103 research outputs found
Results from observations of AGNs with the H.E.S.S. telescope system and Future plans
The H.E.S.S. (High Energy Stereoscopic System) phase I is comprised of four
Imaging Atmospheric Cherenkov telescopes, for observation of galactic and
cosmic sources of very high energy gamma rays. Its installation in the Khomas
highlands, Namibia has been completed in December, 2003. The first of these
telescopes was installed in June 2003, and data-taking has proceeded since that
time. The HESS telescope system provides a significant improvement in
sensitivity and a threshold for detection below that of previous Imaging
Atmospheric Cherenkov Telescopes. The characteristics for the phase-I will be
presented, together with plans for phase-II of the experiment, comprised of a
large telescope in the centre of the current phase-I providing a lowered
threshold and increased sensitivity. We can observe AGNs up to redshift 0.5
with HESS and 2-3 with HESS Phase-2, which provides a unique capability for
study of spectral and temporal characteristics on timescales of several hours
or even less than 1 h (depending on the strength of flares). We will present
the first results from a number of southern AGN observed during the
installation of the phase-I, in particular concerning the detection and
spectral properties of the AGN PKS2155305.Comment: To appear in the Springer-Verlag series "ESO Astrophysics Symposia
The H.E.S.S. View of the Central 200 Parsecs
The inner few hundred parsecs of our galaxy provide a laboratory for the
study of the production and propagation of energetic particles.
Very-high-energy gamma-rays provide an effective probe of these processes and,
especially when combined with data from other wave-bands, gamma-rays
observations are a powerful diagnostic tool. Within this central region, data
from the H.E.S.S. instrument have revealed three discrete sources of
very-high-energy gamma-rays and diffuse emission correlated with the
distribution of molecular material. Here I provide an overview of these recent
results from H.E.S.S.Comment: Proceedings of the Galactic Centre Workshop 200
Discovery of Very High Energy gamma - ray emission from the extreme BL Lac object H2356-309 with H.E.S.S
The understanding of acceleration mechanisms in active galactic nuclei (AGN)
jets and the measurement of the extragalactic-background-light (EBL) density
are closely linked and require the detection of a large sample of
very-high-energy (VHE) emitting extragalactic objects at varying redshifts. We
report here on the discovery with the H.E.S.S. (High Energy Stereoscopic
System) atmospheric-Cherenkov telescopes of the VHE Gamma-ray emission from
H2356 - 309, an extreme BL Lac object located at a redshift of 0.165. The
observations of this object, which was previously proposed as a
southern-hemisphere VHE candidate source, were performed between June and
December 2004. The total exposure is 38.9 hours live time, after data quality
selection, which yields the detection of a signal at the level of 9.0
(standard deviations) .Comment: To appear on proceeding of 29th International Cosmic Ray Conference
(ICRC 2005
Probing Lorentz Invariance at EeV Energy
Pierre Auger experiment has detected at least a couple of ray events above
energy 60 EeV from the direction of the radio-galaxy Centaurus A. Assuming
those events are from Centaurus A, we have calculated the number of neutral
cosmic ray events from this source for small values of the degree of violation
in Lorentz invariance. Our results show that a comparison of our calculated
numbers of events with the observed number of events at EeV energy from the
direction of the source can probe extremely low value of the degree of this
violation.Comment: 8 pages,4 figure
Understanding hadronic gamma-ray emission from supernova remnants
We aim to test the plausibility of a theoretical framework in which the
gamma-ray emission detected from supernova remnants may be of hadronic origin,
i.e., due to the decay of neutral pions produced in nuclear collisions
involving relativistic nuclei. In particular, we investigate the effects
induced by magnetic field amplification on the expected particle spectra,
outlining a phenomenological scenario consistent with both the underlying
Physics and the larger and larger amount of observational data provided by the
present generation of gamma experiments, which seem to indicate rather steep
spectra for the accelerated particles. In addition, in order to study to study
how pre-supernova winds might affect the expected emission in this class of
sources, the time-dependent gamma-ray luminosity of a remnant with a massive
progenitor is worked out. Solid points and limitations of the proposed scenario
are finally discussed in a critical way.Comment: 30 pages, 5 figures; Several comments, references and a figure added.
Some typos correcte
Production of Neutrinos and Secondary Electrons in Cosmic Sources
We study the individual contribution to secondary lepton production in
hadronic interactions of cosmic rays (CRs) including resonances and heavier
secondaries. For this purpose we use the same ethodology discussed earlier
\cite{Huang07}, namely the Monte Carlo particle collision code DPMJET3.04 to
determine the multiplicity spectra of various secondary particles with leptons
as the final decay states, that result from inelastic collisions of cosmic-ray
protons and Helium nuclei with the interstellar medium of standard composition.
