Optical modulation of the new eclipsing XRB in M33
ATel #913; A. Shporer (Wise Obs.), J. Hartman (CfA), T. Mazeh (Wise Obs.), W. Pietsch (MPE)
on 11 Oct 2006; 12:13 UT
Credential Certification: Avi Shporer (shporer@wise.tau.ac.il)
Subjects: Optical, Binary
The variable XMM-Newton source [PMH2004] 47 was recently identified by
Pietsch et al. (ATel #905) as an eclipsing XRB with an orbital period of
1.73245 days. Based on its position and color, Pietsch et al. identified
star #4571 of Massey et al. (2006, AJ 131, 2478) as the optical counterpart
of the X-ray source.
This star was not identified as variable in the M33 CFHT variability survey
(Hartman et al. 2006, MNRAS, 371, 1405). To search for any small optical
modulation, we derived the light curves of this star in the Sloan g',
r' & i' bands directly from the CFHT images. Folding the 31-33
measurements in each of these colors with the X-ray period reveals a clear
periodicity. The
folded light curve is of double sinusoidal shape, with one of the minima
at the phase of mid X-ray eclipse, suggesting an ellipsoidal modulation of a
high-mass optical companion.
The detection of an optical modulation at the X-ray period
confirms the identification of the optical counterpart. This opens the way
to estimate the two masses and determine whether the primary is a neutron
star or a black hole.
