New Time-Resolved, Multi-Band Flares In The GJ 65 System With gPhoton

TL;DR

This study uses GALEX ultraviolet observations to identify and analyze low-energy flares on the active M dwarf system GJ 65, revealing new flare events, their properties, and quasi-periodic pulsations indicative of magnetic activity.

Contribution

First detection of multiple low-energy ultraviolet flares on GJ 65 with high time resolution, including the observation of quasi-periodic pulsations linked to magnetic reconnection processes.

Findings

13 new low-energy UV flares detected

Flare energies range from 10^28.5 to 10^29.5 ergs

Quasi-periodic pulsations at ~50 seconds observed during the largest flare

Abstract

Characterizing the distribution of flare properties and occurrence rates is important for understanding habitability of M dwarf exoplanets. The GALEX space telescope observed the GJ 65 system, composed of the active, flaring M stars BL Cet and UV Cet, for 15900 seconds (~4.4 hours) in two ultraviolet bands. The contrast in flux between flares and the photospheres of cool stars is maximized at ultraviolet wavelengths, and GJ 65 is the brightest and nearest flaring M dwarf system with significant GALEX coverage. It therefore represents the best opportunity to measure low energy flares with GALEX. We construct high cadence light curves from calibrated photon events and find 13 new flare events with NUV energies ranging from 10^28.5 - 10^29.5 ergs and recover one previously reported flare with an energy of 10^31 ergs. The newly reported flares are among the smallest M dwarf flares observed in the ultraviolet with sufficient time resolution to discern light curve morphology. The estimated flare frequency at these low energies is consistent with extrapolation from the distributions of higher-energy flares on active M dwarfs measured by other surveys. The largest flare in our sample is bright enough to exceed the local non-linearity threshold of the GALEX detectors, which precludes color analysis. However, we detect quasi-periodic pulsations (QPP) during this flare in both the FUV and NUV bands at a period of ~50 seconds, which we interpret as a modulation of the flare's chromospheric thermal emission through periodic triggering of reconnection by external MHD oscillations in the corona.