3,676 research outputs found
A re-visit of the phase-resolved X-ray and \gamma-ray spectra of the Crab pulsar
We use a modified outer gap model to study the multi-frequency phase-resolved
spectra of the Crab pulsar. The emissions from both poles contribute to the
light curve and the phase-resolved spectra. Using the synchrotron self-Compton
mechanism and by considering the incomplete conversion of curvature photons
into secondary pairs, the observed phase-averaged spectrum from 100 eV - 10 GeV
can be explained very well. The predicted phase-resolved spectra can match the
observed data reasonably well, too. We find that the emission from the north
pole mainly contributes to Leading Wing 1. The emissions in the remaining
phases are mainly dominated by the south pole. The widening of the azimuthal
extension of the outer gap explains Trailing Wing 2. The complicated
phase-resolved spectra for the phases between the two peaks, namely Trailing
Wing 1, Bridge and Leading Wing 2, strongly suggest that there are at least two
well-separated emission regions with multiple emission mechanisms, i.e.
synchrotron radiation, inverse Compton scattering and curvature radiation. Our
best fit results indicate that there may exist some asymmetry between the south
and the north poles. Our model predictions can be examined by GLAST.Comment: 35 pages, 13 figures, accepted to publish in Ap
Pulse Profiles, Spectra and Polarization Characteristics of Non-Thermal Emissions from the Crab-Like Pulsars
We discuss non-thermal emission mechanism of the Crab-like pulsars with both
a two-dimensional electrodynamical study and a three-dimensional model. We
investigate the emission process in the outer gap accelerator. In the
two-dimensional electrodynamical 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 process and
the pair-creation process. We show a solved gap structure which produces a
consistent gamma-ray spectrum with EGRET observation. Based on the
two-dimensional model, we conduct 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 to
-ray bands to compare 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 with that of the
observations. The calculated phase-resolved spectra are consistent with the
data through optical to the -ray bands. We demonstrate that the
1020 % of the polarization degree in the optical emissions from the Crab
pulsar and the Vela pulsar are explained by the synchrotron emissions with the
particle gyration motion.Comment: 39 pages, 11 figures, Accepted for publication in Ap
X-ray/GeV emissions from Crab-like pulsars in LMC
We discuss X-ray and gamma-ray emissions from Crab-like pulsars,
PSRs~J0537-6910 and~J0540-6919, in Large Magellanic Cloud. Fermi-LAT
observations have resolved the gamma-ray emissions from these two pulsars and
found the pulsed emissions from PSR~J0540-6919. The total pulsed radiation in
the X-ray/gamma-ray energy bands of PSR~J0540-6919 is observed with the
efficiency (in 4 sr), which is about a factor of
ten larger than of the Crab pulsar. Although
PSR~J0537-6910 has the highest spin-down power among currently known pulsars,
the efficiency of the observed X-ray emissions is about two orders of magnitude
smaller than that of PSR~J0540-6919. This paper mainly discusses what causes
the difference in the radiation efficiencies of these three energetic Crab-like
pulsars. We discuss electron/positron acceleration and high-energy emission
processes within the outer gap model. By solving the outer gap structure with
the dipole magnetic field, we show that the radiation efficiency decreases as
the inclination angle between the magnetic axis and the rotation axis
increases. To explain the difference in the pulse profile and in the radiation
efficiency, our model suggests that PSR~J0540-6919 has an inclination angle
much smaller than the that of Crab pulsar (here we assume the inclination
angles of both pulsars are ). On the other hand, we
speculate that the difference in the radiation efficiencies between
PSRs~J0537-6910 and J0549-6919 is mainly caused by the difference in the Earth
viewing angle, and that we see PSR~J0537-6910 with an Earth viewing angle
(or ) measured from the spin axis, while we
see PSR~J0540-6919 with .Comment: 23 pages, 7 figures, ApJ in pres
Three-dimensional Two-Layer Outer Gap Model: Fermi Energy Dependent Light Curves of the Vela Pulsar
We extend the two-dimensional two-layer outer gap model to a
three-dimensional geometry and use it to study the high-energy emission of the
Vela pulsar. In this model, the outer gap is divided into two parts, i.e. the
main acceleration region on the top of last-open field lines and the screening
region around the upper boundary of the gap. In the main acceleration region,
