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No significant enhancement in the VHE gamma-ray flux of the Crab Nebula measured by MAGIC in September 2010

The MAGIC telescopes observed the Crab Nebula in stereoscopic mode during the period of enhanced activity reported by AGILE (ATel #2855) and Fermi-LAT (ATel #2861) in September 2010. The observations started at MJD 55459.2070 (September 20th) lasting for 58 minutes. The average flux and spectrum during these observations were compared to a reference Crab Nebula data sample taken between 2009 October to 2010 January. No significant change was detected in flux or spectral shape: the ratio of the differential flux at 1 TeV in the flare sample and the reference sample is dN/dE(1TeV)_flare/dN/dE(1TeV)_ref=1.06+/-0.15_stat+/-0.15_syst ; the difference between the photon indices, fitting data with energies between 1 and 10 TeV, is Alpha_ref - Alpha_flare=0.06+/-0.14_stat+/-0.15_syst. Within statistical errors, these findings do not support the evidence of an increase in the flux of the Crab Nebula at very high energies by a factor 3 to 4 as reported by ARGO-YBJ (ATel #2921), if this increase was steady. MAGIC consists of two 17m diameter imaging air Cherenkov telescopes located on La Palma, Canary Islands, Spain. Questions regarding the MAGIC observations should be directed to Mose Mariotti (mose.mariotti@pd.infn.it).

Gamma Ray; TeV; Cosmic Rays; Supernova Remnants

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