Ref HAL: in2p3-00147240_v1
Ref Arxiv: 0704.0171
DOI: 10.1051/0004-6361:20077299
Ref. & Cit.: NASA ADS
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87 citations
Résumé:

The complex Monoceros Loop SNR/Rosette Nebula region contains several potential sources of very-high-energy (VHE) gamma-ray emission and two as yet unidentified high-energy EGRET sources. Sensitive VHE observations are required to probe acceleration processes in this region. The H.E.S.S. telescope array has been used to search for very high-energy gamma-ray sources in this region. CO data from the NANTEN telescope were used to map the molecular clouds in the region, which could act as target material for gamma-ray production via hadronic interactions. We announce the discovery of a new gamma-ray source, HESS J0632+058, located close to the rim of the Monoceros SNR. This source is unresolved by H.E.S.S. and has no clear counterpart at other wavelengths but is possibly associated with the weak X-ray source 1RXS J063258.3+054857, the Be-star MWC 148 and/or the lower energy gamma-ray source 3EG J0634+0521. No evidence for an associated molecular cloud was found in the CO data.

Commentaires: 5 pages, 4 figures, to appear in A&A

Ref HAL: in2p3-00142313_v1
Ref Arxiv: astro-ph/0703427
DOI: 10.1051/0004-6361:20066950
Ref. & Cit.: NASA ADS
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99 citations
Résumé:

Results from gamma-ray observations by the H.E.S.S. telescope array in the direction of the young stellar cluster Westerlund 2 are presented. Stereoscopic imaging of Cherenkov light emission of gamma-ray induced showers in the atmosphere is used to study the celestial region around the massive Wolf-Rayet (WR) binary WR 20a. Spectral and positional analysis is performed using standard event reconstruction techniques and parameter cuts. The detection of a new gamma-ray source is reported from H.E.S.S. observations in 2006. HESS J1023-575 is found to be coincident with the young stellar cluster Westerlund 2 in the well-known HII complex RCW 49. The source is detected with a statistical significance of more than 9 sigma, and shows extension beyond a point-like object within the H.E.S.S. point-spread function. The differential gamma-ray spectrum of the emission region is measured over approximately two orders of magnitude in flux. The spatial coincidence between HESS J1023-575 and the young open cluster Westerlund 2, hosting e.g. the massive WR binary WR 20a, requires a look into a variety of potential models to account for the observed very-high-energy (VHE) gamma-ray emission. Considered emission scenarios include emission from the colliding wind zone of WR 20a, collective stellar winds from the extraordinary ensemble of hot and massive stars in the stellar cluster Westerlund 2, diffusive shock acceleration in the wind-blown bubble itself, and supersonic winds breaking out into the interstellar medium (ISM). The observed source extension argues against a single star origin of the observed VHE emission.

Commentaires: 7 pages, 5 figures, accepted for publication in A&A

Ref HAL: in2p3-00130812_v1
Ref Arxiv: astro-ph/0702336
DOI: 10.1051/0004-6361:20066737
Ref. & Cit.: NASA ADS
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20 citations
Résumé:

We present the results of a search for pulsed very-high-energy (VHE) gamma-ray emission from young pulsars using data taken with the H.E.S.S. imaging atmospheric Cherenkov telescope system. Data on eleven pulsars, selected according to their spin-down luminosity relative to distance, are searched for gamma-ray signals with periodicity at the respective pulsar spin period. Special analysis efforts were made to improve the sensitivity in the 100 GeV gamma-ray energy domain in an attempt to reduce the gap between satellite and ground-based gamma-ray instruments. No significant evidence for pulsed emission is found in any data set. Differential upper limits on pulsed energy flux are determined for all selected pulsars in the approximate gamma-ray energy range between 100 GeV and 50 TeV, using different limit determination methods, testing a wide range of possible pulsar light curves and energy spectra. The limits derived here imply that the magnetospheric VHE gamma-ray production efficiency in young pulsars is less than 10^-4 of the pulsar spin-down luminosity, requiring spectral turnovers for the high-energy emission of four established gamma-ray pulsars, and constrain the inverse Compton radiation component predicted by several outer gap models.

