Neutron star blackbody contraction during flaring in X1624-490

We present results of an investigation of the physical changes taking place in the emission regions of the LMXB X1624-490 during strong flaring in RXTE observations. Based on the detailed light curve, we propose that the flaring consists of a superposition of X-ray bursts. It is shown that major changes take place in the blackbody emission component, the temperature kT_BB increasing to ~2.2 keV in flaring. Remarkably, the blackbody area decreases by a factor of ~5 in flaring. During flare evolution, the blackbody luminosity remains approximately constant, constituting a previously unknown Eddington limiting effect which we propose is due to radiation pressure of the blackbody as kT_BB increases affecting the inner disk or accretion flow resulting in a decreased emitting area on the star. We argue that the large decrease in area cannot be explained in terms of modification of the blackbody spectrum by electron scattering in the atmosphere of the neutron star. The height of the emitting region on the non-flaring neutron star is shown to agree with the height of the inner radiatively-supported disk as found for sources in the ASCA survey of LMXB of Church & Balucinska-Church (2001). The decrease in height during flaring is discussed in terms of possible models, including radial accretion flow onto the stellar surface and the theory of accretion flow spreading on the neutron star surface of Inogamov & Sunyaev (1999). We demonstrate that the intensity of the broad iron line at 6.4 keV is strongly correlated with the luminosity of the blackbody emission from the neutron star, and discuss the probable origin of this line in the ADC. Finally, possible reasons for non-detection of a reflection component in this source, and LMXB in general, are discussed.Comment: 14 pages including 11 figures, Astronomy and Astrophysics in pres

Rms-flux relation of Cyg X-1 with RXTE: dipping and nondipping cases

The rms (root mean square) variability is the parameter for understanding the emission temporal properties of X-ray binaries (XRBs) and active galactic nuclei (AGN). The rms-flux relation with Rossi X-ray Timing Explorer (RXTE) data for the dips and nondip of black hole Cyg X-1 has been investigated in this paper. Our results show that there exist the linear rms-flux relations in the frequency range 0.1-10 Hz for the dipping light curve. Moreover, this linear relation still remains during the nondip regime, but with the steeper slope than that of the dipping case in the low energy band. For the high energy band, the slopes of the dipping and nondipping cases are hardly constant within errors. The explanations of the results have been made by means of the ``Propagating Perturbation'' model of Lyubarskii (1997).Comment: 15 pages, 12 figures, Accepted for publication in Astrophysics & Space Scienc