Phase-resolved optical and X-ray spectroscopy of low-mass X-ray binary X1822–371^⋆

¹ Tuorla ObservatoryDepartment of Physics and Astronomy, University of Turku, Väisäläntie 20, 21500 Piikkiö, Finland
e-mail: aunsom@utu.fi
² Finnish Centre for Astronomy with ESO (FINCA), University of Turku, Väisäläntie 20, 21500 Piikkiö, Finland
³ National Land Survey of Finland, Opastinsilta 12C, PL 84, 00521 Helsinki, Finland
⁴ School of Physics & Astronomy, University of Southampton, Southampton SO17 1BJ, UK
⁵ South African Astronomical Observatory, PO Box 9, Observatory 7935, South Africa
⁶ Department of Astronomy, University of Cape Town, Cape Town, South Africa
⁷ Division of Geophysics and Astronomy, Department of Physics, University of Helsinki, PO Box 64, 00014 Helsinki, Finland

Received: 11 November 2011
Accepted: 25 December 2011

Abstract

Context. X1822–371 is the prototypical accretion disc corona X-ray source, a low-mass X-ray binary viewed at very high inclination, thereby allowing the disc structure and extended disc coronal regions to be visible. As the brightest (closest) such source, X1822–371 is ideal for studying the shape and edge structure of an accretion disc, and comparing with detailed models.

Aims. We study the structure of the accretion disc in X1822–371 by modelling the phase-resolved spectra both in optical and X-ray regime.

Methods. We analyse high time resolution optical ESO/VLT spectra of X1822–371 to study the variability in the emission line profiles. In addition, we use data from XMM-Newton space observatory to study phase-resolved as well as high resolution X-ray spectra. We apply the Doppler tomography technique to reconstruct a map of the optical emission distribution in the system. We fit multi-component models to the X-ray spectra.

Results. We find that our results from both the optical and X-ray analysis can be explained with a model where the accretion disc has a thick rim in the region where the accretion stream impacts the disc. The behaviour of the Hβ line complex implies that some of the accreting matter creates an outburst around the accretion stream impact location and that the resulting outflow of matter moves both away from the accretion disc and towards the centre of the disc. Such behaviour can be explained by an almost isotropic outflow of matter from the accretion stream impact region. The optical emission lines of He ii λ4686 and 5411 show double peaked profiles, typical for an accretion disc at high inclination. However, their velocities are slower than expected for an accretion disc in a system like X1822–371. This, combined with the fact that the He ii emission lines do not get eclipsed during the partial eclipse in the continuum, suggests that the line emission does not originate in the orbital plane and is more likely to come from above the accretion disc, for example the accretion disc wind.