Mysterious Radio Flashes from Outer Space

A direct localization of a fast radio burst and its host fast radio bursts are astronomical radio flashes of unknown physical nature with durations of milliseconds. Their dispersive arrival times suggest an extragalactic origin and imply radio luminosities that are orders of magnitude larger than those of all known short-duration radio transients. So far all fast radio bursts have been detected with large single-dish telescopes with arcminute (a unit of angular distance equal to 160 of one degree, 1/3600 of a degree) localizations, and attempts to identify their counterparts (source or host galaxy) have relied on the contemporaneous variability of field sources or the presence of peculiar field stars or galaxies. 

These attempts have not resulted in an unambiguous association with a host or multi-wavelength counterpart. Here we report the subarcsecond (less than an arcsecond which is a unit of angular distance equal to a 160th of a arcminute 1/3600 of a minute) localization of the fast radio burst FRB 121102, the only known repeating burst source, using high-time-resolution radio interferometric observations that directly image the bursts. Our precise localization reveals that FRB 121102 originates within 100 milliarcseconds of a faint 180-microJansky persistent radio source with a continuum spectrum that is consistent with nonthermal emission, and a faint (twenty-fifth magnitude) optical counterpart. The flux density of the persistent radio source varies by around ten per cent on day timescales, and very long baseline radio interferometry yields an angular size of less than 1.7 milliarcseconds.

Our observations are inconsistent with the fast radio burst having a Galactic origin or its source being located within a prominent star-forming galaxy. Instead, the source appears to be co-located with a low-luminosity active galactic nucleus or a previously unknown type of extragalactic source. Localization and identification of a host or counterpart has been essential to understanding the origins and physics of other kinds of transient events, including gamma-ray bursts and tidal disruption events. However, if other fast radio bursts have similarly faint radio and optical counterparts, our findings imply that direct subarcsecond localizations may be the only way to provide reliable associations.

Confounding Transient Event 2 Billion Light Years Away. Shami Chatterjee, Cornell University. @shamichatterjee

​http://www.nature.com/nature/journal/v541/n7635/full/nature20797.html
​Mysterious Fast Radio Bursts Traced to Dwarf Galaxy in the Auriga Constellation