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A Transition to the Soft State in GRS 1758-258

D. M. Smith·W. A. Heindl·C. B. Markwardt·J. H. Swank
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Abstract

Near the end of 2001 February, the black-hole candidate (BHC) GRS 1758-258 made an abrupt transition from a standard hard (low) state to a soft state. Unlike Cyg X-1 and other BHCs, whose luminosity increases during this transition, GRS 1758-258 was dimmer after the transition. We present observations with the Proportional Counter Array on the Rossi X-ray Timing Explorer and interpret the phenomenon in the context of a ``dynamical'' soft state model. Using this model we predicted that mass transfer from the companion had ceased, and that the luminosity should decay on a timescale of a few weeks. The most recent data support this prediction, being consistent with a decay time of 34 dy. The current state is consistent with the ``off'' state of GRS 1758-258 reported by GRANAT/Sigma in 1991-1992.

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D. M. Smith, W. A. Heindl, C. B. Markwardt, J. H. Swank. 2001-05-11. A Transition to the Soft State in GRS 1758-258. https://doi.org/10.1086/320928

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