Fast Radio Bursts (FRBs)

The first example of an FRB was discovered in 2007 in archival data of the Magellanic Clouds taken by the Parkes telescope, Australia, in 2001. Within 480 hours of observations, a lone radio pulse, 5ms long and estimated to contain ~10^33 joules of energy (the total output of the sun over 10 years) was discovered, sparking immense excitement in the astrophysical community. The current tally of published these mysterious signals still stands at less than twenty (17) and yet the field of FRB research is one of the most rapidly evolving areas of radio astronomy. Fast Radio Bursts is one of the research topics of the Pulsars and Time Domain Astrophysics group.

  • Brightness and Dispersion Measures

    The excitement around FRBs is mainly due to two of their attributes- their extreme brightnesses and their high dispersion measures (also known as DMs, measured in pc cm^-3). As with pulsars, FRBs are dispersed by the ionised electron content of the environments they travel through and DM is a direct measure of the amount of matter they traverse on their journey to us. Unlike pulsars, whose DMs vary from tens to hundreds, FRBs may have DMs closer to one thousand, indicating that they pass through far more matter than our galaxy has to offer along those lines of sight. This suggests that FRBs are extragalactic, an exciting prospect as they therefore could eventually be used as probes of cosmological parameters, intergalactic magnetic fields, or to locate missing baryonic matter in the universe.

    Despite being extremely bright, FRBs are rare. Recent calculations estimate their rate to be (6e3) per sky per day and we currently aren’t always watching the skies, thus to date the majority of FRBs have been found by searching through a vast backlog of data from surveys conducted by telescopes stationed around the globe (Australia, HTRU; US, PALFA; Europe, HTRU)

  • FRB Search Techniques

    FRB search techniques have been progressing however, and efforts such as the SUPERB survey are pioneering real-time analysis of vast areas of sky to search for these transients. Their efforts have not gone unrewarded: over the last few years a growing number (3) of FRBs have been spotted in real time and triggered a frenzy of follow-up at all wavelengths.

    The sooner we can detect and alert others to these bursts, the more likely we are to discover clues pointing towards their origins, but regardless of how late we uncover FRBs, reobservation of the areas of sky where they occurred may provide information with which we might infer their origins. If FRBs are discovered to repeat for example, it would indicate that their progenitors survived the initial outburst, which would in turn suggest that the pulses are some of the most extreme symbols ever measured from pulsars, or even signatures of extragalactic planets. Non-repetition may suggest that FRBs result from of devastating cataclysmic events - possibly the signatures of some of the most violent events in the universe - for example the collision of binary neutron stars or the births of black holes. Recent contradictory observations suggest that either, or maybe even both may be the case, and that we have still not quite grasped the bigger picture. Behind our fragmentary observations may hide a much more diverse population of transient radio signals waiting to be uncovered.

    The current difficulty with definitively confirming FRB origins as extragalactic is due disadvantages of the apparatus used to detect them. Single telescopes, for example the Parkes telescope (Australia), have extremely large fields of view (greater than ten arcminutes), which could hold hundreds or even thousands of individual galaxies; within those fields the exact location of any detected FRB is not well known. Thus it can be extremely hard to pin down a host galaxy for a burst, and measure its redshift. One way this may be achieved is via a technique known as radio interferometry, and here at Manchester we are hard at work devising a way for a series of UK based radio telescopes collectively known as the eMERLIN interferometer to confirm or refute the extragalactic origin of FRBs once and for all.

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