TeV BL Lac objects at the dawn of the Fermi era

Author： Tavecchio F. Ghisellini G. Ghirlanda G. Foschini L. Maraschi L.

ISSN： 0035-8711

Source： Monthly Notices of the Royal Astronomical Society, Vol.401, Iss.3, 2010-01, pp. : 1570-1586

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Abstract

ABSTRACTWe reconsider the emission properties of BL Lac objects emitting in the high-energy γ-ray band, by exploiting the information in the MeV–GeV band obtained by the Large Area Telescope (LAT) on board the Fermi Gamma-Ray Space Telescope in its first three months of operation. To this aim we construct the spectral energy distribution of all the BL Lacs revealed by LAT and of the known TeV BL Lacs not detected by LAT, also including data from the Swift satellite, and model them with a simple one-zone leptonic model. The analysis shows that the BL Lacs detected by LAT (whether or not already detected in the TeV band) share similar physical parameters. While some of the TeV BL Lacs not revealed by LAT have spectral energy distributions and physical parameters very similar to the LAT BL Lacs, one group of objects displays peculiar properties (larger electron energies and smaller magnetic fields), suggesting different physical conditions in the emission region. Finally, we discuss possible criteria to select in an effective manner good new candidates for the Cherenkov telescopes among the LAT sources, presenting a list of predicted fluxes in the very high-energy band calculated including the effects of absorption by extragalactic background light.