32 research outputs found
The Contribution of Fermi Gamma-Ray Pulsars to the local Flux of Cosmic-Ray Electrons and Positrons
We analyze the contribution of gamma-ray pulsars from the first Fermi-Large
Area Telescope (LAT) catalogue to the local flux of cosmic-ray electrons and
positrons (e+e-). We present new distance estimates for all Fermi gamma-ray
pulsars, based on the measured gamma-ray flux and pulse shape. We then estimate
the contribution of gamma-ray pulsars to the local e+e- flux, in the context of
a simple model for the pulsar e+e- emission. We find that 10 of the Fermi
pulsars potentially contribute significantly to the measured e+e- flux in the
energy range between 100 GeV and 1 TeV. Of the 10 pulsars, 2 are old EGRET
gamma-ray pulsars, 2 pulsars were discovered with radio ephemerides, and 6 were
discovered with the Fermi pulsar blind-search campaign. We argue that known
radio pulsars fall in regions of parameter space where the e+e- contribution is
predicted to be typically much smaller than from those regions where Fermi-LAT
pulsars exist. However, comparing the Fermi gamma-ray flux sensitivity to the
regions of pulsar parameter space where a significant e+e- contribution is
predicted, we find that a few known radio pulsars that have not yet been
detected by Fermi can also significantly contribute to the local e+e- flux if
(i) they are closer than 2 kpc, and if (ii) they have a characteristic age on
the order of one mega-year.Comment: 21 pages, 6 figures, accepted for publication in JCA
On possibility of measurement of the electron beam energy using absorption of radiation by electrons in a magnetic field
The possibility of the precise measurement of the electron beam energy using
absorption of radiation by electrons in a static and homogeneous magnetic field
in a range up to a few hundred GeV energies, was considered in [1]. With the
purpose of experimental checking of this method in a range of several tens MeV
energies, the possibility of measurement of absolute energy of the electron
beam energy with relative accuracy up to 10^{-4} is examined in details.Comment: 14 pages, 10 figure
Short time scale pulse stability of the Crab pulsar in the optical band
The fine structure and the variations of the optical pulse shape and phase of
the Crab pulsar are studied on various time scales. The observations have been
carried out on 4-m William Hershel and 6-m BTA telescopes with APD photon
counter, photomultiplier based 4-channel photometer and PSD based panoramic
spectrophotopolarimeter with 1s time resolution in 1994, 1999, 2003 and
2005-2006 years. The upper limit on the pulsar precession on Dec 2, 1999 is
placed in the 10 s - 2 hours time range. The evidence of a varying from set to
set fine structure of the main pulse is found in the 1999 and 2003 years data.
No such fine structure is detected in the integral pulse shape of 1994, 1999
and 2003 years.
The drastic change of the pulse shape in the 2005-2006 years set is detected
along with the pulse shape variability and quasi-periodic phase shifts.Comment: 4 pages, 6 figures. To appear in ApSS, in the proceedings of the
conference "Isolated Neutron Stars: from the Interior to the Surface",
London, April 2006; eds. D. Page, R. Turolla and S. Zan
The Geminga Fraction
Radio-quiet gamma-ray pulsars like Geminga may account for a number of the unidentified EGRET sources in the Galaxy. The number of Geminga-like pulsars is very sensitive to the geometry of both the gamma-ray and radio beams. Recent studies of the shape and polarization of pulse profiles of young radio pulsars have provided evidence that their radio emission originates in wide cone beams at altitudes that are a significant fraction (1 -10%) of their light cylinder radius. Such wide radio emission beams will be visible at a much larger range of observer angles than the narrow core components thought to originate at lower altitude. Using 3D geometrical modeling that includes relativistic effects from pulsar rotation, we study the visibility of such radio cone beams as well as that of the gamma-ray beams predicted by slot gap and outer gap models. From the results of this study one can obtain revised predictions for the fraction of Geminga-like, radio quiet pulsars present in the gamma-ray pulsar population
Strong laser fields as a probe for fundamental physics
Upcoming high-intensity laser systems will be able to probe the
quantum-induced nonlinear regime of electrodynamics. So far unobserved QED
phenomena such as the discovery of a nonlinear response of the quantum vacuum
to macroscopic electromagnetic fields can become accessible. In addition, such
laser systems provide for a flexible tool for investigating fundamental
physics. Primary goals consist in verifying so far unobserved QED phenomena.
