Imaging All the Sky All the Time in Search of Radio Exoplanets
All the magnetized planets in our solar system, including Earth, produce bright emission at low radio frequencies, predominantly originating in high magnetic latitudes and powered by magnetospheric currents. It has long been speculated that similar radio emission may be detectable from exoplanets orbiting nearby stars, potentially providing the first direct confirmation of the presence, strength and topology of exoplanet magnetospheres, and informing on their role in shielding the atmospheres of potentially habitable exoplanets. Despite 4 decades of searching, no exoplanet radio emission has been detected. Surprisingly, however, brown dwarfs have been found to produce both radio and optical emissions that are strikingly similar to the auroral emissions from solar system planets, albeit 100,000 times more luminous. I will discuss the radio emission from exoplanets and brown dwarfs with particular focus on the OVRO-LWA, a low frequency radio astronomy array located in the Owens Valley, California, that images the entire sky every 10 seconds to simultaneously monitor 4000 nearby stellar systems in the search for radio emission from exoplanets.
Technical Talk: Superluminal Motion of the Relativistic Jet of GW170817
The spectacular neutron star merger GW170817 was accompanied by radiation across the electromagnetic spectrum. Radio emission was last to be detected, but has proved decisive in establishing the morphology and energetics of the merger ejecta, as well as providing constraints on the circum-merger density. The initial slow continuous rise observed in the radio light curve, as well as in X-rays, requires the presence of a mildly relativistic, wide-angle outflow viewed on axis. This is consistent with the shock breakout of a cocoon of material produced by interaction of a relativistic jet with merger ejecta. Until very recently, the eventual fate of the jet was unknown. It may have eventually burrowed through the ejecta, producing a classical short gamma-ray burst, directed away from Earth, or become trapped (choked) in the ejecta. Recent VLBI results have finally broken the degeneracy between the different models, revealing superluminal motion of the radio afterglow that can only be produced by a very energetic narrowly collimated jet, adding substantial weight to the growing evidence linking neutron star mergers and short gamma-ray bursts.