Discovery of very-high-energy gamma-ray emission from the vicinity of PSR J1913+1011 with HESS

The HESS experiment, an array of four Imaging Atmospheric Cherenkov Telescopes with high sensitivity and large field-of-view, has been used to search for emitters of very-high-energy (VHE, >100 GeV) $\gamma$-rays along the Galactic plane, covering the region 30° $<\, l\, <$ 60°, 280° $<\, l\, <$ 330°, and -3° $<\, b\, <$ 3°. In this continuation of the HESS Galactic Plane Scan, a new extended VHE $\gamma$-ray source was discovered at $\alpha_{2000}$=19$^{\rm h}$12$^{\rm m}$49$^{\rm s}$, $\delta_{2000}$=+10°09´06´´(HESS J1912+101). Its integral flux between 1-10 TeV is ~10% of the Crab Nebula flux in the same energy range. The measured energy spectrum can be described by a power law d $N/{\rm d}E \, \sim \, E^{-\Gamma}$ with a photon index \Gamma = 2.7 \pm 0.2_{\mbox{stat}}\pm 0.3_{\mbox{sys}}. HESS J1912+101 is plausibly associated with the high spin-down luminosity pulsar PSR J1913+1011. We also discuss associations with an as yet unconfirmed SNR candidate proposed from low frequency radio observation and/or with molecular clouds found in 13CO data

Discovery of VHE gamma-rays from the distant BL Lacertae 1ES0347-121

Aims.Our aim is to study the production mechanism for very-high-energy (VHE; >100 GeV) $\gamma$-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 $\Gamma = 3.10 \pm 0.23_{\mathrm{stat}} \pm 0.10_{\mathrm{sys}}$. 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 $\gamma$-rays than previously believed. An SSC model provides a reasonable description of the contemporaneous SED