An exploration of hadronic interactions in blazars using IceCube

Abstract

Context. Hadronic models, involving matter (proton or nuclei) acceleration in blazar jets, imply high energy photon and neutrino emissions due to interactions of high-energy protons with matter and/or radiation in the source environment. Aims. This paper shows that the sensitivity of the IceCube neutrino telescope in its 40-string configuration (IC-40) is already at the level of constraining the parameter space of purely hadronic scenarios of activity of blazars. Methods. Assuming that the entire source power originates from hadronic interactions, and assuming that the model describe the data, we estimate the expected neutrino flux from blazars based on the observed γ-ray flux by Fermi, simultaneously with IC-40 observations. We consider two cases separately to keep the number of constrainable parameters at an acceptable level: proton-proton or proton-gamma interactions are dominant. Comparing the IC-40 sensitivity to the neutrino flux expected from some of the brightest blazars, we constrain model parameters characterizing the parent high-energy proton spectrum. Results. Using together the Fermi photon observations and the IC-40 neutrino sensitivities, we find that when pp interactions dominate, some constraints on the primary proton spectrum can be imposed. For instance, for the tightest constrained source 3C 454.3, the very high energy part of the spectra of blazars is constrained to be harder than E −2 with cut-off energies in the range of E cut ≥ 10 18 eV. When interactions of high-energy protons on soft photon fields dominate, we can find similarly tight constraints on the proton spectrum parameters if the soft photon field is in the UV range or at higher energy, e.g. if it originates from the "big blue bump" produced by the accretion disk. The tightest constraint is for 3C 273, with the cut-off energy constrained to be E cut 10 18 eV for any spectral index and different soft photon fields, including the radiation from the accretions disk, broad line region or the synchrotron radiation from the jet. Conclusions. We have adopted a simplified approach using the IC-40 sensitivity (about one half of the full detector) to constrain parameters of blazar hadronic models. Data of the full detector are already available and corresponding constraints should be about a factor of 3 better than what discussed here.

High-energy cosmic neutrinos from spine-sheath BL Lac jets

“…4 we report in detail the SED and the expected neutrino output for this source. In the SED we also report the IceCube sensitivity curve for 3 years, scaling that provided in Tchernin et al (2013) for one year and about half of the detector (IC-40 configuration). Clearly, the flux limit is very close to that theoretically expected.…”

Time dependent photon and neutrino emission from Mkr 421 in the context of the one-zone leptohadronic model

“…Good fits to the SED of the source are obtained assuming that the protons are accelerated up to E p ≃ 30 PeV, therefore they cannot contribute to the UHECR flux. However, the produced neutrino flux is tantalizingly close to the IC-40 sensitivity limit for Mrk 421 [14] and peaks within the energy range where the first PeV neutrino detection from the IceCube collaboration was reported [15]. A shortcoming of the LHπ model is its low efficiency.…”

“…In general, we find that the inclusion of photopair -a process that is not usually taken into account -as an extra mechanism for injecting secondaries, alters the shape of the radiated photon spectra as for most 05005-p.2 Fermi observations [13] (grey points) are not simultaneous with the rest of the data. The 40-String IceCube limit for muon neutrinos [14] is plotted with a dash-dotted line.…”

Consequences of Proton Acceleration in Blazar Jets

“…are not simultaneous with the rest of the data, and are thus not included in the fit. The 40-String IceCube limit [11] for ν µ is plotted with an orange line. Right panel: cosmic-ray (proton) spectra resulting from neutron decay and obtained within the LHπ (red line) and LHs (blue dashed line) models.…”