11 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
Thermal X-Ray Pulses Resulting From Pulsar Glitches
The non-spherically symmetric transport equations and exact thermal evolution
model are used to calculate the transient thermal response to pulsars. The
three possible ways of energy release originated from glitches, namely the
`shell', `ring' and `spot' cases are compared. The X-ray light curves resulting
from the thermal response to the glitches are calculated. Only the `spot' case
and the `ring' case are considered because the `shell' case does not produce
significant modulative X-rays. The magnetic field () effect, the
relativistic light bending effect and the rotational effect on the photons
being emitted in a finite region are considered. Various sets of parameters
result in different evolution patterns of light curves. We find that this
modulated thermal X-ray radiation resulting from glitches may provide some
useful constraints on glitch models.Comment: 48 pages, 20 figures, submitted to Ap
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
The physics of neutron stars
abstractpublished_or_final_versionPhysicsDoctoralDoctor of Philosoph
Thermal X-ray pulses resulting from pulsar glitches
published_or_final_versiontocabstractPhysicsMasterMaster of Philosoph
Heterogenisation of a c-scorpionate feII complex on carbon materials for cyclohexane oxidation with hydrogen peroxide
The hydrotris(pyrazol-1-yl)methane iron(II) complex [FeCl2{h3-HC(pz)3}] (pz=pyrazol-1-yl) (1) was immobilized on three diferente carbon materials (activated carbon, carbon xerogel and multi-walled carbon nanotubes) with three different surface treatments (original, treated with nitric acid, and treated with nitric acid followed by sodium hydroxide) to produce active, selective and recyclable catalysts. The heterogenisation process was more efficient for carbon nanotubes treated with nitric acid and sodium hydroxide. An outstanding improved catalytic performance of complex 1 upon heterogenisation on carbon nanotubes treated with nitric acid and sodium hydroxide (turnover numbers up to 5.6_103 and overall yield of 21 %), relative to the homogeneous system, was achieved for the single-pot peroxidative oxidation of cyclohexane to the cyclohexanone and cyclohexanol mixture. The heterogenised systems allowed their easy recovery and reuse, at least for five consecutive cycles, maintaining 96% of the initial activity and concomitante rather high selectivity to cyclohexanol and cyclohexanone.info:eu-repo/semantics/publishedVersio