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Discovery of a 30.77-day orbital period in the HMXB IGR J05007-7047

ATel #2594; V. La Parola (INAF IASF Palermo), G. Cusumano (INAF IASF Palermo), A Segreto (INAF IASF Palermo), P. Romano (INAF IASF Palermo), S. Vercellone (INAF IASF Palermo), A. D'Ai' (UniPa)
on 3 May 2010; 16:17 UT
Credential Certification: Valentina La Parola (laparola@ifc.inaf.it)

Subjects: X-ray, Binary, Black Hole, Neutron Star, Star

Referred to by ATel #: 2597, 2601

The discovery of IGR J05007-7047 in the Large Magellanic Cloud is reported in Sazonov et al (2005, A&A, 444, 37), with a 17-60 keV flux of (12+/-2)E-12 erg/cm2/s. A Chandra observation allowed the identification of the counterpart as the bright blue star USNO-B1.00192-00057570 (Halpern ATEL#572) whose location is consistent with the distance of the LMC (Masetti et al 2006, A&A, 459, 21), suggesting that IGR J05007-7047 is a HMXB belonging to the LMC.

The source is detected at 13 standard deviations in the all-sky mosaic obtained from the first 54 months of Swift-BAT survey data in the 15-50 keV energy band. We performed a timing analysis on the BAT light curve in the same energy range through a folding technique. We found a modulation at 30.77+/-0.01 days, that can be interpreted as the orbital period of the binary system. The light curve folded at this period shows a sinusoidal shape with a dip consistent with the occultation of the source by the companion star. The 15-150 KeV spectrum integrated over the 54 months can be modelled with a power-law (Gamma=1.0+/-1.0) with an exponential cut-off (E_cut=17 [-3, +18] keV). The 15-150 keV flux is 1.4E-11 erg/cm2/s.