We have fitted ~200 RXTE and INTEGRAL spectra of the neutron star LMXB GX 9+9 from 2002-2007 with a model consisting of a disc blackbody and another blackbody representing the spreading layer (SL), i.e. an extended accretion zone on the NS surface as opposed to the more traditional disc-like boundary layer. Contrary to theory, the SL temperature was seen to increase towards low SL luminosities, while the approximate angular extent had a nearly linear luminosity dependency. Comptonization was not required to adequately fit these spectra. Together with the ~70 degree upper bound of inclination implied by the lack of eclipses, the best-fitting normalization of the accretion disc blackbody component implies a distance of ~10 kpc, instead of the usually quoted 5 kpc.
Cite
@article{arxiv.0811.0493,
title = {Exploring the spreading layer of GX 9+9 using RXTE and INTEGRAL},
author = {P. Savolainen and D. C. Hannikainen and O. Vilhu and A. Paizis and J. Nevalainen and P. Hakala},
journal= {arXiv preprint arXiv:0811.0493},
year = {2009}
}
Comments
14 pages, 10 figures, accepted for publication in MNRAS