GCN Circular 13742
Subject
GRB 120908A and GRB 120909A : Fermi/LAT upper limit
Date
2012-09-10T19:20:18Z (12 years ago)
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 120908A (Morii et al., GCN 13731)
and GRB 120909A (Immler et al., GCN 13727)
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 in the two GRBs.
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.
For GRB 120908A, the burst location was about 72 degrees from the
LAT boresight, and the zenith angle was about 64 degrees at trigger time.
Using the likelihood method, we estimated the upper limit in LAT energy
range (0.1 - 10 GeV) is 8.3e-09 (photons cm^-2 s^-1) by assuming a
spectral index of -2.2.
The pipeline result of GRB 120908A is given in the following link:
http://www.rotse.net/LAT/SwiftTriggers/368836516/
For GRB 120909A, the burst location was about 65 degrees from the
LAT boresight, and the zenith angle was about 98 degrees at trigger time.
Using the likelihood method, we estimated the upper limit in LAT energy
range (0.1 - 10 GeV) is 2.0e-08 (photons cm^-2 s^-1) by assuming a
spectral index of -2.2.
The pipeline result of GRB 120909A is given in the following link:
http://www.rotse.net/LAT/SwiftTriggers/368847726/