1,518 research outputs found
Constraining pulsar gap models with the light-curve and flux properties of the gamma-ray pulsar population
We compare population synthesis results for inner and outer magnetosphere
emission models with the various characteristics measured in the first LAT
pulsar catalogue for both the radio-loud and radio-weak or radio-quiet
gamma-ray pulsars. We show that all models fail to reproduce the observations:
for each model there is a lack of luminous and energetic objects that suggest a
non dipolar magnetic field structure or spin-down evolution. The large
dispersion that we find in the simulated gamma-ray luminosity versus spin-down
power relation does not allow to use the present trend seen in the Fermi data
to distinguish among models. For each model and each Fermi detected pulsar, we
have generated light curves as a function of obliquity and inclination angles.
The theoretical curves were fitted to the observed one, using a
maximum-likelihood approach, to derive the best-fit orientations and to compare
how well each model can reproduce the data. Including the radio light-curve
gives an additional key constraint to restrict the orientation spaceComment: 4 pages, 3 figures, to appear in the proceedings of the Pulsar 2010
Conference, Italy, 10 - 15 October 201
Population Synthesis of Radio and Gamma-ray Pulsars in the Fermi Era
We present results of our pulsar population synthesis of normal pulsars from
the Galactic disk using our previously developed computer code. On the same
footing, we use slot gap and outer gap models for gamma-ray emission from
normal pulsars to obtain statistics of radio-loud and radio-quiet gamma-ray
pulsars. From recently improved understanding of HII and star forming regions
in the Galaxy, we develop a new surface density model of the birth location of
neutron stars. We explore models of neutron star evolution with magnetic
field-decay, and with different initial period and magnetic field
distributions. We present preliminary results including simulated population
statistics that are compared with recent detections by Fermi of normal,
isolated pulsars.Comment: 4 pages, 3 figures, to appear in the proceedings of the Pulsar 2010
Conference, Italy, 10 - 15 October 201
Pulsar twinkling and relativity
The number of pulsars with detected emission at X-ray and gamma-ray energies
has been steadily growing, showing that beams of high-energy particles are
commonly accelerated in pulsar magnetospheres, even though the location and
number of acceleration sites remain unsettled. Acceleration near the magnetic
poles, close to the polar cap surface or to higher altitudes in the slot gap
along the last open field lines, involves an electric field component due to
inertial-frame dragging. Acceleration can also take place in the outer
magnetosphere where charge depletion due to global currents causes a large
electric field along the magnetic field lines. All models require a detailed
knowledge of the open magnetosphere geometry and its relativistic distortions.
Observational trends with age, spin-down power and magnetic field as well as
population synthesis studies in the Galactic disc and the nearby Gould Belt
provide useful, however not yet conclusive, constraints on the competing
models.Comment: 9 pages, 5 figures, to be published in proceedings of the Albert
Einstein Century International Conference, Paris 200
Radio to Gamma-Ray Emission from Shell-type Supernova Remnants: Predictions from Non-linear Shock Acceleration Models
Supernova remnants (SNRs) are widely believed to be the principal source of
galactic cosmic rays. Such energetic particles can produce gamma-rays and lower
energy photons via interactions with the ambient plasma. In this paper, we
present results from a Monte Carlo simulation of non-linear shock structure and
acceleration coupled with photon emission in shell-like SNRs. These
non-linearities are a by-product of the dynamical influence of the accelerated
cosmic rays on the shocked plasma and result in distributions of cosmic rays
which deviate from pure power-laws. Such deviations are crucial to acceleration
efficiency and spectral considerations, producing GeV/TeV intensity ratios that
are quite different from test particle predictions. The Sedov scaling solution
for SNR expansions is used to estimate important shock parameters for input
into the Monte Carlo simulation. We calculate ion and electron distributions
that spawn neutral pion decay, bremsstrahlung, inverse Compton, and synchrotron
emission, yielding complete photon spectra from radio frequencies to gamma-ray
energies. The cessation of acceleration caused by the spatial and temporal
limitations of the expanding SNR shell in moderately dense interstellar regions
can yield spectral cutoffs in the TeV energy range; these are consistent with
Whipple's TeV upper limits on unidentified EGRET sources. Supernova remnants in
lower density environments generate higher energy cosmic rays that produce
predominantly inverse Compton emission at super-TeV energies; such sources will
generally be gamma-ray dim at GeV energies.Comment: 62 pages, AASTeX format, including 1 table and 11 figures, accepted
for publication in The Astrophysical Journal (Vol 513, March 1, 1999
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