Ultrahigh-energy cosmic ray interactions as the origin of very high energy $\gamma -$rays from BL Lacs

Abstract

We explain the observed multiwavelength photon spectrum of a number of BL Lac objects detected at very high energy (VHE, $E\gtrsim 30$ GeV), using a lepto-hadronic emission model. The one-zone leptonic emission is employed to fit the synchrotron peak. Subsequently, the SSC spectrum is calculated, such that it extends up to the highest energy possible for the jet parameters considered. The data points beyond this energy, and also in the entire VHE range are well explained using a hadronic emission model. The ultrahigh-energy cosmic rays (UHECRs, $E\gtrsim 0.1$ EeV) escaping from the source interact with the extragalactic background light (EBL) during propagation over cosmological distances to initiate electromagnetic cascade down to $\sim 1$ GeV energies. The resulting photon spectrum peaks at $\sim 1$ TeV energies. We consider a random turbulent extragalactic magnetic field (EGMF) with a Kolmogorov power spectrum to find the survival rate of UHECRs within 0.1 degrees of the direction of propagation in which the observer is situated. We restrict ourselves to an RMS value of EGMF, $B_{\mathrm{rms}}\sim 10^{-5}$ nG, for a significant contribution to the photon spectral energy distribution (SED) from UHECR interactions. We found that UHECR interactions on the EBL and secondary cascade emission can fit gamma-ray data from the BL Lacs we considered at the highest energies. The required luminosity in UHECRs and corresponding jet power are below the Eddington luminosities of the super-massive black holes in these BL Lacs.

16 pages, 8 figures, Accepted for publication in ApJ

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• Cosmogenic gamma-ray and neutrino fluxes from blazars associated with IceCube events
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• PeV-EeV neutrinos from gamma-ray blazars due to ultrahigh-energy cosmic-ray propagation
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• Cosmic-Ray Constraints on the Flux of Ultra-High-Energy Neutrino Event KM3-230213A
• Exploring the Emission Mechanisms of Mrk 180 with long term X-ray and $\gamma$-ray data
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• Contribution of Secondary Neutrinos from Line-of-sight Cosmic Ray Interactions to the IceCube Diffuse Astrophysical Flux
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• Blazars Jets and prospects for TeV-PeV neutrinos & gamma-rays through cosmic-ray interactions
• Properties and Possible Physical Origins of $\gamma$-ray Emission in Extreme Synchrotron Blazars
• UHECRs Propagation and their Multimessengers: Upper limits and the Impact of the Extragalactic Magnetic Field
• Hadronic origin of gamma rays and neutrinos from blazars: Multi-messenger implications and observational constraints
• Modeling the imprints of large-scale magnetized structures on $\gamma$-rays from extragalactic transients