A probable accretion-powered X-ray pulsar in IGR J00370+6122

¹ SRON Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands e-mail: jeanz@sron.nl
² Astronomical Institute, Utrecht University, PO Box 80000, 3508 TA Utrecht, The Netherlands
³ Astronomical Institute “Anton Pannekoek”, University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
⁴ X-ray Astrophysics Laboratory, Code 662, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
⁵ Universities Space Research Association, USA

Received: 29 January 2007
Accepted: 24 April 2007

Abstract

Serendipitous and dedicated observations with the Rossi X-ray Timing Explorer (RXTE) and the International Gamma-Ray Astrophysics Laboratory (INTEGRAL) were analyzed to study the transient high-mass X-ray binary IGR J00370+6122, in particular to search for an accretion-powered pulsar as companion to the optically identified (Reig et al. 2005, A&A, 440, 637) B0.5 II-III donor star. Highly variable fluxes were measured in the RXTE data during outbursts of up to 2.2 10^-10 erg cm^-2 s^-1 (3–20 keV; averaged over 1 h). During a 1-h time span with RXTE flaring activity was detected with an oscillating signal repeating 7 times. Epoch folding reveals a 346 ± 6 s period. We propose that this is the period of the putative pulsar. This measurement puts the source in the wind-fed accretion region of the P_orb (=15.7 d) versus P_pulse “Corbet” diagram. The 3 to 60 keV flare spectrum was modeled with an absorbed power law and the absorption column was found to be 15–20 times larger than the interstellar value and the value obtained for the optical counterpart, suggesting an accretor embedded in the wind of the donor star.