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Crawford et al. present four new fast radio bursts discovered in a
search of the Parkes 70-cm pulsar survey data archive for dispersed
single pulses and bursts.
A total of 719905 single pulse candidates were detected in the survey,
of which 75774 were classified as possibly real.
All but 7 of the classified signals were either rejected by eye as
not morphologically realistic or were determined to have come from
known pulsars.
The fact that all but a handful of these signals were associated with known
sources after checking the pulsar catalog illustrates the large number
of known single pulse emitters present in the survey data.
Of the 7 unidentified signals, three were weak pulses with
narrow widths and small Dispersion Measures, indicating likely
Rapidly Rotating Transients (RRATs) in our Galaxy.
The four FRBs
discovered have significantly larger widths (> 50 ms) than almost all
of the FRBs detected and cataloged to date, however, the large pulse widths are
not dominated by interstellar scattering or dispersive smearing within
channels.
The image above shows the detection plot of FRB920913,
which has a Dispersion Measure of 3338 pc/cm^3, the largest measured for any FRB to date,
suggesting it is one of the most distant FRBs detected.
The panels show the dedispersed pulse profile for the burst
(top), signal strength (brightness) vs. frequency and time for the dedispersed
pulse (middle), and signal strength (brightness) vs. DM and time (bottom).
The results suggest that pulsar survey archives remain
important sources of previously undetected FRBs and that searches for
FRBs on time scales extending beyond ∼100 ms may reveal the presence
of a larger population of wide-pulse FRBs.
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