Ref HAL: in2p3-00354648_v1
Ref Arxiv: 0901.2187
DOI: 10.1051/0004-6361:200811072
Ref. & Cit.: NASA ADS
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38 citations
Abstract:

Very-high-energy (VHE; >~100 GeV) gamma-rays are expected from gamma-ray bursts (GRBs) in some scenarios. Exploring this photon energy regime is necessary for understanding the energetics and properties of GRBs. GRBs have been one of the prime targets for the H.E.S.S. experiment, which makes use of four Imaging Atmospheric Cherenkov Telescopes (IACTs) to detect VHE gamma-rays. Dedicated observations of 32 GRB positions were made in the years 2003-2007 and a search for VHE gamma-ray counterparts of these GRBs was made. Depending on the visibility and observing conditions, the observations mostly start minutes to hours after the burst and typically last two hours. Results from observations of 22 GRB positions are presented and evidence of a VHE signal was found neither in observations of any individual GRBs, nor from stacking data from subsets of GRBs with higher expected VHE flux according to a model-independent ranking scheme. Upper limits for the VHE gamma-ray flux from the GRB positions were derived. For those GRBs with measured redshifts, differential upper limits at the energy threshold after correcting for absorption due to extra-galactic background light are also presented.

Comments: 9 pages, 4 tables, 3 figures

Ref HAL: hal-00491481_v1
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Abstract:

On the basis of the extensive air shower (EAS) data obtained by the GAMMA experiment, the energy spectra and elemental composition of the primary cosmic rays are derived in the 1 - 100 PeV energy range. The reconstruction of the primary energy spectra is carried out using an EAS inverse approach with the hypothesis of power-law primary energy spectra with rigidity-dependent knees. The rigidity- dependent knee feature of the primary energy spectra is displayed at the rigidities ER similar or equal to 2.5 +/- 0.2 PeV/Z and ER similar or equal to 3.1 - 4.2 PeV/Z for the SIBYLL and QGSJET interaction models respectively.;Using the event-by-event method of the primary energy evaluation from the measured N-ch, N-mu and shower age (s) parameters, the all-particle energy spectrum is also obtained.

Ref HAL: hal-00491478_v1
DOI: 10.1016/j.asr.2007.06.036
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Abstract:

The investigation of the general properties of non-thermal (NT) X-ray shell supernova remnants (SNRs), of which SN 1006 is the prototype, is important to understand how electrons are accelerated in SNR shocks and what is the origin of cosmic rays. Using the XMM-Newton satellite, we are carrying on a survey of putative non-thermal SNR candidates previously unknown or little studied in the X-ray band, in order to investigate the different manifestations of NT emission in SNR shells. The SNRs we have selected are likely to expand in a low density medium, and therefore to have a low thermal X-ray emission, that usually outshines the non-thermal one. We report here preliminary results obtained on the SNR shell DA 530. (C) 2007 COSPAR. Published by Elsevier Ltd. All rights reserved.

Ref HAL: hal-00489467_v1
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Abstract:

The GAMMA collaboration is studying the possibility of instrumenting the 40 x 40 meter hadron calorimeter structure at the center of the GAMMA array. This mechanical structure, built about 25 years ago, has never been instrumented, and if this could be done, it would provide a valuable addition to the GAMMA array for the investigation of the EAS hadron component and for multivariate analysis of the GAMMA data.

Ref HAL: hal-00430249_v1
DOI: 10.1016/j.nuclphysbps.2007.11.019
Exporter : BibTex | endNote
Abstract:

On the basis of the extensive air shower (EAS) data obtained by the GAMMA experiment, the energy spectra and elemental composition of the primary cosmic rays are derived in the 1–100 PeV energy range. The reconstruction of the primary energy spectra is carried out using an EAS inverse approach with the hypothesis of power-law primary energy spectra with rigidity-dependent knees. The rigidity-dependent knee feature of the primary energy spectra is displayed at the rigidities ER ~= 2.5±0.2 PeV/Z and ER ~= 3.1–4.2 PeV/Z for the SIBYLL and QGSJET interaction models respectively. Using the event-by-event method of the primary energy evaluation from the measured Nch, Nμ and shower age (s) parameters, the all-particle energy spectrum is also obtained.

Comments: Proceedings of the XIV International Symposium on Very High Energy Cosmic Ray Interactions

Ref HAL: hal-00430148_v1
Ref Arxiv: 0809.0584
DOI: 10.1088/0004-637X/690/2/L101
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
86 citations
Abstract:

The High Energy Stereoscopic System (HESS) survey of the Galactic plane hasestablished the existence of a substantial number (~40) of Galactic TeVgamma-ray sources, a large fraction of which remain unidentified. HESSJ0632+057 is one of a small fraction of these objects which is point-like innature(<2' rms), and is one of only two point-like sources that remainunidentified. Follow-up observations of this object with XMM-Newton haverevealed an X-ray source coincident with the TeV source and with the massivestar MWC 148, of the spectral type B0pe. This source exhibits a hard spectrum,consistent with an absorbed power law with Gamma = 1.26 +/- 0.04, and showssignificant variability on hour timescales. We discuss this spatial coincidenceand the implied spectral energy distribution of this object and argue that itis likely a new gamma-ray binary system with a close resemblance to the threeknown members of this class, and in particular to LS I +61 303. Further X-ray,radio and optical observations of this system are needed to firmly establishHESS J0632+057 as a new member of this rare class of Galactic objects.

Ref HAL: hal-00402643_v1
Ref Arxiv: 0808.1421
DOI: 10.1088/0954-3899/35/11/115201
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
37 citations
Abstract:

We present all-particle primary cosmic-ray energy spectrum in the 3-200 PeV energy range obtained by a multi-parametric event-by-event evaluation of the primary energy. The results are obtained on the basis of an expanded EAS dataset detected at mountain level (700 g/cm^2) by the GAMMA experiment. The energy evaluation method has been developed using the EAS simulation with the SIBYLL interaction model taking into account the response of GAMMA detectors and reconstruction uncertainties of EAS parameters. Nearly unbiased (<5%) energy estimations regardless of a primary nuclear mass with an accuracy of about 15-10% in the 3-200 PeV energy range respectively are attained. An irregularity ('bump') in the spectrum is observed at primary energies of ~74 PeV. This bump exceeds a smooth power-law fit to the data by about 4 standard deviations. Not rejecting stochastic nature of the bump completely, we examined the systematic uncertainties of our methods and conclude that they cannot be responsible for the observed feature.