Ref HAL: hal-00288579_v1
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The recent observations of sharp X-ray filaments in many young supernova remnants like CasA, Kepler or Tycho or in older ones like SN1006 led to the conclusion of an amplification of the magnetic field in regards to its standard interstellar medium values. This magnetic field is hardly of external origin and is certainly produced through the acceleration of cosmic-rays around the blast wave. The streaming instability driven by the upstream cosmic-ray gradient is one of the favourite way to generate the magnetic fluctuations to the required level. Recent theoretical progresses conclude that aside the usual resonant interaction an efficient non-resonant regime could be at the origin of the high magnetic fields in supernova blast waves. The present work, investigate this issue. In particular it shown that both non-resonant and resonant regimes should operate in supernova shocks. We discuss the saturation mechanisms of these regimes. We show that the turbulence spectrum is probably highly anisotropic both up- and downstream and we examine the consequences of anisotropy on the values of the magnetic field in the post shock regions as well as the cosmic-ray acceleration process.

Ref HAL: in2p3-00196769_v1
Ref Arxiv: 0712.1173
DOI: 10.1051/0004-6361:20078516
Ref. & Cit.: NASA ADS
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160 citations
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Context.The detection of gamma rays in the very-high-energy (VHE) energy range (100 GeV-100 TeV) provides a direct view of the parent population of ultra-relativistic particles found in astrophysical sources. For this reason, VHE gamma rays are useful for understanding the underlying astrophysical processes in non-thermal sources. Aims.We investigate unidentified VHE gamma-ray sources that have been discovered with HESS in the most sensitive blind survey of the Galactic plane at VHE energies conducted so far. Methods.The HESS array of imaging atmospheric Cherenkov telescopes (IACTs) has a high sensitivity compared with previous instruments (~ in 25 h observation time for a point-source detection), and with its large field of view, is well suited for scan-based observations. The on-going HESS survey of the inner Galaxy has revealed a large number of new VHE sources, and for each we attempt to associate the VHE emission with multi-wavelength data in the radio through X-ray wavebands. Results. For each of the eight unidentified VHE sources considered here, we present the energy spectra and sky maps of the sources and their environment. The VHE morphology is compared with available multi-wavelength data (mainly radio and X-rays). No plausible counterparts are found.

Ref HAL: in2p3-00189509_v1
Ref Arxiv: 0711.3196
DOI: 10.1051/0004-6361:20078604
Ref. & Cit.: NASA ADS
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28 citations
Résumé:

AIMS: Very high energy (VHE; E>100 GeV) gamma-ray studies were performed for 18 active galactic nuclei (AGN) from a variety of AGN classes. METHODS: VHE observations of a sample of 14 AGN, considered candidate VHE emitters, were made with the High Energy Stereoscopic System (HESS) between January 2005 and July 2007. Large-zenith-angle observations of three northern AGN (Mkn 421, Mkn 501, 1ES 1218+304), known to emit VHE gamma rays, were also performed in order to sample their spectral energy distributions (SEDs) above 1 TeV. In addition, the VHE flux from 1ES 1101-232, previously detected by HESS in 2004-2005, was monitored during 2006 and 2007. RESULTS: As significant detections from the HESS observation program are reported elsewhere, the results reported here are primarily integral flux upper limits. The average exposure for each of the 14 VHE-candidate AGN is ~7 h live time, and the observations have an average energy threshold between 230 GeV and 590 GeV. Upper limits for these 14 AGN range from <0.9% to <4.9% of the Crab Nebula flux, and eight of these are the most constraining ever reported for the object. The brief (<2.2 h each) large-zenith-angle observations yield upper limits for Mkn 501 (<20% Crab above 2.5 TeV) and 1ES 1218+304 (<17% Crab above 1.0 TeV), and a marginal detection (3.5 sigma) of Mkn 421 (50% Crab above 2.1 TeV). 1ES 1101-232 was marginally detected (3.6 sigma, 1.7% Crab above 260 GeV) during the 2006 (13.7 h live time) observations, but not in the 2007 (4.6 h live time) data. The upper limit in 2007 (<1.9% Crab above 260 GeV) is below the average flux measured by HESS from 2004-2006.

