Journal Article

X-ray softening in the new X-ray transient XTE J1719−291 during its 2008 outburst decay

M. Armas Padilla, N. Degenaar, A. Patruno, D. M. Russell, M. Linares, T. J. Maccarone, J. Homan and R. Wijnands

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 417, issue 1, pages 659-665
Published in print October 2011 | ISSN: 0035-8711
Published online October 2011 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2011.19308.x
X-ray softening in the new X-ray transient XTE J1719−291 during its 2008 outburst decay

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The X-ray transient XTE J1719−291 was discovered with Rossi X-ray Timing Explorer/Proportional Counter Array (RXTE/PCA) during its outburst in 2008 March, which lasted at least 46 d. Its 2–10 keV peak luminosity is 7 × 1035 erg s−1 assuming a distance of 8 kpc, which classifies the system as a very faint X-ray transient. The outburst was monitored with Swift, RXTE, Chandra and XMM–Newton. We analysed the X-ray spectral evolution during the outburst. We fitted the overall data with a simple power-law model corrected for absorption and found that the spectrum softened with decreasing luminosity. However, the XMM–Newton spectrum cannot be fitted with a simple one-component model, but it can be fitted with a thermal component (blackbody or disc blackbody) plus a power-law model affected by absorption. Therefore, the softening of the X-ray spectrum with decreasing X-ray luminosity might be due to a change in photon index or alternatively it might be due to a change in the properties of the soft component. Assuming that the system is an X-ray binary, we estimated a long-term time-averaged mass accretion rate of ∼ 7.7 × 10−13 M yr−1 for a neutron star as a compact object and ∼ 3.7 × 10−13 M yr−1 in the case of a black hole. Although no conclusive evidence is available about the nature of the accretor, based on the X-ray/optical luminosity ratio we tentatively suggest that a neutron star is present in this system.

Keywords: accretion, accretion discs; stars: individual: XTE J1719−291; X-rays: binaries

Journal Article.  5753 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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