Abstract
After the discovery of powerful relativistic jets from Narrow-Line Seyfert 1 Galaxies, and the understanding of their similarity with those of blazars, a problem of terminology was born. The word blazar is today associated to BL Lac Objects and Flat-Spectrum Radio Quasars, which are somehow different from Narrow-Line Seyfert 1 Galaxies. Using the same word for all the three classes of AGN could drive either toward some misunderstanding, or to the oversight of some important characteristics. I review the main characteristics of these sources, and finally I propose a new scheme of classification.
Highlights
The title is borrowed from Haruki Murakami’s What we talk about when we talk about running, who, in turn, borrowed it from Raymond Carver’s What we talk about when we talk about love
The observed blazar sequence indicated that the spectral energy distribution (SED) of high-power blazar (FSRQs) had the synchrotron and the inverse-Compton peaks at infrared and MeV-GeV energies, respectively, while that of low-power sources (BL Lac Objects) had the peaks shifted to greater energies (UV/X-rays and TeV, respectively) (Fossati et al, 1998)
The words blazar and radio galaxy indicate a certain type of cosmic source characterized by a high black hole mass and hosted by an elliptical galaxy
Summary
The title is borrowed from Haruki Murakami’s What we talk about when we talk about running, who, in turn, borrowed it from Raymond Carver’s What we talk about when we talk about love. Urry and Padovani’s scheme has its pillars in three main factors: viewing angle, optical spectrum, radio emission They suggested a fourth factor, the black hole spin, which should be greater for jetted AGN. The observed blazar sequence indicated that the spectral energy distribution (SED) of high-power blazar (FSRQs) had the synchrotron and the inverse-Compton peaks at infrared and MeV-GeV energies, respectively, while that of low-power sources (BL Lac Objects) had the peaks shifted to greater energies (UV/X-rays and TeV, respectively) (Fossati et al, 1998) This was explained as different cooling of relativistic electrons due to different environment, rich of photons or not (physical blazar sequence, Ghisellini et al, 1998). Coziol et al (2017) confirmed the results of Miley and Miller (1979): small-mass compact objects have generally weak, and compact radio jets
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