Commentaires: 8 Pages, 2 Figures; Accepted on Nov 6, 2007 for publication in Astronomy & Astrophysics

Ref HAL: in2p3-00188227_v1
Ref Arxiv: 0711.2369
DOI: 10.1016/j.astropartphys.2007.11.007
Ref. & Cit.: NASA ADS
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81 citations
Résumé:

Observations of the Sagittarius dwarf spheroidal (Sgr dSph) galaxy were carried out with the H.E.S.S. array of four imaging air Cherenkov telescopes in June 2006. A total of 11 hours of high quality data are available after data selection. There is no evidence for a very high energy gamma-ray signal above the energy threshold at the target position. A 95% C.L. flux limit of 3.6 x 10-12 cm-2s-1 above 250 GeV has been derived. Constraints on the velocity-weighted cross section are calculated in the framework of Dark Matter particle annihilation using realistic models for the Dark Matter halo profile of Sagittarius dwarf galaxy. Two different models have been investigated encompassing a large class of halo types. A 95% C.L. exclusion limit on of the order of 2 x 10-25 cm3s-1 is obtained for a core profile in the 100 GeV - 1 TeV neutralino mass range.

Commentaires: 21 pages, 4 figures, 2 tables; Erratum Astroparticle Physics 33:274-275, 2010; doi:10.1016/j.astropartphys.2010.01.007

Ref HAL: in2p3-00184500_v1
Ref Arxiv: 0710.5740
DOI: 10.1051/0004-6361:20078603
Ref. & Cit.: NASA ADS
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27 citations
Résumé:

AIMS: The properties of the very high energy (VHE; E>100 GeV) gamma-ray emission from the high-frequency peaked BL Lac PG 1553+113 are investigated. An attempt is made to measure the currently unknown redshift of this object. METHODS: VHE Observations of PG 1553+113 were made with the High Energy Stereoscopic System (HESS) in 2005 and 2006. H+K (1.45-2.45 micron) spectroscopy of PG 1553+113 was performed in March 2006 with SINFONI, an integral field spectrometer of the ESO Very Large Telescope (VLT) in Chile. RESULTS: A VHE signal, ~10 standard deviations, is detected by HESS during the 2 years of observations (24.8 hours live time). The integral flux above 300 GeV is (4.6 +- 0.6{stat} +- 0.9{syst}) x 10^{-12} cm^{-2} s^{-1}, corresponding to ~3.4% of the flux from the Crab Nebula above the same threshold. The time-averaged energy spectrum is measured from 225 GeV to ~1.3 TeV, and is characterized by a very soft power law (photon index of Gamma = 4.5 +- 0.3{stat} +- 0.1{syst}). No evidence for any flux or spectral variations is found on any sampled time scale within the VHE data. The redshift of PG 1553+113 could not be determined. Indeed, even though the measured SINFONI spectrum is the most sensitive ever reported for this object at near infrared wavelengths, and the sensitivity is comparable to the best spectroscopy at other wavelengths, no absorption or emission lines were found in the H+K spectrum presented here.

Commentaires: 9 pages, 12 Figures; Accepted for publication in Astronomy & Astrophysics

Ref HAL: in2p3-00186521_v1
Ref Arxiv: 0709.2550
Ref. & Cit.: NASA ADS
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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.

Commentaires: 4 pages, 4 figures, Contribution to the 30th ICRC, Merida Mexico, July 2007

Ref HAL: hal-00177684_v1
Ref Arxiv: 0710.1939
DOI: 10.1111/j.1365-2966.2007.12511.x
Ref. & Cit.: NASA ADS
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9 citations
Résumé:

We present a new code aimed at the simulation of diffusive shock acceleration (DSA), and discuss various test cases which demonstrate its ability to study DSA in its full time-dependent and non-linear developments. We present the numerical methods implemented, coupling the hydrodynamical evolution of a parallel shock (in one space dimension) and the kinetic transport of the cosmic-rays (CR) distribution function (in one momentum dimension), as first done by Falle. Following Kang and Jones and collaborators, we show how the adaptive mesh refinement technique (AMR) greatly helps accommodating the extremely demanding numerical resolution requirements of realistic (Bohm-like) CR diffusion coefficients. We also present the paral lelization of the code, which allows us to run many successive shocks at the cost of a single shock, and thus to present the first direct numerical simulations of linear and non-linear multiple DSA, a mechanism of interest in various astrophysical environments such as superbubbles, galaxy clusters and early cosmological flows.

Commentaires: published in MNRAS by the Royal Astronomical Society and Blackwell Publishing