EDP Sciences
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Volume 380, Number 2, December III 2001
Page(s) 494 - 503
Section Formation, structure and evolution of stars
DOI http://dx.doi.org/10.1051/0004-6361:20011363

A&A 380, 494-503 (2001)
DOI: 10.1051/0004-6361:20011363

A study of the spectral evolution during dipping in XB 1323-619 with Rossi-XTE and BeppoSAX

R. Barnard1, M. Balucinska-Church1, 2, A. P. Smale3 and M. J. Church1, 2

1  School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT, UK
    e-mail: robb@star.sr.bham.ac.uk; mbc@star.sr.bham.ac.uk
2  Institute of Astronomy, Jagiellonian University, ul. Orla 171, 30-244 Cracow, Poland
3  Laboratory for High Energy Astrophysics, Code 662, NASA/Goddard Space Flight Center, Greenbelt, MD 20771, USA
    e-mail: alan@osiris.gsfc.nasa.gov

(Received 18 May 2001 / Accepted 23 September 2001 )

We report results from analysis of the observations of the dipping low mass X-ray binary XB 1323-619 made with BeppoSAX and Rossi-XTE . The dust-scattered halo contributes significantly in this source, and the observation made with BeppoSAX on 1997 August was used to provide MECS radial intensity profiles at several energies. From these, the halo fractions were obtained and thus an optical depth to dust scattering of $1.8\pm0.4$ derived. In the Rossi-XTE observation of April 25-28, 1997, seven X-rays dips were observed together with 7 bursts repeating approximately periodically. Non-dip and dip PCA spectra can be well-described by assuming the emission consists of point-like blackbody emission identified with the neutron star, plus Comptonized emission from an extended ADC. The blackbody temperature is $1.79\pm0.21$ keV and the cut-off power law photon index $1.61\pm0.04$. Spectral evolution in dipping is well described by progressive covering of the extended Comptonizing region by absorber plus more rapid removal of the point-like blackbody. The effects of dust scattering and of the X-ray pulsar 1SAX J1324.4-6200 also in the field of view are included in the fitting. We detect an iron line at ~6.4 keV and its probable origin in the ADC is discussed.

Key words: X-rays: stars -- stars: individual: XB 1323-619 -- stars: neutron -- binaries: close -- accretion: accretion disks -- ISM: dust, extinction

Offprint request: M. J. Church, mjc@star.sr.bham.ac.uk

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