We report the detection of radio emission from the unusually active L5e + T7 binary 2MASS J13153094 - 2649513AB made with the Australian Telescope Compact Array .
Observations at 5.5 GHz reveal an unresolved source with a continuum flux of 370 \pm 50 \mu Jy , corresponding to a radio luminosity of L _ { rad } = { \nu } L _ { \nu } = ( 9 \pm 3 ) \times 10 ^ { 23 } erg s ^ { -1 } and \log _ { 10 } { L _ { rad } / L _ { bol } } = - 5.44 \pm 0.22 .
No detection is made at 9.0 GHz to a 5 \sigma limit of 290 \mu Jy , consistent with a power law spectrum S _ { \nu } \propto \nu ^ { - \alpha } with \alpha \gtrsim 0.5 .
The emission is quiescent , with no evidence of variability or bursts over 3 hr of observation , and no measurable polarization ( V/I < 34 % ) .
2MASS J1315 - 2649AB is one of the most radio-luminous ultracool dwarfs detected in quiescent emission to date , comparable in strength to other cool sources detected in outburst .
Its detection indicates no decline in radio flux through the mid-L dwarfs .
It is unique among L dwarfs in having strong and persistent H \alpha and radio emission , indicating the coexistence of a cool , neutral photosphere ( low electron density ) and a highly active chromosphere ( high electron density and active heating ) .
These traits , coupled with the system ’ s mature age and substellar secondary , makes 2MASS J1315 - 2649AB an important test for proposed radio emission mechanisms in ultracool dwarfs .