91 research outputs found
Very-High Energy Gamma Astrophysics
High-energy photons are a powerful probe for astrophysics and for fundamental
physics under extreme conditions. During the recent years, our knowledge of the
most violent phenomena in the Universe has impressively progressed thanks to
the advent of new detectors for high-energy gamma-rays. Observation of
gamma-rays gives an exciting view of the high-energy universe thanks to
satellite-based telescopes (AGILE, GLAST) and to ground-based detectors like
the Cherenkov telescopes (H.E.S.S. and MAGIC in particular), which recently
discovered more than 60 new very-high-energy sources. The progress achieved
with the last generation of Cherenkov telescopes is comparable to the one drawn
by EGRET with respect to the previous gamma-ray satellite detectors. This
article reviews the present status of high-energy gamma astrophysics, with
emphasis on the recent results and on the experimental developments.Comment: 60 pages, 52 figures, (on line abstract replacement
Evidence for an axion-like particle from blazar spectra?
Observations with the Imaging Atmospheric Cherenkov Telescopes H.E.S.S.,
MAGIC, CANGAROO III and VERITAS have shown that the Universe is more
transparent than expected to gamma rays above 100GeV. As a natural explanation,
the DARMA scenario has previously been proposed, wherein photons can oscillate
into a new very light axionlike particle and vice-versa in the presence of
cosmic magnetic fields. Here we demonstrate that the most recent observations
further support the DARMA scenario, thereby making the existence of a very
light axion-like particle more likely.Comment: 4 pages, 1 figure. Proceeding of the "6th Patras Workshop on Axions,
WIMPs and WISPs", Zurich, Switzerland, 5 - 9 July 2010 (to appear in the
Proceedings
Diffuse non-thermal emission in the disks of the Magellanic Clouds
The Magellanic Clouds, two dwarf galaxy companions to the Milky Way, are
among the Fermi Large Area Telescope (LAT) brightest gamma-ray sources. Aiming
at a comprehensive modeling of the non-thermal electromagnetic and neutrino
emission in both Clouds, we self-consistently model the radio and gamma-ray
spectral energy distribution from their disks based on recently published
Murchison Widefield Array and Fermi/LAT data. All relevant radiative processes
involving relativistic and thermal electrons (synchrotron, Compton scattering,
and bremsstrahlung) and relativistic protons (neutral-pion decay following
interaction with thermal protons) are considered, using exact emission
formulae. Our joint spectral analyses indicate that radio emission in the
Clouds has both primary and secondary electron synchrotron and thermal
bremsstrahlung origin, whereas gamma rays originate mostly from neutral-pion
decay with some contributions from relativistic bremsstrahlung and Compton
scattering off starlight. The proton spectra in both galaxies are modeled as
power laws in energy with similar spectral indices, ~2.4, and energy densities,
~1 eV/cm3. The predicted 0.1-10 GeV neutrino flux is too low for detection by
current and upcoming experiments. Our analyses confirm earlier suggestions of a
largely hadronic origin of the gamma-ray emission in both Magellanic Clouds.Comment: A&A, in press; 11 pages, 7 figure
- …