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We report on gamma-ray analysis of the region containing the bright TeVsource HESS J1640-465 and the close-by TeV source HESS J1641-463 using 64months of observations with the Fermi Large Area Telescope (LAT). Previouslyonly one GeV source was reported in this region and was associated with HESSJ1640-465. With an increased dataset and the improved sensitivity afforded bythe reprocessed data (P7REP) of the LAT, we now report the detection,morphological study and spectral analysis of two distinct sources above 100MeV. The softest emission in this region comes from the TeV source HESSJ1641-463 which is well fitted with a power law of index Gamma = 2.47 +/- 0.05+/- 0.06 and presents no significant gamma-ray signal above 10 GeV, whichcontrasts with its hard spectrum at TeV energies. The Fermi-LAT spectrum of thesecond TeV source, HESS J1640-465 is well described by a power-law shape ofindex Gamma = 1.99 +/- 0.04 +/- 0.07 that links up naturally with the spectraldata points obtained by the High Energy Stereoscopic System (H.E.S.S.). Thesenew results provide new constraints concerning the identification of these twopuzzling gamma-ray sources.

HESS J1640-465 and HESS J1641-463: two intriguing TeV sources in the light of new Fermi LAT observations