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

Context. The substellar triple system VHS J125601.92−125723.9 (hereafter 1256−1257) is composed of an equal-mass M7.5 brown dwarf binary and L7 low-mass object. In Guirado et al. (2018, A&A, 610, A23) we published the detection radio emission at 8.4 GHz coming from central making it excellent target for further observations. Aims. We aim to identify origin occurring in 1256−1257 while discussing expected mechanisms involved ultra-cool dwarfs. Methods. observed this with Karl G. Jansky Very Large Array, European very-long-baseline interferometry (VLBI) Network, enhanced Multi-Element Remotely Linked Interferometer NOrthern Extended Millimeter Atacama Millimetre Array frequencies ranging 5 up 345 several epochs during 2017, 2018, 2019. Results. found 6 33 coincident position 1256−1257. Stokes I density fluxes detected were 73 ± 4 μJy 83 13 μJy, respectively, no detectable circular polarisation or pulses. No higher (230 GHz), nor VLBI arrays. appears be stable over almost three years GHz. To explain constraints obtained both detections non-detections, considered multiple scenarios including thermal nonthermal emission, different contributions each component binary. Conclusions. Our results can well explained by gyrosynchrotron originating radiation belts a low plasma ( n e = 300−700 cm −3 ), moderate magnetic field strength B ≈ 140 G), energy distribution electrons following power-law (d N /d E ∝ − δ ) fixed 1.36. These would need present components also viewed equatorially.