Pulse Profiles, Spectra, and Polarization Characteristics of Nonthermal Emissions from the Crab-like Pulsars

The Astrophysical Journal (Impact Factor: 6.73). 01/2007; 670(1):677-692. DOI: 10.1086/521785
Source: arXiv

ABSTRACT We discuss nonthermal emission mechanisms of the Crab-like pulsars with both a two-dimensional electrodynamic study and a three-dimensional model. We investigate the emission process in the outer gap accelerator. In the two-dimensional electrodynamic study, we solve the Poisson equation of the accelerating electric field in the outer gap and the equation of motion of the primary particles with the synchrotron and the curvature radiation processes and the pair-creation process. We show a solved gap structure that produces a gamma-ray spectrum consistent with EGRET observations. Based on the two-dimensional model, we construct a three-dimensional emission model to calculate the synchrotron and the inverse Compton processes of the secondary pairs produced outside the outer gap. We calculate the pulse profiles, the phase-resolved spectra, and the polarization characteristics in optical through gamma-ray bands for comparison with the observation of the Crab pulsar and PSR B0540-69. For the Crab pulsar, we find that the outer gap geometry extending from near the stellar surface to near the light cylinder produces a complex morphology change of the pulse profiles as a function of the photon energy. This predicted morphology change is quite similar to that of the observations. The calculated phase-resolved spectra are consistent with the data from the optical to the gamma-ray bands. We demonstrate that the 10%-20% of the polarization degree in the optical emissions from the Crab pulsar and the Vela pulsar is explained by the synchrotron emissions from the particle gyration motion. For PSR B0540-69, the observed pulse profile with a single broad pulse is reproduced for an emission region thicker and an inclination angle between the rotational axis and the magnetic axis smaller than the Crab pulsar.

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We review a proposed multicomponent model to explain the features of the pulsed emission and spectrum of the Crab Pulsar, on the light of the recent detection of pulsed emission above 25 GeV from the MAGIC atmospheric Cherenkov telescope. This model explains the evolution of the pulse shape and of the phase-resolved spectra, ranging from the optical/UV to the GeV energy band, on the assumption that the observed emission is due to several components, which have spectra modelled as log-parabolic laws. We show that the new MAGIC data are well consistent with the prevision of our model. Comment: 4 pages, 3 figures. Accepted for publication in Astronomy and Astrophysics
    Astronomy and Astrophysics 03/2009; · 5.08 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We use a modified three-dimensional outer gap model to explain the features of the pulsed emission and spectra of the Crab pulsar from X-ray to above 25 GeV regimes. In such an outer gap model, the phase-averaged spectra below ~1 GeV are mainly produced through the synchrotron self-Compton mechanism, and the spectrum above ~1 GeV are due to the survival curvature photons. Our results show that (1) the observed phase-averaged spectrum from X-rays to γ-rays including the Fermi LAT and MAGIC data can be reproduced well, and (2) the basic properties of both the observed phase-dependent spectra of both X-ray and γ-ray up to >25 GeV can be interpreted in this model.
    The Astrophysical Journal 12/2009; 707(2):L169. · 6.73 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We study the phase-averaged spectra and luminosities of γ-ray emissions from young, isolated pulsars within a revised outer gap model. In the revised version of the outer gap, there are two possible cases for the outer gaps: the fractional size of the outer gap is estimated through the photon-photon pair process in the first case (Case I), and is limited by the critical field lines in the second case (Case II). The fractional size is described by Case I if the fractional size at the null charge surface in Case I is smaller than that in Case II, and vice versa. Such an outer gap can extend from the inner boundary, whose radial distance to the neutron star is less than that of the null charge surface to the light cylinder for a γ-ray pulsar with a given magnetic inclination. When the shape of the outer gap is determined, assuming that high-energy emission at an averaged radius of the field line in the center of the outer gap, with a Gaussian distribution of the parallel electric field along the gap height, represents typical emission, the phase-averaged γ-ray spectrum for a given pulsar can be estimated in the revised model with three model parameters. We apply the model to explain the phase-averaged spectra of the Vela (Case I) and Geminga (Case II) pulsars. We also use the model to fit the phase-averaged spectra of 54 young, isolated γ-ray pulsars, and then calculate the γ-ray luminosities and compare them with the observed data from Fermi-LAT.
    The Astrophysical Journal 02/2013; 765(2):124. · 6.73 Impact Factor

Full-text (2 Sources)

Available from
May 20, 2014