Radio emission in a nearby, ultra-cool dwarf binary: A multifrequency study

DOI: 
10.1051/0004-6361/202142260
Publication date: 
08/04/2022
Main author: 
Climent, J. B.
IAA authors: 
Pérez-Torres, M.
Authors: 
Climent, J. B.;Guirado, J. C.;Zapatero Osorio, M. R.;Zakhozhay, O. V.;Pérez-Torres, M.;Azulay, R.;Gauza, B.;Rebolo, R.;Béjar, V. J. S.;Martín-Pintado, J.;Lefèvre, C.
Journal: 
Astronomy and Astrophysics
Publication type: 
Article
Volume: 
660
Pages: 
A65
Abstract: 
Context. The substellar triple system VHS J125601.92−125723.9 (hereafter VHS 1256−1257) is composed of an equal-mass M7.5 brown dwarf binary and an L7 low-mass substellar object. In Guirado et al. (2018, A&amp;A, 610, A23) we published the detection of radio emission at 8.4 GHz coming from the central binary and making it an excellent target for further observations. <BR /> Aims: We aim to identify the origin of the radio emission occurring in the central binary of VHS 1256−1257 while discussing the expected mechanisms involved in the radio emission of ultra-cool dwarfs. <BR /> Methods: We observed this system with the Karl G. Jansky Very Large Array, the European very-long-baseline interferometry (VLBI) Network, the enhanced Multi-Element Remotely Linked Interferometer Network, the NOrthern Extended Millimeter Array, and the Atacama Large Millimetre Array at frequencies ranging from 5 GHz up to 345 GHz in several epochs during 2017, 2018, and 2019. <BR /> Results: We found radio emission at 6 GHz and 33 GHz coincident with the expected position of the central binary of VHS 1256−1257. The Stokes I density fluxes detected were 73 ± 4 μJy and 83 ± 13 μJy, respectively, with no detectable circular polarisation or pulses. No emission is detected at higher frequencies (230 GHz and 345 GHz), nor at 5 GHz with VLBI arrays. The emission appears to be stable over almost three years at 6 GHz. To explain the constraints obtained both from the detections and non-detections, we considered multiple scenarios including thermal and nonthermal emission, and different contributions from each component of the binary. <BR /> Conclusions: Our results can be well explained by nonthermal gyrosynchrotron emission originating at radiation belts with a low plasma density (n<SUB>e</SUB> = 300−700 cm<SUP>−3</SUP>), a moderate magnetic field strength (B ≈ 140 G), and an energy distribution of electrons following a power-law (dN/dE ∝ E<SUP>−δ</SUP>) with δ fixed at 1.36. These radiation belts would need to be present in both components and also be viewed equatorially.
Database: 
ADS
SCOPUS
URL: 
https://ui.adsabs.harvard.edu/#abs/2022A&A...660A..65C/abstract
ADS Bibcode: 
2022A&A...660A..65C
Keywords: 
brown dwarfs;radio continuum: stars;submillimeter: stars;radiation mechanisms: general;magnetic fields;techniques: interferometric