Astronomy & Telescopes

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

By Keith Cowing
Status Report
astro-ph.SR
May 9, 2026
Filed under , , , , , , , , , , , , , ,
A Single Power Law For The TRAPPIST-1 Flare Distribution Across Four Orders Of Magnitude In Energy
Cumulative flare-frequency distribution of TRAPPIST-1. The cumulative occurrence rate ν(≥ ETESS) is shown as a function of TESS-band flare energy. The K2 FFD from this work is shown in blue, the observed JWST FFD in magenta, and the JWST FFD after applying the injection–recovery completeness correction in purple. The light green curve shows the solar soft X-ray flare distribution, derived from the catalog of N. Plutino et al. (2023) and converted to the TESS band assuming Tflare = 9000 K (M. Kretzschmar 2011). The corrected JWST and K2 samples are consistent with a single power law in ETESS over ∼4 orders of magnitude (dashed black line), with the gray band indicating the 1σ bootstrap uncertainty. At flare energies above ∼ 1029 erg, the flare occurrence rate of TRAPPIST-1 exceeds that of the Sun. — astro-ph.SR

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.

This artist’s impression displays TRAPPIST-1 and its planets reflected in a surface. The potential for water on each of the worlds is also represented by the frost, water pools, and steam surrounding the scene. © NASA/R. Hurt/T. Pyle
This artist’s impression displays TRAPPIST-1 and its planets reflected in a surface. The potential for water on each of the worlds is also represented by the frost, water pools, and steam surrounding the scene. © NASA/R. Hurt/T. Pyle

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 (Tflare=3500,K).

After correcting for flare-detection sensitivities, the combined JWST+K2 cumulative FFD is consistent with a single power law, N(≥ETESS)∝E−βTESS, with β=0.753 over ETESS≃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,

Keith Cowing

Biologist, Explorers Club Fellow, ex-NASA Space Biologist and Payload integrator, Editor of NASAWatch.com and Astrobiology.com, Lapsed climber, Explorer, Synaesthete, Former Challenger Center board member 🖖🏻

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