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Arxiv: Characterizing the Near-infrared Spectra of Flares from TRAPPIST-1 During JWST Transit Spectroscopy Observations Published: 10/5/2023 9:00:02 PM Updated: 10/5/2023 9:00:02 PM

Paper abstract: We present the first analysis of JWST near-infrared spectroscopy of stellarflares from TRAPPIST-1 during transits of rocky exoplanets. Four flares wereobserved from 0.6--2.8 \mum with NIRISS and 0.6--3.5 \mum with NIRSpecduring transits of TRAPPIST-1b, f, and g. We discover P\alpha and Br\betaline emission and characterize flare continuum at wavelengths from 1--3.5\mum for the first time. Observed lines include H\alpha,P\alpha-P\epsilon, Br\beta, He I \lambda0.7062\mum, two Ca IIinfrared triplet (IRT) lines, and the He I IRT. We observe a reversed Paschendecrement from P\alpha-P\gamma alongside changes in the light curve shapesof these lines. The continuum of all four flares is well-described by blackbodyemission with an effective temperature below 5300 K, lower than temperaturestypically observed at optical wavelengths. The 0.6--1 \mum spectra wereconvolved with the TESS response, enabling us to measure the flare rate ofTRAPPIST-1 in the TESS bandpass. We find flares of 10^{30} erg large enoughto impact transit spectra occur at a rate of 3.6\substack{+2.1 \\ -1.3} flared^{-1}, ~10\times higher than previous predictions from K2. We measurethe amount of flare contamination at 2 \mum for the TRAPPIST-1b and ftransits to be 500\pm450 and 2100\pm400 ppm, respectively. We find up to80% of flare contamination can be removed, with mitigation most effective from1.0--2.4 \mum. These results suggest transits affected by flares may still beuseful for atmospheric characterization efforts.