Cygnus X-3 in outburst: quenched radio emission, radiation losses and variable local opacity

Abstract

We present multiwavelength observations of Cygnus X-3 during an extended outburst in 1994 February -March. Intensive radio monitoring at 13.3, 3.6 & 2.0 cm is complemented by observations at (sub)millimetre and infrared wavelengths, which find Cyg X-3 to be unusually bright and variable, and include the first reported detection of the source at 0.45 mm. We report the first confirmation of quenched radio emission prior to radio flaring independent of observations at Green Bank. The observations reveal evidence for wavelength-dependent radiation losses and gradually decreasing opacity in the environment of the radio jet. We find that the radiation losses are likely to be predominantly inverse Compton losses experienced by the radio-emitting electrons in the strong radiation field of a luminous companion to the compact object. We interpret the decreasing opacity during the flare sequence as resulting from a decreasing proportion of thermal electrons entrained in the jet, reflecting a decreasing density in the region of jet formation. We present, drawing in part on the work of other authors, a model based upon mass-transfer rate instability predicting γ-ray, X-ray, infrared and radio trends during a radio flaring sequence.

Infrared spectroscopic variability of Cygnus X-3

“…This has already been suggested as the origin for outbursts from the system van Kerkwijk et al 1996;Fender et al 1997). Given that we have established that the twin-peaked emission lines almost certainly originate in an extended region which is not the jets, and the existing evidence for a strong wind in the Cyg X-3 system, a natural explanation is that the increased line strength in outburst represents an increase in the density of the WR-like wind in the system.…”

“…van Kerkwijk et al (1996) do, however, show there was a marked increase in K-band flux on 14 June 1993. Such near-infrared flux increases on day timescales have been seen during radio outbursts (Fender et al 1997), and appear to be distinct from the more rapid (second to minutes timescales) infrared flaring which is often observed (e.g. Fender et al 1996).…”

“…The explanation put forward for this was enhanced mass loss from the companion during outbursts, which both increases X-ray brightness (more accretion) and emission line strengths. This model was combined with detailed radio, (sub)mm and infrared (photometric) observations obtained during an outburst, and expanded upon in Fender et al (1997). Waltman et al (1997) clearly indicate the epochs of the published infrared spectra against the Green Bank 2 GHz radio monitoring of the system.…”

Synchrotron flaring behaviour of Cygnus X-3 during the February-March 1994 and September 2001 outbursts

“…The maximum flux density of this flaring epoch was ∼5 Jy at 2.25 GHz. The dataset used here has been published by Fender et al (1997). It contains radio lightcurves from the Ryle telescope at 15 GHz, and from the Green Bank Interferometer (GBI) at 2.25 GHz and 8.3 GHz, and infrared data from the United Kingdom Infrared Telescope (UKIRT).…”

Binary corrected X-ray light curve of Cygnus X-3: Implications for the timing properties of the compact binary system

“…There have been several attempts to connect the radio, X-ray, and infrared variations in the source (Watanabe et al 1994;Fender 1997). Recently Choudhury et al (2002), have reported a strong and significant correlation between the radio and X-ray emission in the low-hard state of Cygnus X-3.…”