A comparison of neutron star blackbody luminosities in LMXB with the theory of accretion flow spreading on the stellar surface

¹ School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT, UK e-mail: mjc@star.sr.bham.ac.uk;mbc@star.sr.bham.ac.uk
² Astronomical Observatory, Jagiellonian University, ul. Orla 171, 30-244 Cracow, Poland
³ Landau Institute for Theoretical Physics, Russian Academy of Science, Kosygin Street 2, V-334, 117940 Moscow, Russian Federation e-mail: nail@landau.ac.ru

Corresponding author: M. J. Church, mjc@star.sr.bham.ac.uk

Received: 26 June 2001
Accepted: 11 April 2002

Abstract

We present a comparison of the results of the ASCA survey of LMXB with the Inogamov & Sunyaev theory of accretion flow spreading on the surface of neutron stars. The ASCA survey of LMXB of Church & Bałucińska-Church ([CITE]) revealed a systematic variation of the luminosity of blackbody emission from the neutron star spanning 3 decades in total X-ray luminosity suggesting that the level of blackbody emission is controlled by the physics of the inner disk/stellar interface, which we can hope to understand. Two types of explanation exist: firstly that there is radial flow between the inner disk and star at all vertical positions above the orbital plane so that the height of the disk directly determines the area of star emitting. Secondly, the height of the emitting region on the star is not directly related to the disk properties but depends on the mass accretion rate as suggested by Inogamov & Sunyaev ([CITE]) in their theory of accretion flow spreading on the stellar surface. We find that the survey results for the emitting area agree with this theory at the lowest luminosities. However, for higher luminosities, the blackbody emission is stronger than predicted by spreading theory suggesting that the emitting area is controlled by radial flow between disk and star.