3,944 research outputs found
Hadronic models of blazars require a change of the accretion paradigm
We study hadronic models of broad-band emission of jets in radio-loud active
galactic nuclei, and their implications for the accretion in those sources. We
show that the models that account for broad-band spectra of blazars emitting in
the GeV range in the sample of Boettcher et al. have highly super-Eddington jet
powers. Furthermore, the ratio of the jet power to the radiative luminosity of
the accretion disc is on average and can be as high as .
We then show that the measurements of the radio core shift for the sample imply
low magnetic fluxes threading the black hole, which rules out the
Blandford-Znajek mechanism to produce powerful jets. These results require that
the accretion rate necessary to power the modelled jets is extremely high, and
the average radiative accretion efficiency is . Thus, if
the hadronic model is correct, the currently prevailing picture of accretion in
AGNs needs to be significantly revised. Also, the obtained accretion mode
cannot be dominant during the lifetimes of the sources, as the modelled very
high accretion rates would result in too rapid growth of the central
supermassive black holes. Finally, the extreme jet powers in the hadronic model
are in conflict with the estimates of the jet power by other methods.Comment: MNRAS, in pres
The Spectra of Large Toeplitz Band Matrices with a Randomly Perturbed Entry
This report is concerned with the union of all possible spectra that may emerge when perturbing a large Toeplitz band matrix in the site by a number randomly chosen from some set . The main results give descriptive bounds and, in several interesting situations, even provide complete identifications of the limit of as . Also discussed are the cases of small and large sets as well as the "discontinuity of the infinite volume case", which means that in general does not converge to something close to as , where is the corresponding infinite Toeplitz matrix. Illustrations are provided for tridiagonal Toeplitz matrices, a notable special case. \ud
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The second author was supported by UK Enginering and Physical Sciences Research Council Grant GR/M1241
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