The Proxima Centauri Campaign—First Constraints on Millimeter Flare Rates from ALMA Article Swipe
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· 2025
· Open Access
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· DOI: https://doi.org/10.3847/1538-4357/ada5f2
· OA: W4408529121
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 Atacama Large Millimeter/submillimeter Array (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 hr 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 to 10 27 erg. The brightest and most energetic flare in our sample reached a flux density of 119 ± 7 mJy, increasing by a factor of 1000× the quiescent flux, and reaching an energy of 10 27 erg in the ALMA bandpass, with t 1/2 ≈ 16 s. From a log–log linear regression fit to the FFD, we obtain a power-law index of α FFD = 2.92 ± 0.02, much steeper than α 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.
