arXiv subjects

Adam F. Kowalski

Publications and source records attributed to Adam F. Kowalski.

At least 19 recordsLinked to original sources

arXiv2026

Broadband 12-26 GHz Radio Radiation Reveals Evidence for Micro-flares on AU Mic

We present sequential 12-18 and 18-26 GHz radio-band ($Ku$, $K$) VLA observations of the 22 Myr dM1e star AU Mic. We detect two flares and two marginal events over a total of 3 contiguous hours on source, resulting in a radio flare rate of $\sim$1 flare hour$^{-1}$. While this rate is consistent with previous $Ku$-band observations, both flaring ($<$1 mJy) and quiescent ($\sim$0.4 mJy) flux densities are significantly lower. Furthermore, the quiescent spectral shape here is distinct, allowing for unique constraints on the radio-emitting sources of AU Mic. The time-averaged quiescent spectrum is best described by gyrosynchrotron radiation with a peak around 17 GHz and an optically thin spectral index of $\alpha \approx -0.6$. We estimate that the source regions have magnetic field strengths of $\sim$1 kG and cover a fraction of $<$0.5% of the stellar surface, yet the instantaneous total electron kinetic energies are $\sim$10$^{28}$ erg. The power-law index describing the distribution of electrons with energy derived from the spectral index, $\delta \approx 2$, implies a near-continuous injection of electrons. This could arise from micro-flares that occur over the surface of AU Mic that sustain the radio radiation. One clear flare per band occurs, with decay-to-rise $e$-folding time ratios of $3 - 4$, indicating magnetic trapping of the electrons. The $Ku$-band flare is optically thick during the rise and peak times, indicating a peak frequency above 18 GHz. Together, these quiescent and flaring characteristics suggest that continuous, unresolved micro-flaring and magnetic trapping dominate the non-thermal radio emission of active M-dwarf coronae.

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arXiv2026

ESCAPE: a small explorer mission to study the stellar drivers of exoplanet evolution

The long-term stability of exoplanetary atmospheres depends critically on the extreme-ultraviolet (EUV) photon and high-energy particle fluxes from the host star, which are poorly constrained. To address this key gap in our understanding of atmospheric retention, we present the Extreme-ultraviolet Stellar Characterization for Atmospheric Physics and Evolution (ESCAPE) mission, a NASA Small Explorer concept proposed in 2026. ESCAPE employs extreme- and far-ultraviolet spectroscopy (80 - 1650 Ang) to provide the first comprehensive study of the stellar EUV history and stellar coronal mass ejection (CME) environments that control atmospheric mass-loss and determine the habitability of rocky exoplanets. This paper outlines both the primary science goals of the mission, the breadth of future general observer investigations, and a detailed design study of the mission's instrumentation. The ESCAPE instrument comprises a grazing incidence telescope that feeds multiple diffraction gratings and a photon-counting detector. We describe a demonstration of the Hettrick-Bowyer telescope, etched silicon diffraction gratings, the microchannel plate detector and housing, and gold and zirconium coatings. We present a STOP analysis that verifies ESCAPE's ability to meet its structural integrity, thermal stability, and optical performance requirements throughout the mission environment.

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arXiv2025

A 7 Day Multiwavelength Flare Campaign on AU Mic. IV: Quiescent Gyrosynchrotron and Gyroresonance Radiation from 12 to 25 GHz

We present an analysis of the radio quiescent data from a multiwavelength campaign of the active M-dwarf flare star AU Mic (dM1e) that occurred in October 2018. Using Ku-band data (12 to 18 GHz) from the Very Large Array and K-band data (17 to 25 GHz) from the Australia Telescope Compact Array, we find that the quiescent spectrum can be decomposed into two components: one falling with frequency and one that remains flat. The flat component has a relatively steady flux density of 0.64 $\pm$ 0.14 mJy. The falling component varies in strength, but exhibits a spectral index of $\alpha$ = $-0.88 \pm 0.10$. The falling component is thus consistent with nonthermal, optically thin gyrosynchrotron radiation with a corresponding power-law index similar to flares from AU Mic. While a flat component may arise from thermal, optically thin free-free emission, the observed flux density and inferred mass-loss rate are both too large compared to previous stellar wind and X-ray emission theory and models, necessitating an alternative explanation. This flat component instead matches well with an optically thick gyroresonance component integrated over multiple source regions such that the composite spectra are reasonably flat. The persistence of these components across the rotational period suggests multiple source regions, which may help explain changes in flux density and persistent high-energy electrons.

