Characterisation of the NUV and Optical Emission and Temperature of Flares from Ross 733 with Swift and TESS

TL;DR

This study coordinated optical and NUV observations of Ross 733 to analyze flare characteristics, revealing a higher flare rate and suggesting the need for more detailed models to account for emission line contributions.

Contribution

First simultaneous multi-wavelength campaign on Ross 733 measuring flare temperature and testing NUV flare models, highlighting discrepancies and areas for model improvement.

Findings

Ross 733 flares every 1.5 days with 10^33 erg energy

Measured flare temperature of approximately 7340 K during decay

NUV flare detection exceeds predictions of the 9000 K blackbody model

Abstract

We present the results of a coordinated campaign to simultaneously observe the M star binary Ross 733 simultaneously in the optical and near-ultraviolet (NUV) with TESS and Swift respectively. We observed two flares in the Swift NUV light curve. One of these was decay phase of a flare that was also detected with TESS and the other was only detected in the NUV. We used the TESS light curve to measure the white-light flare rate of Ross 733, and calculate that the system flares with an energy of $10^{33}$ erg once every 1.5 days. We used our simultaneous observations to measure a pseudo-continuum temperature of $7340^{+810}_{-900}$K during the flare decay. We also used our observations to test the NUV predictions of the 9000 K blackbody flare model, and find that it underestimates number of flares we detect in our Swift NUV light curve. We discuss the reasons for this and attribute it to the unaccounted contributions from emission lines and continuum temperatures above 9000 K. We discuss how additional observations are required to break the degeneracy between the two in future multi-wavelength flare campaigns.