Moreover, strong-field experiments can search for new light but weakly
interacting degrees of freedom and are thus complementary to accelerator-driven
experiments. I review recent developments in this field, focusing on photon
experiments in strong electromagnetic fields. The interaction of
particle-physics candidates with photons and external fields can be
parameterized by low-energy effective actions and typically predict
characteristic optical signatures. I perform first estimates of the accessible
new-physics parameter space of high-intensity laser facilities such as POLARIS
and ELI.Comment: 7 pages, Key Lecture at the ELI Workshop and School on "Fundamental
Physics with Ultra-High Fields", 9 September - 2 October 2008 at Frauenworth
Monastery, German
Adjustment of the electric current in pulsar magnetospheres and origin of subpulse modulation
The subpulse modulation of pulsar radio emission goes to prove that the
plasma flow in the open field line tube breaks into isolated narrow streams. I
propose a model which attributes formation of streams to the process of the
electric current adjustment in the magnetosphere. A mismatch between the
magnetospheric current distribution and the current injected by the polar cap
accelerator gives rise to reverse plasma flows in the magnetosphere. The
reverse flow shields the electric field in the polar gap and thus shuts up the
plasma production process. I assume that a circulating system of streams is
formed such that the upward streams are produced in narrow gaps separated by
downward streams. The electric drift is small in this model because the
potential drop in narrow gaps is small. The gaps have to drift because by the
time a downward stream reaches the star surface and shields the electric field,
the corresponding gap has to shift. The transverse size of the streams is
determined by the condition that the potential drop in the gaps is sufficient
for the pair production. This yields the radius of the stream roughly 10% of
the polar cap radius, which makes it possible to fit in the observed
morphological features such as the "carousel" with 10-20 subbeams and the
system of the core - two nested cone beams.Comment: 8 pages, 1 figur
Probing For New Physics and Detecting non linear vacuum QED effects using gravitational wave interferometer antennas
Low energy non linear QED effects in vacuum have been predicted since 1936
and have been subject of research for many decades. Two main schemes have been
proposed for such a 'first' detection: measurements of ellipticity acquired by
a linearly polarized beam of light passing through a magnetic field and direct
light-light scattering. The study of the propagation of light through an
external field can also be used to probe for new physics such as the existence
of axion-like particles and millicharged particles. Their existence in nature
would cause the index of refraction of vacuum to be different from unity in the
presence of an external field and dependent of the polarization direction of
the light propagating. The major achievement of reaching the project
sensitivities in gravitational wave interferometers such as LIGO an VIRGO has
opened the possibility of using such instruments for the detection of QED
corrections in electrodynamics and for probing new physics at very low
energies. In this paper we discuss the difference between direct birefringence
measurements and index of refraction measurements. We propose an almost
parasitic implementation of an external magnetic field along the arms of the
VIRGO interferometer and discuss the advantage of this choice in comparison to
a previously proposed configuration based on shorter prototype interferometers
which we believe is inadequate. Considering the design sensitivity in the
strain, for the near future VIRGO+ interferometer, of in the range 40 Hz Hz leads to a variable
dipole magnet configuration at a frequency above 20 Hz such that Tm/ for a `first' vacuum non linear QED detection
Population statistics study of radio and gamma-ray pulsars in the Galactic plane
We present results of our pulsar population synthesis of ordinary isolated
and millisecond pulsars in the Galactic plane. Over the past several years, a
program has been developed to simulate pulsar birth, evolution and emission
using Monte Carlo techniques. We have added to the program the capability to
simulate millisecond pulsars, which are old, recycled pulsars with extremely
short periods. We model the spatial distribution of the simulated pulsars by
assuming that they start with a random kick velocity and then evolve through
the Galactic potential. We use a polar cap/slot gap model for -ray
emission from both millisecond and ordinary pulsars. From our studies of radio
pulsars that have clearly identifiable core and cone components, in which we
fit the polarization sweep as well as the pulse profiles in order to constrain
the viewing geometry, we develop a model describing the ratio of radio
core-to-cone peak fluxes. In this model, short period pulsars are more
cone-dominated than in our previous studies. We present the preliminary results
of our recent study and the implications for observing these pulsars with GLAST
and AGILE.Comment: 6 pages, 3 figures, 1 table, accepted in Astrophysics and Space
Scienc