New Insight into Gamma-ray Blazars from the Fermi-LAT
Résumé
The first three months of sky-survey operation with the Large Area Telescope (LAT) on board the Fermi satellite revealed 132 bright sources at vertical bar b vertical bar > 10 degrees with test statistic greater than 100 (corresponding to about 10 sigma). Two methods, based on the CGRaBS, CRATES and BZCat catalogs, indicated high-confidence associations of 106 of these sources with known AGNs. This sample is referred to as the LAT Bright AGN Sample (LBAS). It contains two radio galaxies, namely Centaurus A and NGC 1275, and 104 blazars consisting of 58 flat spectrum radio quasars (FSRQs), 42 BL Lac objects, and four blazars with unknown classification. Remarkably, the LBAS includes 10 high-energy-peaked BL Lacs. Only 33 of the sources, plus two at vertical bar b vertical bar < 10 degrees, were previously detected with EGRET, probably due to variability. The analysis of the gamma-ray properties of the LBAS sources reveals that the average GeV spectra of BL Lac objects are significantly harder than the spectra of FSRQs. Other spectral and variability blazar properties are discussed. Some prominent Fermi-detected radiogalaxies are presented.