Properties of serendipitous X-ray flares discovered in XMM-Newton observations

We present the results of a search of the XMM-Newton public data archive for stellar X-ray flares. We find eight flaring sources for which we identify seven optical counterparts. Three of these sources have distance estimates which allow us to determine their luminosities. Based on the decay time of the flares and their luminosity, we derive loop half-lengths of ~2-7 × 10¹⁰ cm and emission measures of ~10⁵⁴ cm^-3 these are similar to values derived for other stellar flaring sources. One of the stars shows two flares in close succession. We discuss the likelihood of this double event being either sympathetic or homologous in nature. A comparison to a pair of similar flares on the Sun suggests that homology is the more likely process driving the flare event.