role in some sources it does not appear to be the dominant effect for most sources in our sample.
- Publication:
-
The Astronomical Journal
- Pub Date:
- July 1995
- DOI:
- 10.1086/117513
- Bibcode:
- 1995AJ....110..238T
- Keywords:
-
- RADIO LINES: GENERAL;
- GALAXY: STRUCTURE