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What powers the most relativistic jets? – I. BL Lacs

Gardner, E.; Done, C.

What powers the most relativistic jets? – I. BL Lacs Thumbnail


Authors

E. Gardner



Abstract

The dramatic relativistic jets pointing directly at us in BL Lacertae (BL Lac) objects can be well modelled by bulk motion beaming of synchrotron self-Compton emission powered by a low Eddington fraction accretion flow. Nearly 500 of these active galactic nuclei (AGN) are seen in the second Fermi Large Area Telescope catalogue of AGN. We combine the jet models which describe individual spectra with the expected jet parameter scalings with mass and mass accretion rate to predict the expected number of Fermi detected sources given the number densities of AGN from cosmological simulations. We select only sources with Eddington scaled mass accretion rate <0.01 (i.e. radiatively inefficient flows), and include cooling, orientation effects and the effects of absorption from pair production on the extragalactic infrared background. These models overpredict the number of Fermi detected BL Lacs by a factor of 1000! This clearly shows that one of the underlying assumptions is incorrect, almost certainly that jets do not scale simply with mass and accretion rate. The most plausible additional parameter which can affect the region producing the Fermi emission is black hole spin. We can reproduce the observed numbers of BL Lacs if such relativistic jets are only produced by the highest spin (a* > 0.8) black holes, in agreement with the longstanding spin–jet paradigm. This also requires that high spins are intrinsically rare, as predicted by the cosmological simulations for growing black hole mass via chaotic (randomly aligned) accretion episodes, where only the most massive black holes have high spin due to black hole–black hole mergers.

Citation

Gardner, E., & Done, C. (2014). What powers the most relativistic jets? – I. BL Lacs. Monthly Notices of the Royal Astronomical Society, 438(1), 779-788. https://doi.org/10.1093/mnras/stt2246

Journal Article Type Article
Acceptance Date Nov 17, 2013
Online Publication Date Dec 4, 2013
Publication Date Feb 11, 2014
Deposit Date Mar 16, 2016
Publicly Available Date Mar 28, 2024
Journal Monthly Notices of the Royal Astronomical Society
Print ISSN 0035-8711
Electronic ISSN 1365-2966
Publisher Royal Astronomical Society
Peer Reviewed Peer Reviewed
Volume 438
Issue 1
Pages 779-788
DOI https://doi.org/10.1093/mnras/stt2246
Related Public URLs http://adsabs.harvard.edu/abs/2014MNRAS.438..779G

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Copyright Statement
This article has been accepted for publication in Monthly notices of the Royal Astronomical Society ©: 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.





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