Observations with the HEGRA stereoscopic system

The HEGRA system of imaging air Cherenkov telescopes has successfully pioneered the stereoscopic observation technique of extensive air showers. The observational method is briefly described and important results of recent observations of sources of photons with TeV($=10^{12}$ eV)-energies are summarized: The first detection of a TeV $\gamma$-ray signal from the shell-type supernova remnant Cassiopeia A and preliminary results obtained from the observation of strong variability of the extragalactic source Mkn 421 during observations carried out from February to May 2000.Comment: 4 pages, 3 figures, to appear in the Proceedings of the XXIst Rencontres de Moriond "Very High Energy Phenomena in the Universe", Les Arcs, France, Jan. 20-27 (2001

Cross Calibration of Imaging Air Cherenkov Telescopes with Fermi

An updated model for the synchrotron and inverse Compton emission from a population of high energy electrons of the Crab Nebula is used to reproduce the measured spectral energy distribution from radio to high energy gamma-rays. By comparing the predicted inverse Compton component with recent Fermi measurements of the nebula's emission, it is possible to determine the average magnetic field in the nebula and to derive the underlying electron energy distribution. The model calculation can then be used to cross calibrate the Fermi observations with ground based air shower measurements. The resulting energy calibration factors are derived and can be used for combining broad energy measurements taken with Fermi in conjunction with ground based measurements.Comment: 2009 Fermi Symposium, eConf Proceedings C091122, 5 pages, 5 figures, 3 table

Multi-wavelength observations of the TeV Blazars Mkn~421, 1ES1959+650, and H1426+428 with the HEGRA Cherenkov telescopes and the RXTE X-ray satellite

Recent results obtained with the HEGRA system of imaging Cherenkov telescopes on the TeV emission of the Blazars Mkn~421 ($z=0.030$), 1ES1959+650 ($z=0.047$), and H1426+428 ($z=0.129$) are reported. For Mkn~421, a close connection of the average flux level and spectral shape has been observed during the periods of increased activity in the years 2000 and 2001. Simultaneously taken data with the RXTE X-ray satellite reveal a complex light curve at X-ray and TeV energies. After a deep exposure of 94 hrs, the object 1ES1959+650 was detected at the significance level of 5.4$\sigma$ with a soft energy spectrum following a power-law with a photon-index of $3.3 \pm 0.7$. During recent observations in May 2002, the source has shown increased activity with indications for a flattening of the energy spectrum. The high energy peaked Blazar H1426+428 has recently been identified as a source of TeV photons. Since the source is fairly distant (z=0.129), absorption of TeV photons due to pair-production on the optical and near infrared extragalactic light becomes important and should leave a signature in the observed TeV energy spectrum. Notably, the TeV energy spectrum determined with the HEGRA system of Cherenkov telescopes agrees with the expectation of a strongly absorbed source spectrum

Indirect search for Dark Matter with H.E.S.S

Observations of the Galactic center region with the H.E.S.S. telescopes have established the existence of a steady, extended source of gamma-ray emission coinciding with the position of the super massive black hole Sgr A*. This is a remarkable finding given the expected presence of dense self-annihilating Dark Matter in the Galactic center region. The self-annihilation process is giving rise to gamma-ray production through hadronization including the production of neutral pions which decay into gamma-rays but also through (loop-suppressed) annihilation into final states of almost mono-energetic photons. We study the observed gamma-ray signal (spectrum and shape) from the Galactic center in the context of Dark Matter annihilation and indicate the prospects for further indirect Dark matter searches with H.E.S.S.Comment: 9 pages, 3 figures. Accepted for Publication in Advances is Space Research, COSPAR meeting Beijing (2006

XMM-Newton observations of the first unidentified TeV gamma-ray source TeV J2032+4130

(abridged) The first unidentified very high energy gamma ray source (TeV J2032+4130) in the Cygnus region has been the subject of intensive search for a counterpart source at other wavelengths. A deep ($\approx 50$ ksec) exposure of TeV J2032+4130 with \textit{XMM-Newton} has been obtained. The contribution of point sources to the observed X-ray emission from TeV J2032+4130 is subtracted from the data. The point-source subtracted X-ray data are analyzed using blank sky exposures and regions adjacent to the position of TeV J2032+4130 in the field of view covered by the XMM-Newton telescopes to search for diffuse X-ray emission. An extended X-ray emission region with a full width half maximum (FWHM) size of $\approx 12$ arc min is found. The centroid of the emission is co-located with the position of TeV J2032+4130.The energy spectrum of the emission coinciding with the position and extension of TeV J2032+4130 can be modeled by a power-law model with a photon index $\Gamma=1.5\pm0.2_\mathrm{stat}\pm0.3_\mathrm{sys}$ and an energy flux integrated between 2 and 10 keV of $f_{2-10 \mathrm{keV}} \approx 7\cdot 10^{-13}$ ergs/(cm$^2$ s) which is lower than the very high energy gamma-ray flux observed from TeV J2032+4130. We conclude that the faint extended X-ray emission discovered in this observation is the X-ray counterpart of TeV J2032+4130. Formally, it can not be excluded that the extended emission is due to an unrelated population of faint, hot ($k_BT\approx 10$ keV) unresolved point-sources which by chance coincides with the position and extension of TeV J2032+4130. We discuss our findings in the frame of both hadronic and leptonic gamma-ray production scenarios.Comment: 5 Pages, 3 Figures, accepted for publication in A&