The mystery of spectral breaks: Lyman continuum absorption by photon-photon pair production in the Fermi GeV spectra of bright blazars

Abstract

We reanalyze Fermi/LAT gamma-ray spectra of bright blazars with a higher photon statistics than in previous works and with new Pass 7 data representation. In the spectra of the brightest blazar 3C 454.3 and possibly of 4C +21.35 we detect breaks at 5 GeV (in the rest frame) associated with the photon-photon pair production absorption by He II Lyman continuum (LyC). We also detect confident breaks at 20 GeV associated with hydrogen LyC both in the individual spectra and in the stacked redshift-corrected spectrum of several bright blazars. The detected breaks in the stacked spectra univocally prove that they are associated with atomic ultraviolet emission features of the quasar broad-line region (BLR). The dominance of the absorption by hydrogen Ly complex over He II, rather small detected optical depth, and the break energy consistent with the head-on collisions with LyC photons imply that the gamma-ray emission site is located within the BLR, but most of the BLR emission comes from a flat disk-like structure producing little opacity. Alternatively, the LyC emission region size might be larger than the BLR size measured from reverberation mapping, and/or the gamma-ray emitting region is extended. These solutions would resolve a long-standing issue how the multi-hundred GeV photons can escape from the emission zone without being absorbed by softer photons.

arXiv comment7 pages, 6 figures; accepted to ApJ

References in corpus (27)

• Fermi Large Area Telescope Second Source Catalog
• The Soft X-Ray Properties of a Complete Sample of Optically Selected Quasars II. Final Results
• The Lick AGN Monitoring Project: Broad-Line Region Radii and Black Hole Masses from Reverberation Mapping of Hbeta
• Reverberation Mapping of High-Luminosity Quasars: First Results
• MAGIC discovery of VHE Emission from the FSRQ PKS 1222+21
• Magnetic acceleration of relativistic AGN jets
• Keplerian Motion of Broad-Line Region Gas as Evidence for Supermassive Black Holes in Active Galactic Nuclei
• GeV breaks in blazars as a result of gamma-ray absorption within the broad-line region
• Spectral Properties of Bright Fermi-detected Blazars in the Gamma-ray Band
• Fermi Gamma-ray Space Telescope Observations of the Gamma-ray Outburst from 3C 454.3 in November 2010
• Early Fermi Gamma-ray Space Telescope Observations of the Quasar 3C 454.3
• Fermi Gamma-ray Space Telescope Observations of Recent Gamma-ray Outbursts from 3C 454.3
• On the origin of the gamma-ray emission from the flaring blazar PKS 1222+216
• The spectrum of the Broad Line Region and the high-energy emission of powerful blazars
• The gamma-ray brightest days of the blazar 3C 454.3
• The Connection Between Jets, Accretion Disks, and Black Hole Mass in Blazars
• Fermi Large Area Telescope Detection of Bright Gamma-ray Outbursts from a Peculiar Quasar 4C +21.35
• Hubble Space Telescope ultraviolet spectroscopy of blazars: emission lines properties and black hole masses
• Geometry and inclination of the broad line region in blazars
• Exploring the blazar zone in High Energy flares of FSRQs
• Radiation from relativistic jets in blazars and the efficient dissipation of their bulk energy via photon breeding
• Variation of the gamma-gamma opacity by the He II Lyman continuum constrains the location of the gamma-ray emission region in the blazar 3C 454.3
• A test on external Compton models for $\gamma$-ray active galactic nuclei
• Fermi Large Area Telescope Detection of Two Very-High-Energy (E>100 GeV) Gamma-ray Photons from the z = 1.1 Blazar PKS 0426-380
• A photon breeding mechanism for the high-energy emission of relativistic jets
• Identifying Breaks and Curvature in the Fermi Spectra of Bright Flat Spectrum Radio Quasars
• The effect of the broad-line region with geometrical structures on gamma-ray absorption in blazars

Cited by in corpus (23)

• Rapid Variability of Blazar 3C 279 during Flaring States in 2013-2014 with Joint Fermi-LAT, NuSTAR, Swift, and Ground-Based Multi-wavelength Observations
• Relativistic Jets in Active Galactic Nuclei und Microquasars
• On the origin of gamma rays in Fermi blazars: beyond the broad line region
• Characterizing the Gamma-Ray Variability of the Brightest Flat Spectrum Radio Quasars Observed with the Fermi LAT
• Gamma rays from the quasar PKS 1441+25: story of an escape
• The most powerful flaring activity from the NLSy1 PMN J0948+0022
• Fermi-LAT Observations of the 2014 May-July outburst from 3C 454.3
• Gamma-ray opacity of the anisotropic stratified broad-line regions in blazars
• Constraints of Flat Spectrum Radio Quasars in the hadronic model: the case of 3C 273
• Locating the gamma-ray emission region in the brightest Fermi-LAT Flat Spectrum Radio Quasars
• Fourier Analysis of Blazar Variability: Klein-Nishina Effects and the Jet Scattering Environment
• Exploring the origin of multiwavelength activities of high-redshift FSRQ PKS 1502+106 during 2014-2018
• Exploring the connection between radio and GeV-TeV gamma-ray emission in the 1FHL and 2FHL AGN samples
• Properties of the narrow line Seyfert 1 galaxies revisited
• On the origin of GeV spectral break for Fermi blazars: 3C 454.3
• Turbulent spectra of the brightest gamma-ray flares of blazars
• VERITAS discovery of very high energy gamma-ray emission from S3 1227+25 and multiwavelength observations
• Imprint of "Local Opacity" Effect in Gamma-Ray Spectrum of Blazar Jet
• Absorption features in sub-TeV gamma-ray spectra of BL Lac objects
• Pair Cascades at the Edge of the Broad-Line Region Shaping the Gamma-Ray Spectrum of 3C 279
• Insights from leptohadronic modelling of the brightest blazar flare
• Blazars and Optical Depth in a non-linear, time-dependent injection and cooling scenario
• The Statistic Analysis of GeV Spectral Breaks in Bright Gamma-Ray FSRQs