We observed the energetic binary Cygnus X-3 in both quiescent and flaring states between 4 and 16 \mu m 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 due to a spherically symmetric , non-accelerating wind is found to be in the range ( 0.4–2.9 ) \times 10 ^ { -4 } M _ { \odot } yr ^ { -1 } , consistent with other infrared and radio observations , but considerably larger than the 10 ^ { -5 } M _ { \odot } yr ^ { -1 } deduced from both the orbital change and the X-ray column density .
There is rapid , large amplitude flaring at 4.5 and 11.5 \mu m at the same time as enhanced radio and X-ray activity , with the infrared spectrum apparently becoming flatter in the flaring state .
We believe non-thermal processes are operating , perhaps along with enhanced thermal emission .