Karl Mannheim’s scientific contributions

Relativistic jets from accreting supermassive black holes at cosmological distances can be powerful emitters of γ -rays. However, the precise mechanisms and locations responsible for the dissipation of energy within these jets, leading to observable γ -ray radiation, remain elusive. We detect evidence for an intrinsic absorption feature in the γ -ray spectrum at energies exceeding 10 GeV, presumably due to the photon–photon pair production of γ -rays with low-ionization lines at the outer edge of broad-line region (BLR), during the high-flux state of the flat-spectrum radio quasar PKS 1424−418. The feature can be discriminated from the turnover at higher energies resulting from γ -ray absorption in the extragalactic background light. It is absent in the low-flux states, supporting the interpretation that powerful dissipation events within or at the edge of the BLR evolve into fainter γ -ray emitting zones outside the BLR, possibly associated with the moving very long baseline interferometry radio knots. The inferred location of the γ -ray emission zone is consistent with the observed variability timescale of the brightest flare, provided that the flare is attributed to external Compton scattering with BLR photons.

Relativistic jets from accreting supermassive black holes at cosmological distances can be powerful emitters of $\gamma$-rays. However, the precise mechanisms and locations responsible for the dissipation of energy within these jets, leading to observable $\gamma$-ray radiation, remain elusive. We detect evidence for an intrinsic absorption feature in the $\gamma$-ray spectrum at energies exceeding $10\,$GeV, presumably due to the photon-photon pair production of $\gamma$-rays with low ionization lines at the outer edge of Broad-line region (BLR), during the high-flux state of the flat-spectrum radio quasar PKS 1424$-$418. The feature can be discriminated from the turnover at higher energies resulting from $\gamma$-ray absorption in the extragalactic background light. It is absent in the low-flux states supporting the interpretation that powerful dissipation events within or at the edge of the BLR evolve into fainter $\gamma$-ray emitting zones outside the BLR, possibly associated with the moving VLBI radio knots. The inferred location of $\gamma$-ray emission zone is consistent with the observed variability time scale of the brightest flare, provided that the flare is attributed to external Compton scattering with BLR photons.

The blazar 3C 279 emits a flux of gamma rays that is variable on timescales as short as the light-crossing time across the event horizon of its central black hole. It is commonly reported that the spectral energy distribution (SED) does not show signs of pair attenuation due to interactions of the gamma rays with ambient ultraviolet photons, concluding that the gamma rays must originate from substructures in the jet outside of the broad-line region (BLR). We address the spectral signature imprinted by atomic emission lines on the gamma-ray spectrum produced by an inverse-Compton pair cascade in the photon field of the BLR. We determine with high precision the gamma-ray SED of 3C 279 using Fermi Large Area Telescope data from MJD 58129−58150 and simulate the pair cascade spectrum for three different injection terms. Satisfactory fits to the observational data are obtained. The obtained SED shows features imprinted by pair production on atomic emission line photons due to optically thick radiation transport, but lacking further exponential attenuation expected if the emission region would lie buried deep within the BLR. The SED of 3C 279 is consistent with an inverse-Compton pair cascade spectrum without exponential external pair absorption. Our findings support the view that the gamma-ray emission in 3C 279 originates from the edge of the BLR.