Swift discovery of the orbital period of the HMXB IGR J015712-7259 in the Small Magellanic Cloud

TL;DR

This paper reports the discovery of a 35.6-day orbital period in the high-mass X-ray binary IGR J015712-7259 in the Small Magellanic Cloud, using 88 months of BAT survey data and broad-band spectral analysis.

Contribution

It presents the first timing analysis revealing the orbital period of IGR J015712-7259 and characterizes its broad-band X-ray spectrum, advancing understanding of this source.

Findings

Detected 35.6-day orbital modulation with 6.1 sigma significance.

Broad-band spectrum fits an absorbed power law with a cutoff at ~13 keV.

Spectral analysis indicates a steepening in the BAT energy range.

Abstract

In the last years the hard X-ray astronomy has made a significant step forward, thanks to the monitoring of the IBIS/ISGRI telescope on board the INTEGRAL satellite and of the Burst Alert Telescope (BAT) on board of the Swift observatory. This has provided a huge amount of novel information on many classes of sources. 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. In this letter we investigate the properties of IGR J015712-7259. We perform 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. We find evidence for a modulation of the hard-X-ray emission with period P_o=35.6 days. The significance of this modulation is 6.1 standard deviations. The broad band spectrum is modeled with an absorbed power law with photon index Gamma 0.4 and a steepening in the BAT energy range modeled with a cutoff at an energy of ~13 keV.}