The eclipsing massive X-ray binary M33 X-7: New X-ray observations and optical identification

Abstract

The eclipsing X-ray binary M33 X-7 was in the field of view during several observations of our XMM-Newton M33 survey and in the archival Chanfdra observation 1730 which cover a large part of the 3.45 d orbital period. We detect emission of M33 X-7 during eclipse and a soft X-ray spectrum of the source out of eclipse that can best be described by bremsstrahlung or disk blackbody models. No significant regular pulsations of the source in the range 0.25-1000 s were found. The average source luminosity out of eclipse is 5E37 erg/s (0.5-4.5 keV). In a special analysis of DIRECT observations we identify as optical counterpart a B0I to O7I star of 18.89 mag in V which shows the ellipsoidal heating light curve of a high mass X-ray binary with the M33 X-7 binary period. The location of the X-ray eclipse and the optical minima allow us to determine an improved binary period and ephemeris of mid-eclipse as HJD (2451760.61+-0.09)+- N * (3.45376+-0.00021). The mass of the compact object derived from orbital parameters and the optical companion mass, the lack of pulsations, and the X-ray spectrum of M33 X-7 may indicate that the compact object in the system is a black hole. M33 X-7 would be the first detected eclipsing high mass black hole X-ray binary.

9 pages including 6 figures, A&A accepted

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• A method for optimal image subtraction
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• A Chandra Spectroscopic Survey of Persistent Black Hole Candidates
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Cited by in corpus (22)

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• A code to compute the emission of thin accretion disks in non-Kerr space-times and test the nature of black hole candidates
• On the development of QPOs in Bondi-Hoyle accretion flows
• XMM-Newton survey of the Local Group galaxy M 33
• Formation of the black-hole binary M33 X-7 via mass-exchange in a tight massive system
• M 33 X-7: ChASeM33 reveals the first eclipsing black hole X-ray binary
• Formation Timescales for High-Mass X-ray Binaries in M33
• The Mass of the Black Hole in the X-ray Binary M33 X-7 and the Evolutionary Status of M33 X-7 and IC 10 X-1
• A Study of the Evolution of the Close Binaries Cyg X-3, IC 10 X-1, NGC 300 X-1, SS 433, and M33 X-7 Using the "Scenario Machine"
• Phase-resolved spectroscopic analysis of the eclipsing black hole X-ray binary M33 X-7: System properties, accretion, and evolution
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• X-ray and Optical Eclipses in ULXs as Possible Indicators of Black Hole Mass
• The X-ray binary population in M33: II. X-ray spectra and variability
• Wolf-Rayet stars, black holes and the first detected gravitational wave source
• Photometric Analysis of the Optical Counterpart of the Black Hole HMXB M33 X-7
• Detection of the second eclipsing high mass X-ray binary in M 33
• Multiwavelength study of the bright X-ray source population in the interacting galaxies NGC5774/NGC5775
• Eclipsing Light-Curve Asymmetry for Black-Hole Accretion Flows
• Detection of X-ray elongated emission from a ultraluminous X-ray source in the interacting pair of galaxies NGC 5953/5954
• Optical Light Curves of Luminous Eclipsing Black Hole X-ray Binaries