M33 X-7: ChASeM33 Reveals the First Eclipsing Black Hole X-Ray Binary
Abstract
The first observations conducted as part of the Chandra ACIS survey of M33 (ChASeM33) sampled the eclipsing X-ray binary M33 X-7 over a large part of the 3.45 day orbital period and have resolved eclipse ingress and egress for the first time. The occurrence of the X-ray eclipse allows us to determine an improved ephemeris of mid-eclipse and binary period as HJD (2,453,639.119 ± 0.005) ± N(3.453014 ± 0.000020) and constrain the eclipse half-angle to 26°.5 ± 1°.1. There are indications for a shortening of the orbital period. The X-ray spectrum is best described by a disk blackbody spectrum typical for black hole X-ray binaries in the Galaxy. We find a flat power density spectrum, and no significant regular pulsations were found in the frequency range of 10^(-4) to 0.15 Hz. HST WFPC2 images resolve the optical counterpart, which can be identified as an O6 III star with the help of extinction and color corrections derived from the X-ray absorption. Based on the optical light curve, the mass of the compact object in the system most likely exceeds 9 M_☉. This mass, the shape of the X-ray spectrum, and the short-term X-ray time variability identify M33 X-7 as the first eclipsing black hole high-mass X-ray binary.
Additional Information
© 2006 American Astronomical Society. Received 2005 December 29; accepted 2006 March 24. Support for this work was provided by the National Aeronautics and Space Administration through Chandra award G06-7073A issued by the Chandra X-Ray Observatory Center, which is operated by the Smithsonian Astrophysical Observatory for and on behalf of the National Aeronautics Space Administration, under contract NAS8-03060. T. J. G. and P. P. P. acknowledge support under NASA contract NAS8-03060. This research has made use of data obtained through the High Energy Astrophysics Science Archive Research Center Online Service, provided by the NASA/Goddard Space Flight Center; of the USNOFS Image and Catalogue Archive operated by the United States Naval Observatory, Flagstaff Station (http://www.nofs.navy.mil/ data/fchpix/ ); and of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. The authors thank Michael Bauer for his introduction to the "PHysics Of Eclipsing BinariEs" program PHOEBE. We thank the anonymous referee for his/her comments and suggestions for improving the manuscript. Facilities: CXO(ACIS), HST(WFPC2), ROSAT(HRI ), EINSTEIN( IPC)Attached Files
Published - PIEapj06.pdf
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Additional details
- Eprint ID
- 24249
- Resolver ID
- CaltechAUTHORS:20110629-104942564
- G06-7073A
- NASA Chandra X-Ray Observatory Center
- NAS8-03060
- NASA
- Created
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2011-06-29Created from EPrint's datestamp field
- Updated
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2021-11-09Created from EPrint's last_modified field