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SPACE SCIENCES



        Researchers have known since 1983 that gamma-ray bursts can ionise Earth’s atmosphere
        and thus disturb the great wave guide. This appears to be the first time anyone has
        recorded the effect using an earth probe antenna.
           The outburst on 9 October shocked astronomers.
           Phil Evans of the University of Leicester tweeted on the immediate aftermath of the
        burst: “It’s bright, really bright. Like stupidly, really bright.” Evans works with data from
        NASA’s Swift gamma-ray observatory, and the overflowing signal had apparently broken
        some of his plotting software.
           Researchers have since pinpointed the burst. It came from a dusty galaxy 2.4 billion
        light years away, almost certainly triggered by a supernova explosion giving birth to a
        black hole. This is the closest gamma-ray burst (GRB) ever recorded, thus accounting for
        its extreme intensity.





                                                                                  using the Gemini South telescope in
                                                                                  Chile.
                                                                                    Meanwhile, other observers in the
                                                                                  UK and Germany have also reported
                                                                                  ionospheric disturbances resulting from
                                                                                  the burst. They all used regular above-
                                                                                  ground antennas.
                                                                                    When black holes form, they drive
                                                                                  powerful jets of particles that are
                                                                                  accelerated to nearly the speed of light.
                                                                                  These jets then pierce through what
                                                                                  remains of the progenitor star, emitting
                                                                                  X-rays and gamma rays as they stream
                                                                                  into space. If these jets are pointed in
                                                                                  the general direction of Earth, they are
                                                                                  observed as bright flashes of X-rays and
                                                                                  gamma rays.
                                                                                    Another gamma-ray burst this bright
                                                                                  may not appear for decades or even
                                                                                  centuries.                    n



                                                                                   The first observation of an ionospheric
                                                                                   disturbance from a gamma-ray
                                                                                   occurred at 22:14:18 UTC on 1 August
                                                                                   1983 and was one of the strongest
                                                                                   ever observed. The total fluence
                                                                                   was 2 x 10  erg cm , most of which
                                                                                           –3
                                                                                                 –2
                                                                                   occurred in the first four seconds of
                                                                                   the burst. Simultaneously, a change
        Swift’s X-Ray telescope captured the afterglow of GRB 221009A about an hour after it   was observed in the amplitude of
        was first detected. The bright rings form as a result of X-rays scattered by otherwise   a very-low-frequency (VLF) radio
        unobservable dust layers within our galaxy that lie in the direction of the burst.   signal from a transmitter in Rugby,
        The dark vertical line is an artifact of the imaging system.               England, monitored at Palmer
        Credit: NASA/Swift/A. Beardmore (University of Leicester)                  Station, Antarctica, indicative of an
                                                                                   ionospheric disturbance. Weaker
        “In our research group, we’ve been referring to this burst as the ‘BOAT’, or Brightest   disturbances were also recorded at
        Of All Time, because when you look at the thousands of bursts gamma-ray telescopes   the same receiving site on signals
        have been detecting since the 1990s, this one stands apart,” says Jillian Rastinejad, an   from VLF stations in Annapolis,
        astronomer at Northwestern University who has been monitoring the burst’s afterglow   Maryland and Lualualei, Hawaii.


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