Radio emission in ultracool dwarfs: the nearby substellar triple system VHS 1256$-$1257

Abstract

With the purpose to investigate the radio emission of new ultracool objects, we carried out a targeted search in the recently discovered system VHS J125601.92$-$125723.9 (hereafter VHS 1256$-$1257); this system is composed by an equal-mass M7.5 binary and a L7 low-mass substellar object located at only 15.8\,pc. We observed in phase-reference mode the system VHS 1256$-$1257 with the Karl G. Jansky Very Large Array at $X$- and $L$- band and with the European VLBI Network at $L$-band in several epochs during 2015 and 2016. We discovered radio emission at $X$-band spatially coincident with the equal-mass M7.5 binary with a flux density of 60 $\mu$Jy. We determined a spectral index $\alpha =-1.1\pm 0.3$ between 8 and 12 GHz, suggesting that non-thermal, optically-thin, synchrotron or gyrosynchrotron radiation is responsible for the observed radio emission. Interestingly, no signal is seen at $L$-band where we set a 3-$\sigma$ upper limit of 20 $\mu$Jy. This might be explained by strong variability of the binary or self-absorption at this frequency. By adopting the latter scenario and gyrosynchrotron radiation, we constrain the turnover frequency to be in the interval 5--8.5 GHz, from which we infer the presence of kG-intense magnetic fields in the M7.5 binary. Our data impose a 3-$\sigma$ upper bound to the radio flux density of the L7 object of 9 $\mu$Jy at 10\,GHz.

6 pages, 4 figures. Accepted for publication in A&A

References in corpus (7)

• New evolutionary models for pre-main sequence and main sequence low-mass stars down to the hydrogen-burning limit
• Discovery of a young planetary mass companion to the nearby M dwarf VHS J125601.92-125723.9
• A Panchromatic View of Brown Dwarf Aurorae
• Steady and Transient Radio Emission from Ultracool Dwarfs
• Radio Constraints on Activity in Young Brown Dwarfs
• Variable Radio Emission from the Young Stellar Host of a Hot Jupiter
• Thermal Infrared Imaging and Atmospheric Modeling of VHS J125601.92-125723.9 b: Evidence for Moderately Thick Clouds and Equilibrium Carbon Chemistry in a Hierarchical Triple System

Cited by in corpus (9)

• Radio Stars: from kHz to THz
• On the Correlation between L Dwarf Optical and Infrared Variability and Radio Aurorae
• The Occurrence Rate of Quiescent Radio Emission for Ultracool Dwarfs using a Generalized Semi-Analytical Bayesian Framework
• Radio Emission from Binary Ultracool Dwarf Systems
• Radio emission in a nearby ultracool dwarf binary: a multi-frequency study
• The milliarcsecond-scale radio structure of AB Dor A
• Detection of photometric variability in the very low-mass binary VHS J1256-1257AB using TESS and Spitzer
• The Potential of Detecting Radio-flaring Ultracool Dwarfs at L band in the FAST Drift-scan Survey
• New constraints on the presence of debris disks around G 196-3 B and VHS J125601.92-125723.9 b