The Mouse That Squeaked: A Small Flare from Proxima Cen Observed in the Millimeter, Optical, and Soft X-Ray with Chandra and ALMA

Howard, Ward S.; MacGregor, Meredith A.; Osten, Rachel A.; Forbrich, Jan; Cranmer, Steven R.; Tristan, Isaiah; Weinberger, Alycia J.; Youngblood, Allison; Barclay, Thomas; Loyd, R. O. Parke; Shkolnik, Evgenya L.; Zic, Andrew; Wilner, David J.

doi:10.3847/1538-4357/ac9134

Cited by 9 publications

(2 citation statements)

References 68 publications

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“…However, if UV Ceti exhibited similar millimeter flares, these fast flares would occur too infrequently to expect a detection in an observation of the length we have in the ALMA archive. Millimeter flares on M dwarfs have been detected with timescales ranging from seconds (MacGregor et al 2018(MacGregor et al , 2020(MacGregor et al , 2021Howard et al 2022) to tens of minutes or longer 4 (Guns et al 2021;Naess et al 2021). It is possible that the millimeter variability we observe on UV Ceti is part of a gradual flare.…”

Section: Millimeter Emissionmentioning

confidence: 85%

Radio Emission from the Magnetically Active M Dwarf UV Ceti from 1 to 105 GHz

Plant,

Hallinan,

Bastian

2024

ApJ

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BL and UV Ceti are a nearby (2.7 pc) binary system with similar masses, spectral types, and rapid rotation rates, but very different magnetic activity. UV Ceti’s much stronger large-scale magnetic field may cause this difference, highlighting key unanswered questions about dynamo processes in fully convective objects. Here, we present multiepoch characterization of the radio spectrum of UV Ceti spanning 1–105 GHz, exhibiting flared emission similar to coronal activity, auroral-like emission analogous to planetary magnetospheres, and slowly varying persistent emission. Radio observations are a powerful means to probe the role that the large-scale magnetic field of UV Ceti has in nonthermal particle acceleration because radio-frequency phenomena result from both the activity of small-scale field features as well as large-scale auroral current systems. We find temporal variability at all bands observed, and a hint of rotational modulation in the degree of circular polarization up to 40 GHz. The persistent component of the emission is fairly constant from 1 to 105 GHz, making optically thick emission or optically thin gyrosynchrotron from electrons with an isotropic pitch angle distribution unlikely. We discuss the possibility of emission mechanisms analogous to Jupiter’s radiation belts.

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Section: Millimeter Emissionmentioning

confidence: 85%

Radio Emission from the Magnetically Active M Dwarf UV Ceti from 1 to 105 GHz

Plant,

Hallinan,

Bastian

2024

ApJ

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“…Stellar flares are extreme radiation outbursts from the surfaces of stars, analogous to solar flares commonly observed on the Sun, whereby stored magnetic energy accelerates charged particles through surrounding stellar plasma, radiating brightly across the electromagnetic spectrum (Dulk 1985;Feigelson & Montmerle 1999;Güdel 2002;Fletcher et al 2011;Candelaresi et al 2014). At millimeter wavelengths, stellar variability campaigns have mostly targeted nearby main sequence M-type stars, such as Proxima Centauri and AU Mic, finding extreme flaring events on timescales of 1-10 s (MacGregor et al 2020(MacGregor et al , 2021Howard et al 2022). A handful of millimeter flares have also been detected from the closest Sun-like star, ò Eridani (Burton et al 2022), and a range of other M-and K-type stars from millimeter survey telescopes (e.g., the South Pole Telescope and the Atacama Cosmology Telescope; see, e.g., Guns et al 2021;Naess et al 2021).…”

Section: Introductionmentioning

confidence: 99%

SMA Detection of an Extreme Millimeter Flare from the Young Class III Star HD 283572

Lovell,

Keating,

Wilner

et al. 2024

ApJL

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We present evidence of variable 1.3 mm emission from the 1 to 3 Myr, spectral-type G2–G5 class III young stellar object (YSO), HD 283572. HD 283572 was observed on eight dates with the Submillimeter Array between 2021 December and 2023 May, with a total on-source time of 10.2 hr, probing a range of timescales down to 5.2 s. Averaging all data obtained on 2022 January 17 shows a 4.4 mJy (8.8σ) point source detection with a negative spectral index (α = −2.7 ± 1.2), with peak emission rising to 13.8 mJy in one 3 minute span, and 25 mJy in one 29.7 s integration (L ν = 4.7 × 1017 erg s−1 Hz−1). Combining our data for the other seven dates shows no detection, with an rms noise of 0.24 mJy beam−1. The stochastic millimeter enhancements on time frames of seconds–minutes–hours with negative spectral indices are most plausibly explained by synchrotron or gyrosynchrotron radiation from stellar activity. HD 283572's 1.3 mm lightcurve has similarities with variable binaries, suggesting HD 283572's activity may have been triggered by interactions with an as-yet undetected companion. We additionally identify variability of HD 283572 at 10 cm, from VLASS data. This study highlights the challenges of interpreting faint millimeter emission from evolved YSOs that may host tenuous disks, and suggests that a more detailed temporal analysis of spatially unresolved data is generally warranted. The variability of class III stars may open up new ground for understanding the physics of flares in the context of terrestrial planet formation.

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Stellar flares

Kowalski

2024

Living Rev Sol Phys

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Magnetic storms on stars manifest as remarkable, randomly occurring changes of the luminosity over durations that are tiny in comparison to the normal evolution of stars. These stellar flares are bursts of electromagnetic radiation from X-ray to radio wavelengths, and they occur on most stars with outer convection zones. They are analogous to the events on the Sun known as solar flares, which impact our everyday life and modern technological society. Stellar flares, however, can attain much greater energies than those on the Sun. Despite this, we think that these phenomena are rather similar in origin to solar flares, which result from a catastrophic conversion of latent magnetic field energy into atmospheric heating within a region that is relatively small in comparison to normal stellar sizes. We review the last several decades of stellar flare research. We summarize multi-wavelength observational results and the associated thermal and nonthermal processes in flaring stellar atmospheres. Static and hydrodynamic models are reviewed with an emphasis on recent progress in radiation-hydrodynamics and the physical diagnostics in flare spectra. Thanks to their effects on the space weather of exoplanetary systems (and thus in our search for life elsewhere in the universe) and their preponderance in Kepler mission data, white-light stellar flares have re-emerged in the last decade as a widely-impactful area of study within astrophysics. Yet, there is still much we do not understand, both empirically and theoretically, about the spectrum of flare radiation, its origin, and its time evolution. We conclude with several big-picture questions that are fundamental in our pursuit toward a greater understanding of these enigmatic stellar phenomena and, by extension, those on the Sun.

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The Mouse That Squeaked: A Small Flare from Proxima Cen Observed in the Millimeter, Optical, and Soft X-Ray with Chandra and ALMA

Cited by 9 publications

References 68 publications

Radio Emission from the Magnetically Active M Dwarf UV Ceti from 1 to 105 GHz

Radio Emission from the Magnetically Active M Dwarf UV Ceti from 1 to 105 GHz

SMA Detection of an Extreme Millimeter Flare from the Young Class III Star HD 283572

Stellar flares

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