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
Résumé:

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: in2p3-00175791_v1
Ref Arxiv: 0709.4584
DOI: 10.1051/0004-6361:20078462
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162 citations
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AIMS: To investigate the very high energy (VHE: >100 GeV) gamma-ray emission from the high-frequency peaked BL Lac 1ES 0229+200. METHODS: Observations of 1ES 0229+200 at energies above 580 GeV were performed with the High Energy Stereoscopic System (HESS) in 2005 and 2006. RESULTS: 1ES 0229+200 is discovered by HESS to be an emitter of VHE photons. A signal is detected at the 6.6 sigma level in the HESS observations (41.8 h live time). The integral flux above 580 GeV is (9.4 +- 1.5 {stat} +- 1.9 {syst}) x 10^{-13} cm^{-2} s^{-1}, corresponding to ~1.8% of the flux observed from the Crab Nebula. The data show no evidence for significant variability on any time scale. The observed spectrum is characterized by a hard power law (Gamma = 2.50 +- 0.19 {stat} +- 0.10 {syst}) from 500 GeV to ~15 TeV. CONCLUSIONS: The high-energy range and hardness of the observed spectrum, coupled with the object's relatively large redshift (z=0.1396), enable the strongest constraints so far on the density of the Extragalactic Background Light (EBL) in the mid-infrared band. Assuming that the emitted spectrum is not harder than Gamma_{int} ~ 1.5, the HESS data support an EBL spectrum ~ lambda^{-1} and density close to the lower limit from source counts measured by Spitzer, confirming the previous indications from the HEGRA data of 1ES 1426+428 (z=0.129). Irrespective of the EBL models used, the intrinsic spectrum of 1ES 0229+200 is hard, thus locating the high-energy peak of its spectral energy distribution above a few TeV.

Commentaires: 5 pages, 4 figures;

Ref HAL: in2p3-00177454_v1
DOI: 10.1051/0004-6361:20078412
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94 citations
Résumé:

Aims.Our aim is to study the production mechanism for very-high-energy (VHE; >100 GeV) ?-rays in distant active galactic nuclei (AGN) and use the observed VHE spectrum to derive limits on the Extragalactic Background Light (EBL). We also want to determine physical quantities through the modeling of the object's broad-band spectral energy distribution (SED). Methods: VHE observations (~25 h live time) of the BL Lac 1ES 0347-121 (redshift z = 0.188) were conducted with the High Energy Stereoscopic System (HESS) between August and December 2006. Contemporaneous X-ray and UV/optical observations from the SWIFT satellite are used to interpret the SED of the source in terms of a synchrotron self Compton (SSC) model. Results: An excess of 327 events, corresponding to a statistical significance of 10.1 standard deviations, is detected from 1ES 0347-121. Its photon spectrum, ranging from ~250 GeV to ~3 TeV, is well described by a power law with a photon index of ? = 3.10 ± 0.23stat ± 0.10sys. The integral flux above 250 GeV corresponds to ~2% of the flux of the Crab Nebula above the same threshold. No VHE flux variability is detected within the data set. Conclusions: Constraints on the EBL density at optical to near-infrared wavelengths derived from the photon spectrum of 1ES 0347-121 are close to the strongest limits derived previously. The strong EBL limits confirm earlier findings, that the EBL density in the near-infrared is close to the lower limits from source counts. This implies that the universe is more transparent to VHE ?-rays than previously believed. An SSC model provides a reasonable description of the contemporaneous SED. Affiliations are only available in electronic form at http://www.aanda.org

Ref HAL: hal-00263554_v1
DOI: 10.1088/1742-6596/60/1/061
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4 citations
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We review recent application specific integrated circuits developed for high energy neutrino, gamma ray and cosmic ray detectors, which share constraints of the same kind. We compare various technical concepts used to fulfil similar requirements. We suggest some ways which could be followed in the near future to answer the needs of next generation experiments.