Imprint of "Local Opacity" Effect in Gamma-Ray Spectrum of Blazar Jet
Abstract
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.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- June 2024
- DOI:
- 10.3847/2041-8213/ad4994
- arXiv:
- arXiv:2405.09612
- Bibcode:
- 2024ApJ...968L...1A
- Keywords:
-
- High energy astrophysics;
- Flat-spectrum radio quasars;
- Galactic and extragalactic astronomy;
- Relativistic jets;
- Gamma-ray astronomy;
- Blazars;
- 739;
- 2163;
- 563;
- 1390;
- 628;
- 164;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 10 pages, 3 figures, 1 table, Accepted for publication in ApJL