Chandra, Swift, and HST studies of the CXOM31 J004253.1+411422
Very bright X-ray transient in M 31
N. Nooraee1,2, P. J. Callanan2, R. Barnard3, M. R. Garcia3, S. S. Murray4 and A. Moss2
1 Dublin Institute for Advanced Studies, 31 Fitzwilliam Place, Dublin 2, Ireland
2 University College Cork, Cork, Ireland
3 Smithsonian Astrophysical Observatory, 60 Garden Street, Cambridge, MA 02138, USA
4 Johns Hopkins University, Physics and Astronomy, 3400 N Charles Street, Baltimore, MD 21218, USA
Received: 16 September 2011
Accepted: 7 April 2012
Context. A very bright transient X-ray source, CXOM 31 J004253.1+411422, was found by Chandra/HRC in the M 31 bulge. We present Chandra, Swift, and Hubble Space Telescope (HST) observations of this source.
Aims. Since this source is the brightest known X-ray transient in M 31, we want to study its nature with Chandra and Swift. Comparing the results of Galactic transients and M 31 transients can give a better understanding of the nature of extragalactic binaries.
Methods. We fitted disk black body and power law models to X-ray data from Chandra and Swift. Follow-up HST/ACS imaging during and after the outburst revealed a transient optical counterpart.
Results. Our HST observations show an optical counterpart with optical magnitude B = 23.91 ± 0.08. Using the empirical relations between X-ray luminosity and absolute visual magnitude, we estimate the orbital period of the system is about ~15 h.
Conclusions. Our optical identification of the brightest X-ray transient so far discovered in M 31 suggests an orbital period of about 15 h. The decay light curve is consistent with previous models of X-ray novae outbursts.
Key words: X-rays: general / X-rays: binaries / galaxies: groups: individual: M 31
© ESO, 2012