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

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Title: Probing large-scale wind structures in Vela X–1 using off-states with INTEGRAL
Authors: Sidoli, Lara | Paizis, Adamantia | Fürst, Felix | Torrejon, Jose M. | Kretschmar, Peter | Bozzo, Enrico | Pottschmidt, Katja
Research Group/s: Astronomía y Astrofísica
Center, Department or Service: Universidad de Alicante. Departamento de Física, Ingeniería de Sistemas y Teoría de la Señal | Universidad de Alicante. Instituto Universitario de Física Aplicada a las Ciencias y las Tecnologías
Keywords: Stars: neutron | X-rays: binaries | X-rays: individual: Vela X–1
Knowledge Area: Física Aplicada
Issue Date: 21-Feb-2015
Publisher: Royal Astronomical Society
Citation: Monthly Notices of the Royal Astronomical Society. 2015, 447(2): 1299-1303. doi:10.1093/mnras/stu2533
Abstract: 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 ∼3 × 1035 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 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.
Sponsor: 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). JMT acknowledges grant AYA2010-15431. LS and AP acknowledge the Italian Space Agency financial support INTEGRAL ASI/INAF agreement no. 2013-025.R.0.
ISSN: 0035-8711 (Print) | 1365-2966 (Online)
DOI: 10.1093/mnras/stu2533
Language: eng
Type: info:eu-repo/semantics/article
Rights: © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society
Peer Review: si
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Appears in Collections:INV - Astronomía y Astrofísica - Artículos de Revistas

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