Peculiar radio$-$X-ray relationship in active stars

Abstract

The empirical relationship between the non-thermal 5GHz radio luminosity and the soft X-ray luminosity of active stellar coronae, canonically called the Güdel-Benz relationship (Güdel & Benz 1993), has been a cornerstone of stellar radio astronomy as it explicitly ties the radio emission to the coronal heating mechanisms. The relationship extends from microflares on the Sun to the coronae of the most active stars suggesting that active coronae are heated by a flare-like process (Benz & Güdel 1994). The relationship is thought to originate from a consistent partition of the available flare energy into relativistic charges, that emit in the radio-band via the incoherent gyrosynchrotron mechanism, and heating of the bulk coronal plasma, that emits in the X-ray band via the Bremsstrahlung mechanism. Consequently, coherent emission from stellar and sub-stellar objects is not expected to adhere to this empirical relationship, as is observed in ultracool dwarf stars and brown dwarfs. Here we report a population of radio-detected chromospherically active stars that surprisingly follows the Güdel-Benz relationship despite their radio emission being classified as coherent emission by virtue of its high circularly polarised fraction and high brightness temperature. Our results prompt a re-examination of the physics behind the Güdel-Benz relationship, its implication for the mechanism of coronal heating and particle acceleration in active stars and the phenomenological connection between solar and stellar flares.

Under review, ApJL

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Cited by in corpus (9)

• V-LoTSS: The Circularly-Polarised LOFAR Two-metre Sky Survey
• Sporadic radio pulses from a white dwarf binary at the orbital period
• Detection of radio emission from stars via proper-motion searches
• Plausible association of distant late M dwarfs with low-frequency radio emission
• Discovery and origin of the radio emission from the multiple stellar system KQVel
• Spectral features and variable circular polarisation in the radio emission from the pre-cataclysmic variable QS Vir
• Radio emission from flaring stars and brown dwarfs
• First detection of variable radio emission originating from the infant planetary system V1298 Tau
• Spectroscopic Characterization of LOFAR Radio-emitting M dwarfs