12,509 research outputs found
Diffuse gamma-ray emission from galactic pulsars
Millisecond Pulsars are second most abundant source population discovered by
the Fermi-LAT. They might contribute non-negligibly to the diffuse emission
measured at high latitudes by Fermi-LAT, the IDGRB. Gamma-ray sources also
contribute to the anisotropy of the IDGRB measured on small scales by
Fermi-LAT. We aim to assess the contribution of the unresolved counterpart of
the detected MSPs population to the IDGRB and the maximal fraction of the
measured anisotropy produced by this source class. We model the MSPs spatial
distribution in the Galaxy and the gamma-ray emission parameters by considering
radio and gamma-ray observational constraints. By simulating a large number of
MSPs populations, we compute the average diffuse emission and the anisotropy
1-sigma upper limit. The emission from unresolved MSPs at 2 GeV, where the peak
of the spectrum is located, is at most 0.9% of the measured IDGRB above 10
degrees in latitude. The 1-sigma upper limit on the angular power for
unresolved MSP sources turns out to be about a factor of 60 smaller than
Fermi-LAT measurements above 30 degrees. Our results indicate that this
galactic source class represents a negligible contributor to the high-latitude
gamma-ray sky and confirm that most of the intensity and geometrical properties
of the measured diffuse emission are imputable to other extragalactic source
classes. Nevertheless, given the MSP distribution, we expect them to contribute
significantly to the gamma-ray diffuse emission at low latitudes. Since, along
the galactic disk, the population of young Pulsars overcomes in number the one
of MSPs, we compute the gamma-ray emission from the whole population of
unresolved Pulsars in two low-latitude regions: the inner Galaxy and the
galactic center.Comment: 19 pages, 26 figures. It matches the published version, minor changes
onl
Interpretation of AMS-02 electrons and positrons data
We perform a combined analysis of the recent AMS-02 data on electrons,
positrons, electrons plus positrons and positron fraction, in a self-consistent
framework where we realize a theoretical modeling of all the astrophysical
components that can contribute to the observed fluxes in the whole energy
range. The primary electron contribution is modeled through the sum of an
average flux from distant sources and the fluxes from the local supernova
remnants in the Green catalog. The secondary electron and positron fluxes
originate from interactions on the interstellar medium of primary cosmic rays,
for which we derive a novel determination by using AMS-02 proton and helium
data. Primary positrons and electrons from pulsar wind nebulae in the ATNF
catalog are included and studied in terms of their most significant (while
loosely known) properties and under different assumptions (average contribution
from the whole catalog, single dominant pulsar, a few dominant pulsars). We
obtain a remarkable agreement between our various modeling and the AMS-02 data
for all types of analysis, demonstrating that the whole AMS-02 leptonic data
admit a self-consistent interpretation in terms of astrophysical contributions.Comment: 33 pages, 26 figures and 4 tables, v2: accepted for publication in
JCAP, minor changes relative to v
On the reliability of electrical drives for safety-critical applications
The aim of this work is to present some issues related to fault tolerant electric drives,which are able to overcome different types of faults occurring in the sensors, in thepower converter and in the electrical machine, without compromising the overallfunctionality of the system. These features are of utmost importance in safety-criticalapplications. In this paper, the reliability of both commercial and innovative driveconfigurations, which use redundant hardware and suitable control algorithms, will beinvestigated for the most common types of fault: besides standard three phase motordrives, also multiphase topologies, open-end winding solutions, multi-machineconfigurations will be analyzed, applied to various electric motor technologies. Thecomplexity of hardware and control strategies will also be compared in this paper, sincethis has a tremendous impact on the investment costs
A kpc-scale X-ray jet in the BL Lac source S5 2007+777
X-ray jets in AGN are commonly observed in FRII and FRI radio-galaxies, but
rarely in BL Lacs, most probably due to their orientation close to the line of
sight and the ensuing foreshortening effects. Only three BL Lacs are known so
far to contain a kpc-scale X-ray jet. In this paper, we present the evidence
for the existence of a fourth extended X-ray jet in the classical
radio-selected source S5 2007+777, which for its hybrid FRI/II radio morphology
has been classified as a HYMOR (HYbrid MOrphology Radio source). Our Chandra
ACIS-S observations of this source revealed an X-ray counterpart to the
19"-long radio jet. Interestingly, the X-ray properties of the kpc-scale jet in
S5 2007+777 are very similar to those observed in FRII jets. First, the X-ray
morphology closely mirrors the radio one, with the X-rays being concentrated in
the discrete radio knots. Second, the X-ray continuum of the jet/brightest knot
is described by a very hard power law, with photon index Gamma_x~1, although
the uncertainties are large. Third, the optical upper limit from archival HST
data implies a concave radio-to-X-ray SED. If the X-ray emission is attributed
to IC/CMB with equipartition, strong beaming (delta=13) is required, implying a
very large scale (Mpc) jet. The beaming requirement can be somewhat relaxed
assuming a magnetic field lower than equipartition. Alternatively, synchrotron
emission from a second population of very high-energy electrons is viable.
Comparison to other HYMOR jets detected with Chandra is discussed, as well as
general implications for the origin of the FRI/II division.Comment: Accepted for publication in ApJ, 19 pages, 3 figure
Interpreting the recent results on direct search for dark matter particles in terms of relic neutralino
The most recent results from direct searches for dark matter particles in the
galactic halo are examined in terms of an effective Minimal Supersymmetric
extension of the Standard Model at the electroweak scale without gaugino masses
unification. We show that the annual modulation effect at 8.2 C.L.
recently presented by the DAMA Collaboration, as the result of a combined
analysis of the DAMA/NaI and the DAMA/LIBRA experiments for a total exposure of
0.82 ton yr, fits remarkably well with what expected for relic neutralinos for
a wide variety of WIMP distribution functions. Bounds derivable from other
measurements of direct searches for dark matter particles are analyzed. We
stress the role played by the uncertainties affecting the neutralino--quark
couplings arising from the involved hadronic quantities. We also examine how
present data on cosmic antiprotons can help in constraining the neutralino
configurations selected by the DAMA effect, in connection with the values of
the astrophysical parameters.
Perspectives for measurement of antideuterons possibly produced in the
galactic halo by self--annihilation of neutralinos belonging to the DAMA
configurations are examined. Finally, we discuss how findings at LHC would
impact on these issues.Comment: 18 pages, 10 figures a few minor comments and two references adde
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