First Millimeter Flares Detected from ϵ Eridani with the Atacama Large Millimeter/submillimeter Array

• Published in: Astrophysical journal. Letters 2022-11, Vol.939 (1), p.L6
• Main Authors: Burton, Kiana, MacGregor, Meredith A., Osten, Rachel A.
• Format: Article
• Language: English
• Subjects: Arrays; Circumstellar disks; Debris disks; Flux density; Linear polarization; Luminosity; Radio astronomy; Radio telescopes; Solar flares; Stellar activity; Stellar flares; Submillimeter astronomy; Wavelengths
• ISSN: 2041-8205; 2041-8213
• DOI: 10.3847/2041-8213/ac9973

We report the detection of three large millimeter flaring events from the nearby Sun-like, ϵ Eridani, found in archival Atacama Large Millimeter/submillimeter Array (ALMA) 12 m and Atacama Compact Array observations at 1.33 mm taken from 2015 January 17 to 18 and 2016 October 24 to November 23, respectively. This is the first time that flares have been detected from a Sun-like star at millimeter wavelengths. The largest flare among our data was detected in the ALMA observations on 2015 January 17 from 20:09:10.4–21:02:49.3 UT with a peak flux density of 28 ± 7 mJy and a duration of 9 s. The peak brightness of the largest flare is 3.4 ± 0.9 × 10 14 erg s −1 Hz −1 , a factor of >50× times brighter than the star’s quiescent luminosity and >10× brighter than solar flares observed at comparable wavelengths. We find changes in the spectral index (F ν ∝ ν α ) at the flare peak, with α = 1.81 ± 1.94 and a lower limit on the fractional linear polarization ∣ Q / I ∣ = 0.08 ± 0.12. This positive spectral index is more similar to millimeter solar flares, differing from M-dwarf flares also detected at millimeter wavelengths that exhibit steeply negative spectral indices.