Detection of 2$-$4 GHz Continuum Emission from $\epsilon$ Eridani

Abstract

The nearby star $\epsilon \mathrm{Eridani}$ has been a frequent target of radio surveys for stellar emission and extraterrestial intelligence. Using deep $2-4\mathrm{GHz}$ observations with the Very Large Array, we have uncovered a $29\mu \mathrm{Jy}$ compact, steady continuum radio source coincident with $\epsilon \mathrm{Eridani}$ to within 0.06 arcseconds ($\lesssim 2\sigma$; 0.2 au at the distance of the star). Combining our data with previous high frequency continuum detections of $\epsilon \mathrm{Eridani}$, our observations reveal a spectral turnover at $6\mathrm{GHz}$. We ascribe the $2-6\mathrm{GHz}$ emission to optically thick, thermal gyroresonance radiation from the stellar corona, with thermal free-free opacity likely becoming relevant at frequencies below $1\mathrm{GHz}$. The steep spectral index ($\alpha \simeq 2$) of the $2-6\mathrm{GHz}$ spectrum strongly disfavors its interpretation as stellar wind-associated thermal bremsstrahlung ($\alpha \simeq 0.6$). Attributing the entire observed $2-4\mathrm{GHz}$ flux density to thermal free-free wind emission, we thus, derive a stringent upper limit of $3\times 10^{-11}{M}_{\odot }{\mathrm{yr}}^{-1}$ on the mass loss rate from $\epsilon \mathrm{Eridani}$. Finally, we report the non-detection of flares in our data above a $5\sigma$ threshold of $95\mu \mathrm{Jy}$. 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 $\epsilon \mathrm{Eridani}$.

13 pages, 4 figures, accepted to ApJ

References in corpus (13)

• The NumPy array: a structure for efficient numerical computation
• The Gaia mission
• Improved Age Estimation for Solar-Type Dwarfs Using Activity-Rotation Diagnostics
• The Extrasolar Planet epsilon Eridani b - Orbit and Mass
• Revising the ages of planet-hosting stars
• Magnetic Activity Cycles in the Exoplanet Host Star epsilon Eridani
• Stellar Coronal Mass Ejections I. Estimating occurrence frequencies and mass-loss rates
• The Northern Arc of $\epsilon$ Eridani's Debris Ring as Seen by ALMA
• Radio emission and mass loss rate limits of four young solar-type stars
• First Detection of Thermal Radio Emission from Solar-Type Stars with the Karl G. Jansky Very Large Array
• MAMBO image of the debris disk around epsilon Eridani : robustness of the azimuthal structure
• Magnetic field measurements of $\epsilon$ Eridani from Zeeman broadening
• Transient Events in Archival Very Large Array Observations of the Galactic Center

Cited by in corpus (9)

• Multi-instrumental view of magnetic fields and activity of $\epsilon$ Eridani with SPIRou, NARVAL, and TESS
• The clumpy structure of $\epsilon$ Eridani's debris disc revisited by ALMA
• Coronal mass ejections and type II radio emission variability during a magnetic cycle on the solar-type star $\epsilon$ Eridani
• EMISSA -- Exploring Millimeter Indicators of Solar-Stellar Activity I. The Initial mm-cm Main Sequence Star Sample
• Radio emission in a nearby ultracool dwarf binary: a multi-frequency study
• EMISSA -- Exploring Millimetre Indicators of Solar-Stellar Activity II. Towards a robust indicator of stellar activity
• First Millimeter Flares Detected from Epsilon Eridani with ALMA
• Comparison of solar multifrequency microwave data with other solar indices for understanding solar and stellar microwave data
• Role of non-thermal processes in the quiescent and active millimeter spectrum of a young M dwarf