Research Note

Swift discovery of the orbital period of the high mass X-ray binary IGR J015712−7259 in the Small Magellanic Cloud

¹ INAF − Istituto di Astrofisica Spaziale e Fisica Cosmica di Palermo, via U. La Malfa 153, 90146 Palermo, Italy
e-mail: cusumano@ifc.inaf.it
² Dipartimento di Fisica e Chimica, Università di Palermo, via Archirafi 36, 90123 Palermo, Italy
³ INAF − Istituto di Astrofisica Spaziale e Fisica Cosmica di Bologna, via Gobetti 101, 40129 Bologna, Italy
⁴ INAF − Brera Astronomical Observatory, via Bianchi 46, 23807 Merate (LC), Italy

Received: 15 May 2013
Accepted: 13 August 2013

Abstract

Context. In the past few years, the hard X-ray astronomy has made a significant step forward, thanks to the monitoring of the IBIS/ISGRI telescope onboard the INTEGRAL satellite and of the Burst Alert Telescope (BAT) onboard the Swift observatory. This has provided a huge amount of novel information on many classes of sources.

Aims. We have been exploiting the BAT survey data to study the variability and the spectral properties of the new high mass X-ray binary sources detected by INTEGRAL. We investigate the properties of IGR J015712−7259.

Methods. We performed timing analysis on the 88-month BAT survey data and on the XRT pointed observations of this source. We also report on the broad-band 0.2−150 keV spectral analysis.

Results. We find evidence of a modulation of the hard-X-ray emission with period P_o = 35.6 d. The significance of this modulation is 6.1 standard deviations. The broad band spectrum is modeled with an absorbed power law with photon index Γ ~ 0.4 and a steepening in the BAT energy range modeled with a cutoff at an energy of ~13 keV.