Abstract
The Fermi Gamma-ray Space Telescope with its main instrument on-board, the Large Area Telescope (LAT), opened a new era in the study of high-energy emission from Active Galactic Nuclei (AGN). When combined with contemporaneous ground- and space-based observations, Fermi-LAT achieves its full capability to characterize the jet structure and the emission mechanisms at work in radio-loud AGN with different black hole mass and accretion rate, from flat spectrum radio quasars to narrow-line Seyfert 1 (NLSy1) galaxies. Here, I discuss important findings regarding the blazar population included in the third LAT catalog of AGN and the gamma-ray emitting NLSy1. Moreover, the detection of blazars at redshift beyond three in gamma rays allows us to constrain the growth and evolution of heavy black holes over cosmic time, suggesting that the radio-loud phase may be important for a fast black hole growth in the early Universe. Finally, results on extragalactic objects from the third catalog of hard LAT sources are presented.
Highlights
Relativistic jets are one of the most powerful manifestations of the release of energy related to the super-massive black hole (SMBH) at the center of active galactic nuclei (AGN)
A new classification based on the luminosity of the broad line region (BLR) in Eddington luminosity was proposed by Ghisellini et al (2011): sources with LBLR/LEdd higher or lower than 5 × 10−4 being classified as flat spectrum radio quasars (FSRQ) or BL Lacs, respectively, in agreement with a transition of the accretion regime from efficient to inefficient between these classes
The 3FGL includes 3033 sources detected after four years of operation with a Test Statistic1 greater than 25, corresponding to a significance > 4σ ; 2,192 sources are detected at Galactic latitude |b| > 10◦. 1,563 sources (71% of the 3FGL objects at |b| > 10◦) are associated at high-confidence with 1,591 AGN (28 objects have two possible associations), 1The Test Statistic is defined as TS = 2×(logL1 - logL0), where L is the likelihood of the data given the model with (L1) or without (L0) a point source at the position of the target (e.g., Mattox et al, 1996)
Summary
Relativistic jets are one of the most powerful manifestations of the release of energy related to the super-massive black hole (SMBH) at the center of active galactic nuclei (AGN). The spectral energy distribution (SED) of blazars are characterized by two bumps with the lower energy peak occurring in the IR/optical band in the FSRQ and at UV/X-rays in the BL Lacs This first peak is univocally interpreted as synchrotron radiation from highly relativistic electrons. Fossati et al (1998) proposed that the SEDs of blazars form a spectral sequence, with the position of the two peaks governed by the observed bolometric luminosity: blazars with lower luminosities have the peaks at higher energies This was theoretically interpreted by Ghisellini et al (1998) in terms of different radiative cooling suffered by the electrons emitting at the two peaks. The discovery by Fermi-LAT of variable γ-ray emission from a few radio-loud narrow-line Seyfert 1 galaxies (NLSy1) suggested this as the third class of AGN with a relativistic jet (Abdo et al, 2009).
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