Author(s): A. Abdo A., Ackermann M., Ajello M., B. Atwood W., Axelsson M., Ballet J., Bruel P., M. Casandjian J., Cohen-Tanugi J., Dumora D., Farnier C., J. Fegan S., Fortin P., Giebels B., A. Grenier I., Grondin M.-H., Guillemot L., Horan D., Knödlseder J., Lemoine-Goumard M., Lott B., Nuss E., Parent D., Pelassa V., Piron F., Reposeur T., Sanchez D., A. Smith D., Tibaldo L., Vilchez N.
(Article) Published:
The Astrophysical Journal / The Astrophysical Journal Letters, vol. 710 p.1271-1285 (2010)
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Ref Arxiv: 1001.4097
DOI: 10.1088/0004-637X/710/2/1271
Ref. & Cit.: NASA ADS
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Abstract:
The gamma-ray energy spectra of bright blazars of the LAT Bright AGN Sample (LBAS) are investigated using Fermi-LAT data. Spectral properties (hardness, curvature and variability) established using a data set accumulated over 6 months of operation are presented and discussed for different blazar classes and subclasses: Flat Spectrum Radio Quasars (FSRQs), Low-synchrotron peaked BLLacs (LSP-BLLacs), Intermediate-synchrotron peaked BLLacs (ISP-BLLacs) and High-synchrotron peaked BLLacs (HSP-BLLacs). The distribution of photon index (obtained from a power-law fit above 100 MeV) is found to correlate strongly with blazar subclass. The change in spectral index from that averaged over the six month observing period is < 0.2-0.3 when the flux varies by about an order of magnitude, with a tendency toward harder spectra when the flux is brighter for FSRQs and LSP-BLLacs. A strong departure from a single power-law spectrum appears to be a common feature for FSRQs. This feature is also present for some high-luminosity LSP-BLLacs, and a small number of ISP-BLLacs. It is absent in all LBAS HSP-BLLacs. For 3C 454.3 and AO 0235+164, the two brightest FSRQ source and LSP-BLLac source respectively, a broken power law gives the most acceptable of power law, broken power law, and curved forms. The consequences of these findings are discussed.
Comments: 15 figures, 2 tables