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

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.