Separating flare and secondary atmospheric signals with RADYN modeling of near-infrared JWST transmission spectroscopy observations of TRAPPIST-1

TL;DR

This study combines spectrotemporal analysis and physics-based modeling to characterize TRAPPIST-1 flares, aiming to improve mitigation of flare contamination in exoplanet transmission spectroscopy and assess their impact on planetary atmospheres.

Contribution

It introduces RADYN-based models and empirical pipelines to separate stellar flare signals from planetary atmospheres in JWST data, advancing flare mitigation techniques.

Findings

Flares are caused by moderate electron beams with fluxes of 10^12 erg s^-1 cm^-2.

Models predict XUV, FUV, NUV flare counterparts with specific flux ranges.

Residual contamination in transmission spectra can be reduced to 54-65 ppm.

Abstract

Although TRAPPIST-1's temperate planets have the highest transmission signals of any known system, flares contaminate 50-70% of transits at the 1000 ppm level, far above 100 ppm secondary atmospheres. Efforts to mitigate flare contamination and assess impacts on radiation environments are each hampered by a lack of empirical spectral analysis and physics-based modeling. We present spectrotemporal analysis and radiative-hydrodynamic modeling of 5.5 hr of NIRISS and NIRSpec observations of 6 TRAPPIST-1 flares of 2.2-8.7x10^30 erg. Flare lines and continua are characterized using grid searches of RADYN beam-heating models spanning 10$^4\times$ in electron beam parameters. Best-fit models indicate these flares result from moderate-intensity beams with emergent electron fluxes of 10^12 erg s^-1 cm^-2 and energies $\leq$37 keV, although all models over-predict the Paschen jump. These models predict XUV, FUV, and NUV counterparts to the infrared peak fluxes of 8.9-28.9x10^27, 4.3-13.9x10^26, and 3.4-11.4x10^27 erg s^-1, respectively. Scaling the flare rate into the XUV suggests flaring contributes 1.35$_{-0.15}^{+2.0}\times$ quiescence yr$^{-1}$. We bin integrations of similar flare effective temperature to construct fiducial flare spectra from 2000-4500 K in order to develop separate empirical and RADYN-based mitigation pipelines. Both pipelines are applied to all 5.5 hr of R=10 data, resulting in maximum residuals from 1-2.8$\mu$m of 100-140 ppm and typical residuals of 54$\pm$14 and 65$\pm$17 ppm for the empirical and RADYN-based pipelines, respectively. Injection testing supports 3$\sigma$ detection capability for CO2 atmospheres with features of 150-250 ppm, with weak evidence (BF$\approx$3) still obtained at 130 ppm. Our results motivate multi-wavelength observations to improve model fidelity and test high-energy predictions.