The Fermi blazars' divide

By G. Ghisellini, L. Maraschi, F. Tavecchio. 2009

218 citations recorded by the source corpus.

Flat-spectrum radio quasars (FSRQs) and BL Lac objects detected in the first three months of the Fermi survey neatly separate in the γ-ray spectral index versus γ-ray luminosity plane. BL Lac objects are less luminous and have harder spectra than broad-line blazars. We suggest that this division has its origin in the different accretion regimes of the two classes of objects. Using the γ-ray luminosity as a proxy for the observed bolometric one, we show that the boundary between the two subclasses of blazars can be associated with the threshold between the regimes of optically thick accretion discs and of radiatively inefficient accretion flows, which lies at an accretion rate of the order of 10−2 the Eddington rate. The spectral separation in hard (BL Lacs) and soft (FSRQs) objects can then result from the different radiative cooling suffered by the relativistic electrons in jets propagating in different ambients. We argue that the bulk of the most luminous blazars already detected by Fermi should be characterized by large black hole masses, around 109 solar masses, and predict that lowering the γ-ray flux threshold the region of the αγ–Lγ plane corresponding to steep spectral indices and lower luminosities will be progressively populated by FSRQs with lower mass black holes, while the region of hard spectra and large luminosities will remain forbidden.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/a858875347794e50a9e10bd93a39a43bb87f399e

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Citations in the corpus

THE COSMIC EVOLUTION OF FERMI BL LACERTAE OBJECTS (2013, methodology): “The correlation between index and luminosity reported by Ghisellini et al. (2009) is much stronger than that which we find here (∆Γ/∆LogLγ ∼0.25 versus ∼0.06); this was thus likely dominated by the uncorrected selection effects.”
The Blazar TXS 0506+056 Associated with a High-energy Neutrino: Insights into Extragalactic Jets and Cosmic-Ray Acceleration (2018, background): “These values are somewhat larger than that derived for BL Lac objects through purely leptonic models that do not account for accelerated protons (Ghisellini et al. 2009).”
THREE-YEAR SWIFT–BAT SURVEY OF ACTIVE GALACTIC NUCLEI: RECONCILING THEORY AND OBSERVATIONS? (2010, methodology): “Around this Eddington ratio, the accretion process experiences a transition from an optically thick, geometrically thin disk (λEdd > 0.01) to a radiatively inefficient geometrically thick disk Ghisellini et al. (2009).”
THE THIRD CATALOG OF ACTIVE GALACTIC NUCLEI DETECTED BY THE FERMI LARGE AREA TELESCOPE (2015, methodology): “This correlation has been widely discussed in the context of the “blazar divide” or “blazar sequence” (Ghisellini et al. 2009, 2012; Meyer et al. 2012; Padovani et al. 2012; Finke 2013; Giommi et al. 2013).”
THE FIRST CATALOG OF ACTIVE GALACTIC NUCLEI DETECTED BY THE FERMI LARGE AREA TELESCOPE (2010, methodology): “It has been suggested (Ghisellini et al. 2009) that this separation results from different radiative cooling of the electrons due to distinct accretion regimes in the two blazar classes.”
General physical properties of bright Fermi blazars (2009, background): “This cannot be accounted for by the simple models, and require other emitting zones or extra population of electrons (see e.g. Ghisellini & Tavecchio 2008; Ghisellini et al. 2009b; Giannios, Uzdensky & Begelman 2009).”
INSIGHTS INTO THE HIGH-ENERGY γ-RAY EMISSION OF MARKARIAN 501 FROM EXTENSIVE MULTIFREQUENCY OBSERVATIONS IN THE FERMI ERA (2011, methodology): “Here we therefore adopt the ‘standard’ one-zone SSC model, which has had moderate success in accounting for the spectral and temporal properties of the TeV-emitting BL Lacs analyzed so far (e.g., Finke et al. 2008; Ghisellini et al. 2009a, and references therein).”
FERMIGAMMA-RAY SPACE TELESCOPE OBSERVATIONS OF THE GAMMA-RAY OUTBURST FROM 3C454.3 IN NOVEMBER 2010 (2011, background): “The moderately hard spectrum during the large luminosity ﬂare deviates from the trend seen in the blazar divide (Ghisellini et al. 2009), where the most γ -ray luminous blazars generally have Γ 2 .”