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Session 35 - Galactic X-Ray (XTE) Sources.
Display session, Tuesday, January 14
Metropolitan Ballroom,

[35.04] The 1996 Outburst of GRO J1655-40: III Spectral Evolution of the Accretion Disk

R. I. Hynes (U. Sussex), C. A. Haswell (U. Sussex and U. Columbia), W. Chen, C. R. Shrader (NASA/GSFC)

The Black Hole X-Ray Transient GRO J1655-40 was observed throughout the outburst of May 1996 and subsequent decline using HST and a multiwavelength network (Chen et al. and Shrader et al., these proceedings). The spectral evolution was monitored with a series of five successful HST/FOS visits between 1996 May 13 and 1996 July 24, during which time the UV flux declined by a factor of 4. The HST data cover the wavelength region longwards of 1250 ÅWe determine the reddening, E(B-V), from the prominent 2200 Åinterstellar absorption feature observed during the first visit, when the source was brightest. The changes in the emitted spectrum during the decline from maximum allow the underlying physical mechanism for the time-dependent accretion to be constrained. We present the results of modelling the spectral evolution assuming first a "standard" black body disk, then including the effects of irradiation. Models including irradiation exhibit noticable excess optical/UV emission above the standard black body disk spectrum, permitting us to empirically determine the importance of this effect, and to assess the applicability of the assumptions of the standard black body model. We discuss the deduced parameters for the system, and compare them with those obtained from other methods.

Program listing for Tuesday