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Optical Counterpart of XTE J0103-728 (SXP6.85)

ATEL # 1181; P.C. Schmidtke (ASU) and A.P. Cowley (ASU)
on 14 Aug 2007; 20:46 UT
Password Certification: Paul Schmidtke (

Subjects: Optical, X-ray, Binaries, Neutron Stars, Pulsars, Variables

Variability of the optical counterpart of the 6.85 s pulsar XTE J0103-728, whose position is given in ATel #1095, has been studied. The X-ray source is coincident with MACHO 206.16768.5 and OGLE-II smc_sc9_146936. Both data sets show the source has a `swooping' lightcurve, varying over half a magnitude, with a recurrence time of ~658 days. The maximum brightness is fairly constant (I_max=14.5), while MACHO data show the depth of minima decreased over the 7.5 years of observations. The color varies through the cycle, with the source being bluest (V-R=-0.15) at minimum light and reddest (V-R=+0.08) approximately 100 days after maximum light. After removing this longterm variation from the I data, we find a weak periodicity at P=24.82 days. The folded light curve shows an `outburst' of ~0.02 mag lasting about 0.2P. This could be the orbital period, but confirmation with X-ray or radial velocity data is needed.

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