Echoes of Crab Pulsar Giant Radio Pulses

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Echoes of Crab Pulsar Giant Radio Pulses

• Jared Crossley
• Tim Hankins
• Jean Eilek

10 February 2005
Special thanks to Chris Jordan of Jodrell Bank
Observatory
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Talk Outline

• Introduction to pulsars and the Crab
• What is known about Crab echoes
• Our new data
• Analysis
• Interpretation
• Conclusions

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The basic model

• Rotating neutron star
• Dipolar magnetic field
• Photons emerge from the open field line region
• When the dipole moment points at us we see a pulse

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The Crab Pulsar and Nebula
From http//chandra.harvard.edu
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Previous Crab echo events
echo
150 days
Dickerson 2003 Backer, Wong, Valanju 2000
Pulse period (33 ms)
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Crab echo events
Echoes events occur often at least 19 in past 20
years
Lyne, Pritchard Graham-Smith 2001
Do the new data fit the old filament model?
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Example of giant pulse and echo
1.4 GHz, 1.5 ?s resolution
Primary
Echo
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Echo event of 1997
1.4 GHz, 1.5 ?s resolution
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Echo event of 1996
1.4 GHz, 500 ns resolution
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Data Summary

• Of 38 data sets, only 2 have echoes.
• 45 of 77 pulses have clearly visible echoes at
  1.4 GHz.
• The other pulses had low signal to noise,
  complex microstructure, and/or weak or absent
  echo component
• For the 1996 event
• Observations 2 days before and after show no
  echoes.
• No echo is visible in simultaneous 4.8 GHz data
• Further analysis was performed using fits of the
  exponential scattering function

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power
Equal power
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width
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toa
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Interpretation
Our Echoes Previous Echoes
Echoes lag primary by 120 ?s 1 - 4 ms
Event lifetimes 4 days (1996) 6 - 50 days
Frequency dependence Strong (1996) weak
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Interpretation

1. Assume echoes are produced by small angle
   refraction in the nebula
2. Note the frequency dependence

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Refraction from wisps?
We seek a smaller pulsar-refraction distance and
a rapidly variable refracting medium One
possibility is the wisp-like region associated
with the pulsar wind shock
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Conclusions

• Crab data from 1996 and 1997 show an echo-like
  pulse component following the normal component.
• This echo emission differs from other echo
  emission reported previously.
• It is improbable that our refraction events
  occurred in the nebular filaments. We propose
  refraction may be caused by the wisp-like
  structures associated with the pulsar wind.