TITLE: GCN CIRCULAR NUMBER: 7635 SUBJECT: GRB080319A: MAGIC telescope GeV observation DATE: 08/04/20 19:22:07 GMT FROM: Markus Garczarczyk at MPI/MAGIC Garczarczyk M., Gaug M., Antonelli A., Bastieri D., Covino S., Galante N., La Barbera A., Longo F. and Scapin V. for the MAGIC collaboration The MAGIC Imaging Atmospheric Cherenkov Telescope performed a follow-up observation of the BAT burst GRB080319A (GCN circular 7426, Pagani et al.). We received the GCN alert at 05:46:45 UT (T0+63s), data taking with MAGIC started at 05:50:32 UT (T0+290s). The observation continued for 1736s, starting at the zenith angle of 35 degrees. No evidence for VHE gamma-ray emission above the analysis threshold of 175 GeV was found. The observation was carried out in (less sensitive) moon-observation mode. 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 (125- 175 GeV): 0.57 * 10^-10 erg/cm^2/s E (175- 300 GeV): 0.11 * 10^-10 erg/cm^2/s E (300-1000 GeV): 0.06 * 10^-10 erg/cm^2/s for a time window from 05:50:01 UT to 06:19:01 UT. For the same time window, we can also exclude emission of a constant flux in any 100s time bin smaller than: E (125- 175 GeV): 13.97 * 10^-10 erg/cm^2/s E (175- 300 GeV): 4.34 * 10^-10 erg/cm^2/s E (300-1000 GeV): 1.46 * 10^-10 erg/cm^2/s This message can be cited.