We report the detection of a new \gamma -ray source in the Fermi -LAT sky using a source detection tool based on the minimal spanning tree algorithm .
The source , not reported in previous LAT catalogues but very recently observed in the X-rays and optical bands , is characterized by an increasing \gamma -ray activity in 2012 June–September that reached a weekly peak flux of ( 3.3 \pm 0.6 ) \cdot 10 ^ { -7 } photons cm ^ { -2 } s ^ { -1 } .
A search for a possible counterpart provides indication that it can be associated with the radio source NVSS J141828+354250 , whose optical SDSS colours are typical of a blazar .