TITLE: GCN CIRCULAR NUMBER: 8867 SUBJECT: GRB090113: MAGIC telescope GeV observation DATE: 09/02/01 19:34:26 GMT FROM: Markus Garczarczyk at MPI/MAGIC Becerra Gonzalez J. (IAC Tenerife), Gaug M. (IAC Tenerife), Antonelli L.A. (INAF Rome), Bastieri D. (Univ. Padova), Becker J. (Univ. Dortmund), Carosi A. (INAF Rome), Covino S. (INAF Rome), Galante N. (MPI Munich), Garczarczyk M. (IFAE Barcelona), La Barbera A. (INAF Palermo), Longo F. (INFN Trieste), Lorenz E. (ETH Zuerich), Paoletti R. (Univ. Siena), Persic M. (INAF and INFN Trieste), Scapin V. (Univ. Udine), Spiro S. (INAF Rome) and Teshima M.(MPI Munich) for the MAGIC collaboration The MAGIC Imaging Atmospheric Cherenkov Telescope performed a follow-up observation of the BAT burst GRB090113 (GCN circular 8804, Krimm et al.). We received the GCN alert at 18:41:01 UT (T0+20s), before the sunset. Data taking with MAGIC started at 20:06:08 UT (T0+4603s), when the GRB zenith angle reached 5 degrees. The observation continued for 9405 s. No evidence for VHE gamma-ray emission above the analysis threshold of 94 GeV was found. The observation was carried out in (less sensitive) moon-observation mode from 21:39:01 UT on. A preliminary analysis, 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, including a 30% systematic uncertainty on the telescope efficiency. E ( 80- 125 GeV): 0.54 * 10^-10 erg cm^-2 s^-1 E ( 125- 175 GeV): 0.99 * 10^-10 erg cm^-2 s^-1 E ( 175- 300 GeV): 0.10 * 10^-10 erg cm^-2 s^-1 E ( 300-1000 GeV): 0.08 * 10^-10 erg cm^-2 s^-1 for a time window from 20:06:01 UT to 21:37:01 UT E ( 125- 175 GeV): 0.93 * 10^-10 erg cm^-2 s^-1 E ( 175- 300 GeV): 0.23 * 10^-10 erg cm^-2 s^-1 E ( 300-1000 GeV): 0.08 * 10^-10 erg cm^-2 s^-1 for a time window from 21:39:01 UT to 22:32:01 UT We can also exclude emission of a constant flux in any 100s time bin smaller than: E ( 80- 125 GeV): 13.89 * 10^-10 erg cm^-2 s^-1 E ( 125- 175 GeV): 8.88 * 10^-10 erg cm^-2 s^-1 E ( 175- 300 GeV): 3.40 * 10^-10 erg cm^-2 s^-1 E ( 300-1000 GeV): 1.22 * 10^-10 erg cm^-2 s^-1 for a time window from 20:06:01 UT to 21:37:01 UT E ( 125- 175 GeV): 13.20 * 10^-10 erg cm^-2 s^-1 E ( 175- 300 GeV): 3.88 * 10^-10 erg cm^-2 s^-1 E ( 300-1000 GeV): 2.30 * 10^-10 erg cm^-2 s^-1 for a time window from 21:39:01 UT to 22:32:01 UT This message can be cited.