The Blazar Sequence 2.0
Abstract
:1. Introduction
2. The Blazar Sequence 1.0
3. The Sample
4. Results
4.1. Accretion and Jets
4.2. Low Black Hole Mass and Low Power FSRQs
4.3. Host Galaxies of BL Lacs
5. Phenomenological SEDs
6. Discussion and Conclusions
- There still is a blazar sequence, with the same overall properties of the “1.0” version: the SED becomes redder, and the Compton dominance increases as the total luminosity increases.
- In a sizeable fraction of FSRQs, the accretion disk becomes visible through an upturn of the IR–optical spectrum. Pure data show that the accretion luminosity is related to the observed beamed non-thermal luminosity.
- On average, the Compton dominance in powerful blazars is slightly smaller than in [1]. This is the main difference from the old sequence, and it is fully understood: the increased sensitivity of Fermi/LAT allows the exploration of more “normal” blazars, and not only the most luminous. As a consequence, the average γ-ray luminosity is less than in [1]. This explains the puzzling result of [29] when synthesizing the blazar contribution to the γ-ray background. They found that in assuming the blazar radio luminosity function and the same γ-ray-to-radio luminosity ratio as in the original F98 blazar sequence, one overestimates the background, especially at high energies. With the new sequence, the problem is solved (Bonnoli et al. in prep).
- The γ-ray spectrum becomes steeper as the γ–ray luminosity increases. On the other hand, low power BL Lacs do not show, on average, a very hard high energy spectrum (rising in ) in the 0.1–100 GeV band, as was the case in [1] (based on only three sources).
- At intermediate γ-ray luminosities, red FSRQs and blue BL Lacs share the same γ-ray luminosity. This is explained by a difference in black hole masses.
- One can define the average synchrotron () and inverse Compton () peak frequencies for each luminosity bin, but perhaps it is better to define them separately for BL Lacs and FSRQs. This is done in Figure 7 (blue squares: BL Lacs, red circles: FSRQs), showing and as a function of . Both BL Lacs and FSRQs form a sequence, much more pronounced in the BL Lac case.
- The smallest is ∼10 Hz, coincident with of the most compact component. This suggests that there should be even more powerful blazars, with the real synchrotron peak hidden by self-absorption. These blazars should have 1 MeV (i.e., at or below Hz) with a steep spectrum above. In this case, the flux in the 0.1–100 GeV band could become undetectable by Fermi/LAT, and thus be not represented in the new blazar sequence. However, they should be detectable in hard X-rays, and indeed in the Swift/BAT 3 year survey [30] we find ten very powerful blazars with , and five of them are still not detected by Fermi/LAT. These are shown in the right panel of Figure 7.
Conflicts of Interest
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Ghisellini, G. The Blazar Sequence 2.0. Galaxies 2016, 4, 36. https://doi.org/10.3390/galaxies4040036
Ghisellini G. The Blazar Sequence 2.0. Galaxies. 2016; 4(4):36. https://doi.org/10.3390/galaxies4040036
Chicago/Turabian StyleGhisellini, Gabriele. 2016. "The Blazar Sequence 2.0" Galaxies 4, no. 4: 36. https://doi.org/10.3390/galaxies4040036