Low frequency radio monitoring of Cygnus X-1 and Cygnus X-3

We present the results of monitoring observations of the micro-quasars Cygnus X-1 and Cygnus X-3 at 0.61 and 1.28 GHz. The observations were performed with the Giant Meter-wave Radio Telescope between 2003 June and 2005 January. Variable, unresolved sources were found in both cases. Cyg X-1 was detected in about half of the observations, with a median flux density about 7 mJy at each frequency. The variations in Cyg X-1 may be due to refractive interstellar scintillation. Cyg X-3 was detected in each observation, and varied by a factor of 4. For this source, models of the scintillation suggest a very long timescale (the order of 40 yr at 1.28 GHz), therefore, we believe that the variations are intrinsic to the source.