Insights from leptohadronic modelling of the brightest blazar flare

TL;DR

The study probes whether the exceptionally bright 2010 flare of 3C 454.3 can be captured by a standing-feature leptonic model with the emission beyond the BLR, and it quantifies the associated high-energy neutrino output. It contrasts this with a moving-blob leptonic scenario, finding the standing-feature model provides a robust fit to seven daily SEDs and that a pure leptonic framework suffices for the electromagnetic data. When a leptohadronic component is allowed, the X-ray data constrain the proton energy density and yield a predicted IceCube neutrino rate of about $6\times10^{-3}$ muon neutrinos per year for $E_ u\ge100$ TeV, with neutrino production potentially lagging months to years behind the electromagnetic flare. Extrapolating to the FSRQ population suggests a sub-dominant contribution to the IceCube flux (roughly $\lesssim 1\%$ of alerts), while next-generation neutrino telescopes could detect roughly one multimessenger blazar flare per year, enabling multi-messenger studies of jet physics and particle acceleration.

Abstract

The blazar 3C 454.3 experienced a major flare in November 2010, making it the brightest $γ$-ray source in the sky of the Fermi Large Area Telescope (LAT). We obtain seven daily consecutive spectral-energy distributions (SEDs) of the flare in the infrared, optical, ultraviolet, X-ray and $γ$-ray bands with publicly available data. We simulate the physical conditions in the blazar and show that the observed SEDs are well reproduced in the framework of a "standing feature" where the position of the emitting region is almost stationary, located beyond the outer radius of the broad-line region and into which fresh blobs of relativistically moving magnetised plasma are continuously injected. Meanwhile, a model with a single "moving blob" does not describe the data well. We obtain a robust upper limit to the amount of high-energy protons in the jet of 3C 454.3 from the electromagnetic SED. We construct a neutrino light curve of 3C 454.3 and estimate the expected neutrino yield at energies $\geq 100$ TeV for 3C 454.3 to be up to $6 \times 10^{-3}$ $ν_μ$ per year. Finally, we extrapolate our model findings to the light curves of all Fermi-LAT flat-spectrum radio quasars. We find that next-generation neutrino telescopes are expected to detect approximately one multimessenger ($γ+ ν_μ$) flare per year from bright blazars with neutrino peak energy in the hundreds TeV -- hundreds PeV energy range and show that the electromagnetic flare peak can precede the neutrino arrival by months to years.

Figures (30)

• Figure 1: Geometrical scheme of the emitting region in the jet of 3C 454.3 (figure adapted from 2022MNRAS.515.5242D).
• Figure 2: The optical depth of $\gamma\gamma$ pair production for $\gamma$ rays with the observed (at Earth) energy $E^{o}_{\gamma}$ emitted in a blob with $\Gamma = 25$ and $z = 0.859$ at a particular distance $x$ from the SMBH as indicated in the legend.
• Figure 3: The dependence of the dissipation radius $x$ on the maximum observed (on Earth) $\gamma$-ray energy assuming it corresponds to pair production at the threshold on photons from the He II Ly $\alpha$ line in the blob with Lorentz factor $\Gamma = 25$ at redshift $z = 0.859$. The dashed-dotted vertical lines show the central energies of the last observed Fermi-LAT bins during one-day periods as indicated in the legend (closely plotted lines correspond to the same energy but slightly shifted for better visibility).
• Figure 4: Phenomenological fits to the synchrotron, X-ray, and $\gamma$-ray parts of the SED averaged over 55517--55524. Data for each energy segment are normalized by the maximum value of the SED in the energy range. See Table \ref{['table:game_of_slopes']} for the details of the fits.
• Figure 5: The results of the fits to the normalised Fermi-LAT SED averaged over MJD 55517--55524 by subexponential cutoff (Eq. \ref{['eq:superexp']}) and biquadratic function (Eq. \ref{['eq:quartic']}).