Potential Chromospheric Evaporation in A M-dwarf's Flare Triggered by Einstein Probe Mission

TL;DR

This study reports multi-wavelength observations of an M-dwarf flare triggered by the Einstein Probe, providing evidence for chromospheric evaporation and estimating the mass of evaporating plasma and possible prominence eruption.

Contribution

First detection of chromospheric evaporation in an M-dwarf flare using multi-wavelength follow-up observations from the Einstein Probe.

Findings

Detected blue asymmetry in Hα line indicating chromospheric evaporation.

Estimated the evaporating plasma mass to be approximately 1.2×10^18 g.

Identified possible prominence eruption with mass between 7×10^15 g and 7×10^18 g.

Abstract

Although flares from late-type main-sequence stars have been frequently detected in multi-wavelength, the associated dynamical process has been rarely reported so far. Here, we report follow-up observations of an X-ray transient triggered by WXT onboard the Einstein Probe at UT08:45:08 in 2024, May 7. The photometry in multi-bands and time-resolved spectroscopy started at 3 and 7.5 hours after the trigger, respectively, which enables us to identify the transient as a flare of the M-dwarf 2MASS J12184187-0609123. The bolometric energy released in the flare is estimated to be $\sim10^{36}\ \mathrm{erg}$ from its X-ray light curve. The H$\alpha$ emission-line profile obtained at about 7 hours after the trigger shows an evident blue asymmetry with a maximum velocity of $200-250\ \mathrm{km\ s^{-1}}$. The blue wing can be likely explained by the chromospheric temperature (cool) upflow associated with chromospheric evaporation, in which the mass of the evaporating plasma is estimated to be $1.2\times10^{18}$g. In addition, a prominence eruption with an estimated mass of $7\times10^{15}\mathrm{g}<M_{\mathrm{p}}<7\times10^{18}\mathrm{g}$ can not be entirely excluded.