SIMBAD references

A hard X-ray (low state) outburst lasting for about 170-days was observed with the Burst and Transient Source Experiment (BATSE) Large Area Detectors (LADs) from the X-ray burster 4U 1608-522 from June to December 1991. During the outburst, the flux slowly varied between 75mCrab and 150mCrab. Combined with a near simultaneous observation with the Ginga satellite, the low energy spectrum before the break energy is well 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-ray outburst from a neutron star system is associated with a soft X-ray (<10keV) low state and the power law photon spectrum breaks at about 65keV.