By combining the simulation results with parametric models for secondary
particle (with resonances included) for incident cosmic-ray energies below a
few GeV, where DPMJET appears unreliable, we thus derive production matrices
for all stable secondary particles in cosmic-ray interactions with energies up
to about 10 PeV. We apply the production matrices to calculate the radio
synchrotron radiation of secondary electrons in a young shell-type SNR, RX
J1713.7-3946, which is a measure of the age, the spectral index of hadronic
cosmic rays, and most importantly the magnetic field strength. We find that the
multi-mG fields recently invoked to explain the X-ray flux variations are
unlikely to extend over a large fraction of the radio-emitting region,
otherwise the spectrum of hadronic cosmic rays in the energy window 0.1-100 GeV
must be unusually hard. We also use the production matrices to calculate the
muon event rate in an IceCube-like detector that are induced by muon neutrinos
from high-energy -ray sources such as RX J1713.7-3946, Vela Jr. and
MGRO J2019+37. At muon energies of a few TeV, or in other word, about 10 TeV
neutrino energy, an accumulation of data over about five to ten years would
allow testing the hadronic origin of TeV -rays.Comment: 21 Pages; 3 Figures; 1 Table; Astroparticle Physics Minor Revise
Two photon annihilation of Kaluza-Klein dark matter
We investigate the fermionic one-loop cross section for the two photon
annihilation of Kaluza-Klein (KK) dark matter particles in a model of universal
extra dimensions (UED). This process gives a nearly mono-energetic gamma-ray
line with energy equal to the KK dark matter particle mass. We find that the
cross section is large enough that if a continuum signature is detected, the
energy distribution of gamma-rays should end at the particle mass with a peak
that is visible for an energy resolution of the detector at the percent level.
This would give an unmistakable signature of a dark matter origin of the
gamma-rays, and a unique determination of the dark matter particle mass, which
in the case studied should be around 800 GeV. Unlike the situation for
supersymmetric models where the two-gamma peak may or may not be visible
depending on parameters, this feature seems to be quite robust in UED models,
and should be similar in other models where annihilation into fermions is not
helicity suppressed. The observability of the signal still depends on largely
unknown astrophysical parameters related to the structure of the dark matter
halo. If the dark matter near the galactic center is adiabatically contracted
by the central star cluster, or if the dark matter halo has substructure
surviving tidal effects, prospects for detection look promising.Comment: 17 pages, 3 figures; slightly revised versio
Determining Supersymmetric Parameters With Dark Matter Experiments
In this article, we explore the ability of direct and indirect dark matter
experiments to not only detect neutralino dark matter, but to constrain and
measure the parameters of supersymmetry. In particular, we explore the
relationship between the phenomenological quantities relevant to dark matter
experiments, such as the neutralino annihilation and elastic scattering cross
sections, and the underlying characteristics of the supersymmetric model, such
as the values of mu (and the composition of the lightest neutralino), m_A and
tan beta. We explore a broad range of supersymmetric models and then focus on a
smaller set of benchmark models. We find that by combining astrophysical
observations with collider measurements, mu can often be constrained far more
tightly than it can be from LHC data alone. In models in the A-funnel region of
parameter space, we find that dark matter experiments can potentially determine
m_A to roughly +/-100 GeV, even when heavy neutral MSSM Higgs bosons (A, H_1)
cannot be observed at the LHC. The information provided by astrophysical
experiments is often highly complementary to the information most easily
ascertained at colliders.Comment: 46 pages, 76 figure
Diffuse Neutrino and Gamma-ray Emissions of the Galaxy above the TeV
We simulate the neutrino and -ray emissions of the Galaxy which are
originated from the hadronic scattering of cosmic rays (CR) with the
interstellar medium (ISM).
Rather than assuming a uniform CR density, we estimate the spatial
distribution of CR nuclei by means of numerical simulations. We consider
several models of the galactic magnetic field and of the ISM distribution
finding only a weak dependence of our results on their choice. We found that by
extrapolating the predicted -ray spectra down to few GeV we get a good
agreement with EGRET measurements. Then, we can reliably compare our
predictions with available observations above the TeV both for the
-rays and the neutrinos. We confirm that the excesses observed by
MILAGRO in the Cygnus region and by HESS in the Galactic Centre Ridge cannot be
explained without invoking significant CR over-densities in those regions.
Finally, we discuss the perspectives that a km neutrino telescope based in
the North hemisphere has to measure the diffuse emission from the inner Galaxy.Comment: 27 pages, 13 figures. Several figures have been added or replaced. A
new model for the ISM distribution has been considered. Accepted for
publication in JCA
Dark Matter And With Minimal Soft SUSY Breaking II
We update and extend to larger masses our previous analysis of the MSSM with
minimal [MSOSM] soft SUSY breaking boundary conditions. We
find a well--defined, narrow region of parameter space which provides the
observed relic density of dark matter, in a domain selected to fit precision
electroweak data, including top, bottom and tau masses. The model is highly
constrained which allows us to make several predictions. We find the light
Higgs mass GeV and also upper bounds on the mass of the
gluino \mgluino\lsim3.1 TeV and lightest neutralino \mchi\lsim450 GeV. As
the CP odd Higgs mass increases, the region of parameter space consistent
with WMAP data is forced to larger values of and smaller values of
. Hence, we find an upper bound m_A \lsim 1.3 TeV. This in turn leads to
lower bounds on (assuming minimal
flavor violation) and on the dark matter spin independent detection cross
section \sigsip > 10^{-9} pb. Finally, we extend our previous analysis to
include WIMP signals in indirect detection and find prospects for WIMP
detection generally much less promising than in direct WIMP searches.Comment: 24 page
- …