The massive black hole + Wolf-Rayet binary IC10 X-1 was observed in a series of 10 Chandra and 2 XMM-Newton observations spanning 2003-2012 , showing consistent variability around 7 \times 10 ^ { 37 } 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 \sim 5 hr which together with the optical radial velocity curve for the companion yields a radius for the eclipsing body of 8-10 R _ { \odot } for the allowed range of masses .
The orbital separation ( a _ { 1 } + a _ { 2 } ) = 18.5-22 R _ { \odot } then provides a limiting inclination i > 63 ^ { \circ } for total eclipses to occur .
The eclipses are asymmetric ( egress duration \sim 0.9 hr ) and show energy dependence , suggestive of an accretion-disk hotspot and corona .
The eclipse is much ( \sim 5X ) wider than the 1.5-2 R _ { \odot } 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 [ \lambda \lambda 4686 ] 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 \sim 90 ^ { \circ } , 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 .