Detection of 2−4 GHz Continuum Emission from ε Eridani

Detection of 2—4 GHz continuum emission associated with  Eri at epochs 1 (left) and 2 (right). From outer to inner, the solid gray contours label 2, 3, 4, 5, 6, 7, and 8 times the rms intensity, σIν = 3.4 µJy beam−1 . The dotted contours mark −3σIν and −2σIν levels. The red crosshairs in each panel indicate the Gaia DR2 position (with 1σ errors) of  Eri corrected for proper motion and annual parallax to the respective epochs. The black solid ellipse at the bottom left corner of each panel illustrates the VLA synthesized beam of size 0. 0063 × 0. 0044.

The nearby star ϵ Eridani has been a frequent target of radio surveys for stellar emission and extraterrestial intelligence. Using deep 2−4 GHz observations with the Very Large Array, we have uncovered a 29 μJy compact, steady continuum radio source coincident with ϵ Eridani to within 0.06 arcseconds (≲2σ; 0.2 au at the distance of the star).

Combining our data with previous high frequency continuum detections of ϵ Eridani, our observations reveal a spectral turnover at 6 GHz. We ascribe the 2−6 GHz emission to optically thick, thermal gyroresonance radiation from the stellar corona, with thermal free-free opacity likely becoming relevant at frequencies below 1 GHz. The steep spectral index (α≃2) of the 2−6 GHz spectrum strongly disfavors its interpretation as stellar wind-associated thermal bremsstrahlung (α≃0.6).

Attributing the entire observed 2−4 GHz flux density to thermal free-free wind emission, we thus, derive a stringent upper limit of 3×10−11 M⊙ yr−1 on the mass loss rate from ϵ Eridani. Finally, we report the non-detection of flares in our data above a 5σ threshold of 95 μJy. Together with the optical non-detection of the most recent stellar maximum expected in 2019, our observations postulate a likely evolution of the internal dynamo of ϵ Eridani.

Akshay Suresh, Shami Chatterjee, James M. Cordes, Timothy S. Bastian, Gregg Hallinan
Comments: 13 pages, 4 figures, accepted to ApJ
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Earth and Planetary Astrophysics (astro-ph.EP); Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:2010.05929 [astro-ph.SR] (or arXiv:2010.05929v1 [astro-ph.SR] for this version)
Submission history
From: Akshay Suresh
[v1] Mon, 12 Oct 2020 18:00:13 UTC (74 KB)
https://arxiv.org/abs/2010.05929
Astrobiology, SETI,

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