Swift J053041.9-665426, the new LMC X-ray transient, has a variable optical counterpart
ATel #3751; P. A. Charles (Southampton), A. Rajoelimanana (Cape Town), T. J. Maccarone (Southampton)
on 9 Nov 2011; 14:31 UT
Credential Certification: Tom Maccarone (tjm@phys.soton.ac.uk)
Subjects: Optical, X-ray, Request for Observations, Binary, Transient
Referred to by ATel #: 3753
We have extracted the MACHO blue and red light-curves of the proposed counterpart of this new LMC X-ray transient, Swift J053041.9-665426. These cover the interval MJD49000-51600. The star is highly variable (by up to 0.3 mag) in both bands, and exhibits a ~415d candidate quasi-periodic
modulation in the blue (although there are only approximately 4 cycles in the light-curve). Towards the end of the MACHO coverage (~MJD51400) the star has a large (~0.3mag) outburst that lasts ~200d.
With blue and red magnitudes of ~15.3 and 15.5 respectively, and U-B of -0.7 (Zaritsky et al., 2004, AJ, 128, 1606) the source colors are consistent with expectations from an early-type star located at the distance of the LMC, making it clearly an HMXB, likely a Be X-ray binary. Its X-ray spectrum (ATel 3747) suggests that this might not be a neutron star system, and could, instead be the first Be black hole X-ray binary, and so further observations at all wavelengths are strongly urged during this current outburst.
