956 research outputs found
Xeff analysis method optimization to enhance IACTs performances
The seek of high precision analyses in -ray astronomy leads to the
implementation of multivariate combination, benefiting from several
reconstruction methods. Such analysis, called , was developed for the
H.E.S.S. data using three shower reconstruction methods. This paper presents
the improvement granted to this analysis by refining the distribution
calculation of discriminant variables, considering observation conditions, and
adding new variables in the combination. The efficiency of the
analysis is presented using simulations and real data. A comparison with the
standard analysis (model++), for a typical set of sources, shows a significant
gain in sensitivity.Comment: Contribution to the Proceedings of the 34th International Cosmic Ray
Conference (ICRC 2015), The Hague, The Netherland
Systematic effects in the estimate of the local gamma-ray emissivity
We show in this letter that estimates of the local emissivity of
{\gamma}-rays in the GeV-TeV range suffer uncertainties which are of the same
order of magnitude as the current Fermi results. Primary cosmic-ray fluxes,
cosmic-ray propagation, interstellar helium abundance and {\gamma}-ray
production crosssections all affect the estimate of this quantity. We also show
that the so-called nuclear enhancement factor -- though widely used so far to
model the {\gamma}-ray emissivity -- is no longer a relevant quantity given the
latest measurements of the primary cosmic ray proton and helium spectra
Optimization of multivariate analysis for IACT stereoscopic systems
Multivariate methods have been recently introduced and successfully applied
for the discrimination of signal from background in the selection of genuine
very-high energy gamma-ray events with the H.E.S.S. Imaging Atmospheric
Cerenkov Telescope. The complementary performance of three independent
reconstruction methods developed for the H.E.S.S. data analysis, namely Hillas,
model and 3D-model suggests the optimization of their combination through the
application of a resulting efficient multivariate estimator. In this work the
boosted decision tree method is proposed leading to a significant increase in
the signal over background ratio compared to the standard approaches. The
improved sensitivity is also demonstrated through a comparative analysis of a
set of benchmark astrophysical sources.Comment: 10 pages, 8 figures, 3 tables, accepted for publication in
Astroparticle Physic
The Monoceros very-high-energy gamma-ray source
The H.E.S.S. telescope array has observed the complex Monoceros Loop
SNR/Rosette Nebula region which contains unidentified high energy EGRET sources
and potential very-high-energy (VHE) gamma-ray source. We announce the
discovery of a new point-like VHE gamma-ray sources, HESS J0632+057. It is
located close to the rim of the Monoceros SNR and has no clear counterpart at
other wavelengths. Data from the NANTEN telescope have been used to investigate
hadronic interactions with nearby molecular clouds. We found no evidence for a
clear association. The VHE gamma-ray emission is possibly associated with the
lower energy gamma-ray source 3EG J0634+0521, a weak X-ray source 1RXS
J063258.3+054857 and the Be-star MWC 148.Comment: 4 pages, 4 figures, Contribution to the 30th ICRC, Merida Mexico,
July 200
New unidentified H.E.S.S. Galactic sources
H.E.S.S. is one of the most sensitive instruments in the very high energy
(VHE; > 100 GeV) gamma-ray domain and has revealed many new sources along the
Galactic Plane. After the successful first VHE Galactic Plane Survey of 2004,
H.E.S.S. has continued and extended that survey in 2005-2008, discovering a
number of new sources, many of which are unidentified. Some of the unidentified
H.E.S.S. sources have several positional counterparts and hence several
different possible scenarios for the origin of the VHE gamma-ray emission;
their identification remains unclear. Others have so far no counterparts at any
other wavelength. Particularly, the lack of an X-ray counterpart puts serious
constraints on emission models. Several newly discovered and still unidentified
VHE sources are reported here.Comment: ICRC 2009 proceeding
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