Supergiant Fast X-ray Transients in outburst: new Swift observations of XTE J1739−302, IGR J17544−2619 and IGR J08408−4503 |
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Authors: | L Sidoli P Romano L Ducci A Paizis G Cusumano V Mangano H A Krimm S Vercellone D N Burrows J A Kennea N Gehrels |
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Institution: | INAF, Istituto di Astrofisica Spaziale e Fisica Cosmica, Via E. Bassini 15, I-20133 Milano, Italy;INAF, Istituto di Astrofisica Spaziale e Fisica Cosmica, Via U. La Malfa 153, I-90146 Palermo, Italy;Dipartimento di Fisica e Matematica, Universitàdell'Insubria, Via Valleggio 11, I-22100 Como, Italy;Universities Space Research Association, Columbia, MD 21044-34342, USA;NASA/Goddard Space Flight Center, Greenbelt, MD 20771, USA;Department of Astronomy and Astrophysics, Pennsylvania State University, University Park, PA 16802, USA |
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Abstract: | We report on new X-ray outbursts observed with Swift from three Supergiant Fast X-ray Transients (SFXTs): XTE J1739?302, IGR J17544?2619 and IGR J08408?4503. XTE J1739?302 underwent a new outburst on 2008 August 13, IGR J17544?2619 on 2008 September 4 and IGR J08408?4503 on 2008 September 21. While the XTE J1739?302 and IGR J08408?4503 bright emission triggered the Swift /Burst Alert Telescope, IGR J17544?2619 did not, thus we could perform a spectral investigation only of the spectrum below 10 keV. The broad-band spectra from XTE J1739?302 and IGR J08408?4503 were compatible with the X-ray spectral shape displayed during the previous flares. A variable absorbing column density during the flare was observed in XTE J1739?302 for the first time. The broad-band spectrum of IGR J08408?4503 requires the presence of two distinct photon populations, a cold one (~0.3 keV) most likely from a thermal halo around the neutron star and a hotter one (1.4–1.8 keV) from the accreting column. The outburst from XTE J1739?302 could be monitored with a very good sampling, thus revealing a shape which can be explained with a second wind component in this SFXT, in analogy to what we have suggested in the periodic SFXT IGR J11215?5952. The outburst recurrence time-scale in IGR J17544?2619 during our monitoring campaign with Swift suggests a long orbital period of ~150 d (in a highly eccentric orbit), compatible with what previously observed with INTEGRAL . |
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Keywords: | X-rays: binaries X-rays: individual: XTE J1739?302 X-rays: individual: IGR J17544?2619 X-rays: individual: IGR J08408?4503 |
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