A Flaring X-ray Source with an Halpha-bright Counterpart toward the SMC

TL;DR

This paper reports the discovery of a flaring X-ray source with an optical counterpart showing Halpha emission in the SMC, likely a nearby active star, with detailed X-ray and optical observations.

Contribution

The study presents the first detailed analysis of a flaring X-ray source with an Halpha-bright optical counterpart in the SMC, identifying it as a nearby active star.

Findings

X-ray flare lasted 6 ksec with a thermal plasma temperature of 2.5 keV

Optical counterpart shows Halpha emission and high proper motion

Source likely a nearby Galactic BY Draconis type star

Abstract

We report the discovery of a flaring X-ray source with an optical counterpart with Halpha 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 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 Halpha emission (Halpha - r = -0.88), 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.