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

At 1.3 parsecs away, Proxima Centauri is the closest M dwarf to Earth which also hosts a planetary system, creating the best opportunity to probe the effects of M dwarf activity levels on exoplanetary atmospheres. We explore the frequency of stellar flares at millimeter wavelengths from Proxima Centauri using ALMA. These results are part of a large multiwavelength observing campaign with roughly 40 hours of simultaneous observations spanning millimeter to X-ray wavelengths. The first results of this campaign (MacGregor et al., 2021) caught the brightest flare ever recorded from Proxima Cen, where the star brightened by a factor of >1000 times in the millimeter and >14000 in the FUV as observed by ALMA and the Hubble Space Telescope (HST), respectively. These results also revealed a correlation between the millimeter and FUV continuum emission. Here, we analyze all of the available ALMA data from this campaign to measure the first flare frequency distribution at millimeter wavelengths. These ALMA observations considerably increase the sample of millimeter flares observed to date, allowing us to improve data analysis techniques to identify small flares and better constrain stellar millimeter flaring properties. We also further explore the connection between the FUV and millimeter continuum emission to investigate if millimeter emission could serve as a proxy for FUV stellar flaring emission.