Ref HAL: in2p3-00024064_v1
Ref Arxiv: astro-ph/0504380
DOI: 10.1126/science.1108643
Ref. & Cit.: NASA ADS
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275 citations
Résumé:

Very high energy gamma-rays probe the long-standing mystery of the origin of cosmic rays. Produced in the interactions of accelerated particles in astrophysical objects, they can be used to image cosmic particle accelerators. A first sensitive survey of the inner part of the Milky Way with the High Energy Stereoscopic System (H.E.S.S.) reveals a population of eight previously unknown firmly detected sources of very high energy gamma-rays. At least two have no known radio or X-ray counterpart and may be representative of a new class of `dark' nucleonic cosmic ray sources.

Ref HAL: in2p3-00024066_v1
Ref Arxiv: astro-ph/0504120
DOI: 10.1051/0004-6361:200500105
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122 citations
Résumé:

The Supernova Remnant MSH 15-52 has been observed in very high energy (VHE) gamma-rays using the H.E.S.S. 4-telescope array located in Namibia. A gamma-ray signal is detected at the 25 sigma level during an exposure of 22.1 hours live time. The image reveals an elliptically shaped emission region around the pulsar PSR B1509-58, with semi-major axis 6' in the NW-SE direction and semi-minor axis 2' approximately. This morphology coincides with the diffuse pulsar wind nebula as observed at X-ray energies by ROSAT. The overall energy spectrum from 280 GeV up to 40 TeV can be fitted by a power law with photon index Gamma = 2.27 +/- 0.03(stat.) +/- 0.20(syst.). The detected emission can be plausibly explained by inverse Compton scattering of accelerated relativistic electrons with soft photons.

Ref HAL: in2p3-00024315_v1
Ref Arxiv: astro-ph/0504520
DOI: 10.1051/0004-6361:200500113
Ref. & Cit.: NASA ADS
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57 citations
Résumé:

The high-frequency peaked BL Lac PKS 2005-489 (z=0.071) was observed in 2003 and 2004 with the H.E.S.S. stereoscopic array of imaging atmospheric-Cherenkov telescopes in Namibia. A signal was detected at the 6.7 sigma level in the 2004 observations (24.2 hrs live time), but not in the 2003 data set (27.3 h live time). PKS 2005-489 is the first blazar independently discovered by H.E.S.S. to be an emitter of VHE photons, and only the second such blazar in the Southern Hemisphere. The integral flux above 200 GeV observed in 2004 is (6.9$\pm$ 1.0$_{stat} \pm 1.4_{syst}$) x 10$^{-12}$ cm$^{-2}$ s$^{-1}$, corresponding to $\sim$ 2.5% of the flux observed from the Crab Nebula. The 99% upper limit on the flux in 2003, I(>200 GeV) < 5.2 x 10$^{-12}$ cm$^{-2}$ s$^{-1}$, is smaller than the flux measured in 2004, suggesting an increased level of activity in 2004. However, the data show no evidence for significant variability on any time scale less than a year. An energy spectrum is measured and is characterized by a very soft power law (photon index of $\Gamma$= 4.0 $\pm$ 0.4).

Ref HAL: in2p3-00024439_v1
Ref Arxiv: astro-ph/0506319
DOI: 10.1051/0004-6361:20053050
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69 citations
Résumé:

Mkn 421 was observed during a high flux state for nine nights in April and May 2004 with the fully operational High Energy Stereoscopic System (H.E.S.S.) in Namibia. The observations were carried out at zenith angles of 60$^\circ$--65$^\circ$, which result in an average energy threshold of 1.5 TeV and a collection area reaching 2 km$^2$ at 10 TeV. Roughly 7000 photons from Mkn 421 were accumulated with an average gamma-ray rate of 8 photons/min. The overall significance of the detection exceeds 100 standard deviations. The light-curve of integrated fluxes above 2 TeV shows changes of the diurnal flux up to a factor of 4.3. For nights of high flux, intra-night variability is detected with a decay time of less than 1 hour. The time averaged energy spectrum is curved and is well described by a power-law with a photon index $\egamm$ and an exponential cutoff at $\ecut$ TeV and an average integral flux above 2 TeV of 3 Crab flux units. Significant variations of the spectral shape are detected with a spectral hardening as the flux increases. Contemporaneous multi-wavelength observations at lower energies (X-rays and gamma-rays above $\approx 300$ GeV) indicate smaller relative variability amplitudes than seen above 2 TeV during high flux state observed in April 2004.