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arXiv2025

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

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.

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arXiv2025

The Atmospheric Response to Large Electron Beam Fluxes in Solar Flares III: Comprehensive Modeling of the Brightest Observed Near-Ultraviolet Continuum Source in an X9 Solar Flare

I report on the high resolution spectra of the remarkable X9 solar flare of 2024 Oct 03 (SOL2024-10-03T12:08) and evaluate the extent to which nonthermal electron beams that generate dense chromospheric condensations can power very bright kernels in solar flares. 1D Radiative-hydrodynamic models predict extreme H$\alpha$ near-wing broadening, bright continuum intensities, and a rapid Fe II red wing asymmetry evolution at the brightest NUV continuum source in the flare. Detailed comparisons to the spectral observations reveal that the H$\alpha$ line is too broad, the Fe II red wing is too bright, and the NUV continuum decays too slowly in a fiducial high-flux beam model. However, chromospheric condensations with maximum electron densities of $n_e \approx 5 \times 10^{14}$ cm$^{-3}$ and optical depths $\tau \approx 1$ in the near wing of H$\alpha$ are consistent with the observed intensity of a broad spectrum in the Southern ribbon. Model similarities demonstrate that Fe I emission lines and the FUV continuum intensity can form at chromospheric heights during flares, but I find that the ratios of the NUV to FUV continuum intensities are generally too large in the models. This suggests that radiative-hydrodynamic models of chromospheric condensations cool through $T \approx 30,000$ K too rapidly. The larger than expected FUV continuum intensities are not nearly bright enough to explain recent stellar megaflare spectra from the Hubble Space Telescope.

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arXiv2025

Radio and Optical Flares on the dMe Flare Star EV Lac

We present the results of a coordinated campaign to observe radio and optical stellar flares from the nearby M dwarf flare star EV~Lac. From a total of 27 hours of radio and 29 hours of optical observations, we examine the correspondence of the action of accelerated electrons of different energies in two distinct regions of the stellar atmosphere. We find that out of 9 optical flares with suitable radio coverage, only four have plausible evidence for a radio response. Optical photometric properties cannot predict which flares will have a radio response. From flares with time-resolved optical spectroscopy available, optical-only flares have similar implied electron distributions, while those with radio responses better correlate with higher low-energy cutoffs. The optical flares with a radio response all exhibit a delay between the optical and radio peaks of $\approx$1-7 minutes, with the optical flare peaking earlier in all cases. This likely indicates multiple loops are involved in the event, and/or the different impacts on electrons trapped in a magnetic loop (producing radio emission), versus those directly precipitating from the loop (producing the optical flare). We also remark on the radio spectral index behavior at early times for the largest radio flare observed in this study, which we interpret as evidence for increased opacity from a chromospheric evaporation front.

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arXiv2025

A Seven-Day Multi-Wavelength Flare Campaign on AU Mic III: Quiescent and Flaring Properties of the X-ray Spectra and Chromospheric lines

We present the X-ray quiescent and flaring properties from a unique, 7-day multiwavelength observing campaign on the M1 flare star AU Mic. Combining the XMM-Newton X-ray spectra with the chromospheric line and broadband NUV and optical continuum observations provides a dataset that is one of the most comprehensive to date. We analyze the sample of 38 X-ray flares and study in detail the X-ray flare temperature ($T$) and emission measure (EM) evolutions of three largest flares with the X-ray flare energies of $>10^{33}$ erg. The $T-\mathrm{EM}$ evolution tracks and multi-wavelength emission evolutions of the largest-amplitude Neupert-type flare reveal that the so-called ``Flare H-R diagram" is consistent with thermal coronal flare emission evolution. The two other more gradual and longer duration X-ray flares are interpreted as having larger size scales. None of the 17 H$\alpha$ and H$\beta$ flares show clear blue/red wing asymmetries, including the ones associated with the potential X-ray dimming event previously reported. The above largest-amplitude Neupert flare shows clear symmetric H$\alpha$ and H$\beta$ broadenings with roughly $\pm$400 and $\pm$600 km s$^{-1}$, respectively, which are synchronized with the optical/NUV continuum emission evolution. Radiative hydrodynamic modeling results suggest that electron beam heating parameters that have been used to reproduce M-dwarf flare NUV/optical continuum emissions can reproduce these large broadenings of H$\alpha$ and H$\beta$ lines. These results suggest that these most energetic M-dwarf flares are associated with stronger magnetic field flux densities and larger size scales than solar flares but can be interpreted in terms of the standard flare model.

