INTEGRALobservations of the Be/X-ray binary EXO 2030+375 during outburst

Abstract

We present a type-I outburst of the high-mass X-ray binary EXO 2030+375, detected during INTEGRAL's Performance and Verification phase in December 2002 (on-source time about 10 6 s). In addition, six more outbursts have been observed during INTEGRAL's Galactic Plane Scans. X-ray pulsations have been detected with a pulse period of 41.691798 ± 0.000016 s. The X-ray luminosity in the 5-300keV energy range was 9.7 x 10 36 erg s -1 , for a distance of 7.1 kpc. Two unusual features were found in the light curve, with an initial peak before the main outburst and another possible spike after the maximum. RXTE observations confirm only the existence of the initial spike. Although the initial peak appears to be a recurrent feature, the physical mechanisms producing it and the possible second spike are unknown. Moreover, a four-day delay between periastron passage and the peak of the outburst is observed. We present for the first time a 5-300 keV broad-band spectrum of this source. It can be modelled by the sum of a disk black body (kT BB ∼ 8 keV) with either a power law model with r = 2.04 ± 0.11 keV or a Comptonized component (spherical geometry, kT e = 30 keV, r = 2.64, kT w = 1.5 keV).