Kavli Affiliate: Kiyoshi W. Masui
| First 5 Authors: Thierry Serafin Nadeau, Thierry Serafin Nadeau, , ,
| Summary:
The Crab Pulsar is known to feature plasma lensing events known as echoes.
These events show additional components in the pulse profile which are produced
by signal that is deflected by ionized nebular material and are therefore
delayed relative to the primary emission. We observed the Crab pulsar with
acCHIME during its daily transits, creating an archive of baseband
recordings of bright single pulses (known as giant pulses) in the
400$-800,unitMHz$ band. From these, we produced daily stacks of aligned
pulses between late October 2021 and March 2024. We find that in these
averages, echoes are readily visible throughout the observation period, and we
identify clear groups of echoes with distinct behaviour in terms of their
evolution with time and frequency. Many echoes exhibit dispersive delays
consistent with being observed through excess column densities relative to the
unscattered rays, but we also find two events where the dispersive delays
indicate column density deficits. For the first time, we also find echoes for
which the line of sight never directly intersects the intervening structures,
resulting in events with non-zero minimum delays, of around $0.5 rm,ms$.
The frequency and diversity of the observed echoes make the Crab an excellent
target for long-term studies of astrophysical plasma lensing.
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