C. Stegmann

A multi-wavelength study of the unidentified TeV gamma-ray source HESS J1626−490

Aims. To explore the nature of the unidentified very-high-energy (VHE, E > 100 GeV) gamma-ray source HESS J1626−490, we investigated the region in X-ray, sub-millimeter, and infrared energy bands. Methods. So far only detected with the HESS array of imaging atmospheric Cherenkov telescopes, HESS J1626−490 could not be unambiguously identified with any source seen at lower energies. Therefore, we analyzed data from an archival XMM-Newton observation, pointed towards HESS J1626−490, to classify detected X-ray point sources according to their spectral properties and their near-infrared counterparts from the 2MASS catalog. Furthermore, we characterized in detail the diffuse X-ray emission from a region compatible with the extended VHE signal. To characterize the interstellar medium surrounding HESS J1626−490 we analyzed 12 CO(J = 1−0) molecular line data from the Nanten Galactic plane survey, H i data from the Southern Galactic Plane Survey (SGPS) and Spitzer data from the GLIMPSE and MIPSGAL surveys. Results. None of the detected X-ray point sources fulfills the energy requirements to be considered as the synchrotron radiation counterpart to the VHE source assuming an inverse-Compton (IC) emission scenario. We did not detect any diffuse X-ray excess emission originating in the region around HESS J1626−490 above the Galactic background and the derived upper limit for the total X-ray flux disfavors a purely leptonic emission scenario for HESS J1626−490. We found a good morphological match between molecular and atomic gas in the −27 km s −1 to −18 km s −1 line-of-sight velocity range and HESS J1626−490. The cloud has a mass

Potential neutrino signals from galactic γ-ray sources

Recent measurements of the energy spectra of Galactic TeV γ-ray sources with the H.E.S.S. instrument have been used to calculate the expected high energy neutrino fluxes from these sources. Based on the results the expected event rates in a next generation neutrino telescope in the Mediterranean Sea, KM3NeT, have been estimated, assuming an instrumented volume of 1 km3. We find that for energies above 1TeV event rates of a few neutrinos per year can be expected from the brightest γ-ray sources. Although these rates are comparable to those of the background from atmospheric neutrinos a detection of individual sources seems possible.

A search for very high energy gamma-ray emission from the starburst galaxy NGC253 with HESS

We present the result of 28 hours of observations of the nearby starburst galaxy NGC 253 with the H.E.S.S. detector in 2003. We find no evidence for very high energy gamma-ray emission from this object. Gamma-ray emission above 400 GeV from NGC 253 had been reported by the CANGAROO collaboration in 2002. From the H.E.S.S. data we derive upper limits on the flux above 300 GeV of 1.9 * 10^-12 photons cm^-2 s^-1 for a point-like source and 6.3 * 10^-12 photons cm^-2 s^-1 for a source of radius 0.5 degrees as reported by CANGAROO, both at a confidence level of 99%. These upper limits are inconsistent with the spectrum reported by CANGAROO. The expected very high energy gamma-ray emission from this object is discussed in the framework of a galactic wind propagation model.We present the result of 28 hours of observations of the nearby starburst galaxy NGC 253 with the H.E.S.S. detector in 2003. We find no evidence for very high energy gamma-ray emission from this object. Gamma-ray emission above 400 GeV from NGC 253 had been reported by the CANGAROO collaboration in 2002. From the H.E.S.S. data we derive upper limits on the flux above 300 GeV of 1.9 * 10^-12 photons cm^-2 s^-1 for a point-like source and 6.3 * 10^-12 photons cm^-2 s^-1 for a source of radius 0.5 degrees as reported by CANGAROO, both at a confidence level of 99%. These upper limits are inconsistent with the spectrum reported by CANGAROO. The expected very high energy gamma-ray emission from this object is discussed in the framework of a galactic wind propagation model.