* Astronomy

Title: The orbital period of Swift J1816.7-1613 revealed by the Swift-BAT telescope
Author: V. La Parola (1), A. Segreto (1), G. Cusumano (1), N. Masetti (2), A. D'Ai, A. Melandri (3) ((1) INAF - IASF-Palermo, (2) INAF - IASF-Bologna, (3) INAF - OAB)

We have analysed the Swift data relevant to the high mass X-ray binary Swift J1816.7-1613. The timing analysis of the BAT survey data unveiled a modulation at a period of P_0=118.5±0.8 days that we interpret as the orbital period of the X-ray binary system. The modulation is due to a sequence of bright flares, lasting ~30 d, separated by long quiescence intervals. This behavior is suggestive of a Be binary system, where periodic or quasi-periodic outbursts are the consequence of an enhancement of the accretion flow from the companion star at the periastron passage. The position of Swift J1816.7-1613 on the Corbet diagram strengthens this hypothesis. The broad band 0.2-150 keV spectrum is well modeled with a strongly absorbed power-law with a flat photon index Gamma~ 0.2 and a cut-off at ~ 10 keV.

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