Possible Periodic Activity Of A Fast Radio Burst Brings Into Question How They Form

Artist's impression of an orbital modulation model where the FRB progenitor (blue) is in an orbit with a companion astrophysical object (pink). Kristi Mickaliger 

Fast radio bursts (FRBs) are incredible emissions of radio waves that last just a few milliseconds. Less than 100 of these events are known and only a tiny fraction repeat regularly. Among the latter group there’s FRB 121102, the first of these phenomena tracked back to its own galaxy.

New research has now unveiled that this FRB might recur with a certain period that's detectable for about 90 days, followed by 57 days of silence, before starting again. These observations were conducted over five years and are reported in the Monthly Notices of the Royal Astronomical Society.

The cause of FRB 121102 is believed to be a strongly magnetic neutron star, or magnetar, that is going around precessing – in other words, no longer spinning vertically but at an angle, moving like a spinning top would. Under this scenario, the emission is under some kind of alignment between the magnetic axis of the star and Earth. Yet, this explanation doesn’t easily fit with the possible 157-day period from the observations.  
"This is an exciting result as it is only the second system where we believe we see this modulation in burst activity. Detecting a periodicity provides an important constraint on the origin of the bursts and the activity cycles could argue against a precessing neutron star," lead author Dr Kaustubh Rajwade, of The University of Manchester, said in a statement.
Artist's impression of an orbital modulation model where the FRB progenitor (blue) is in an orbit with a companion astrophysical object (pink). Kristi Mickaliger 

From the early detections of this event, researchers have been toying with the idea that the magnetar is moving through an intense magnetic field, which is creating the pulses. This scenario has been rethought with the neutron star instead orbiting around an object such as a massive star, a neutron star, or a black hole. The pulses are only released during certain times in the orbit.

This work continues to show the variety of FRB-related phenomena. Since their discovery in 2007, these events continue to surprise. Even similar events to this are in reality quite different. FRB 180916 was the first repeating source with an established period of 16 days, one-tenth of what FRB 121102 appears to be showing.

"This exciting discovery highlights how little we know about the origin of FRBs," explained co-author Duncan Lorimer, from West Virginia University and who along with PhD student Devansh Agarwal helped develop the data analysis technique that led to the discovery. "Further observations of a larger number of FRBs will be needed in order to obtain a clearer picture about these periodic sources and elucidate their origin."


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