Dieter.Horns@mpi-hd.mpg.de -2 -The Crab supernova remnant has been observed regularly with the stereoscopic system of 5 imaging air Cherenkov telescopes that was part of the High Energy Gamma Ray Astronomy (HEGRA) experiment. In total, close to 400 hours of useful data have been collected from 1997 until 2002. The differential energy spectrum of the combined data-set can be approximated by a powerlaw type energy spectrum: dΦ/dE = Φ 0 · (E/TeV) Γ , Φ 0 = (2.83 ± 0.04 stat ± 0.6 sys ) ·10 −11 ph cm −2 s −1 TeV −1 and Γ = −2.62 ± 0.02 stat. ± 0.05 sys. . The spectrum extends up to energies of 80 TeV and is well matched by model calculations in the framework of inverse Compton scattering of various seed photons in the nebula including for the first time a recently detected compact emission region at mm-wavelengths. The observed indications for a gradual steepening of the energy spectrum in data is expected in the inverse Compton emission model. The average magnetic field in the emitting volume is determined to be (161.6 ± 0.8 stat ± 18 sys ) µG. The presence of protons in the nebula is not required to explain the observed flux and upper limits on the injected power of protons are calculated being as low as 20 % of the total spin down luminosity for bulk Lorentz factors of the wind in the range of 10 4 − 10 6 . The position and size of the emission region have been studied over a wide range of energies. The position is shifted by 13 ′′ to the west of the pulsar with a systematic uncertainty of 25 ′′ . No significant shift in the position with energy is observed. The size of the emission region is constrained to be less than 2 ′ at energies between 1 and 10 TeV. Above 30 TeV the size is constrained to be less than 3 ′ . No indications for pulsed emission has been found and upper limits in differential bins of energy have been calculated reaching typically 1-3 % of the unpulsed component.

Abstract. 232 hours of data were accumulated from 1997 to 1999, using the HEGRA Stereoscopic Cherenkov Telescope System to observe the supernova remnant Cassiopeia A. TeV γ-ray emission was detected at the 5 σ level, and a flux of (5.8 ± 1.2stat ± 1.2syst) 10 −9 ph m −2 s −1 above 1 TeV was derived. The spectral distribution is consistent with a power law with a differential spectral index of −2.5 ± 0.4stat ± 0.1syst between 1 and 10 TeV. As this is the first report of the detection of a TeV γ-ray source on the "centi-Crab" scale, we present the analysis in some detail. Implications for the acceleration of cosmic rays depend on the details of the source modeling. We discuss some important aspects in this paper.

Abstract. Deep observation (∼113 hrs) of the Cygnus region at TeV energies using the HEGRA stereoscopic system of aiř Cerenkov telescopes has serendipitously revealed a signal positionally inside the core of the OB association Cygnus OB2, at the edge of the 95% error circle of the EGRET source 3EG J2033+4118, and ∼0.5• north of Cyg X-3. The source centre of gravity is RA α J2000 : 20 hr 32 m 07 s ± 9.2 s stat ± 2.2 s sys , Dec δ J2000 : +41• 30 30 ± 2.0 stat ± 0.4 sys . The source is steady, has a post-trial significance of +4.6σ, indication for extension with radius 5.6 at the ∼3σ level, and has a differential power-law flux with hard photon index of −1.9 ± 0.3 stat ± 0.3 sys . The integral flux above 1 TeV amounts ∼3% that of the Crab. No counterpart for the TeV source at other wavelengths is presently identified, and its extension would disfavour an exclusive pulsar or AGN origin. If associated with Cygnus OB2, this dense concentration of young, massive stars provides an environment conducive to multi-TeV particle acceleration and likely subsequent interaction with a nearby gas cloud. Alternatively, one could envisage γ-ray production via a jet-driven termination shock.

Abstract. For the first time an excess of photons above an energy threshold of 730 GeV from the giant radio galaxy M 87 has been measured at a significance level above 4 σ. The data have been taken during the years 1998 and 1999 with the HEGRA stereoscopic system of 5 imaging atmospheric Cherenkov telescopes. The excess of 107.4 ± 26.8 events above 730 GeV corresponds to an integral flux of 3.3% of the Crab flux or N γ (E > 730 GeV) = (0.96 ± 0.23) × 10 −12 phot cm −2 s −1 . M 87 is located at the center of the Virgo cluster of galaxies at a relatively small redshift of z = 0.00436 and is a promising candidate among the class of giant radio galaxies for the emission of TeV γ-radiation. The detection of TeV γ-rays from M 87 -if confirmed -would establish a new class of extragalactic source in this energy regime since all other AGN detected to date at TeV energies are BL Lac type objects.

(MJD 51989-51991, March 21-23, 2001), this correlation of spectral hardness and change in flux has been observed within a few hours. The cut-off energy for the Mkn 421 TeV spectrum remains within the errors constant for the different flux levels and differs by ∆E = 2.6 ± 0.6 stat ± 0.6 sys TeV from the value determined for Mkn 501. This indicates that the observed exponential cut-off in the energy spectrum of Mkn 421 is not solely caused by absorption of multi-TeV photons by pair-production processes with photons of the extragalactic near/mid infrared background radiation.