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Session 104 - Accretion-Powered X-Ray Sources.
Display session, Thursday, January 18
North Banquet Hall, Convention Center

[104.01] Precursor, Outburst and Irradiated Companion in the Unstable Irradiated Disks in Black Hole X-Ray Novae

S. W. Kim, J. C. Wheeler (University of Texas at Austin), S. Mineshige (Kyoto University)

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We study the time-dependent irradited accretion disks in black hole X-ray novae. The black hole disk irradiated by the inner hot disk and coronae successfully produces the primary maximum and the phenomenon of secondary reflare observed in many X-ray novae such as A0620-00, GS 2000+25, GRO J0422+32 and Nova Mus 1991 (Kim, Wheeler amp; Mineshige 994, BAAS, 26, 1325). The optical light curve of Nova Sco 1994 displayed a precursor peak that dimmed by \sim 0.6 mag, before rising to maximum light (Bailyn et al. 1995, Nature, 374, 701). We find that the disk instability model qualitatively displays such precursor activity. In the models, there is a precursor with an amplitude of \sim 1.1-1.4 mag in the rise phase due to the initiation of the disk instability in the outer disk. We also investigate the irradiation effect on the companion stars. Study of the evolution of irradiated low mass companions shows that the mass transfer rate will be increased if the irradiated fluxes exceed \gta 10^9-10^10 erg cm^-2 s^-1 for 0.2-0.4 M_ødot, typical for the companions in X-ray novae (e.g., Podsiadlowski 1991, Nature, 350, 136). The irradiated disk model indicates that, to reproduce the secondary reflare, the irradiated flux that a companion of 0.27 M_ødot will receive is \lta 10^9 erg cm^-2 s^-1. This suggests the hypothesis that the observed secondary reflare, 50-100 days after the maximum light, is due to the sudden enhancement of mass transfer from the companion (the so-called mass transfer burst model) is unlikely. The detailed time-dependent features of the model will be presented elsewhere (Kim, Wheeler amp; Mineshige 1995, and Kim, Mineshige amp; Wheeler 1995, to be submitted to ApJ).

Program listing for Thursday