# Detection of a Millimeter Flare From Proxima Centauri

February 26, 2018
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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

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