GCN Circular 8816

Gaug M. (IAC Tenerife), Antonelli L. A. (INAF Rome),
Bastieri D. (Univ. Padova), Becerra J. G. (IAC Tenerife),
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), Persic M. (Univ. Udine), Scapin V. (Univ. Udine), 
and Teshima M. (MPI Munich) for the MAGIC collaboration

The MAGIC Imaging Atmospheric Cherenkov Telescope performed a follow-up
observation of GRB090102 (Mangano et al., circular 8762). We started data 
taking with MAGIC at 03:14:52 UT under excellent observation conditions. 
The observation continued for 13149 s.

No evidence for VHE gamma-ray emission above a (preliminary) analysis 
threshold of 89 GeV was found.

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. (Because of the 
changing telescope sensitivities due to different zenith angle ranges 
during the observation of GRB090102, the data sample was split into
5 parts):

E (  80- 125 GeV): 2.30 * 10^-10 erg/cm^2/s
E ( 125- 175 GeV): 1.61 * 10^-10 erg/cm^2/s
E ( 175- 300 GeV): 0.34 * 10^-10 erg/cm^2/s
E ( 300-1000 GeV): 0.04 * 10^-10 erg/cm^2/s
for a time window from 03:14:01 UT to 04:21:01 UT

E (  80- 125 GeV): 1.12 * 10^-10 erg/cm^2/s
E ( 125- 175 GeV): 0.50 * 10^-10 erg/cm^2/s
E ( 175- 300 GeV): 0.20 * 10^-10 erg/cm^2/s
E ( 300-1000 GeV): 0.07 * 10^-10 erg/cm^2/s
for a time window from 04:21:01 UT to 05:31:00 UT

E ( 125- 175 GeV): 1.02 * 10^-10 erg/cm^2/s
E ( 175- 300 GeV): 0.30 * 10^-10 erg/cm^2/s
E ( 300-1000 GeV): 0.20 * 10^-10 erg/cm^2/s
for a time window from 05:39:00 UT to 06:02:00 UT

E ( 125- 175 GeV): 2.40 * 10^-10 erg/cm^2/s
E ( 175- 300 GeV): 0.49 * 10^-10 erg/cm^2/s
E ( 300-1000 GeV): 0.25 * 10^-10 erg/cm^2/s
for a time window from 06:02:00 UT to 06:25:00 UT

E ( 175- 300 GeV): 0.40 * 10^-10 erg/cm^2/s
E ( 300-1000 GeV): 0.11 * 10^-10 erg/cm^2/s
for a time window from 06:25:00 UT to 07:02:00 UT

We can also exclude emission of a constant flux in any 100s time bin 
smaller than:

E (  80- 125 GeV): 12.58 * 10^-10 erg/cm^2/s
E ( 125- 175 GeV):  7.53 * 10^-10 erg/cm^2/s
E ( 175- 300 GeV):  3.27 * 10^-10 erg/cm^2/s
E ( 300-1000 GeV):  1.41 * 10^-10 erg/cm^2/s
for a time window from 03:14:01 UT to 04:21:01 UT

E (  80- 125 GeV): 18.16 * 10^-10 erg/cm^2/s
E ( 125- 175 GeV): 15.56 * 10^-10 erg/cm^2/s
E ( 175- 300 GeV):  3.46 * 10^-10 erg/cm^2/s
E ( 300-1000 GeV):  1.40 * 10^-10 erg/cm^2/s
for a time window from 04:21:01 UT to 05:31:00 UT

E ( 125- 175 GeV): 11.61 * 10^-10 erg/cm^2/s
E ( 175- 300 GeV):  2.47 * 10^-10 erg/cm^2/s
E ( 300-1000 GeV):  0.91 * 10^-10 erg/cm^2/s
for a time window from 05:39:00 UT to 06:02:00 UT

E ( 125- 175 GeV): 12.38 * 10^-10 erg/cm^2/s
E ( 175- 300 GeV):  5.38 * 10^-10 erg/cm^2/s
E ( 300-1000 GeV):  1.53 * 10^-10 erg/cm^2/s
for a time window from 06:02:00 UT to 06:25:00 UT

E ( 175- 300 GeV): 10.06 * 10^-10 erg/cm^2/s
E ( 300-1000 GeV):  1.28 * 10^-10 erg/cm^2/s
for a time window from 06:25:00 UT to 07:02:00 UT

Further analysis, exploiting the recently upgraded event trigger, is still 
underway for energies below 80 GeV.

This message can be cited.