2.5 Years Of Observation Of Grbs With Fermi Lat
Abstract
The Fermi/LAT instrument observed new and puzzling features in some Gamma-Ray Bursts, like the delay in the beginning of the high energy emission (> 100 MeV) with respect to the lower-energy signal detected by the Fermi/GBM, and the presence of an extra spectral component in addition to the Band function. In one case (GRB 090926A) the extra component showed a spectral break around ∼ 1 GeV. It also confirmed that the high energy emission can last much longer than the emission at lower energies (< 100 MeV). Recently the new LAT Low Energy technique (LLE) has been introduced. It allows to recover effective area at tens of MeV and to fill the gap between the energy range of Fermi/GBM (∼ 8 keV to ∼ 40 MeV) and the LAT. Using this technique, we detected a few more GRBs of the GBM sample in LAT data. We will present a summary of all these discoveries, discussing the results contained in the first official catalog of GRBs observed by the LAT.
More recently, using the LLE technique, we observed for the first time a spectral cut off around ∼50 MeV in some GRBs. We will present these results as well, discussing also the theoretical implications of such observations.- Publication:
-
AAS/High Energy Astrophysics Division #12
- Pub Date:
- September 2011
- Bibcode:
- 2011HEAD...12.0105V