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Ground-based gamma-ray astronomy has had a major breakthrough with the impressive results obtained using systems of imaging atmospheric Cherenkov telescopes. Ground-based gamma-ray astronomy has a huge potential in astrophysics, particle physics and cosmology. CTA is an international initiative to build the next generation instrument, with a factor of 5-10 improvement in sensitivity in the 100 GeV-10 TeV range and the extension to energies well below 100 GeV and above 100 TeV. CTA will consist of two arrays (one in the north, one in the south) for full sky coverage and will be operated as open observatory. The design of CTA is based on currently available technology. This document reports on the status and presents the major design concepts of CTA.

The presumed Wolf-Rayet star progenitors of Type Ib/c supernovae have fast, low density winds and the shock waves generated by the supernova interaction with the wind are not expected to be radiative at typical times of observation. The injected energy spectrum of radio emitting electrons typically has an observed index p=3, which is suggestive of acceleration in cosmic ray dominated shocks. The early, absorbed part of the radio light curves can be attributed to synchrotron self-absorption, which leads to constraints on the magnetic field in the emitting region and on the circumstellar density. The range of circumstellar densities inferred from the radio emission is somewhat broader than that for Galactic Wolf-Rayet stars, if similar efficiencies of synchrotron emission are assumed in the extragalactic supernovae. For the observed and expected ranges of circumstellar densities to roughly overlap, a high efficiency of magnetic field production in the shocked region is required (epsilon_B ~ 0.1). For the expected densities around a Wolf-Rayet star, a nonthermal mechanism is generally required to explain the observed X-ray luminosities of Type Ib/c supernovae. Although the inverse Compton mechanism can explain the observed X-ray emission from SN 2002ap if the wind parameters are taken from the radio model, the mechanism is not promising for other supernovae unless the postshock magnetic energy density is much smaller than the electron energy density. In some cases another mechanism is definitely needed and we suggest that it is X-ray synchrotron emission in a case where the shock wave is cosmic ray dominated so that the electron energy spectrum flattens at high energy. More comprehensive X-ray observations of a Type Ib/c supernova are needed to determine whether this suggestion is correct.Comment: 31 pages, 2 figures, ApJ, accepted, corrected typ

HST and ground based observations of the Type IIn SN 2010jl are analyzed, including photometry, spectroscopy in the ultraviolet, optical and NIR bands, 26 − 1128 days after first detection. At maximum the bolometric luminosity was ∼ 3 × 10 43 erg s −1 and even at 850 days exceeds 10 42 erg s −1 . A NIR excess, dominating after 400 days, probably originates in dust in the circumstellar medium (CSM). The total radiated energy is 6.5 × 10 50 ergs, excluding the dust component. The spectral lines can be separated into one broad component due to electron scattering, and one narrow with expansion velocity ∼ 100 km s −1 from the CSM. The broad component is initially symmetric around zero velocity but becomes blueshifted after ∼ 50 days, while remaining symmetric about a shifted centroid velocity. Dust absorption in the ejecta is unlikely to explain the line shifts, and we attribute the shift instead to acceleration by the SN radiation. From the optical lines and the X-ray and dust properties, there is strong evidence for large scale asymmetries in the CSM. The ultraviolet lines indicate CNO processing in the progenitor, while the optical shows a number of narrow coronal lines excited by the X-rays. The bolometric light curve is consistent with a radiative shock in an r −2 CSM with a mass loss rate ofṀ ∼ 0.1 M ⊙ yr −1 . The total mass lost is 3 M ⊙ . These properties are consistent with the SN expanding into a CSM characteristic of an LBV progenitor with a bipolar geometry. The apparent absence of nuclear processing is attributed to a CSM still opaque to electron scattering.