Introduction A pulsar magnetosphere can be divided into two zones: The closed zone filled with a dense plasma co-rotating with the neutron star (NS), and the open zone in which plasmas flow along B to escape as a pulsar wind. The last-open field lines form the border of them. In all pulsar emission models, particle acceleration takes place within the open zone. To explain pulsating high-energy emissions, two scenarios have been proposed: the slot-gap (SG) model with acceleration taking place along the last-open field lines, and the outer-gap (OG) model with acceleration occurring between the null surface and the light cylinder (fig 1). It is currently a hot topic how to discriminate them observationally. However, before comparing the model predictions with observations, we must draw attention to theoretical consistency and feasibility. Therefore, in this poster, I quantitatively examine both models by solving the Maxwell equations, the Boltzmann equations of e-’s and e+’s, and the radiative transfer equations self-consistently and compare their predictions.

OG predicts a consistent spectrum (red line in fig. 4) for the Crab pulsar.

The present method uniquely gives the OG solution, if we specify pulse period, period derivative, magnetic inclination, NS surface temperature, distance, and observer’s viewing angle.

High Energy Emission from Pulsars: Theory vs. TheoryKouichi HIROTANI

TIARA (Theoretical Institute for Advanced Research in Astrophysics)Department of Physics, National Tsing Hua University, Hsin-chu, Taiwan

AbstractThe study of emission from rotation-powered pulsars will soon undergo a major advance with observations by the Large Area Telescope (LAT) aboard the Gamma-Ray Large Area Space Telescope (GLAST) by virtue of its unprecedented sensitivity and energy resolution in 20 MeV-300 GeV. This paper adds to this effort by presenting, for the first time, results of a full model for the two representative pulsar emission models: outer-gap (OG) and slot-gap (SG) models. Solving the particle accelerator in the pulsar magnetosphere from the first principles in the six dimensional phase space, I find that the OG solution can be naturally obtained under appropriate boundary conditions and qualitatively reproduces previous high-energy observations. On the other hand, SG solution is obtained only under several unnatural assumptions and cannot reproduce the observations at all, because of its small potential drop in the accelerator.

Crab pulsar

SG model I apply the same method to the SG model and confirmed that previous dimensional analysis (f~0.04) is correct (fig 5). Since the SG is assumed to be pair-free, /B should distribute as the dashed green line in higher altitudes (fig 6). However, to extend a negative magnetic-field-aligned electric field, E||, one must artificially assume /B as the green solid line. Note that /B should decrease outwards, in fact, by the discharge of created pairs (if there are) because E|| <0 holds in SG.

OG model The gap activity is essentially determined by two quantities: gap trans-field thickness, f, and the real charge density, . In previous OG models, f~0.15 has been estimated for Crab. Computing - and -B pair production in 3D magnetosphere, I confirm that 10-20% of the open B fluxes thread the gap (fig 2). In previous OG models, only a vacuum gap (i.e., =0) has been considered when they solve divE=4; however, in this work, I first solve a non-vacuum gap (fig 3).

Fig. 1 Sideview of a pulsar magnetosphere

Fig. 2 Fractional gap thickness, f, on the 2-D last-open B line bundle. Red curve denotes the null surface intersection.

s

Fig. 3 Solved real (black) and Goldreich-Julian (red) charge densities per B flux tube along four different field lines.

s

Fig. 4 Spectral energy distribution of pulsed photons from the Crab pulsar.

Fig. 5 Same figure as fig 2, for the SG.

Fig. 6 Assumed real (green) and Goldreich-Julian (red) charge densities per B flux tube.

Under the same pulsar parameters, SG predicts too small fluxes (fig 7). Previous SG models, in fact, have overestimated the electron Lorentz factor (~2*107), compared with the analytically correct value, (~107).

Fig. 7 SED of the Crab pulsar.

Crab pulsar