A Flaring X-ray Source with an Hα-bright Counterpart toward the Smc

We report the discovery of a flaring X-ray source with an optical counterpart with Hα emission and red-excess, in the direction of the SMC. A 100 ksec X-ray observation with Chandra detected a flare lasting ∼6 ksec in the source CXO J005428.9-723107. The X-ray spectrum during the flare was consistent with a thermal plasma of temperature kT=2.5±0.4 keV. In quiescence following the flare the spectrum was softer (kT∼ 0.4 keV). Timing analysis did not reveal any significant periodicities or QPOs. Optical images taken with the Magellan-Baade 6.5m telescope show a single star in the (0.9”) error circle. This star has apparent magnitude V=19.17, exhibits enhanced Hα emission (Hα–r = -0.88±0.02), and has a large proper motion. Alternative explanations are explored, leading to identification as a relatively nearby (Galactic) coronally active star of the BY Draconis class. Subject headings: X-rays stars:flare galaxies:Magellanic Clouds