Detection of a Millimeter Flare From Proxima Centauri

Understand

We present new analyses of ALMA 12-m and ACA observations at 233 GHz (1.3 mm) of the Proxima Centauri system with sensitivities of 9.5 and 47 $\mu$Jy beam$^{-1}$, respectively, taken from 2017 January 21 through 2017 April 25.

• These analyses reveal that the star underwent a significant flaring event during one of the ACA observations on 2017 March 24.
• The complete event lasted for approximately 1 minute and reached a peak flux density of $100\pm4$ mJy, nearly a factor of $1000\times$ brighter than the star's quiescent emission.
• At the flare peak, the continuum emission is characterized by a steeply falling spectral index with frequency, $F_\nu \propto \nu^\alpha$ with $\alpha = -1.77\pm0.45$, and a lower limit on the fractional linear polarization of $|Q/I| = 0.19\pm0.02$.