Low frequency radio monitoring of Cygnus X-1 and Cygnus X-3
  We present results of monitoring observations of the micro-quasars CygnusX-1 and Cygnus X-3 at 0.61 and 1.28 GHz. The observations were performed with Giant Meter-wave Radio Telescope, GMRT, 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 results show clearly that there is a break in the spectrum above 1.28 GHz. 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 (of the order of 40 yr at 1.28 GHz), and therefore we believe that the variations are intrinsic to the source. 
M. Pandey, A. P. Rao, G. G. Pooley, P. Durouchoux, R. K. Manchanda, C.   H. Ishwara-Chandra