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

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 Porb − Pspin space.