Giant pulses from the Crab pulsar: A joint radio and gamma-ray study

S. C. Lundgren*, J. M. Cordes, M. Ulmer, S. M. Matz, S. Lomatch, R. S. Foster, T. Hankins

*Corresponding author for this work

Research output: Contribution to journalArticle

142 Scopus citations

Abstract

The Crab Nebula pulsar emits bursts of radio emission as strong as 2000 times the average pulse amplitude. Using joint radio and gamma-ray observations of these giant radio pulses, we characterized intensity variations, measured absolute timing with 70 μs precision, and determined the spin-down model and interstellar dispersion. Fitting the flux-density histogram requires a two-component model - a narrow distribution of weak (but nonzero) pulses and a power-law component for giant pulses with an index of -3.3 and a low-intensity cutoff that is 33 times the mean of the weak pulses. The lack of time delay between giant pulses and weak pulses (Δt = 6 ± 12 μs) suggests that the two emission mechanisms operate within a 4 km region. Daily changes in the apparent rate of giant pulses are caused by propagation effects in the interstellar medium (scintillation) rather than intrinsic variability of the giant-pulse mechanism. The distribution of time separations between giant pulses implies that the mechanism is a Poisson process. We interpret giant-pulse properties in the context of temporal-modulation and beam-waver models. Only the temporal-modulation model is consistent with the data. Empirical measurements place limits on the duration, size, and rate of temporal modulations in the magnetosphere. Gamma-ray flux increases in the 50-220 keV range are limited to less than a factor of 2.5 concurrent with radio bursts. We discuss how the lack of gamma-ray variation constrains radio coherence mechanisms, the steadiness of electron-positron outflow, and the amount of inverse-Compton scattering of radio photons to gamma rays.

Original languageEnglish (US)
Pages (from-to)433-445
Number of pages13
JournalAstrophysical Journal
Volume453
Issue number1
DOIs
StatePublished - Nov 1 1995

Keywords

  • Gamma rays: observations
  • Pulsars: individual (Crab pulsar)
  • Radiation mechanisms: nonthermal

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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    Lundgren, S. C., Cordes, J. M., Ulmer, M., Matz, S. M., Lomatch, S., Foster, R. S., & Hankins, T. (1995). Giant pulses from the Crab pulsar: A joint radio and gamma-ray study. Astrophysical Journal, 453(1), 433-445. https://doi.org/10.1086/176404