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arXiv2025

Unveiling Unprecedented Fine Structure in Coronal Flare Loops with the DKIST

We present the highest-resolution H$\alpha$ observations of a solar flare to date, collected during the decay phase of an X1.3-class flare on 8 August 2024 at 20:12 UT. Observations with the Visible Broadband Imager at the National Science Foundation's (NSF) Daniel K. Inouye Solar Telescope reveal dark coronal loop strands at unprecedented spatial resolution in the flare arcade above highly structured chromospheric flare ribbons. After surveying the 20 best-seeing images, we calculate a mean loop width near the top of the arcade of 48.2 km, with a minimum loop width of ~21 km and distribution mode of ~43 km. The distributions of loop widths observed by the DKIST in our study are often symmetric about the mean loop width. This is initial evidence that the DKIST may be capable of resolving the fundamental scale of coronal loops, although further investigation is required to confirm this result. We demonstrate that the resolving power of the DKIST represents a significant step towards advancing modern flare models and our understanding of fine structure in the coronal magnetic field.

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arXiv2025

Far-Ultraviolet Emission Line Investigation of Flares on AU Mic

The role of non-thermal proton energy transportation during solar and stellar flares is largely unknown; a better understanding of this physical process will allow us to rectify longstanding deficiencies in flare models. One way to detect the presence of non-thermal protons during flares is through the Orrall-Zirker (OZ) effect, proposed by Orrall & Zirker (1976), whereby an enhanced red wing appears in hydrogen emission lines (e.g., Lyman-$\alpha$ at 1215.67 angstroms). We analyze archival Hubble Space Telescope/Cosmic Origins Spectrograph G130M (1060 - 1360 angstroms) observations of the young M dwarf, AU Mic to search for evidence of OZ effect during the impulsive phase of six stellar flares with $E_\textrm{flare} \approx 10^{30 - 31}$ erg. While we found non-detections of the OZ effect, we note there is a pronounced blue enhancement in several C II and C III emission lines during one of the high-energy flares. We propose that either filament eruptions or chromospheric evaporation could be the mechanism driving this observed blue enhancement. We compare the far-ultraviolet (FUV) spectra to 1D radiative-hydrodynamic stellar flare models, which are unable to reproduce the blue enhancement and broadening in these cool flare lines. By completing a line-by-line analysis of the FUV spectrum of AU Mic, we provide further constraints on the physical mechanisms producing stellar flares on M dwarfs.

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arXiv2025

A 7-Day Multi-Wavelength Flare Campaign on AU Mic. II: Electron Densities and Kinetic Energies from High-Frequency Radio Flares

M dwarfs are the most common type of star in the solar neighborhood, and many exhibit frequent and highly energetic flares. To better understand these events across the electromagnetic spectrum, a campaign observed AU Mic (dM1e) over 7 days from the X-ray to radio regimes. Here, we present high-time-resolution light curves from the Karl G. Jansky Very Large Array (VLA) Ku band (12--18 GHz) and the Australia Telescope Compact Array (ATCA) K band (16--25 GHz), which observe gyrosynchrotron radiation and directly probe the action of accelerated electrons within flaring loops. Observations reveal 16 VLA and 3 ATCA flares of varying shapes and sizes, from a short (30 sec) spiky burst to a long-duration ($\sim$5 hr) decaying exponential. The Ku-band spectral index is found to often evolve during flares. Both rising and falling spectra are observed in the Ku-band, indicating optically thick and thin flares, respectively. Estimations from optically thick radiation indicate higher loop-top magnetic field strengths ($\sim$1 kG) and sustained electron densities ($\sim$10$^{6}$ cm$^{-3}$) than previous observations of large M-dwarf flares. We estimate the total kinetic energies of gyrating electrons in optically thin flares to be between 10$^{32}$ and 10$^{34}$ erg when the local magnetic field strength is between 500 and 700 G. These energies are able to explain the combined radiated energies from multi-wavelength observations. Overall, values are more aligned with modern radiative-hydrodynamic simulations of M-dwarf flares, and future modeling efforts will better constrain findings.