the charge density is much lower than the Goldreich-Julian charge density and
the charged particles are accelerated by the electric field along the magnetic
field to emit multi-GeV photons. In the screening region, the charge density is
larger than the Goldreich-Julian value to close the gap and particles in this
region are responsible for multi-100MeV photon emission. We apply this three
dimensional two-layer model to the Vela pulsar and compare the model light
curves, the phase-averaged spectrum and the phase-resolved spectra with the
recent Fermi observations, which also reveals the existence of the third peak
between two main peaks. The phase position of the third peak moves with the
photon energy, which cannot be explained by the geometry of magnetic field
structure and the caustic effects of the photon propagation. We suggest that
the existence of the third peak and its energy dependent movement results from
the azimuthal structure of the outer gap.Comment: 11 pages, 15 figures, accepted for publication in MNRA
Population study for -ray emitting Millisecond Pulsars and unidentified sources
The -LAT has revealed that rotation powered millisecond pulsars (MSPs)
are a major contributor to the Galactic -ray source population. We
discuss the -ray emission process within the context of the outer gap
accelerator model, and use a Monte-Calro method to simulate the Galactic
population of the -ray emitting MSPs. We find that the outer gap
accelerator controlled by the magnetic pair-creation process is preferable in
explaining the possible correlation between the -ray luminosity and the
spin down power. Our Monte-Calro simulation implies that most of the
-ray emitting MSPs are radio quiet in the present sensitivity of the
radio survey, indicating that most of the -ray MSPs have been
unidentified. We argue that the Galactic unidentified sources located
at high latitudes should be dominated by MSPs, whereas the sources in the
galactic plane are dominated by radio-quiet canonical pulsars.Comment: 2011 Fermi Symposium proceedings - eConf C11050
Three-dimensional Two-Layer Outer Gap Model: the Third Peak of Vela Pulsar
We extend the two-dimensional two-layer outer gap model to a
three-dimensional geometry and use it to study the high-energy emission of the
Vela pulsar. We apply this three-dimensional two-layer model to the Vela pulsar
and compare the model light curves, the phase-averaged spectrum and the
phase-resolved spectra with the recent Fermi observations, which also reveals
the existence of the third peak between two main peaks. The phase position of
the third peak moves with the photon energy, which cannot be explained by the
geometry of magnetic field structure and the caustic effect of the photon
propagation. We suggest that the existence of the third peak and its energy
dependent movement results from the azimuthal structure of the outer gap.Comment: 2011 Fermi Symposium proceedings - eConf C11050
Radiation Mechanism of the Soft Gamma-ray Pulsar PSR B1509-58
The outer gap model is used here to explain the spectrum and the energy
dependent light curves of the X-ray and soft gamma-ray radiations of the
spin-down powered pulsar PSR B1509-58.In the outer gap model, most pairs inside
the gap are created around the null charge surface and the gap's electric field
separates the two charges to move in opposite directions. Consequently, the
region from the null charge surface to the light cylinder is dominated by the
outflow of particles and that from the null charge surface to the star is
dominated by the inflow of particles. The inflow and outflow of particles move
along the magnetic field lines and emit curvature photons, and the incoming
curvature photons are converted to pairs by the strong magnetic field of the
star. These pairs emit synchrotron photons. We suggest that the X-rays and soft
gamma-rays of PSR B1509-58 result from the synchrotron radiation of these
pairs, and the viewing angle of PSR B1509-58 only receives the inflow
radiation. The magnetic pair creation requires a large pitch angle, which makes
the pulse profile of the synchrotron radiation distinct from that of the
curvature radiation. We carefully trace the pulse profiles of the synchrotron
radiation with different pitch angles. We find that the differences between the
light curves of different energy bands are due to the different pitch angles of
the secondary pairs, and the second peak appearing at E>10MeV comes from the
region near the star, where the stronger magnetic field allows the pair
creation to happen with a smaller pitch angle.Comment: 5 pages, 8 figures, 2012 Fermi Symposium proceedings - eConf C12102
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