Investigations of Single Pulses from Radio Pulsars

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Investigations of Single Pulses from Radio Pulsars
Emily Alicea Muñoz University of Puerto
Rico Mayagüez Campus Department of
Physics Advisor Dr. Leszek Nowakowski
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What is a Pulsar?

• The current theoretical model states that a
  pulsar is a highly magnetized, rapidly rotating
  neutron star.
• The magnetic axis is tilted with respect to the
  rotation axis. This is why we see pulses one for
  each rotation.

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Our Main Objective

• We want to determine what is the physical process
  that makes pulsars behave the way they do.
• We also want to determine the height of the
  emitting region in the pulsar magnetosphere.

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Data Preparation

• We use the 305m Arecibo Radiotelescope to record
  our data.
• The raw data goes through the process of
  dedispersion and baseline removal.
• The data is integrated to produce the average
  profile for the pulsar.
• We then perform integration in intensity bins and
  in subwindows, which is done in order to
  determine the number of components in the average
  profile.

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The Gaussian Fit

• For a long time, people have been fitting
  Gaussian components to average profiles.

Gaussian

• The Gaussian fit works well when the components
  of the average profile do not overlap (for
  example, PSR 123725)

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Problems with the Gaussians

• For some pulsars, such as PSR 061122, the
  Gaussian fitting procedure does not produce good
  results.
• The reason for this is that the components of the
  average profile of this pulsar overlap, and the
  Gaussian fitting do not separate the components.

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The Lorentzian Fit

• We decided to fit Lorentzian curves (instead of
  Gaussian curves) in the average profile of PSR
  061122

Lorentzian

• The results were better than the Gaussian fits,
  but the residual line was negative, so we had to
  try something else.

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The Combination Fit

• By combining Gaussians and Lorentzians, we got
  better fits for the average profile of PSR
  061122.

Comparison between Gaussian, Lorentzian and a
combination of them

• Different proportions of Gaussians and
  Lorentzians gave different results.
• Fits in which the Lorentzian weighed more than
  the Gaussian usually gave the best results.

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PSR 061122

• Intensity bin analysis of the average profile for
  this pulsar shows that the position of the
  components depend on the intensity of the pulse
• Weaker profiles are wide
• Stronger profiles are narrow
• This may mean that stronger pulses are produced
  in a lower region of the magnetosphere, while
  weaker pulses are produced at a greater height.

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PSR 061122

• This pulsar also shows mode switching, and our
  analysis suggests that it is caused by a vertical
  jump of the emitting region in the pulsar
  magnetosphere.
• Retardation, aberration and the geometry of the
  magnetic field lines predict that as the emitting
  region goes higher, the beginning of the profile
  should expand more than the end.

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PSR 061122

• Our analysis also shows that as the intensity
  increases, the position of the components drift
  towards the center of the profile, therefore
  making it more narrow.

• These results confirm the results of earlier
  analysis of data, taken before the upgrade of the
  Arecibo Radiotelescope, that the intensity and
  shape of the average profile depend on the height
  of the emitting region in the pulsar
  magnetosphere.
• The difference between previous analysis and this
  one is that now we can see the separate
  components in the average profile.

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Conclusions (1)

• Gaussian fitting works well for pulsars in which
  the components of the average profile do not
  overlap too much.
• When components overlap, Lorentzian fitting
  usually gives better results.
• Intensity bin analysis of PSR 061122 shows more
  than one component in the average profile.
• The components of PSR 061122 seem to be
  Lorentzian rather than Gaussian.

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Conclusions (2)

• The behavior of the components in the average
  profile of PSR 061122 suggests that mode
  switching is caused by a vertical jump in the
  emitting region in the pulsar magnetosphere.
• Preliminary results show that the intensity of
  the pulse depends on the height of the emitting
  region in the pulsar magnetosphere.
• We hope that further analysis, which will include
  polarized data, will continue to confirm and
  refine these results, and that it will give a
  better understanding of the physical process that
  makes pulsars work.