AAS 207th Meeting, 8-12 January 2006
Session 102 Black Holes II
Oral, Tuesday, 2:00-3:30pm, January 10, 2006, Wilson A/B

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[102.06] GRO J1655-40: Early Stage of the 2005 Outburst

N. Shaposhnikov (USRA/GSFC), J. H. Swank (GSFC), C. R. Shrader (USRA/GSFC), M. Rupen (NRAO), V. Beckmann (GSFC)

The black-hole X-ray binary transient GRO J1655-40 underwent an outburst beginning in early 2005. We present results from INTEGRAL,RXTE and the VLA, part of a multiwavelength observational campaign to study the spectral and temporal evolution in the very early part of the outburst. The high-energy spectra during the initial 15 day of the outburst seemed typical of the well known low-hard-state (LHS) configuration (power law dominated with the spectral index ~1.6), most commonly interpreted as thermal Comptonization emission. Then the source makes a transition to a high-soft-state (HSS) with a strong thermal component. We investigate dipping behavior in the RXTE band LHS and compare our results to the 1996/97 case, when the source was predominantly in the HSS. We consider the evolution of the 0.1~17 Hz QPO behavior, and find that the frequency strongly correlates with the spectral characteristics, before shutting off prior to the HSS transition. We model the broad-band high-energy spectrum in the context of empirical, generic Comptonization and Compton reflection models.

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