Swift-BAT hard X-ray sky monitoring unveils the orbital period of the HMXB IGR J18219-1347

Abstract

IGR J18219-1347 is a hard X-ray source discovered by INTEGRAL in 2010. We have analyzed the X-ray emission of this source exploiting the BAT survey data up to March 2012 and the XRT data that include also an observing campaign performed in early 2012. The source is detected at a significance level of ~14 standard deviations in the 88-month BAT survey data, and shows a strong variability along the survey monitoring, going from high intensity to quiescent states. A timing analysis on the BAT data revealed an intensity modulation with a period of 72.46 days. The significance of this modulation is about 7 standard deviations in Gaussian statistics. We interpret it as the orbital period of the binary system. The light curve folded at P_0 shows a sharp peak covering ~30% of the period, superimposed to a flat level roughly consistent with zero. In the soft X-rays the source is detected only in 5 out of 12 XRT observations, with the highest recorded count rate corresponding to a phase close to the BAT folded light curve peak. The long orbital period and the evidence that the source emits only during a small fraction of the orbit suggests that the IGR J18219-1347 binary system hosts a Be star. The broad band XRT+BAT spectrum is well modeled with a flat absorbed power law with a high energy exponential cutoff at ~11 keV.

6 pages, 3 figures. Accepted for publication on ApJ. Changes: Refined timing and spectral analysis. New long term light curve light curve plot

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• Be/X-ray binaries
• Catalogue of high-mass X-ray binaries in the Galaxy ($4^{th}$ edition)
• INTEGRAL/IBIS 7-year All-Sky Hard X-Ray Survey. Part II: Catalog of Sources
• Detection of an orbital period in the supergiant high mass X-ray binary IGR J16465$-$4507 with Swift-BAT
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Cited by in corpus (8)

• A catalogue of high-mass X-ray binaries in the Galaxy: from the INTEGRAL to the Gaia era
• Advances in Understanding High-Mass X-ray Binaries with INTEGRAL and Future Directions
• INTEGRAL/IBIS 17-yr hard X-ray all-sky survey
• Catalog of the Galactic population of X-ray pulsars in High-mass X-ray binary systems
• NuSTAR observations of the unidentified INTEGRAL sources: constraints on the Galactic population of HMXBs
• Identification of an X-ray Pulsar in the BeXRB system IGR J18219$-$1347
• Swift unveils the orbital period of IGR J18214-1318
• Spectral and timing characterization of the X-ray source 1RXS J194211.9+255552