出版社：SISSA, Scuola Internazionale Superiore di Studi Avanzati
摘要：Simultaneous optical and X-ray observations of black holes in X-ray binaries (GX 339–4, XTE J1118+480, SWIFT J1753.5–0127) show complicated shape of the cross-correlation function (CCF), with an anti-correlation preceding positive correlation. Similar CCFs were found in two neutron star X-ray binaries, Sco X-1 and Cyg X-2. We propose a novel model capable of ex- plaining timing properties of these objects. We argue that the X-ray emission is produced by synchrotron self-Compton mechanism, which also contributes to the optical luminosity. Small variations in the accretion rate cause changes of parameters of the flow (optical depth, total lumi- nosity), leading to variations in X-rays and optical luminosities. By simulating spectra for specific parameters, we show that fluxes in the two bands are anti-correlated. Additional contribution to the optics comes from reprocessing of the X-rays by the outer regions of the accretion disk. We find that our model is consistent with the CCFs recently observed in Galactic black holes. From the presence of the dips in the CCFs, we can estimate the size of the synchrotron-emitting re- gion, and from the relative amplitude of the dips to the peaks we constrain the contribution of synchrotron radiation in the optical energy band.
