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arXiv · 2503.21890

The Proxima Centauri Campaign -- First Constraints On Millimeter Flare Rates from ALMA

Kiana Burton·Meredith A. MacGregor·Rachel A. Osten·Ward S. Howard·Alycia J. Weinberger·Evgenya Shkolnik·David J. Wilner·Jan Forbrich·Thomas Barclay
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Abstract

Proxima Centauri (Cen) has been the subject of many flaring studies due to its proximity and potential to host habitable planets. The discovery of millimeter flares from this M dwarf with ALMA has opened a new window into the flaring process and the space-weather environments of exoplanets like Proxima b. Using a total of ~50 hours of ALMA observations of Proxima Cen at 1.3 mm (233 GHz), we add a new piece to the stellar flaring picture and report the first cumulative flare frequency distribution (FFD) at millimeter wavelengths of any M dwarf. We detect 463 flares ranging from energies 10$^{24}$ erg to 10$^{27}$ erg. The brightest and most energetic flare in our sample reached a flux density of 119 $\pm$ 7 mJy, increasing by a factor of 1000x the quiescent flux, and reaching an energy of 10$^{27}$ erg in the ALMA bandpass, with t$_{1/2}$~16s. From a log-log linear regression fit to the FFD, we obtain a power law index of $\alpha_\mathrm{FFD}$ = 2.92 $\pm$ 0.02, much steeper than $\alpha_\mathrm{FFD}$ values (~2) observed at X-ray to optical wavelengths. If millimeter flare rates are predictive of flare rates at extreme-UV wavelengths, the contribution of small flares to the radiation environment of Proxima b may be much higher than expected based on the shallower power-law slopes observed at optical wavelengths.

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Kiana Burton, Meredith A. MacGregor, Rachel A. Osten, Ward S. Howard, Alycia J. Weinberger, Evgenya Shkolnik, David J. Wilner, Jan Forbrich, Thomas Barclay. 2025-03-27. The Proxima Centauri Campaign -- First Constraints On Millimeter Flare Rates from ALMA. https://doi.org/10.3847/1538-4357%2Fada5f2

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