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ATEL # 2257; P. Esposito (INAF-IASF Milano), P. Romano (INAF-IASF Palermo), L. Sidoli (INAF-IASF Milano), D. N. Burrows (PSU), N. Gehrels (GSFC), J.A. Kennea (PSU), V. La Parola (INAF-IASF Palermo), S. Vercellone (INAF-IASF Palermo)
on 24 Oct 2009; 14:03 UT
Password Certification: Paolo Esposito (email@example.com)
Subjects: X-ray, Binaries, Neutron Stars
The supergiant fast X-ray transient (SFXT) IGR J11215-5952 is known to undergo periodic outbursts separated by about 165 days (Sidoli et al. 2007, A&A 476, 1307). Based on this periodicity, which most likely reflects the orbital period of the binary system, we observed the source with Swift/XRT at the time of the new outburst, that was expected on 2009 October 23 at about 14 UT, based on the ephemeris of Romano et al. (2009, ApJ, 696, 2068).
The observation started on 2009 Oct 23 at 17:06:59 and the XRT effective exposure time was 2.2 ks. IGR J11215-5952 was detected with a mean count rate of 0.48±0.02 counts s-1 (1-10 keV). The average spectrum can be fit with a power-law with photon index 0.9±0.2, modified for the absorption with a column density of (1.2±0.3)×1022 cm-2. This yields an observed 1-10 keV flux of (4.5-0.7+0.3)×10-11 erg cm-2 s-1, corresponding to an unabsorbed flux of about 5.2×10-11 erg cm-2 s-1 and to a luminosity of about 2.4×1035 erg s-1 at 6.2 kpc.
(1-sigma c.l. uncertainties are reported above.)