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Repeating Fast Radio Burst (FRB)

Fast Radio Burst (FRB) is short radio pulse of few milliseconds (10-3 sec) duration. The first FRB was discovered in 2007 from archival pulsar survey data (up to 2001). About 40 FRBs have since been identified, including two repeating FRBs (the first one by the Arecibo radio telescope in 2015, the 2018 discovery is by the CHIME in Canada, see Figure 08-26d). The sources distribute over all directions in the sky. When the FRBs are polarized, it indicates that they are synchrotron radiation generated by extremely powerful magnetic field. The origin of the FRBs is unknown; proposals range from a rapidly rotating neutron star and a black hole, to extraterrestrial intelligence.

Magnetar, Transient Magnetar A search of astronomical objects reveals that the "magnetar" seems to fit the above description quite well. The match is based on the size, location, polarization, and amount of energy released. A magnetar is a type of neutron star with very strong magnetic field ~ 1015 Gauss. They can be produced in two different ways.

  • One type appears to be a transient object in supernova explosion. It exists only several 100 seconds before collapsing into a black hole
  • Figure 08-26f Magnetar, Transient [view large image]

    Figure 08-26g Magnetar [view large image]

    (Figure 08-26f). Thus, it can never be a repeating FRB.


    Starquake
  • The other kind is produced in a process similar to the production of pulsar (Figure 08-26g). The difference is its very fast spinning rate generating the very strong magnet field, which decays in about 10000 years. Extremely violent starquakes are believed to be induced when the intense magnetic fields fracture the crusts, Figure 08-27h depicts the sequence of events which could lead up to FRB instead of GRB in some cases. Similar to Earthquakes, Starquake can be repeating called aftershocks.
  • Figure 08-26h Starquake [view large image]

    The Figure below shows the CHIME measurements of the repeating FRB 180814.

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