Orateur
Description
We present a measurement of the cosmic ray energy spectrum by the Telescope
Array Low-Energy Extension (TALE) air fluorescence detector (FD). The TALE FD
is also sensitive to the Cherenkov light produced by shower particles. Low
energy cosmic rays, in the PeV energy range, are detectable by TALE as
``Cherenkov Events''. Using these events, we measure the energy spectrum from
a low energy of ~2 PeV to an energy greater than 100 PeV. Above 100 PeV TALE
uses the air fluorescence technique to reach energies of a few EeV. In
this talk, we will describe the detector, explain the technique, and present
results from a measurement of the spectrum using ~1080 hours of observation.
The observed spectrum shows a clear steepening near 10^{17.1} eV, along with
an ankle-like structure at 10^{16.2} eV. These features present important
constraints on galactic cosmic rays origin and propagation models. The feature
at 10^{17.1} eV may also mark the end of the galactic cosmic rays flux and the
start of the transition to extra-galactic sources.
