The broad-band spectrum of Cyg X-2 with INTEGRAL
  We study the broad band (3-100 keV) spectrum of Cygnus X-2 with INTEGRAL. We find that the spectrum is well fitted by a Comptonized component with a seed-photons temperature of ~1 keV, an electron temperature of ~3 keV and an optical depth tau ~ 8. Assuming spherical geometry, the radius of the seed-photons emitting region is ~17 km. The source shows no hard X-ray emission; it was detected only at a 3 sigma level above 40 keV. We also analyzed public ISGRI data of Cyg X--2 to investigate the presence of a hard X-ray component. We report the possible presence of hard X-ray emission in one data set. 
G. Lavagetto, T. Di Salvo, M. Falanga, R. Iaria, N. R. Robba, L.   Burderi, W. H. G. Lewin, M. Mendez, L. Stella and M. van ...