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Discovery of radio emission from the brown dwarf LP944-20


Brown dwarfs are not massive enough to sustain thermonuclear fusion of hydrogen at their centres, but are distinguished from gas-giant planets by their ability to burn deuterium1. Brown dwarfs older than 10 Myr are expected to possess short-lived magnetic fields2 and to emit radio and X-rays only very weakly from their coronae. An X-ray flare was recently detected3 on the brown dwarf LP944-20, whereas previous searches4,5,6,7 for optical activity (and one X-ray search1) yielded negative results. Here we report the discovery of quiescent and flaring radio emission from LP944-20, with luminosities several orders of magnitude larger than predicted by the empirical relation8,9 between the X-ray and radio luminosities that has been found for many types of stars. Interpreting the radio data within the context of synchrotron emission, we show that LP944-20 has an unusually weak magnetic field in comparison to active M-dwarf stars10,11, which might explain the previous null optical4,5,6,7 and X-ray1 results, as well as the strength of the radio emissions compared to those at X-ray wavelengths.

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Figure 1: Light curves for the flaring radio emission from LP944-20.


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We thank B. Clark for the allocation of ad hoc VLA time. We also thank S. R. Kulkarni, D. E. Gary and R. Sari for helpful discussions. The initial observation of LP944-20 was undertaken as part of the National Radio Astronomy Observatory (NRAO) VLA Summer Program funded by the National Science Foundation (NSF). The National Radio Astronomy Observatory is a facility of the NSF operated under cooperative agreement by Associated Universities, Inc.

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Correspondence to E. Berger.

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Berger, E., Ball, S., Becker, K. et al. Discovery of radio emission from the brown dwarf LP944-20. Nature 410, 338–340 (2001).

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