  The breakthrough developments of Cherenkov telescopes in the last decade have
led to angular resolution of 0.1{\deg} and an unprecedented sensitivity. This
has allowed the current generation of Cherenkov telescopes to discover a
population of supernova remnants (SNRs) radiating in very-high-energy (VHE,
E>100 GeV) gamma-rays. A number of those VHE SNRs exhibit a shell-type
morphology spatially coincident with the shock front of the SNR. The members of
this VHE shell SNR club are RX J1713.7-3946, Vela Jr, RCW 86, SN 1006, and HESS
J1731-347. The latter two objects have been poorly studied in high-energy (HE,
0.1<E<100 GeV) gamma-rays and need to be investigated in order to draw the
global picture of this class of SNRs and constrain the characteristics of the
underlying population of accelerated particles. Using 6 years of Fermi P7
reprocessed data, we studied the HE counterpart of the SNRs HESS J1731-347 and
SN 1006. The two SNRs are not detected in the data and given that there is no
hint of detection, we do not expect any detection in the coming years from the
SNRs. However in both cases, we derived upper limits that significantly
constrain the gamma-ray emission mechanism and can rule out a standard hadronic
scenario with a confidence level > 5 sigma. With this Fermi analysis, we now
have a complete view of the HE to VHE gamma-ray emission of TeV shell SNRs. All
five sources have a hard HE photon index (<1.8) suggesting a common scenario
where the bulk of the emission is produced by accelerated electrons radiating
from radio to VHE gamma-rays through synchrotron and inverse Compton processes.
In addition when correcting for the distance, all SNRs show a surprisingly
similar gamma-ray luminosity supporting the idea of a common emission
mechanism. While the gamma-ray emission is likely to be leptonic dominated,
this does not rule out efficient hadron acceleration in those SNRs.
