Detection of a Millimeter Flare From Proxima Centauri

Meredith A. MacGregor, Alycia J. Weinberger, David J. Wilner, Adam F. Kowalski, Steven R. Cranmer
(Submitted on 22 Feb 2018)

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 $|Q/I| = 0.19\pm0.02$. Since the ACA observations do not show any quiescent excess emission, we conclude that there is no need to invoke the presence of a dust belt at $1-4$ AU. We also posit that the slight excess flux density of $101\pm9$ $\mu$Jy observed in the 12-m observations compared to the photospheric flux density of $74\pm4$ $\mu$Jy extrapolated from infrared wavelengths may be due to coronal heating from continual smaller flares, as is seen for AU Mic, another nearby, well-studied, M dwarf flare star. If this is true, then the need for warm dust at $\sim0.4$ AU is also removed.

Comments:    7 pages, 3 figures; Submitted to ApJL 2017 December 22; Accepted to ApJL 2018 February 5
Subjects:    Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as:    arXiv:1802.08257 [astro-ph.EP] (or arXiv:1802.08257v1 [astro-ph.EP] for this version)
Submission history
From: Meredith MacGregor
[v1] Thu, 22 Feb 2018 19:00:01 GMT (326kb)
https://arxiv.org/abs/1802.08257