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Probing large-scale wind structures in Vela X-1 using off-states with INTEGRAL

Sidoli, L. ; Paizis, A. ; Fürst, F. ; Torrejón, J. M. ; Kretschmar, P. ; Bozzo, E. ; Pottschmidt, K.

In: Monthly Notices of the Royal Astronomical Society, 2014, vol. 447, no. 2, p. 1299-1303

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    Titre
    • Probing large-scale wind structures in Vela X-1 using off-states with INTEGRAL
    Auteur
    • Sidoli, L.. INAF, Istituto di Astrofisica Spaziale e Fisica Cosmica, Via E. Bassini 15, I-20133 Milano, Italy
    • Paizis, A.. INAF, Istituto di Astrofisica Spaziale e Fisica Cosmica, Via E. Bassini 15, I-20133 Milano, Italy
    • Fürst, F.. Cahill Center for Astronomy and Astrophysics, California Institute of Technology, Pasadena, CA 91125, USA
    • Torrejón, J. M.. Instituto Universitario de Física Aplicada a las Ciencias y las Tecnologías, Universidad de Alicante, E-03690 Alicante, Spain
    • Kretschmar, P.. European Space Astronomy Centre (ESA/ESAC), Science Operations Department, E-28691 Villanueva de la Cañada (Madrid), Spain
    • Bozzo, E.. INTEGRAL Science Data Centre, Université de Genève, Chemin d'Écogia 16, CH-1290 Versoix, Switzerland
    • Pottschmidt, K.. Center for Space Science and Technology, University of Maryland Baltimore County, Baltimore, MD 21250, USA
    Type de document
    • Postprint
    Langue
    • Anglais
    Publié dans
    • Monthly Notices of the Royal Astronomical Society, 2014, vol. 447, no. 2, p. 1299-1303. Oxford University Press
    Autre version électronique
    Identifiant OAI-PMH
    • oai:doc.rero.ch:289251
    Summary
    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 10years of INTEGRAL data of VelaX-1 (22-50keV) and we found that when outside the X-ray eclipse, the source undergoes several luminosity drops where the hard X-rays luminosity goes below ∼3×1035ergs−1, 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 VelaX-1∼8.9d 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 VelaX-1