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.

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We present a model of X-ray emission from rotation-powered pulsars, which in general consist of one nonthermal component, two hard thermal components, and one soft thermal component. The nonthermal X-rays come from synchrotron radiation of eB pairs created in the strong magnetic Ðeld near the neutron star surface by curvature photons emitted by charged particles on their way from the outer gap to the neutron star surface. The Ðrst hard thermal X-ray component results from polar-cap heating by the return current in the polar gap. The second hard thermal X-ray component results from polar-cap heating by the return particles from the outer gap. Because of cyclotron resonance scattering, most of the hard thermal X-rays will be e †ectively reÑected back to the stellar surface and eventually reemitted as soft thermal X-rays. However, some of the hard thermal X-rays can still escape along the open magnetic Ðeld lines, where the e`/e~pair density is low. Furthermore, the characteristic blackbody temperatures of the two hard X-ray components emitted from the polar-cap area inside the polar gap and the polarcap area deÐned by the footprints of the outer-gap magnetic Ðeld lines are strongly a †ected by the surface magnetic Ðeld, which can be much larger than the dipolar Ðeld. In fact, the strong surface magnetic Ðeld can explain why the e †ective blackbody radiation area is nearly 2 orders of magnitude larger than that deduced from the dipolar Ðeld for young pulsars (2 orders of magnitude less for old pulsars). Our model indicates how several possible X-ray components may be observed, depending on the magnetic inclination angle and viewing angle. Using the expected X-ray luminosity and spectra, we explain the observed X-ray spectra from pulsars such as Geminga, PSR B1055[52, PSR B0656]14, and PSR B1929]10.

The extended TeV gamma-ray source ARGO J2031+4157 (or MGRO J2031+41) is positionally consistent with the Cygnus Cocoon discovered by Fermi-LAT at GeV energies in the Cygnus superbubble. Reanalyzing the ARGO-YBJ data collected from 2007 November to 2013 January, the angular extension and energy spectrum of ARGO J2031+4157 are evaluated. After subtracting the contribution of the overlapping TeV sources, the ARGO-YBJ excess map is fitted with a two-dimensional Gaussian function in a square region of 10 • × 10 • , finding a source extension σ ext = 1. • 8 ± 0. • 5. The observed differential energy spectrum is dN/dE = (2.5 ± 0.4) × 10 −11 (E/1 TeV) −2.6±0.3 photons cm −2 s −1 TeV −1 , in the energy range 0.2-10 TeV. The angular extension is consistent with that of the Cygnus Cocoon as measured by Fermi-LAT and the spectrum also shows a good connection with the one measured in the 1-100 GeV energy range. These features suggest to identify ARGO J2031+4157 as the counterpart of the Cygnus Cocoon at TeV energies. The Cygnus Cocoon, located in the star-forming region of Cygnus X, is interpreted as a cocoon of freshly accelerated cosmic rays related to the Cygnus superbubble. The spectral similarity with supernova remnants (SNRs) indicates that the particle acceleration inside a superbubble is similar to that in an SNR. The spectral measurements from 1 GeV to 10 TeV allows for the first time to determine the possible spectrum slope of the underlying particle distribution. A hadronic model is adopted to explain the spectral energy distribution.

Abstract.We consider a possible contribution of mature γ-ray pulsars (with ages of ≥ 10 5 yrs) to cosmic ray positrons. Within the framework of the γ-ray pulsar outer gap model, e ± pairs in the pulsar magnetosphere are produced by the cascade of e ± pairs through synchrotron radiation of the return current from the outer gap. A good fraction of these cascade e ± pairs are reflected by the hard X-rays from the polar cap via resonant scattering and escape from the pulsar through the light cylinder. The escaped pairs are accelerated to relativistic energies in the pulsar wind driven by low-frequency electromagnetic waves. Using Monte Carlo simulations, we generate a sample of the mature γ-ray pulsars in our Galaxy and calculate the positron production rate from these pulsars. In a simple "leaky box" model, we calculate the ratio of cosmic-ray positrons to total electrons. Our result indicates that the pulsar contribution to the cosmic ray positrons peaks at about 60 GeV and the observed e + /(e − + e + ) ratio can be explained in this model.

Abstract. We present a self-consistent model to describe X-ray and γ-ray emission from millisecond pulsars (MSPs). The X-rays of MSPs are produced by the backflow of primary charged particles from the outer gap and most likely consist of three components, two thermal components and one power law component if there is a strong multipole magnetic field on the stellar surface. The backflow of ultra-relativistic particles emits photons with energies about several tens of GeV via curvature radiation. These photons cause an electromagnetic cascade about 2-3 stellar radii above the polar cap. The synchrotron radiation of these cascade e ± pairs produces hard X-rays with a power law index ∼1.5. Near 10 5 cm above the stellar surface, the primary charged particles encounter the strong surface magnetic field, which alters the local radius of curvature greatly, and they quickly loose more than half of their remaining energies to curvature radiation. These curvature photons heat up the polar cap area with a radius ∼10 5 cm, which produce the softer thermal X-ray component. Finally, the primary charged particles deposit their remaining energies in a much smaller polar cap area, which corresponds to the footprints of outer gap and produce the medium hard X-ray component. γ-rays are produced in the outer gap through synchro-curvature radiation. We have applied this model to the MSPs which emit pulsed X-rays and likely γ-rays such as PSR J0437-4715, PSR J2124-3358, PSR J0218+4232 and PSR B1821-24. Our results give an agreement between predicted spectrum and the observed spectrum of MSP emission.

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The Astrophysical Radiation with Ground-based Observatory at Yang Ba Jing (ARGO-YBJ) detector is an extensive air shower array that has been used to monitor the northern γ-ray sky at energies above 0.3 TeV from 2007 November to 2013 January. In this paper, we present the results of a sky survey in the declination band from −10 • to 70 • , using data recorded over the past five years. With an integrated sensitivity ranging from 0.24 to ∼1 Crab units depending on the declination, six sources have been detected with a statistical significance greater than five standard deviations. Several excesses are also reported as potential γ-ray emitters. The features of each source are presented and discussed. Additionally, 95% confidence level upper limits of the flux from the investigated sky region are shown. Specific upper limits for 663 GeV γ-ray active galactic nuclei inside the ARGO-YBJ field of view are reported. The effect of the absorption of γ-rays due to the interaction with extragalactic background light is estimated.