An interpretation of the radio outbursts of Cygnus X-3

We describe the radio bursts from Cyg X-3 by an expanding cloud of relativistic particles and magnetic fields that is uniformly mixed with an ionized thermal gas. We follow the time evolution of the synchrotron radiation from such a cloud including both synchrotron losses and adiabatic losses in the calculation. In the immediate postmaximum period, synchrotron losses dominate and determine the character of the subsequent decay of the burst; this is reflected in an exponential form of the decay near maximum. At later times, adiabatic losses are more important and the later stages of the decay follow a power law; this behavior is in keeping with the observations. The coexpansive thermal gas attenuates the low-frequency radio spectrum via free-free absorption, a process which effectively competes with synchrotron self-absorption in determining the optical depth at all frequencies. The agreement obtained with this model between the observed and calculated radio bursts is very satisfactory. Subject headings: radio sources - synchrotron radiation - X-ray sources