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arXiv2024

Rising Near-Ultraviolet Spectra in Stellar Megaflares

Flares from M-dwarf stars can attain energies up to $10^4$ times larger than solar flares but are generally thought to result from similar processes of magnetic energy release and particle acceleration. Larger heating rates in the low atmosphere are needed to reproduce the shape and strength of the observed continua in stellar flares, which are often simplified to a blackbody model from the optical to the far-ultraviolet (FUV). The near-ultraviolet (NUV) has been woefully undersampled in spectral observations despite this being where the blackbody radiation should peak. We present Hubble Space Telescope NUV spectra in the impulsive phase of a flare with $E_{\rm{TESS}} \approx 7.5 \times 10^{33}$ erg and a flare with $E_{\rm{TESS}} \approx 10^{35}$ erg and the largest NUV flare luminosity observed to date from an M star. The composite NUV spectra are not well represented by a single blackbody that is commonly assumed in the literature. Rather, continuum flux rises toward shorter wavelengths into the FUV, and we calculate that an optical $T=10^4$ K blackbody underestimates the short wavelength NUV flux by a factor of $\approx 6$. We show that rising NUV continuum spectra can be reproduced by collisionally heating the lower atmosphere with beams of $E \gtrsim 10$ MeV protons or $E \gtrsim 500$ keV electrons and flux densities of $10^{13}$ erg cm$^{-2}$ s$^{-1}$. These are much larger than canonical values describing accelerated particles in solar flares.

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arXiv2024

Searching for GEMS: Characterizing Six Giant Planets around Cool Dwarfs

Transiting giant exoplanets around M-dwarf stars (GEMS) are rare, owing to the low-mass host stars. However, the all-sky coverage of TESS has enabled the detection of an increasingly large number of them to enable statistical surveys like the \textit{Searching for GEMS} survey. As part of this endeavour, we describe the observations of six transiting giant planets, which includes precise mass measurements for two GEMS (K2-419Ab, TOI-6034b) and statistical validation for four systems, which includes validation and mass upper limits for three of them (TOI-5218b, TOI-5616b, TOI-5634Ab), while the fourth one -- TOI-5414b is classified as a `likely planet'. Our observations include radial velocities from the Habitable-zone Planet Finder on the Hobby-Eberly Telescope, and MAROON-X on Gemini-North, along with photometry and high-contrast imaging from multiple ground-based facilities. In addition to TESS photometry, K2-419Ab was also observed and statistically validated as part of the K2 mission in Campaigns 5 and 18, which provides precise orbital and planetary constraints despite the faint host star and long orbital period of $\sim 20.4$ days. With an equilibrium temperature of only 380 K, K2-419Ab is one of the coolest known well-characterized transiting planets. TOI-6034 has a late F-type companion about 40\arcsec~away, making it the first GEMS host star to have an earlier main-sequence binary companion. These confirmations add to the existing small sample of confirmed transiting GEMS.

