The observation of a gamma-ray line in the cosmic-ray fluxes would be a smoking-gun signature for dark matter annihilation or decay in the Universe .
We present an improved search for such signatures in the data of the Fermi Large Area Telescope ( LAT ) , concentrating on energies between 20 and 300 \text { GeV } .
Besides updating to 43 months of data , we use a new data-driven technique to select optimized target regions depending on the profile of the Galactic dark matter halo .
In regions close to the Galactic center , we find a 4.6 \sigma indication for a gamma-ray line at E _ { \gamma } \approx 130 \text { GeV } .
When taking into account the look-elsewhere effect the significance of the observed excess is 3.2 \sigma .
If interpreted in terms of dark matter particles annihilating into a photon pair , the observations imply a dark matter mass of m _ { \chi } = 129.8 \pm 2.4 ^ { +7 } _ { -13 } \text { GeV } and a partial annihilation cross-section of \langle \sigma v \rangle _ { \chi \chi \to \gamma \gamma } = \left ( 1.27 \pm 0.32 ^ { +0.18 } _ % { -0.28 } \right ) \times 10 ^ { -27 } \text { cm } ^ { 3 } \text { s } ^ { -1 } when using the Einasto dark matter profile .
The evidence for the signal is based on about 50 photons ; it will take a few years of additional data to clarify its existence .