Discovery of the orbital period in the supergiant fast X-ray transient IGR J17544-2619

D. J. Clark, A. B. Hill, A. J. Bird, V. A. McBride, S. Scaringi, A. J. Dean

Published 2009-08-07Version 1

The supergiant fast X-ray transient (SFXT) system IGR J17544-2619 has displayed many large outbursts in the past and is considered an archetypal example of SFXTs. A search of the INTEGRAL/ISGRI data archive from MJD 52698-54354 has revealed 11 outbursts and timing analysis of the light curve identifies a period of 4.926$\pm$0.001 days which we interpret as the orbital period of the system. We find that large outbursts occasionally occur outside of periastron and place an upper limit for the radius of the supergiant of <23R$_{\sun}$.