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arXiv2024

Time-dependent Stellar Flare Models of Deep Atmospheric Heating

Optical flares have been observed from magnetically active stars for many decades; unsurprisingly, the spectra and temporal evolution are complicated. For example, the shortcomings of optically thin, static slab models have long been recognized when confronted with the observations. A less incorrect -- but equally simple -- phenomenological $T \approx 9000$ K blackbody model has instead been widely adopted in the absence of realistic (i.e., observationally-tested) time-dependent, atmospheric models that are readily available. We use the RADYN code to calculate a grid of 1D radiative-hydrodynamic stellar flare models that are driven by short pulses of electron-beam heating. The flare heating rates in the low atmosphere vary over many orders of magnitude in the grid, and we show that the models with high-energy electron beams compare well to the global trends in flux ratios from impulsive-phase stellar flare, optical spectra. The models also match detailed spectral line shape properties. We find that the pressure broadening and optical depths account for the broad components of the hydrogen Balmer $\gamma$ lines in a powerful flare with echelle spectra. The self-consistent formation of the wings and nearby continuum level provide insight into how high-energy electron beam heating evolves from the impulsive to the gradual decay phase in white-light stellar flares. The grid is publicly available, and we discuss possible applications.

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arXiv2024

A Multiwavelength Survey of Nearby M dwarfs: Optical and Near-Ultraviolet Flares and Activity with Contemporaneous TESS, Kepler/K2, \textit{Swift}, and HST Observations

We present a comprehensive multiwavelength investigation into flares and activity in nearby M~dwarf stars. We leverage the most extensive contemporaneous dataset obtained through the Transiting Exoplanet Sky Survey (TESS), Kepler/K2, the Neil Gehrels Swift Observatory (\textit{Swift}), and the Hubble Space Telescope (HST), spanning the optical and near-ultraviolet (NUV) regimes. In total, we observed 213 NUV flares on 24 nearby M dwarfs, with $\sim$27\% of them having detected optical counterparts, and found that all optical flares had NUV counterparts. We explore NUV/optical energy fractionation in M dwarf flares. Our findings reveal a slight decrease in the ratio of optical to NUV energies with increasing NUV energies, a trend in agreement with prior investigations on G-K stars' flares at higher energies. Our analysis yields an average NUV fraction of flaring time for M0-M3 dwarfs of 2.1\%, while for M4-M6 dwarfs, it is 5\%. We present an empirical relationship between NUV and optical flare energies and compare to predictions from radiative-hydrodynamic and blackbody models. We conducted a comparison of the flare frequency distribution (FFDs) of NUV and optical flares, revealing the FFDs of both NUV and optical flares exhibit comparable slopes across all spectral subtypes. NUV flares on stars affect the atmospheric chemistry, the radiation environment, and the overall potential to sustain life on any exoplanets they host. We find that early and mid-M dwarfs (M0-M5) have the potential to generate NUV flares capable of initiating abiogenesis.

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arXiv2024

Stellar flares

Magnetic storms on stars manifest as remarkable, randomly occurring changes of the luminosity over durations that are tiny in comparison to the normal evolution of stars. These stellar flares are bursts of electromagnetic radiation from X-ray to radio wavelengths, and they occur on most stars with outer convection zones. They are analogous to the events on the Sun known as solar flares, which impact our everyday life and modern technological society. Stellar flares, however, can attain much greater energies than those on the Sun. Despite this, we think that these phenomena are rather similar in origin to solar flares, which result from a catastrophic conversion of latent magnetic field energy into atmospheric heating within a region that is relatively small in comparison to normal stellar sizes. We review the last several decades of stellar flare research. We summarize multi-wavelength observational results and the associated thermal and nonthermal processes in flaring stellar atmospheres. Static and hydrodynamic models are reviewed with an emphasis on recent progress in radiation-hydrodynamics and the physical diagnostics in flare spectra. Thanks to their effects on the space weather of exoplanetary systems (and thus in our search for life elsewhere in the universe) and their preponderance in \emph{Kepler} mission data, white-light stellar flares have re-emerged in the last decade as a widely-impactful area of study within astrophysics. Yet, there is still much we do not understand, both empirically and theoretically, about the spectrum of flare radiation, its origin, and its time evolution. We conclude with several big-picture questions that are fundamental in our pursuit toward a greater understanding of these enigmatic stellar phonemena and, by extension, those on the Sun.

