Volume 529, May 2011
|Number of page(s)||7|
|Published online||25 March 2011|
The Swift-BAT survey reveals the orbital period of three high-mass X-ray binaries
Dipartimento di Scienze Fisiche ed Astronomiche, Università di Palermo, via Archirafi 36, 90123, Palermo, Italy
2 INAF, Istituto di Astrofisica Spaziale e Fisica Cosmica, via U. La Malfa 153, 90146 Palermo, Italy
Received: 23 December 2010
Accepted: 22 February 2011
Aims. A growing number of previously hidden Galactic X-ray sources are now detected with recent surveys performed by the INTEGRAL and Swift satellites. Most of these new sources eluded past surveys due to their large local X-ray extinction and consequent low soft X-ray flux. The Swift-BAT performs daily monitoring of the sky in an energy band (15–150 keV) which is only marginally affected by X-ray extinction, thus allowing for the search of long periodicities in the light curve and identification of the nature of the X-ray sources.
Methods. We performed a period search using the folding technique in the Swift-BAT light curves of three INTEGRAL sources: IGR J05007−7047, IGR J13186−6257 and IGR J17354−3255. Their periodograms show significant peaks at 30.77 ± 0.01 d, 19.99 ± 0.01 d and 8.448 ± 0.002 d, respectively. We estimate the significance of these features from the χ2 distribution of all the trials, finding a probability ≤ 1.5 × 10-4 that the detections occurred due to chance. We complement our analysis with the study of their broadband X-ray emission.
Results. We identify the periodicities with the orbital periods of the sources. The periods are typical for the wind accretors X-ray binaries and we support this identification showing that also their energy spectra are compatible with an X-ray spectral emission characteristic of high-mass X-ray binaries. The spectrum of IGR J05007−704 that resides in the Large Magellanic Cloud, does not show any intrinsic local absorption, whereas the spectra of the Galactic sources IGR J17354−3255 and IGR J13186−6257 may be affected by a local absorber. The folded light curve for IGR J13186−6257 suggests a possible Be companion star.
Key words: X-rays: binaries / X-rays: individuals: IGR J05007−7047 / X-rays: individuals: IGR J13186−6257 / X-rays: individuals: IGR J17354−3255
© ESO, 2011
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