Discovery of transient high-energy gamma-ray emission from the BL Lacertae object 5C 3.178

• 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 similar to 8 sigma during a 200 day period which began on November 17th 2011 (MJD 55 882). The observed gamma-ray emission is characterised by a moderate 0.2-300 GeV flux F0.2-300 (GeV) = (8.22 +/- 2.04) x 10(-9) ph cm(-2) s(-1) and a hard power law spectrum with spectral index Gamma = 1.76 +/- 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 similar to 200 day timescales may represent a rewarding strategy.

Ämnesord

NATURVETENSKAP  -- Fysik -- Astronomi, astrofysik och kosmologi (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences -- Astronomy, Astrophysics and Cosmology (hsv//eng)

Nyckelord

astroparticle physics

BL Lacertae objects: individual: 5C 3.178

gamma rays: galaxies

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