ALBERT

Beschreibung: A deep observation campaign carried out by the High Energy Stereoscopic System (HESS) on Centaurus A enabled the discovery of -rays from the blazar 1ES 1312–423, 2° away from the radio galaxy. With a differential flux at 1 TeV of (1 TeV) = (1.9 ± 0.6 stat  ± 0.4 sys )  x 10 –13 cm –2 s –1 TeV –1 corresponding to 0.5 per cent of the Crab nebula differential flux and a spectral index  = 2.9 ± 0.5 stat  ± 0.2 sys , 1ES 1312–423 is one of the faintest sources ever detected in the very high energy ( E  〉 100 GeV) extragalactic sky. A careful analysis using three and a half years of Fermi Large Area Telescope ( Fermi -LAT) data allows the discovery at high energies (E 〉 100 MeV) of a hard spectrum ( = 1.4 ± 0.4 stat  ± 0.2 sys ) source coincident with 1ES 1312–423. Radio, optical, UV and X-ray observations complete the spectral energy distribution of this blazar, now covering 16 decades in energy. The emission is successfully fitted with a synchrotron self-Compton model for the non-thermal component, combined with a blackbody spectrum for the optical emission from the host galaxy.

Beschreibung: The non-thermal nature of the X-ray emission from the shell-type supernova remnants (SNRs) G1.9+0.3 and G330.2+1.0 is an indication of intense particle acceleration in the shock fronts of both objects. This suggests that the SNRs are prime candidates for very-high-energy (VHE; E  〉 0.1 TeV) -ray observations. G1.9+0.3, recently established as the youngest known SNR in the Galaxy, also offers a unique opportunity to study the earliest stages of SNR evolution in the VHE domain. The purpose of this work is to probe the level of VHE -ray emission from both SNRs and use this to constrain their physical properties. Observations were conducted with the H.E.S.S. (High Energy Stereoscopic System) Cherenkov Telescope Array over a more than six-year period spanning 2004–2010. The obtained data have effective livetimes of 67 h for G1.9+0.3 and 16 h for G330.2+1.0. The data are analysed in the context of the multiwavelength observations currently available and in the framework of both leptonic and hadronic particle acceleration scenarios. No significant -ray signal from G1.9+0.3 or G330.2+1.0 was detected. Upper limits (99 per cent confidence level) to the TeV flux from G1.9+0.3 and G330.2+1.0 for the assumed spectral index  = 2.5 were set at 5.6 10 –13  cm –2  s –1 above 0.26 TeV and 3.2 10 –12  cm –2  s –1 above 0.38 TeV, respectively. In a one-zone leptonic scenario, these upper limits imply lower limits on the interior magnetic field to B G1.9   12 μG for G1.9+0.3 and to B G330   8 μG for G330.2+1.0. In a hadronic scenario, the low ambient densities and the large distances to the SNRs result in very low predicted fluxes, for which the H.E.S.S. upper limits are not constraining.

Beschreibung: The results of follow-up observations of the TeV -ray source HESS J1640–465 from 2004 to 2011 with the High Energy Stereoscopic System (HESS) are reported in this work. The spectrum is well described by an exponential cut-off power law with photon index  = 2.11 ± 0.09 stat ± 0.10 sys , and a cut-off energy of $E_{\rm c} = 6.0^{+2.0}_{-1.2}$  TeV. The TeV emission is significantly extended and overlaps with the northwestern part of the shell of the SNR G338.3–0.0. The new HESS results, a re-analysis of archival XMM–Newton data and multiwavelength observations suggest that a significant part of the -ray emission from HESS J1640–465 originates in the supernova remnant shell. In a hadronic scenario, as suggested by the smooth connection of the GeV and TeV spectra, the product of total proton energy and mean target density could be as high as W p n H ~ 4 10 52 ( d /10kpc) 2 erg cm –3 .

Beschreibung: The region around the supernova remnant (SNR) W41 contains several TeV sources and has prompted the HESS Collaboration to perform deep observations of this field of view. This resulted in the discovery of the new very high energy (VHE) source HESS J1832–093, at the position ${\rm RA=18^h 32^m 50^s \pm 3^s_{stat} \pm 2^s_{syst}}, {\rm Dec=-9^\circ 22^{\prime } 36^{\prime \prime } \pm 32^{\prime \prime }_{stat} \pm 20^{\prime \prime }_{syst} (J2000)}$ , spatially coincident with a part of the radio shell of the neighbouring remnant G22.7–0.2. The photon spectrum is well described by a power law of index  = 2.6 ± 0.3 stat  ± 0.1 syst and a normalization at 1 TeV of $\Phi _0=(4.8 \pm 0.8_{\rm stat}\pm 1.0_{\rm syst})\,\times \,10^{-13}\,{\rm cm} ^{-2}\,\rm s^{-1}\,\rm TeV^{-1}$ . The location of the gamma-ray emission on the edge of the SNR rim first suggested a signature of escaping cosmic rays illuminating a nearby molecular cloud. Then a dedicated XMM–Newton observation led to the discovery of a new X-ray point source spatially coincident with the TeV excess. Two other scenarios were hence proposed to identify the nature of HESS J1832–093. Gamma-rays from inverse Compton radiation in the framework of a pulsar wind nebula scenario or the possibility of gamma-ray production within a binary system are therefore also considered. Deeper multiwavelength observations will help to shed new light on this intriguing VHE source.