The 1–50 keV spectral and timing analysis of IGR J18027-2016: an eclipsing, high mass X-ray binary

¹ School of Physics and Astronomy, University of Southampton, Highfield, SO17 1BJ, UK e-mail: abh@astro.soton.ac.uk
² Geneva Observatory, INTEGRAL Science Data Centre, Chemin d'Ecogia 16, 1291 Versoix, Switzerland
³ IASF-Rm, INAF, via Fosso del Cavaliere 100, 00133 Rome, Italy
⁴ CEA-Saclay, DAPNIA/Service d'Astrophysique, 91191 Gif-sur-Yvette Cedex, France
⁵ IASF-Bo, INAF, via Gobetti 101, 40129 Bologna, Italy

Received: 25 February 2005
Accepted: 24 April 2005

Abstract

We report the association of the INTEGRAL source IGR J18027-2016 with the BeppoSAX source SAX J1802.7-2017. IGR J18027-2016 is seen to be a weak, persistent source by the IBIS/ISGRI instrument on board INTEGRAL with an average source count rate of 0.58 counts s^-1 (~6.4 mCrab) in the 20-40 keV band. Timing analysis performed on the ISGRI data identifies an orbital period of of  days and gives an ephemeris of mid-eclipse as,  MJD. Re-analysis of archival BeppoSAX data has provided a mass function for the donor star, and a projected semimajor axis of  lt-s. We conclude that the donor is an OB-supergiant with a mass of 18.8-29.3  and a radius of 15.0-23.4 . Spectra obtained by XMM-Newton and ISGRI indicate a high hydrogen column density of  cm^-2, which suggests intrinsic absorption. The source appears to be a high mass X-ray binary with the neutron star emitting X-rays through wind-fed accretion while in an eclipsing orbit around an OB-supergiant.