Simultaneous Multiwavelength Flare Observations of EV Lacertae

TL;DR

This study presents simultaneous multiwavelength observations of flares on the active M dwarf EV Lac, analyzing flare energies, frequencies, and elemental effects across UV, X-ray, and optical bands over 25 days.

Contribution

First simultaneous multiwavelength flare observations on EV Lac, providing detailed flare energy distributions and insights into coronal elemental effects.

Findings

Flare frequency distributions have similar slopes in TESS and NICER data.

UV flares exhibit a shallower frequency distribution slope.

No conclusive evidence of FIP or inverse FIP effect during flares.

Abstract

We present the first results of our ongoing project conducting simultaneous multiwavelength observations of flares on nearby active M dwarfs. We acquired data of the nearby dM3.5e star EV Lac using 5 different observatories: NASA's Transiting Exoplanet Survey Satellite (TESS), NASA's Neil Gehrels Swift Observatory (\textit{Swift}), NASA's Neutron Interior Composition Explorer (NICER), the University of Hawaii 2.2-m telescope (UH88) and the Las Cumbres Observatory Global Telescope (LCOGT) Network. During the $\sim$25 days of TESS observations, we acquired three simultaneous UV/X-ray observations using \textit{Swift} that total $\sim$18 ks, 21 simultaneous epochs totaling $\sim$98 ks of X-ray data using NICER, one observation ($\sim$ 3 hours) with UH88, and one observation ($\sim$ 3 hours) with LCOGT. We identified 56 flares in the TESS light curve with estimated energies in the range log $E_{\rm T}$ (erg) = (30.5 - 33.2), nine flares in the \textit{Swift} UVM2 light curve with estimated energies in the range log $E_{UV}$ (erg) = (29.3 - 31.1), 14 flares in the NICER light curve with estimated minimum energies in the range log $E_{N}$ (erg) = (30.5 - 32.3), and 1 flare in the LCOGT light curve with log $E_{L}$ (erg) = 31.6. We find that the flare frequency distributions (FFDs) of TESS and NICER flares have comparable slopes, $\beta_{T}$ = -0.67$\pm$0.09 and $\beta_{N}$ = -0.65$\pm$0.19, and the FFD of UVOT flares has a shallower slope ($\beta_{U}$ = -0.38$\pm$0.13). Furthermore, we do not find conclusive evidence for either the first ionization potential (FIP) or the inverse FIP effect during coronal flares on EV Lac.