New clues to the origin of fast radio bursts in neutron stars

An article published in the journal “Astronomy & Astrophysics” reports a study of the data about 43 fast radio bursts (FRBs) that offers new clues to their origin in neutron stars. A team of Italian researchers associated with the National Institute of Astrophysics used observations made with the ASKAP and Parkes radio telescopes, adapting a test from the 1960s to try to establish their distribution by comparing it with that of stars. The results gave some surprises and are not conclusive, but a method was offered that could be the key to solving the mystery for good.

Fast radio bursts were detected for the first time in 2007 by analyzing archive data collected in 2001 and are still a mystery because such powerful radio emissions require an estimated energy that’s about what the Sun emitted in 80 years despite their duration of a few milliseconds.

In January 2018 an article published in the journal “Nature” reported evidence that the fast radio burst cataloged as FRB 121102 was generated by a neutron star, perhaps of the magnetar type characterized by an extremely intense magnetic field. At that moment it was the only repeated burst detected whose origin was traced to a galaxy about 3 billion light years from Earth.

Brian Metzger and Ben Margalit are two researchers who carried out various studies on the subject and in particular on that repeated fast radio burst offering a possible explanation to the mechanism of origin, again in a magnetar, in an article published in early May 2019 on the journal “Monthly Notices of the Royal Astronomical Society”.

One of the problems in research on fast radio bursts is given by their scarcity and the ASKAP radio telescope is a great help as it practically doubled the number of known events. In fact, of the 43 examined by Nicola Locatelli, Michele Ronchi, Giancarlo Ghirlanda and Gabriele Ghisellini, 23 were detected by that new instrument and 20 by another Australian radio telescope, the Parkes.

The top image (Courtesy D. Kaplan (UWM), E. F. Keane (SKAO). All rights reserved), shows the field of view of the Parkes radio telescope on the left. On the right there are successive zoom-ins of the area from which a fast radio burst arrived. The image at the bottom right shows the galaxy from which the event was originated seen by the Subaru telescope with a view of the Australian Telescope Compact Array (ATCA) superimposed.

The hypothesis to be tested was that fast radio bursts were generated by neutron stars and the four researchers added the idea that in that case their distribution in the universe should match that of stars.

In the 1960s a great cosmological mystery concerned the origin of quasars and at the time the method called luminosity–volume or V/Vmax was invented to study its distribution. Applying that method to fast radio bursts, the result was rather surprising because the distribution of the sources is not uniform. In essence, there are few of these events near the Milky Way, they increase until about seven billion light years away and fall again with higher distances.

This research was based on 43 fast radio bursts, too few to obtain conclusive results. The ASKAP radio telescope already gave a big hand, recently other events were discovered by the CHIME (Canadian Hydrogen Intensity Mapping Experiment) radio telescope, in Canada, which saw the so-called first light on September 7, 2017, which uses four semi-cylinders instead of the classic circular antennas. In the future, the researchers expect to be able to test their method on many more fast radio bursts.

The CHIME radiotelescope's antennas (Photo Mateus A. Fandiño)
The CHIME radiotelescope’s antennas (Photo Mateus A. Fandiño)

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