Observations of giant outbursts from Cygnus X-1
  We present interplanetary network localization, spectral, and time history information for 7 episodes of exceptionally intense gamma-ray emission from Cygnus X-1. The outbursts occurred between 1995 and 2003, with durations up to \~28000 seconds. The observed 15 - 300 keV peak fluxes and fluences reached 3E-7 erg /cm2 s, and 8E-4 erg / cm2 respectively. By combining the triangulations of these outbursts we derive an ~1700 square arcminute (3 sigma) error ellipse which contains Cygnus X-1 and no other known high energy sources. The outbursts reported here occurred both when Cyg X-1 was in the hard state as well as in the soft one, and at various orbital phases. The spectral data indicate that these outbursts display the same parameters as those of the underlying hard and soft states, suggesting that they represent another manifestation of these states. 
S. Golenetskii, R. Aptekar, D. Frederiks, E. Mazets, V. Palshin, K.   Hurley, T. Cline, and B. Stern