2001MNRAS.322..177O

We have observed the energetic binary Cygnus X-3 in both quiescent and flaring states between 4 and 16µm using the ISO satellite. We find that the quiescent source shows the thermal free-free spectrum typical of a hot, fast stellar wind, such as from a massive helium star. The quiescent mass-loss rate arising from a spherically symmetric, non-accelerating wind is found to be in the range (0.4-2.9)x10^–4M_☉yr^–1, consistent with other infrared and radio observations, but considerably larger than the 10^–5M_☉.yr^–1 deduced from both the orbital change and the X-ray column density. There is rapid, large-amplitude flaring at 4.5 and 11.5µm at the same time as enhanced radio and X-ray activity, with the infrared spectrum apparently becoming flatter in the flaring state. We believe that non-thermal processes are operating, perhaps along with enhanced thermal emission.