258 research outputs found
CTA and cosmic-ray diffusion in molecular clouds
Molecular clouds act as primary targets for cosmic-ray interactions and are
expected to shine in gamma-rays as a by-product of these interactions. Indeed
several detected gamma-ray sources both in HE and VHE gamma-rays (HE: 100 MeV <
E 100 GeV) have been directly or indirectly associated with
molecular clouds. Information on the local diffusion coefficient and the local
cosmic-ray population can be deduced from the observed gamma-ray signals. In
this work we concentrate on the capability of the forthcoming Cherenkov
Telescope Array Observatory (CTA) to provide such measurements. We investigate
the expected emission from clouds hosting an accelerator, exploring the
parameter space for different modes of acceleration, age of the source, cloud
density profile, and cosmic ray diffusion coefficient. We present some of the
most interesting cases for CTA regarding this science topic. The simulated
gamma-ray fluxes depend strongly on the input parameters. In some cases, from
CTA data it will be possible to constrain both the properties of the
accelerator and the propagation mode of cosmic rays in the cloud.Comment: In Proceedings of the 2012 Heidelberg Symposium on High Energy
Gamma-Ray Astronomy. All CTA contributions at arXiv:1211.184
H.E.S.S. observations of galaxy clusters
Clusters of galaxies, the largest gravitationally bound objects in the
universe, are expected to contain a significant population of hadronic and
leptonic cosmic rays. Potential sources for these particles are merger and
accretion shocks, starburst driven galactic winds and radio galaxies.
Furthermore, since galaxy clusters confine cosmic ray protons up to energies of
at least 1 PeV for a time longer than the Hubble time they act as storehouses
and accumulate all the hadronic particles which are accelerated within them.
Consequently clusters of galaxies are potential sources of VHE (> 100 GeV)
gamma rays. Motivated by these considerations, promising galaxy clusters are
observed with the H.E.S.S. experiment as part of an ongoing campaign. Here,
upper limits for the VHE gamma ray emission for the Abell 496 and Coma cluster
systems are reported.Comment: Contribution to the 30th ICRC, Merida Mexico, July 200
Gamma-ray signatures of cosmic ray acceleration, propagation, and confinement in the era of CTA
Galactic cosmic rays are commonly believed to be accelerated at supernova
remnants via diffusive shock acceleration. Despite the popularity of this idea,
a conclusive proof for its validity is still missing. Gamma-ray astronomy
provides us with a powerful tool to tackle this problem, because gamma rays are
produced during cosmic ray interactions with the ambient gas. The detection of
gamma rays from several supernova remnants is encouraging, but still does not
constitute a proof of the scenario, the main problem being the difficulty in
disentangling the hadronic and leptonic contributions to the emission. Once
released by their sources, cosmic rays diffuse in the interstellar medium, and
finally escape from the Galaxy. The diffuse gamma-ray emission from the
Galactic disk, as well as the gamma-ray emission detected from a few galaxies
is largely due to the interactions of cosmic rays in the interstellar medium.
On much larger scales, cosmic rays are also expected to permeate the
intracluster medium, since they can be confined and accumulated within clusters
of galaxies for cosmological times. Thus, the detection of gamma rays from
clusters of galaxies, or even upper limits on their emission, will allow us to
constrain the cosmic ray output of the sources they contain, such as normal
galaxies, AGNs, and cosmological shocks. In this paper, we describe the impact
that the Cherenkov Telescope Array, a future ground-based facility for
very-high energy gamma-ray astronomy, is expected to have in this field of
research.Comment: accepted to Astroparticle Physics, special issue on Physics with the
Cherenkov Telescope Arra
Binaries with the eyes of CTA
The binary systems that have been detected in gamma rays have proven very
useful to study high-energy processes, in particular particle acceleration,
emission and radiation reprocessing, and the dynamics of the underlying
magnetized flows. Binary systems, either detected or potential gamma-ray
emitters, can be grouped in different subclasses depending on the nature of the
binary components or the origin of the particle acceleration: the interaction
of the winds of either a pulsar and a massive star or two massive stars;
accretion onto a compact object and jet formation; and interaction of a
relativistic outflow with the external medium. We evaluate the potentialities
of an instrument like the Cherenkov telescope array (CTA) to study the
non-thermal physics of gamma-ray binaries, which requires the observation of
high-energy phenomena at different time and spatial scales. We analyze the
capability of CTA, under different configurations, to probe the spectral,
temporal and spatial behavior of gamma-ray binaries in the context of the known
or expected physics of these sources. CTA will be able to probe with high
spectral, temporal and spatial resolution the physical processes behind the
gamma-ray emission in binaries, significantly increasing as well the number of
known sources. This will allow the derivation of information on the particle
acceleration and emission sites qualitatively better than what is currently
available.Comment: 23 pages, 13 figures, accepted for publication in Astroparticle
Physics, special issue on Physics with the Cherenkov Telescope Arra
Progress in Monte Carlo design and optimization of the Cherenkov Telescope Array
The Cherenkov Telescope Array (CTA) will be an instrument covering a wide
energy range in very-high-energy (VHE) gamma rays. CTA will include several
types of telescopes, in order to optimize the performance over the whole energy
range. Both large-scale Monte Carlo (MC) simulations of CTA super-sets
(including many different possible CTA layouts as sub-sets) and smaller-scale
simulations dedicated to individual aspects were carried out and are on-going.
We summarize results of the prior round of large-scale simulations, show where
the design has now evolved beyond the conservative assumptions of the prior
round and present first results from the on-going new round of MC simulations.Comment: 4 pages, 5 figures. In Proceedings of the 33rd International Cosmic
Ray Conference (ICRC2013), Rio de Janeiro (Brazil). All CTA contributions at
arXiv:1307.223
Prospects for Observations of Pulsars and Pulsar Wind Nebulae with CTA
The last few years have seen a revolution in very-high gamma-ray astronomy
(VHE; E>100 GeV) driven largely by a new generation of Cherenkov telescopes
(namely the H.E.S.S. telescope array, the MAGIC and MAGIC-II large telescopes
and the VERITAS telescope array). The Cherenkov Telescope Array (CTA) project
foresees a factor of 5 to 10 improvement in sensitivity above 0.1 TeV,
extending the accessible energy range to higher energies up to 100 TeV, in the
Galactic cut-off regime, and down to a few tens GeV, covering the VHE photon
spectrum with good energy and angular resolution. As a result of the fast
development of the VHE field, the number of pulsar wind nebulae (PWNe) detected
has increased from one PWN in the early '90s to more than two dozen firm
candidates today. Also, the low energy threshold achieved and good sensitivity
at TeV energies has resulted in the detection of pulsed emission from the Crab
Pulsar (or its close environment) opening new and exiting expectations about
the pulsed spectra of the high energy pulsars powering PWNe. Here we discuss
the physics goals we aim to achieve with CTA on pulsar and PWNe physics
evaluating the response of the instrument for different configurations.Comment: accepted for publication in Astroparticle Physic
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