Neutron star blackbody contraction during flaring in X1624-490

We present results of an extensive investigation of the physical changes ta king place in the emission regions of the LMXB X1624-490 during strong flar ing in observations made using RXTE in 1997 and 1999. 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 emis sion component, the temperature kT(BB) increasing to similar to 2.2 keV in flaring. Remarkably, the blackbody area decreases by a factor of similar to 5 in flaring. During are evolution, the blackbody luminosity remains appro ximately constant, constituting a previously unknown Eddington limiting eff ect which we propose is due to radiation pressure of the blackbody as kTBB increases affecting the inner disk or accretion ow 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 electro n scattering in the atmosphere of the neutron star. The height of the emitt ing region on the non-flaring neutron star is shown to agree with the heigh t of the inner radiatively-supported accretion 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, includi ng radial accretion ow onto the stellar surface and the theory of accretion ow 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 strongl y correlated with the luminosity of the blackbody emission from the neutron star, and discuss the probable origin of this line in the ADC. Finally, po ssible reasons for non-detection of a reflection component in this source, and LMXB in general, are discussed.