XMM-Newton Spectroscopy of the Galactic Microquasar GRS 1758-258 in the Peculiar Off/Soft State

Abstract

We report on an XMM-Newton Reflection Grating Spectrometer observation of the black hole candidate and Galactic microquasar GRS 1758-258. The source entered a peculiar "off/soft" state in late February, 2001, in which the spectrum softened while the X-ray flux -- and the inferred mass accretion rate -- steadily decreased. We find no clear evidence for emission or absorption lines in the dispersed spectra, indicating that most of the observed soft flux is likely from an accretion disk and not from a cool plasma. The accretion disk strongly dominates the spectrum in this lower-luminosity state, and is only mildly recessed from the marginally stable orbit. These findings may be difficult to explain in terms of advection-dominated accretion flow, or "ADAF" models. We discuss these results within the context of ADAF models, simultaneous two-flow models, and observed correlations between hard X-ray flux and jet production.

arXiv comment14 pages, 4 figures (3 in color), ApJ accepted Oct. 1 2001

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• INTEGRAL and RXTE monitoring of GRS 1758-258 in 2003 and 2004. A transition from the dim soft state to the hard state
• Accretion states of the Galactic microquasar GRS 1758-258
• Broadband X-ray properties of black holes GRS 1758-258 and 1E 1740.7-2942: AstroSat and NuSTAR results