No abstract

A three-dimensional pulsar magnetosphere model is used to study the geometry of outer magnetospheric gap accelerators, following seminal work of Romani and coworkers. The size of the outer gap is self-consistently limited by pair production from collisions of thermal photons from polar cap heating of backÑow outer gap current with curvature photons emitted by gap-accelerated charged particles. In principle, there could be two topologically disconnected outer gaps. Conditions for local pair production such as local Ðeld line curvature, soft X-ray density, electric Ðeld, etc., support pair production inside an outer gap only between (the radius of the null surface at azimuthal angle /) and r in (/) r lim (/) B 6r in (/ \ (the light cylinder radius). Secondary pairs, on the other hand, are produced almost everywhere 0) > R L outside the outer gap by collisions between curvature photons and synchrotron X-rays emitted by these secondary pairs. These processes produce a wide X-ray fan beam in the outgoing direction and a very narrow beam in the incoming direction for each outer gap. For pulsars with a large magnetic dipole inclination angle, part of the incoming c-ray beam will be absorbed by the stellar magnetic Ðeld. If the surface magnetic Ðeld is dominated by a far o †-center dipole moment (e.g., as in a proposed "" plate tectonic ÏÏ model), gravitational bending of photons from polar cap accelerators and their ultimate conversion into outÑowing eB pairs can result in the quenching of one of these two outer gaps. Various emission morphologies for the pulsar (depending on magnetic inclination angle and viewing angle) are presented. Double-peak light curves with strong bridges are most common. From the three-dimensional structure of the outer gap and its local properties, we calculate phase-resolved spectra of gamma-ray pulsars and apply them to observed spectra of the Crab pulsar.

We propose a self-consistent mechanism to estimate the size of the acceleration region in the outer magnetosphere of pulsars (outer gap) and calculate the high-energy radiation produced by the synchrocurvature mechanism from the outer gap. We Ðnd that a power-law energy distribution of the accelerated particles can be obtained if the outer gap is thick enough that inside the gap can be E AE BOE approximately proportional to ()r/c)1@2B(r). We apply our model to explain X-rays and c-rays from Geminga and PSR B1055[52, whose outer gaps may occupy D70% of the outer magnetosphere region. If the radius of curvature near the light cylinder of the medium outer gap is larger than the dipolar structure, then perhaps this model may also apply to PSR B1951]32, PSR B1706[44, and others.

No abstract

Fermi has discovered two giant gamma-ray-emitting bubbles that extend nearly 10kpc in diameter north and south of the galactic center (GC). The existence of the bubbles was first evidenced in X-rays detected by ROSAT and later WMAP detected an excess of radio signals at the location of the gammaray bubbles. We propose that periodic star capture processes by the galactic supermassive black hole, Sgr A * , with a capture rate 3 × 10 −5 yr −1 and energy release ∼ 3 × 10 52 erg per capture can produce very hot plasma ∼ 10keV with a wind velocity ∼ 10 8 cm/s injected into the halo and heat up the halo gas to ∼ 1keV, which produces thermal X-rays. The periodic injection of hot plasma can produce shocks in the halo and accelerate electrons to ∼TeV, which produce radio emission via synchrotron radiation, and gamma-rays via inverse Compton scattering with the relic and the galactic soft photons.