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

Sidoli, L. and Paizis, A. and Fürst, F. and Torrejón, J. M. and Kretschmar, P. and Bozzo, E. and Pottschmidt, K. (2015) Probing large-scale wind structures in Vela X–1 using off-states with INTEGRAL. Monthly Notices of the Royal Astronomical Society, 447 (2). pp. 1299-1303. ISSN 0035-8711.

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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 analyzed in a systematic way ten years of INTEGRAL data of VelaX–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 ~5×10^(34) erg s^(−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 ~8.9 day 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 photo-ionization 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.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Sidoli, L.0000-0001-9705-2883
Paizis, A.0000-0001-5067-0377
Fürst, F.0000-0003-0388-0560
Kretschmar, P.0000-0001-9840-2048
Pottschmidt, K.0000-0002-4656-6881
Additional Information:© 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2014 November 28. Received 2014 November 28; in original form 2014 October 17. First published online December 24, 2014. Based on observations with INTEGRAL, an ESA project with instruments and science data centre funded by ESA member states (especially the PI countries: Denmark, France, Germany, Italy, Spain and Switzerland), Czech Republic and Poland, and with the participation of Russia and the USA. This work has made use of the INTEGRAL archive developed at INAF-IASF Milano,∼ada/GOLIA.html. We acknowledge support from ISSI through funding for the International Team on ‘Unified View of Stellar Winds in Massive X-ray Binaries’ (PI: S. Martínez-Nuñez). LS thanks L. Oskinova for interesting discussions. JMT acknowledges grant AYA2010-15431. LS and AP acknowledge the Italian Space Agency financial support INTEGRAL ASI/INAF agreement no. 2013-025.R.0.
Funding AgencyGrant Number
International Space Science Institute (ISSI)UNSPECIFIED
Ministerio de Ciencia, Tecnología e Innovación (MCINN)AYA2010-15431
Agenzia Spaziale Italiana (ASI)2013-025
Subject Keywords:stars: neutron X-rays: binaries X-rays: individual: Vela X–1
Issue or Number:2
Record Number:CaltechAUTHORS:20141217-121732827
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Official Citation:L. Sidoli, A. Paizis, F. Fürst, J. M. Torrejón, P. Kretschmar, E. Bozzo, and K. Pottschmidt Probing large-scale wind structures in Vela X–1 using off-states with INTEGRAL MNRAS (February 21, 2015) Vol. 447 1299-1303 doi:10.1093/mnras/stu2533 First published online December 24, 2014
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:52963
Deposited By: Ruth Sustaita
Deposited On:17 Dec 2014 21:17
Last Modified:17 Dec 2019 22:47

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