Commentaires: 13 pages, 11 figures, accepted for publication in A&A

Ref HAL: in2p3-00134805_v1
Ref Arxiv: astro-ph/0701766
DOI: 10.1103/PhysRevD.75.042004
Ref. & Cit.: NASA ADS
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24 citations
Résumé:

A recently proposed novel technique for the detection of cosmic rays with arrays of Imaging Atmospheric Cherenkov Telescopes is applied to data from the High Energy Stereoscopic System (H.E.S.S.). The method relies on the ground based detection of Cherenkov light emitted from the primary particle prior to its first interaction in the atmosphere. The charge of the primary particle (Z) can be estimated from the intensity of this light, since it is proportional to Z$^2$. Using H.E.S.S. data, an energy spectrum for cosmic-ray iron nuclei in the energy range 13--200 TeV is derived. The reconstructed spectrum is consistent with previous direct measurements and is one of the most precise so far in this energy range.

Commentaires: 14 pages, 13 figures, accepted for publication in Phys. Rev. D

Ref HAL: in2p3-00142311_v1
Ref Arxiv: astro-ph/0603723
DOI: 10.1051/0004-6361:20064985
Ref. & Cit.: NASA ADS
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146 citations
Résumé:

Constraints on the diffusion and acceleration parameters in five young supernova remnants (SNRs) are derived from the observed thickness of their X-ray rims, as limited by the synchrotron losses of the highest energy electrons, assuming uniform and isotropic turbulence. It is shown that the magnetic field must be amplified up to values between 250 and 500 microGauss in the case of Cas A, Kepler, and Tycho, or ~ 100 microGauss in the case of SN 1006 and G347.3-0.5. The diffusion coefficient at the highest electron energy can also be derived from the data, by relating the X-ray energy cutoff to the acceleration timescale. Values typically between 1 and 10 times the Bohm diffusion coefficient are found to be required. We also find interesting constraints on the energy dependence of the diffusion coefficient. This favours diffusion regimes between the Kraichnan and the Bohm regime, and rejects turbulence spectrum indices larger than ~ 3/2. Finally, the maximum energy of the accelerated particles is found to lay between 10^13 and 5 10^13 eV for electrons, and around Z \times 8 10^14 eV at most for nuclei (or ~ 2.5 times less if a Bohm diffusion regime is assumed), roughly independently of the compression ratio assumed at the shock. Even by taking advantage of the uncertainties on the measured parameters, it appears very difficult for the considered SNRs in their current stage of evolution to produce protons up to the knee of the cosmic-ray spectrum, at ~ 3 10^15 eV, and essentially impossible to accelerate Fe nuclei up to either the ankle at ~ 3 10^18 eV or the second knee at ~ 5 10^17 eV.

Commentaires: 11 pages, 3 figures

Ref HAL: in2p3-00135989_v1
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Résumé:

We present here the current Nançay observing program gathering the pulsar french community around the radio follow-up of X- and gamma-ray pulsars for the building of a complete multi-wavelength sample. The goal of this project is double : 1) provide strong constraints on the physics and emission mechanisms of pulsars , 2) guarantee the success of pulsar harvest at high energy by providing good and contemporaneous ephemerides for folding the few gamma and X-ray photons . The community is well involved in the last generation of gamma-ray and X-ray detectors and the availability of the NRT and its dedicated backend BON represents a very good opportunity for acquiring the necessary and complementary radio data.

Commentaires: texte intégral disponible sur http://proc.sf2a.asso.fr/2006/2006sf2a.conf..0197T.pdf

Ref HAL: in2p3-00124615_v1
Ref Arxiv: astro-ph/0612495
DOI: 10.1086/512603
Ref. & Cit.: NASA ADS
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144 citations
Résumé:

The shell-type supernova remnant RX J0852.0-4622 was observed with the High Energy Stereoscopic System (H.E.S.S.) of Atmospheric Cherenkov Telescopes between December 2004 and May 2005 for a total observation time of 33 hours, above an average gamma-ray energy threshold of 250 GeV. The angular resolution of ~0.06 degree (for events triggering 3 or 4 telescopes) and the large field of view of H.E.S.S. ($5^{\circ}$ diameter) are well adapted to studying the morphology of the object in very high energy gamma-rays, which exhibits a remarkably thin shell very similar to the features observed in the radio range and in X-rays. The spectral analysis of the source from 300 GeV to 20 TeV is also presented. Finally, the possible origins of the very high energy gamma-ray emission (Inverse Compton scattering by electrons or the decay of neutral pions produced by proton interactions) are discussed, on the basis of morphological and spectral features obtained at different wavelengths.

Commentaires: 42 pages, 20 figures, accepted for publication in ApJ