2015MNRAS.447.1299S -
Mon. Not. R. Astron. Soc., 447, 1299-1303 (2015/February-3)
Probing large-scale wind structures in Vela X-1 using off-states with INTEGRAL.
SIDOLI L., PAIZIS A., FURST F., TORREJON J.M., KRETSCHMAR P., BOZZO E. and POTTSCHMIDT K.
Abstract (from CDS):
Vela X-1 is the prototype of the class of wind-fed accreting pulsars in high-mass X-ray binaries hosting a supergiant donor. We have analysed in a systematic way 10 years of INTEGRAL data of Vela X-1 (22-50 keV) and we found that when outside the X-ray eclipse, the source undergoes several luminosity drops where the hard X-rays luminosity goes below ∼ 3x1035 erg/s, becoming undetected by INTEGRAL. These drops in the X-ray flux are usually referred to as `off-states' in the literature. We have investigated the distribution of these off-states along the Vela X-1 ∼ 8.9 d orbit, finding that their orbital occurrence displays an asymmetric distribution, with a higher probability to observe an off-state near the pre-eclipse than during the post-eclipse. This asymmetry can be explained by scattering of hard X-rays in a region of ionized wind, able to reduce the source hard X-ray brightness preferentially near eclipse ingress. We associate this ionized large-scale wind structure with the photoionization wake produced by the interaction of the supergiant wind with the X-ray emission from the neutron star. We emphasize that this observational result could be obtained thanks to the accumulation of a decade of INTEGRAL data, with observations covering the whole orbit several times, allowing us to detect an asymmetric pattern in the orbital distribution of off-states in Vela X-1.
Abstract Copyright:
© 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society (2014)
Journal keyword(s):
stars: neutron - X-rays: binaries - X-rays: individual: Vela X-1
Simbad objects:
2
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