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Fermi LAT detection of a GeV flare from AP Librae (PKS 1514-241)

Davide Donato (Center for Research and Exploration in Space Science and Technology (CRESST) and NASA Goddard Space Flight Center), Pascal Fortin (LLR/Ecole Polytechnique/CNRS/IN2P3); on behalf of the Fermi Large Area Telescope Collaboration.

The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed a short, bright gamma-ray flare from a source positionally consistent with the low-frequency-peaked BL Lac object AP Librae (RA: 15h17m41.8s, Dec: -24d22m19s , J2000, K.J. Johnston et al. 1995, AJ, 110, 880) with a redshift of z=0.049. This source was recently detected at very-high energies (E>100 GeV) by the H.E.S.S. collaboration (ATel #2743).

Preliminary analysis indicates that the source on February 21, 2011, between 06:00 and 12:00 UT was in a high state with a gamma-ray flux (E>100MeV) of (1.4+/-0.6)E-06 photons cm-2 s-1, which represents an increase of a factor of ~20 with respect to the source flux level reported in the 1FGL catalog (Abdo et al. 2010, ApJS, 188, 405), which reports the average flux from August 2008 through June 2009.

Because Fermi operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. The Fermi LAT contact people for this source is Pascal Fortin (

The Fermi LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden.