X-ray Flares of EV Lac: Statistics, Spectra, Diagnostics

TL;DR

This study analyzes the spectral and temporal properties of X-ray flares from EV Lac, revealing diverse flare durations, spectral evolution indicating sustained heating, and providing insights into flare structures and plasma conditions.

Contribution

It introduces a comprehensive analysis of flare parameters, spectral evolution, and physical diagnostics for EV Lac's X-ray flares, highlighting differences based on flare duration and heating processes.

Findings

Short flares are significantly hotter than long flares.

Flares exhibit sustained heating during evolution.

Upper limit on Fe K fluorescent flux consistent with compact loops.

Abstract

We study the spectral and temporal behavior of X-ray flares from the active M-dwarf EV Lac in 200 ks of exposure with the Chandra/HETGS. We derive flare parameters by fitting an empirical function which characterizes the amplitude, shape, and scale. The flares range from very short (<1 ks) to long (10 ks) duration events with a range of shapes and amplitudes for all durations. We extract spectra for composite flares to study their mean evolution and to compare flares of different lengths. Evolution of spectral features in the density-temperature plane shows probable sustained heating. The short flares are significantly hotter than the longer flares. We determined an upper limit to the Fe K fluorescent flux, the best fit value being close to what is expected for compact loops.