TITLE: GCN CIRCULAR NUMBER: 6854 SUBJECT: GRB070920A: MAGIC telescope GeV observation DATE: 07/10/06 08:21:21 GMT FROM: Nicola Galante at MPI,Muenchen Galante N. (MPI/Muenchen), Garczarczyk M. (MPI/Muenchen), Gaug M. (IAC/Tenerife), Bastieri D. (U. Padova), Longo F. (INFN/Trieste) and Scapin V. (U. Udine), for the MAGIC Collaboration The MAGIC Imaging Atmospheric Cherenkov Telescope performed a follow-up observation of the SWIFT/BAT burst GRB070920A (GCN circular 6805, Grupe D., et al.). We received the GCN alert at T0+539s. The data taking by MAGIC started at T0+690s, 2.5 minutes after the alert income. We observed the sky positon for 36min spanning a zenith angle in the range 53-50 degrees. No evidence for VHE gamma-ray emission above the analysis threshold of about 250 GeV was found. A preliminary analysis, taking advantage for the first time of the fast 2GHz digitalization from the new data acquisition system, and for the hypothesis of steady emission and assumption of a differential photon spectral index of -2.5, yields the following 95% CL differential flux upper limits (inc. 30% systematic error on the efficiency): E(225-300 GeV) : 7.1 x 10^(-8) erg/cm^2 E(300-400 GeV) : 4.6 x 10^(-8) erg/cm^2 E(400-1000 GeV) : 2.2 x 10^(-8) erg/cm^2 E(1-10 TeV) : 0.53 x 10^(-8) erg/cm^2 The upper limits correspond to the time period between T0+690s and T0+2490s. We can also exclude emission of a constant flux during our observation in any 100s time bin higher than: E(225-300 GeV) : 1.9 x 10^(-7) erg/cm^2 E(300-400 GeV) : 1.0 x 10^(-7) erg/cm^2 E(400-1000 GeV) : 2.4 x 10^(-8) erg/cm^2 This message can be cited.