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

¹ Dept. of Physics, Mumbai University, Mumbai 400 098, India e-mail: mamta@ncra.tifr.res.in
² NCRA, TIFR, Post Bag 3, Ganeshkhind, Pune 411 007, India
³ Cavendish Laboratory, University of Cambridge, Madingley Road, Cambridge CB3 0HE, UK
⁴ CNRS FRE 2591/CEA Saclay, DSM/DAPNIA/SAP, 91191 Gif-sur-Yvette Cedex, France
⁵ Tata Institute of Fundamental Research, Mumbai 400005, India

Received: 16 May 2005
Accepted: 4 October 2005

Abstract

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.