On the temperature profile of radiatively efficient geometrically thin disks in black hole binaries with the ASCA GIS

Abstract

X-ray spectra of black hole binaries(BHBs) in the high/soft state were studied comprehensively by using ASCA GIS data, and partially RXTE PCA data. A mathematical disk model was applied to several BHBs to see if the observed accretion disk temperature profile was consistent with that expected from the standard accretion disk model. This model is called p-free disk, and assumes that the spectrum is composed of multi-temperature blackbody emission of which the local temperature T(r) at radius r is given by T(r) ~ r^-p with p being a positive free parameter. The standard disk roughly requires p~3/4, while a small deviation is expected depending on the inner boundary conditions, general relativistic effects and disk vertical structures.Our sample objects included LMC X-1, LMC X-3, XTE J2012+381, and GRO J1655-40. During the ASCA observations, these BHBs showed characteristics of the standard high/soft state. Under the standard modeling of high-state black hole binaries, the sources show Tin=0.76-1.17keV, the disk fraction to the total 0.7-10keV flux of 54-98%, and Nh=(0.7--12)E21/cm^2. The best-fit p-values were found in 0.6-0.8, and the standard value of p=3/4 was accepted for all the sources.The obtained p-values are also compared with those expected for the standard accretion disk in the Schwarzschild metric, and they were consistent with those expected from the standard accretion disk.