An empirical kernel for Bethe-Heitler pair spectra is introduced and applied to argue that synchrotron emission from these pairs can explain gamma-ray emission in low- and intermediate-peaked blazars for jet regions of size ~10^15 cm and B = 5-500 G.
A hadronic origin for ultra-high-frequency-peaked BL Lac objects
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abstract
Current Cherenkov telescopes have identified a population of ultra-high-frequency peaked BL Lac objects (UHBLs), also known as extreme blazars, that exhibit exceptionally hard TeV spectra, including 1ES 0229+200, 1ES 0347-121, RGB J0710+591, 1ES 1101-232, and 1ES 1218+304. Although one-zone synchrotron-self-Compton (SSC) models have been generally successful in interpreting the high-energy emission observed in other BL Lac objects, they are problematic for UHBLs, necessitating very large Doppler factors and/or extremely high minimum Lorentz factors of the emitting leptonic population. In this context, we have investigated alternative scenarios where hadronic emission processes are important, using a newly developed (lepto-)hadronic numerical code to systematically explore the physical parameters of the emission region that reproduces the observed spectra while avoiding the extreme values encountered in pure SSC models. Assuming a fixed Doppler factor $\delta=30$, two principal parameter regimes are identified, where the high-energy emission is due to: 1) proton-synchrotron radiation, with magnetic fields $B \sim 1-100\ \textrm{G}$ and maximum proton energies $E_{p;max} \lesssim 10^{19}$ eV; and 2) synchrotron emission from p-$\gamma$-induced cascades as well as SSC emission from primary leptons, with $B \sim 0.1-1\ \textrm{G}$ and $E_{p;max} \lesssim 10^{17}$ eV. This can be realized with plausible, sub-Eddington values for the total (kinetic plus magnetic) power of the emitting plasma, in contrast to hadronic interpretations for other blazar classes that often warrant highly super-Eddington values.
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UNVERDICTED 5representative citing papers
A sample of 69 HBLs yields intrinsic radio-X-ray correlation L_R,int ∝ L_X,int^0.68 and fundamental plane log L_R,int = 0.57 log L_X,int + 0.33 log M_BH + 12.65, consistent with synchrotron cooling model for X-ray emission.
New IXPE X-ray polarimetry and optical monitoring of PG 1553+113 reveal variable polarization and a large EVPA swing, supporting jet models with related but non-co-spatial X-ray and optical emission regions.
EHSP blazars exhibit hard intrinsic GeV-TeV spectra with high-energy peaks near TeV energies after EBL correction, based on combined Fermi-LAT and ground-based telescope data.
Review summarizing correlations between astrophysical neutrinos and gamma-ray/radio AGN, specific source associations, proposed production mechanisms, and future prospects.
citing papers explorer
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A closer look at the electromagnetic signatures of Bethe-Heitler pair production process in blazars
An empirical kernel for Bethe-Heitler pair spectra is introduced and applied to argue that synchrotron emission from these pairs can explain gamma-ray emission in low- and intermediate-peaked blazars for jet regions of size ~10^15 cm and B = 5-500 G.
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The Fundamental Planes of Black Hole Activity for High-Synchrotron-Peaked BL Lacertae Objects
A sample of 69 HBLs yields intrinsic radio-X-ray correlation L_R,int ∝ L_X,int^0.68 and fundamental plane log L_R,int = 0.57 log L_X,int + 0.33 log M_BH + 12.65, consistent with synchrotron cooling model for X-ray emission.
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Tracking down the broadband polarimetric properties of PG 1553+113
New IXPE X-ray polarimetry and optical monitoring of PG 1553+113 reveal variable polarization and a large EVPA swing, supporting jet models with related but non-co-spatial X-ray and optical emission regions.
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Intrinsic GeV-TeV gamma-ray emission from EHSP blazars
EHSP blazars exhibit hard intrinsic GeV-TeV spectra with high-energy peaks near TeV energies after EBL correction, based on combined Fermi-LAT and ground-based telescope data.
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Active Galactic Nuclei as high-energy neutrino sources
Review summarizing correlations between astrophysical neutrinos and gamma-ray/radio AGN, specific source associations, proposed production mechanisms, and future prospects.