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arXiv2024

Deconstructing Photospheric Spectral Lines in Solar and Stellar Flares

During solar flares, spectral lines formed in the photosphere have been shown to exhibit changes to their profiles despite the challenges of energy transfer to these depths. Recent work has shown that deep-forming spectral lines are subject to significant contributions from regions above the photosphere throughout the flaring period, resulting in a composite emergent intensity profile from multiple layers of the atmosphere. We employ radiative-hydrodynamic and radiative transfer calculations to simulate the response of the solar/stellar atmosphere to electron beam heating and synthesize spectral lines of Fe I to investigate the line-of-sight velocity fields information available from Doppler shifts of the emergent intensity profile. By utilizing the contribution function to deconstruct the line profile shape into its constituent sources, we show that variations in the line profiles are primarily caused by changes in the chromosphere. Up-flows in this region were found to create blueshifts or "false" redshifts in the line core dependent on the relative contribution of the chromosphere compared to the photosphere. In extreme solar and stellar flare scenarios featuring explosive chromospheric condensations, red-shifted transient components can dominate the temporal evolution of the profile shape, requiring a tertiary component consideration to fully characterize. We conclude that deep-forming lines require a multi-component understanding and treatment, with different regions of the spectral line being useful for probing individual regions of the atmosphere's velocity flows.

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arXiv2023

An Optically Thin View of the Flaring Chromosphere: Nonthermal widths in a chromospheric condensation during an X-class solar flare

The bulk of solar flare energy is deposited in the chromosphere. Flare ribbons and footpoints in the chromosphere therefore offer great diagnostic potential of flare energy release and transport processes. High quality observations from the IRIS spacecraft have transformed our view of the Sun's atmospheric response to flares. Since most of the chromospheric lines observed by IRIS are optically thick, forward modelling is required to fully appreciate and extract the information they carry. Reproducing certain aspects of the Mg II lines remain frustratingly out of reach in state-of-the-art flare models, which are unable to satisfactorily reproduce the very broad line profiles. A commonly proposed resolution to this is to assert that very large values of `microturbulence' is present. We asses the validity of that approach by analysing optically thin lines in the flare chromosphere from the X-class flare SOL2014-10-25T17:08:00, using the derived value of nonthermal width as a constraint to our numerical models. A nonthermal width of the order 10~km~s$^{-1}$ was found within the short-lived red wing components of three spectral lines, with relatively narrow stationary components. Simulations of this flare were produced, and in the post-processing spectral synthesis we include within the downflows a microturbulence of 10~km~s$^{-1}$. While we can reproduce the O I 1355.598~Å line rather well, and we can capture the general shape and properties of the Mg II line widths, the synthetic lines are still too narrow.

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arXiv2023

Characterizing the Near-infrared Spectra of Flares from TRAPPIST-1 During JWST Transit Spectroscopy Observations

We present the first analysis of JWST near-infrared spectroscopy of stellar flares from TRAPPIST-1 during transits of rocky exoplanets. Four flares were observed from 0.6--2.8 $μ$m with NIRISS and 0.6--3.5 $μ$m with NIRSpec during transits of TRAPPIST-1b, f, and g. We discover P$α$ and Br$β$ line emission and characterize flare continuum at wavelengths from 1--3.5 $μ$m for the first time. Observed lines include H$α$, P$α$-P$ε$, Br$β$, He I $λ$0.7062$μ$m, two Ca II infrared triplet (IRT) lines, and the He I IRT. We observe a reversed Paschen decrement from P$α$-P$γ$ alongside changes in the light curve shapes of these lines. The continuum of all four flares is well-described by blackbody emission with an effective temperature below 5300 K, lower than temperatures typically observed at optical wavelengths. The 0.6--1 $μ$m spectra were convolved with the TESS response, enabling us to measure the flare rate of TRAPPIST-1 in the TESS bandpass. We find flares of 10$^{30}$ erg large enough to impact transit spectra occur at a rate of 3.6$\substack{+2.1 \\ -1.3}$ flare d$^{-1}$, $\sim$10$\times$ higher than previous predictions from K2. We measure the amount of flare contamination at 2 $μ$m for the TRAPPIST-1b and f transits to be 500$\pm$450 and 2100$\pm$400 ppm, respectively. We find up to 80% of flare contamination can be removed, with mitigation most effective from 1.0--2.4 $μ$m. These results suggest transits affected by flares may still be useful for atmospheric characterization efforts.

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