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

[35.09] The Spectral Evolution of GRS 1915+105 During the Dips

J. H. Swank (GSFC/NASA), X. Chen (UCO/Lick Obs.), R. E. Taam (Northwestern U.)

Between April and October 1996, as has been reported, several RXTE observations of GRS 1915+105 revealed the existence of large dips in the light curve in which the intensity was reduced by up to a factor of ten from the mean. These dips have varying duration (of several hundred seconds) and repetition time-scales (up to a few thousand seconds). From detailed energy spectra, it is found that the spectral evolution during the dips is dramatic but nevertheless similar for all these observations. In comparison with the mean spectrum, the spectrum during the dip is much harder. A spectral transition occurs at the phase corresponding to a sudden increase in source intensity. In particular, the spectrum jumps discontinuously from the hard dip spectrum to a one which is softer than the mean. It is suggested that the dips are a result of a rapid evacuation of the cold inner accretion disk. The evacuated mass may fall into the black hole or be ejected in the vertical direction. In both cases the gravitatational potential energy is converted into kinetic energy without significant radiative losses.

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Program listing for Tuesday