A Single Power Law For The TRAPPIST-1 Flare Distribution Across Four Orders Of Magnitude In Energy

TRAPPIST-1 is an ultra-cool dwarf that flares frequently. These flares shape the surrounding planets’ high-energy irradiation environments, with consequences for atmospheric chemistry and escape, and they can contaminate transmission spectroscopy of those planets.

A quantitative flare-frequency distribution (FFD) spanning the full energy range is therefore essential for both interpreting JWST spectra and modeling the planets’ irradiation histories.

Here we present a unified FFD over four orders of magnitude in energy by jointly analyzing ≈87 hr of JWST/NIRISS and JWST/NIRSpec time-series spectroscopy together with ≈74 days of Kepler/K2 photometry. To enable a consistent comparison across these heterogeneous datasets, we convert all events to energies in the TESS bandpass. For the Kepler-to-TESS conversion we adopt a cooler flare continuum appropriate for ultra-cool dwarfs (T_flare=3500,K).

After correcting for flare-detection sensitivities, the combined JWST+K2 cumulative FFD is consistent with a single power law, N(≥ET_ESS)∝E^−β_TESS, with β=0.753 over E_TESS≃10²⁹-10³³ erg. The slope of the distribution indicates that the time-averaged flare energy budget is dominated by rare, high-energy events rather than by the more numerous low-energy flares. This bandpass-consistent FFD provides a practical basis for JWST transit-spectroscopy planning and for modeling the flare-driven irradiation environment of the TRAPPIST-1 planets.

Valeriy Vasilyev, Alexander I. Shapiro, Nadiia Kostogryz, Chia-Lung Lin, Greg Kopp, Benjamin V. Rackham, Astrid M. Veronig, Olivia Lim, Julien de Wit, Daniel Apai, Laurent Gizon, Sami K. Solanki

Comments: submitted to ApJL
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2605.05468 [astro-ph.SR] (or arXiv:2605.05468v1 [astro-ph.SR] for this version)
https://doi.org/10.48550/arXiv.2605.05468
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Submission history
From: Valeriy Vasilyev
[v1] Wed, 6 May 2026 21:48:44 UTC (492 KB)
https://arxiv.org/abs/2605.05468
Astrobiology, heliophysics, space weather,