LOW STATE HARD X-RAY OUTBURST FROM THE X-RAY BURSTER 4U-1608-522 OBSERVED BY BATSE CGRO/

A hard X-ray (low state) outburst lasting for about 170 days was obser ved with the Burst and Transient Source Experiment (BATSE) Large Area Detectors (LADs) from the X-ray burster 4U 1608-522 from June to Decem ber 1991. During the outburst, the flux slowly varied between 75 mCrab and 150 mCrab. Combined with a near simultaneous observation with the Ginga satellite, the low energy spectrum before the break energy is w ell determined to be a power law with photon index of about 1.75. The high energy spectrum above the break energy can be fit equally well by either the Sunyaev-Titarchuk (S-T) model or a broken power law model. For the first time, we have determined that a rather intense hard X-r ay outburst from a neutron star system is associated with a soft X-ray (< 10 keV) low state and the power law photon spectrum breaks at abou t 65 keV.