Supergiant Fast X-ray Transients in outburst: New Swift observations of XTE J1739-302, IGR J17544-2619 and IGR J08408-4503

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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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.

Original languageEnglish (US)
Pages (from-to)1528-1538
Number of pages11
JournalMonthly Notices of the Royal Astronomical Society
Issue number3
StatePublished - Aug 2009

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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