X-ray pulsations from the region of the supergiant fast X-ray transient IGR J17544−2619

¹ School of Physics and Astronomy, University of Southampton, University Road, Southampton SO17 1BJ, UK
e-mail: sd805@soton.ac.uk
² Astronomy, Gravity and Cosmology Centre, Department of Astronomy, University of Cape Town, Rondebosch 7701, South Africa
³ South African Astronomical Observatory, PO Box 9, Observatory 7935, South Africa
⁴ INAF – IASF, Istituto di Astrofisica Spaziale e Fisica Cosmica, via Gobetti 101, Bologna, Italy
⁵ INAF – IASF, Istituto di Astrofisica Spaziale e Fisica Cosmica, via del Fosso del Cavaliere 100, 00133 Roma, Italy
⁶ Centre d’Étude Spatiale des Rayonnements, CNRS/UPS, BP 4346, 31028 Toulouse, France
⁷ CREATEC, Unit 8, Derwent Mill Commercial Park, Cockermouth, Cumbria CA13 0HT, UK

Received: 25 August 2011
Accepted: 7 January 2012

Abstract

Phase-targeted RXTE observations have allowed us to detect a transient 71.49 ± 0.02 s signal that is most likely to be originating from the supergiant fast X-ray transient IGR J17544−2619. The phase-folded light curve shows a possible double-peaked structure with a pulsed flux of  ~4.8 × 10^-12 erg cm^-2 s^-1 (3−10 keV). Assuming the signal to indicate the spin period of the neutron star in the system, the provisional location of IGR J17544−2619 on the Corbet diagram places the system within the classical wind-fed supergiant XRB region. Such a result illustrates the growing trend of supergiant fast X-ray transients to span across both of the original classes of HMXB in P_orb − P_spin space.