Very high energy (VHE) γ-ray emission from the flat spectrum radio quasar (FSRQ) PKS 1222+21 (4C 21.35, z = 0.432) was detected with the MAGIC Cherenkov telescopes during a short observation (∼0.5 hr) performed on 2010 June 17. The MAGIC detection coincides with high-energy MeV/GeV γ-ray activity measured by the Large Area Telescope (LAT) on board the Fermi satellite. The VHE spectrum measured by MAGIC extends from about 70 GeV up to at least 400 GeV and can be well described by a power-law dN/dE ∝ E −Γ with a photon index Γ = 3.75 ± 0.27 stat ± 0.2 syst. The averaged integral flux above 100 GeV is (4.6 ± 0.5) × 10 −10 cm −2 s −1 (∼1 Crab Nebula flux). The VHE flux measured by MAGIC varies significantly within the 30 minute exposure implying a flux doubling time of about 10 minutes. The VHE and MeV/GeV spectra, corrected for the absorption by the extragalactic background light (EBL), can be described by a single power law with photon index 2.72 ± 0.34 between 3 GeV and 400 GeV, and is consistent with emission belonging to a single component in the jet. The

The giant radio galaxy M 87 with its proximity (16 Mpc), famous jet, and very massive black hole ((3−6)×10 9 M ) provides a unique opportunity to investigate the origin of very high energy (VHE; E > 100 GeV) γ -ray emission generated in relativistic outflows and the surroundings of supermassive black holes. M 87 has been established as a VHE γ -ray emitter since 2006. The VHE γ -ray emission displays strong variability on timescales as short as a day. In this paper, results from a joint VHE monitoring campaign on M 87 by the MAGIC and VERITAS instruments in 2010 are reported. During the campaign, a flare at VHE was detected triggering further observations at VHE (H.E.S.S.), X-rays (Chandra), and radio (43 GHz Very Long Baseline Array, VLBA). The excellent sampling of the VHE γ -ray light curve enables one to derive a precise temporal characterization of the flare: the single, isolated flare is well described by a two-sided exponential function with significantly different flux rise and decay times of τ rise (1-3) × 10 −11 photons cm −2 s −1 ), and VHE spectra. VLBA radio observations of 43 GHz of the inner jet regions indicate no enhanced flux in 2010 in contrast to observations in 2008, where an increase of the radio flux of the innermost core regions coincided with a VHE flare. On the other hand, Chandra X-ray observations taken ∼3 days after the peak of the VHE γ -ray emission reveal an enhanced flux from the core (flux increased by factor ∼2; variability timescale <2 days). The long-term (2001-2010) multi-wavelength (MWL) light curve of M 87, spanning from radio to VHE and including data from Hubble Space Telescope, Liverpool Telescope, Very Large Array, and European VLBI Network, is used to further investigate the origin of the VHE γ -ray emission. No unique, common MWL signature of the three VHE flares has been identified. In the outer kiloparsec jet region, in particular in HST-1, no enhanced MWL activity was detected in 2008 and 2010, disfavoring it as the origin of the VHE flares during these years. Shortly after two of the three flares (2008 and 2010), the X-ray core was observed to be at a higher flux level than its characteristic range (determined from more than 60 monitoring observations: [2002][2003][2004][2005][2006][2007][2008][2009]). In 2005, the strong flux dominance of HST-1 could have suppressed the detection of such a feature. Published models for VHE γ -ray emission from M 87 are reviewed in the light of the new data.

MAGIC is a system of two Imaging Atmospheric Cherenkov Telescopes located in the Canary island of La Palma. Since autumn 2009 both telescopes have been working together in stereoscopic mode, providing a significant improvement with respect to the previous single-telescope observations. We use observations of the Crab Nebula taken at low zenith angles to assess the performance of the MAGIC stereo system. The trigger threshold of the MAGIC telescopes is 50 − 60 GeV. Advanced stereo analysis techniques allow MAGIC to achieve a sensitivity as good as (0.76 ± 0.03) % of the Crab Nebula flux in 50 h of observations above 290 GeV. The angular resolution at those energies is better than ∼ 0.07 • . We also perform a detailed study of possible systematic effects which may influence the analysis of the data taken with the MAGIC telescopes.

We use 73 h of stereoscopic data taken with the MAGIC telescopes to investigate the very high-energy (VHE) gamma-ray emission of the Crab pulsar. Our data show a highly significant pulsed signal in the energy range from 50 to 400 GeV in both the main pulse (P1) and the interpulse (P2) phase regions. We provide the widest spectra to date of the VHE components of both peaks, and these spectra extend to the energy range of satellite-borne observatories. The good resolution and background rejection of the stereoscopic MAGIC system allows us to cross-check the correctness of each spectral point of the pulsar by comparison with the corresponding (strong and well-known) Crab nebula flux. The spectra of both P1 and P2 are compatible with power laws with photon indices of 4.0 ± 0.8 (P1) and 3.42 ± 0.26 (P2), respectively, and the ratio P1/P2 between the photon counts of the two pulses is 0.54 ± 0.12. The VHE emission can be understood as an additional component produced by the inverse Compton scattering of secondary and tertiary e ± pairs on IR-UV photons.