A study of the accretion mechanisms of the high-mass X-ray binary IGR J00370+6122

Abstract

Abstract IGR J00370+6122 is a high-mass X-ray binary with a B1 Ib primary star and a companion suggested to be a neutron star because of the detection of a 346 s pulsation in a one-off 4 ks observation. To better understand the nature of the compact companion, the present work performs timing and spectral studies of the X-ray data of this object, taken with XMM-Newton, Swift, Suzaku, RXTE, and INTEGRAL. In the XMM-Newton data, a sign of coherent 674 s pulsation was detected, for which the previous 346 s period may be the second harmonic. The spectra exhibited the “harder when brighter” trend in the 1–10 keV range, and a flat continuum without clear cutoff in the 10–80 keV range. These properties are both similar to those observed from several low-luminosity accreting pulsars, including X Persei in particular. Thus, the compact object in IGR J00370+6122 is considered to be a magnetized neutron star with a rather low luminosity. The orbital period was refined to 15.6649 ± 0.0014 d. Along the orbit, the luminosity changes by three orders of magnitude, involving a sudden drop from ∼4 × 1033 to ∼1 × 1032 erg s−1 at an orbital phase of 0.3 (and probably vice verse at 0.95). Although these phenomena cannot be explained by simple Hoyle–Lyttleton accretion from the primary’s stellar winds, they can be explained when incorporating the propeller effect with a strong dipole magnetic field of ∼5 × 1013 G. Therefore, the neutron star in IGR J00370+6122 may have a stronger magnetic field compared to ordinary X-ray pulsars.