TITLE:   GCN CIRCULAR
NUMBER:  13752
SUBJECT: GRB 120911A: Fermi/LAT upper limit
DATE:    12/09/11 21:05:23 GMT
FROM:    Weikang Zheng at U.of Michigan  <zwk@umich.edu>

Weikang Zheng and Carl Akerlof (Umich), report on behalf of the ROTSE
collaboration:

We analyzed Fermi/LAT data of GRB 120911A (Cannizzo et al., GCN 13744)
as a follow-up of routine search in Swift trigger catalogs in our LAT
data processing pipeline using both the matched filter technique
(Akerlof et al. 2010, ApJ, 725, L15; 2011 ApJ, 726, 22; 2012,
arXiv:1205.3066; Zheng et al. 2012, ApJ 745,72; ApJ, 756, 64)
and likelihood method. We do NOT detect high energy photon emission
from both methods.

A standard data selection method is applied when extracting the LAT
photon data with energy E > 100 MeV, and a duration of T0 - T0+47.5s
after the trigger. A zenith angle cut of <105 degree is applied to
all photons.

The burst location of GRB 120911A was only ~14 degrees from the
LAT boresight, almost in the center of the LAT field of view, and
the zenith angle was about 40 degrees at trigger time.
Using the likelihood method, we estimated the upper limit in LAT energy
range (0.1 - 10 GeV) is 1.1e-05 (photons cm^-2 s^-1) by assuming a
spectral index of -2.2.
The pipeline result of GRB 120911A is given in the following link:
http://www.rotse.net/LAT/SwiftTriggers/369040116/