We report the serendipitous discovery of transient , point-like high energy \gamma -ray emission coincident with the position of the suspected BL Lac object 5C 3.178 .
The source was detected using the Fermi Large Area Telescope ( LAT ) at a significance level of \sim 8 \sigma during a 200 day period which began on November 17th 2011 ( MJD 55882 ) .
The observed \gamma -ray emission is characterised by a moderate 0.2-300 GeV flux F _ { 0.2 - 300 { GeV } } = ( 8.22 \pm 2.04 ) \times 10 ^ { -9 } ph cm ^ { -2 } s ^ { -1 } and a hard power law spectrum with spectral index \Gamma = 1.76 \pm 0.09 .
These properties appear consistent with the known sub-population of TeV \gamma -ray-emitting BL Lac objects , implying that the source may be detectable using atmospheric Cherenkov telescope arrays .
Moreover , the temporal variability of the source suggests that real-time searches of the Fermi -LAT all-sky dataset for weak emission on \sim 200 day timescales may represent a rewarding strategy .