Journal Article

Exploring the spreading layer of GX 9+9 using <i>RXTE</i> and <i>INTEGRAL</i>

P. Savolainen, D. C. Hannikainen, O. Vilhu, A. Paizis, J. Nevalainen and P. Hakala

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 393, issue 2, pages 569-578
Published in print February 2009 | ISSN: 0035-8711
Published online February 2009 | e-ISSN: 1365-2966 | DOI:
Exploring the spreading layer of GX 9+9 using RXTE and INTEGRAL

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We have fitted ∼200 RXTE and INTEGRAL spectra of the neutron star (NS) low-mass X-ray binary (LMXB) GX 9+9 from 2002 to 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° 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.

Keywords: accretion, accretion discs; stars: individual: GX 9+9; X-rays: binaries

Journal Article.  5947 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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