Chandra and XMM monitoring of the black hole X-ray binary IC 10 X-1
Abstract
The massive black hole (BH)+Wolf-Rayet (WR) binary IC 10 X-1 was observed in a series of 10 Chandra and two XMM-Newton observations spanning 2003-2012, showing consistent variability around 7 × 1037 erg s-1, with a spectral hardening event in 2009. We phase connected the entire light curve by folding the photon arrival times on a series of trial periods spanning the known orbital period and its uncertainty, refining the X-ray period to P = 1.45175(1) d. The duration of minimum flux in the X-ray eclipse is ∼5 h which together with the optical radial velocity (RV) curve for the companion yields a radius for the eclipsing body of 8-10 R⊙ for the allowed range of masses. The orbital separation (a1 + a2) = 18.5-22 R⊙ then provides a limiting inclination i > 63° for total eclipses to occur. The eclipses are asymmetric (egress duration ∼0.9 h) and show energy dependence, suggestive of an accretion disc hotspot and corona. The eclipse is much (∼5×) wider than the 1.5-2 R⊙ WR star, pointing to absorption/scattering in the dense wind of the WR star. The same is true of the close analog NGC 300 X-1. RV measurements of the He II [λλ4686] line from the literature show a phase shift with respect to the X-ray ephemeris such that the velocity does not pass through zero at mid-eclipse. The X-ray eclipse leads inferior conjunction of the RV curve by ∼90°, so either the BH is being eclipsed by a trailing shock/plume, or the He II line does not directly trace the motion of the WR star and instead originates in a shadowed partially ionized region of the stellar wind.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- January 2015
- DOI:
- 10.1093/mnras/stu2151
- arXiv:
- arXiv:1410.3417
- Bibcode:
- 2015MNRAS.446.1399L
- Keywords:
-
- binaries: eclipsing;
- stars: black holes;
- stars: Wolf-Rayet;
- X-rays: binaries;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- Submitted to MNRAS. 13 Pages with 10 Figures