Sep 8 – 13, 2019
Europe/Rome timezone
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CG X-1: AN ECLIPSING WOLF-RAYET ULX IN THE CIRCINUS GALAXY

Sep 13, 2019, 3:50 PM
2m

Speaker

Ms Yanli Qiu (National Astronomical Observatories Of China (NAOC))

Description

Compact Wolf-Rayet X-ray binaries with orbital periods of less than a day are a rare class of sources, probing a short-lived (few 10^5 yr) but key evolutionary stage of binary systems. They emerge from a common envelope phase and (if they survive the second SN explosion) they form double compact objects that can merge via gravitational decay in less than a Gyr. We studied the candidate Wolf-Rayet X-ray binary CG X-1 in the Circinus galaxy, using 20 years of Chandra and XMM-Newton data. CG X-1 is an eclipsing source and one of the most luminous ULXs in the local universe (peak L_X = 3 x 10^{40} erg/s at a distance of 4.2 Mpc). We phase connected the lightcurves in the archival data and derived a period of (25,970.0 +/- 0.1) s and a period derivative Pdot/P = (10.2 +/- 4.6) x 10^{-7} yr^{-1}. The intriguing dipping and eclipsing behavior of CG X-1 is different from the orbital modulations seen in other classes of X-ray binaries. We suggest that such lightcurves are a defining property of this class of super-Eddington sources, in which both the primary and the secondary launch dense, fast outflows with similar kinetic power. We propose a model for the asymmetric dips and occultations, based on partial covering by Compton-thick clouds. We speculate that the main occulting material is dense, shocked wind between black hole and donor star, and in a bow shock ahead of the black hole.

Affiliation National Astronomical Observatories Of China (NAOC)
Topic Compact and diffuse sources in galaxies and in the Galactic Center

Primary authors

Prof. Roberto Soria (UCAS) Ms Yanli Qiu (National Astronomical Observatories Of China (NAOC))

Co-authors

Prof. Jifeng Liu (NAOC) Dr Song Wang (NAOC)

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