Space Telescope Observations of the Quasar 3 C 454 . 3
نویسندگان
چکیده
This is the first report of Fermi Gamma-ray Space Telescope observations of the quasar 3C 454.3, which has been undergoing pronounced long-term outbursts since 2000. The data from the Large Area Telescope (LAT), covering 2008 July 7– October 6, indicate strong, highly variable γ-ray emission with an average flux of ∼ 3×10 photons cm s, for energies > 100MeV. The γ-ray flux is variable, with strong, distinct, symmetrically-shaped flares for which the flux increases by a factor of several on a time scale of about three days. This variability indicates a compact emission region, and the requirement that the source is optically thin to pair-production implies relativistic beaming with Doppler factor δ > 8, consistent with the values inferred from VLBI observations of superluminal expansion (δ ∼ 25). The observed γ-ray spectrum is not consistent with a simple power-law, but instead steepens strongly above ∼ 2 GeV, and is well described by a broken power-law with photon indices of ∼ 2.3 and ∼ 3.5 below and above the break, respectively. This is the first direct observation of a break in the spectrum of a high luminosity blazar above 100MeV, and it is likely direct evidence for an intrinsic break in the energy distribution of the radiating particles. Alternatively, the spectral softening above 2GeV could be due to γ-ray absorption via photonphoton pair production on the soft X-ray photon field of the host AGN, but such an interpretation would require the dissipation region to be located very close (. 100 gravitational radii) to the black hole, which would be inconsistent with the X-ray spectrum of the source. Subject headings: Galaxies: active – quasars: individual: 3C 454.3 – Gamma rays: observations
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تاریخ انتشار 2009