The Proxima Centauri Campaign—First Constraints on Millimeter Flare Rates from ALMA | CU Experts

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 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 1024 to 1027 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 1027 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.

Burton K; MacGregor MA; Osten RA; Howard WS; Weinberger AJ; Shkolnik E; Wilner DJ; Forbrich J; Barclay T

VIVO