GCN Circular 7635

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
Not found
 
 
, 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

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