5,387 research outputs found
Exploring Particle Acceleration in Gamma-Ray Binaries
Binary systems can be powerful sources of non-thermal emission from radio to
gamma rays. When the latter are detected, then these objects are known as
gamma-ray binaries. In this work, we explore, in the context of gamma-ray
binaries, different acceleration processes to estimate their efficiency: Fermi
I, Fermi II, shear acceleration, the converter mechanism, and magnetic
reconnection. We find that Fermi I acceleration in a mildly relativistic shock
can provide, although marginally, the multi-10 TeV particles required to
explain observations. Shear acceleration may be a complementary mechanism,
giving particles the final boost to reach such a high energies. Fermi II
acceleration may be too slow to account for the observed very high energy
photons, but may be suitable to explain extended low-energy emission. The
converter mechanism seems to require rather high Lorentz factors but cannot be
discarded a priori. Standard relativistic shock acceleration requires a highly
turbulent, weakly magnetized downstream medium; magnetic reconnection, by
itself possibly insufficient to reach very high energies, could perhaps
facilitate such a conditions. Further theoretical developments, and a better
source characterization, are needed to pinpoint the dominant acceleration
mechanism, which need not be one and the same in all sources.Comment: 7 pages, 1 figure, proceedings of the 13th ICATPP Conference on
Astroparticle, Particle, Space Physics and Detectors for Physics Applications
(Villa Olmo, Como 3-7 October 2011
A new direction for Japan
Economic policy - Japan ; Japan ; International trade - Japan
Ramanujan sums as supercharacters
The theory of supercharacters, recently developed by Diaconis-Isaacs and
Andre, can be used to derive the fundamental algebraic properties of Ramanujan
sums. This machinery frequently yields one-line proofs of difficult identities
and provides many novel formulas. In addition to exhibiting a new application
of supercharacter theory, this article also serves as a blueprint for future
work since some of the abstract results we develop are applicable in much
greater generality.Comment: 32 pages. Comments welcom
Electromagnetic radiation initiated by hadronic jets from microquasars in the ISM
Microquasars are potential candidates to produce a non-negligible fraction of
the observed galactic cosmic rays. The protons accelerated at the jet
termination shock interact with the interstellar medium and may produce
detectable fluxes of extended emission at different energy bands: high-energy
and very high-energy gamma-rays produced by neutral pion-decay, synchrotron and
bremsstrahlung emission in a wide energy range generated by the secondary
electrons produced by charged pion-decay. We discuss the association between
this scenario and some of the unidentified EGRET sources in the galactic plane.Comment: (1)Universitat de Barcelona (2)Max Planck institute fur kernphysik,
11 pages, 14 figures, accepted for publication in Astronomy & Astrophysic
Broad-band electromagnetic radiation from microquasars interacting with ISM
Microquasars (MQs) are galactic objects with relativistic jets that
constitute a source population which can be responsible for production of a
non-negligible fraction of the observed galactic cosmic rays. These
relativistic protons, associated with the termination of the jet, interact with
the interstellar medium and, at certain surrounding conditions, may lead to
production of detectable fluxes of high-energy and very high-energy gamma-rays.
This radiation is accompanied by the broad-band emission of secondary electrons
from decays of -mesons produced through synchrotron, bremstrahlung and
inverse Compton process. The features of broad-band emission initiated by
proton-proton (pp) interactions in such a scenario is discussed in the context
of the strategy of search for counterparts of high-energy and very high-energy
gamma-ray sources in the galactic plane.Comment: High Energy Gamma-Ray Astronomy: 2nd International Symposium,
Proceedings of the conference held 26-30 July 2004 in Heidelberg (Germany).
Edited by Felix A. Aharonian, Heinz J. Volk, and Dieter Horns. AIP Conference
Proceedings, Volume 745. New York: American Institute of Physics, 2005.,
p.317-32
Constructing the secular architecture of the solar system I: The giant planets
Using numerical simulations, we show that smooth migration of the giant
planets through a planetesimal disk leads to an orbital architecture that is
inconsistent with the current one: the resulting eccentricities and
inclinations of their orbits are too small. The crossing of mutual mean motion
resonances by the planets would excite their orbital eccentricities but not
their orbital inclinations. Moreover, the amplitudes of the eigenmodes
characterising the current secular evolution of the eccentricities of Jupiter
and Saturn would not be reproduced correctly; only one eigenmode is excited by
resonance-crossing. We show that, at the very least, encounters between Saturn
and one of the ice giants (Uranus or Neptune) need to have occurred, in order
to reproduce the current secular properties of the giant planets, in particular
the amplitude of the two strongest eigenmodes in the eccentricities of Jupiter
and Saturn.Comment: Astronomy & Astrophysics (2009) in pres
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