Commentaires: 5 pages, 4 figures

Ref HAL: in2p3-00024436_v1
Ref Arxiv: astro-ph/0502239
DOI: 10.1051/0004-6361:20042522
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41 citations
Résumé:

Observations of the shell-type supernova remnant SN1006 have been carried out with the HESS system of Cherenkov telescopes during 2003 (18.2 h with two operating telescopes) and 2004 (6.3 h with all four telescopes). No evidence for TeV $\gamma$-ray emission from any compact or extended region associated with the remnant is seen and resulting upper limits at the 99.9% confidence level are up to a factor 10 lower than previously-published fluxes from CANGAROO. For SN1006 at its current epoch of evolution we define limits for a number of important global parameters. Upper limits on the $\gamma$-ray luminosity (for E = 0.26 to 10 TeV, distance d = 2 kpc) of $L_\gamma < 1.7$ $\times$ 1033 erg s-1, and the total energy in corresponding accelerated protons, $W_{\rm p}<1.6$ $\times$ 1050 erg are estimated (for proton energies $E_{\rm p} \sim 1.5$ to 60 TeV and assuming the lowest value n=0.05 cm-3 of the ambient target density discussed in literature). Extending this estimate to cover the range of proton energies observed in the cosmic ray spectrum up to the knee (we take here $E_{\rm p} \sim$ 1 GeV to 3 PeV, assuming a differential particle index -2) gives $W_{\rm p}<6.3$ $\times$ 1050 erg. A lower limit on the post-shock magnetic field of $B>25~\mu$G results when considering the synchrotron/inverse-Compton framework for the observed X-ray flux and $\gamma$-ray upper limits.

Ref HAL: in2p3-00024345_v1
Ref Arxiv: astro-ph/0505380
DOI: 10.1051/0004-6361:200500130
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173 citations
Résumé:

We report the detection of TeV $\gamma$-rays from the shell-type supernova remnant RX J0852.0-4622 with data of 3.2 h of live time recorded with H.E.S.S. in February 2004. An excess of (700 $\pm$ 60) events from the whole remnant with a significance of 12 $\sigma$ was found. The observed emission region is clearly extended with a radius of the order of 1 degree and the spatial distribution of the signal correlates with X-ray observations. The spectrum in the energy range between 500 GeV and 15 TeV is well described by a power law with a photon index of $\Gamma=2.1 \pm 0.1_{stat} \pm 0.2_{syst}$ and a differential flux at 1 TeV of $\varphi$ 1TEV= (2.1 $\pm 0.2_{stat} \pm 0.6_{syst}) \times 10^{-11} cm^{-2} s^{-1} TeV^{-1}$. The integral flux above 1 TeV was measured to be $\Phi$ (E > 1 TeV) = (1.9 $\pm 0.3_{stat} \pm 0.6_{syst}) \times 10^{-11} cm^{-2} s^{-1}$, which is at the level of the flux of the Crab nebula at these energies. More data are needed to draw firm conclusions on the magnetic field in the remnant and the type of the particle population creating the TeV $\gamma$-rays.

Commentaires: SIMBAD objects in preparation

Ref HAL: in2p3-00024532_v1
Ref Arxiv: astro-ph/0508298
DOI: 10.1126/science.1113764
Ref. & Cit.: NASA ADS
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255 citations
Résumé:

X-ray binaries are composed of a normal star in orbit around a neutron star or stellar-mass black hole. Radio and X-ray observations have led to the presumption that some X-ray binaries called microquasars behave as scaled down active galactic nuclei. Microquasars have resolved radio emission that is thought to arise from a relativistic outflow akin to active galactic nuclei jets, in which particles can be accelerated to large energies. Very high energy gamma-rays produced by the interactions of these particles have been observed from several active galactic nuclei. Using the High Energy Stereoscopic System, we find evidence for gamma-ray emission >100 GeV from a candidate microquasar, LS 5039, showing that particles are also accelerated to very high energies in these systems.

Commentaires: Originally published in Science Express on 7 July 2005