Resolved imaging of an extrasolar radiation belt around an ultracool dwarf
arxiv(2023)
摘要
Radiation belts are present in all large-scale Solar System planetary
magnetospheres: Earth, Jupiter, Saturn, Uranus, and Neptune. These persistent
equatorial zones of trapped high energy particles up to tens of MeV can produce
bright radio emission and impact the surface chemistry of close-in moons.
Recent observations confirm planet-like radio emission such as aurorae from
large-scale magnetospheric current systems on very low mass stars and brown
dwarfs. These objects, collectively known as ultracool dwarfs, also exhibit
quiescent radio emission hypothesized to trace stellar coronal flare activity
or extrasolar radiation belt analogs. Here we present high resolution imaging
of the ultracool dwarf LSR J1835+3259 demonstrating that this radio emission is
spatially resolved and traces a long-lived, double-lobed, and axisymmetric
structure similar in morphology to the Jovian radiation belts. Up to 18
ultracool dwarf radii separate the two lobes. This structure is stably present
in three observations spanning >1 year. We infer a belt-like distribution of
plasma confined by the magnetic dipole of LSR J1835+3259, and we estimate 15
MeV electron energies that are consistent with those measured in the Jovian
radiation belts. Though more precise constraints require higher frequency
observations, a unified picture where radio emissions in ultracool dwarfs
manifest from planet-like magnetospheric phenomena has emerged.
Submitted, under review.
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