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Detection of Orbital Period in the Wolf-Rayet X-ray Binary IC 10 X-1

ATEL # 955; A.H. Prestwich (SAO), R.E. Kilgard (SAO), S. Carpano (ESA), S Saar (SAO), K. Page (Leicester), Andy Pollock (ESA) T. Roberts (Durham), M. Ward (Durham), A. Zezas(SAO)
on 29 Nov 2006; 21:03 UT
Password Certification: Andrea Prestwich (andreap@head.cfa.harvard.edu)

Subjects: X-ray, Binaries, Black Holes, Neutron Stars

We detect periodic flux modulations in the Wolf-Rayet X-ray binary IC 10 X-1 using the SWIFT X-ray Telescope and the Chandra X-ray Observatory, with period of 34.82h 0.94h. The Local Group dwarf galacy IC 10 was observed twice with Chandra on 2006 2 Nov. and 2006 4 Nov. for apx. 45 ks per observation and has been observed for ~700s per SWIFT orbit continuously beginning on 2006 21 Nov. for a cumulative total of apx. 86 ks spanning 200 hours to date. This covers apx. 6 full orbital periods. Flux varies by > a factor of 5 between the high and low states with peak luminosity of 2e38 erg/s in the 0.3-10 keV Chandra and SWIFT band. The period was determined by FFT, Lomb-Scargle periodogram and Lomb-Normalized periodogram, with all 3 methods in strong agreement. Due to the sharp flux modulations, we speculate that the periodic signal is due to the WR star eclipsing the X-ray emitting disc around the compact object. A SWIFT lightcurve is given below. Overplotted in blue is a sinusoid with period from the FFT (with arbitrary normalization) and in red is the Chandra data scaled to the SWIFT count rate and shifting the Chandra ingress start time forward by 13 times the period. The 35 hour orbital period is consistent with the models of wind-fed Wolf-Rayet X-ray binaries (Ergma and Yungelson (1998, A&A 333, 151) Lommen et al (2005 A&A, 443, 231L). We thank Neil Gehrels and Dave Burrows for approving the SWIFT observing time.

IC 10 X-1 SWIFT/Chandra Lightcurve


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