LEIA discovery of the longest-lasting and most energetic stellar X-ray flare ever detected

TL;DR

LEIA detected the longest-lasting and most energetic stellar X-ray flare on a nearby star, lasting 40 days with a peak luminosity of 1.1×10^34 erg/s, revealing new insights into stellar flare phenomena.

Contribution

This study presents the discovery and detailed analysis of the most energetic and longest-duration stellar X-ray flare ever observed, using LEIA data.

Findings

Flare lasted about 40 days with peak luminosity ~1.1×10^34 erg/s.

X-ray spectra showed evolving plasma temperature and emission measure.

Estimated energy released was approximately 3×10^39 erg.

Abstract

The Lobster Eye Imager for Astronomy (LEIA) detected a new X-ray transient on 2022 November 7, identified as a superflare event occurring on a nearby K-type giant star HD 251108. The flux increase was also detected in follow-up observations at X-ray, UV and optical wavelengths. The flare lasted for about 40 days in soft X-ray observations, reaching a peak luminosity of ~1.1 * 10^34 erg/s in 0.5-4.0 keV, which is roughly 60 times the quiescent luminosity. Optical brightening was observed for only one night. The X-ray light curve is well described by a double fast rise and exponential decay model, attributed to the cooling process of a loop arcade structure formed subsequent to the initial large loop with a half-length of ~1.9 * 10^12 cm. Time-resolved X-ray spectra were fitted by a four-temperature apec model (with three components being the quiescent background), showing significant evolution of plasma temperature and emission measure over time. The estimated energy released in the LEIA band is ~3 * 10^39 erg, suggesting that this is likely the most energetic X-ray stellar flare with the longest duration detected to date.