Xeff analysis method optimization to enhance IACTs performances

The seek of high precision analyses in $\gamma$-ray astronomy leads to the implementation of multivariate combination, benefiting from several reconstruction methods. Such analysis, called $X_{eff}$, 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 $X_{eff}$ 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

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

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

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

Discovery of VHE gamma-rays from the vicinity of the shell-type SNR G318.2+0.1 with H.E.S.S

The on-going H.E.S.S. Galactic Plane Survey continues to reveal new sources of VHE gamma-rays. In particular, recent re-observations of the region around the shell-type supernova remnant (SNR) G318.2+0.1 have resulted in the discovery of statistically-significant very-high-energy (VHE) gamma-ray emission from an extended region. Although the source remains unidentified, archival observations of CO12 in the region provide an opportunity to investigate a potential SNR/molecular cloud interaction. The morphological properties of this newly-discovered VHE gamma-ray source HESSJ1457-593 are presented and discussed in light of the multi-wavelength data available.Comment: 7 pages, 2 figures. Proc. of the 25th TEXAS Symposium on Relativistic Astrophysics. To appear in Proceedings of Scienc

Improved sensitivity of H.E.S.S.-II through the fifth telescope focus system

The Imaging Atmospheric Cherenkov Telescope (IACT) works by imaging the very short flash of Cherenkov radiation generated by the cascade of relativistic charged particles produced when a TeV gamma ray strikes the atmosphere. This energetic air shower is initiated at an altitude of 10-30 km depending on the energy and the arrival direction of the primary gamma ray. Whether the best image of the shower is obtained by focusing the telescope at infinity and measuring the Cherenkov photon angles or focusing on the central region of the shower is a not obvious question. This is particularly true for large size IACT for which the depth of the field is much smaller. We address this issue in particular with the fifth telescope (CT5) of the High Energy Stereoscopic System (H.E.S.S.); a 28 m dish large size telescope recently entered in operation and sensitive to an energy threshold of tens of GeVs. CT5 is equipped with a focus system, its working principle and the expected effect of focusing depth on the telescope sensitivity at low energies (50-200 GeV) is discussed.Comment: In Proceedings of the 33rd International Cosmic Ray Conference (ICRC2013), Rio de Janeiro (Brazil

VHE gamma-rays from the other side of the Milky-Way: SNR G349.7+0.2

Young massive star clusters as sites of strong stellar winds and supernova explosions may accelerate charged particles at high energies and produce gamma-rays. These sources may also contribute to the production of cosmic rays in our galaxy. At TeV energies several candidates have already been detected: Cygnus OB2, Westerlund 1 \& 2, W43, Pismis 22 and W49A. Our study addresses the issue of very young star clusters where no supernova has occurred yet. During the lifetime of a massive star (M$> 20 M_{\odot}$), supersonic stellar winds do indeed release as much energy as a supernova explosion. As supernova remnants are already known as gamma-ray emitters our purpose is to avoid any ambiguity on the origin of a possible gamma ray emission and to fully assume a stellar wind contribution. In this work we first present a catalogue of potential gamma-ray emitting clusters and discuss the criteria used to built the catalogue. We hence model the expected energetic particle spectrum including escapes and losses. We deduce gamma-ray luminosities produced by Inverse Compton and pion decay emission of each cluster and their associated HII regions. We finally compare these gamma-ray luminosities with HESS-II and CTA Cherenkov telescopes sensitivities

Probing cosmic ray acceleration through molecular clouds in the vicinity of supernova remnants

International audienceVery high energy gamma-ray emission has been recently detected by H.E.S.S. from the direction of associations between supernova remnants and molecular clouds. In such associations dense molecular clouds may reveal accelerated cosmic rays in the vicinity of supernova remnant forward shocks. Hadronic interactions could explain part or all of the observed gamma -ray fluxes. The discovery of a new VHE gamma -ray source, HESS J1923+141, coincident with the supernova remnant W51C, is reported. Amongst possible associations for this source is a shocked molecular cloud