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Black hole X-ray novae (BHXNe) are LMXBs in which irregular mass transfer via an accretion disk on to the black hole causes sporadic large outbursts. There are two competing mechanisms, the secondary mass transfer instability and the accretion disk thermal instability3, for the outbursts of BHXNe. We show that the secondary maxima, observed in the X-ray, UV, and optical light curves of BHXNe, is important in our understanding of the X-ray nova phenomena. We discuss the observational characteristics of the secondary maxima and their possible origin. We suggest that the main outburst is triggered by a disk instability, the second maximum is caused by the X-ray heating of the L1 region when the disk becomes optically thin, and the third maximum is from a small scale mass transfer instability due to the hard X-ray heating of the sub-photosphere of the secondary. Our proposed scenario predicts that the new X-ray nova GRO J0422+32 may develop a final mini-outburst in early 1993 and its binary orbital period is less than 7 hours.
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