Figure 8 - available via license: Creative Commons Attribution 4.0 International
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SEDs of the source fitted with the Jetset code for the γ-ray flaring and quiescent epochs. The optical/UV photometric data were obtained from Swift UVOT filters (V, B, U, UVW1, UVM2, and UVW2), and the X-ray (0.3-10 keV) spectra were taken from XRT observations. LAT spectra were used for the high-energy γ-ray emission. The upper limits in the LAT spectra are plotted as downward arrows.
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The γ -ray emission from flat-spectrum radio quasars (FSRQs) is thought to be dominated by the inverse Compton scattering of the external sources of photon fields, e.g., accretion disk, broad-line region (BLR), and torus. FSRQs show strong optical emission lines and hence can be a useful probe of the variability in BLR output, which is the reproces...
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... Low-activity periods are typically associated with the outer parsec-scale regions of the jet or result from combined emissions along the entire jet length in the absence of a dominant emission zone. High-activity periods are primarily linked to emission originating from energetic particles within the inner jet at parsec scales from black hole (Ezhikode et al. 2022). Additionally, high Compton dominance in the source (q ∼ 30; Abhir et al. 2021) indicates that accelerated high-energy electrons in the jet scatter a fraction of soft photons, emitting γ-rays. ...
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.
... Low-activity periods are typically associated with the outer parsec-scale regions of the jet or result from combined emissions along the entire jet length in the absence of a dominant emission zone. High-activity periods are primarily linked to emission originating from energetic particles within the inner jet at parsec scales from black hole (Ezhikode et al. 2022). Additionally, high Compton dominance in the source (q ∼ 30; Abhir et al. 2021) indicates that accelerated high-energy electrons in the jet scatter a fraction of soft photons, emitting γ-rays. ...
Relativistic jets from accreting supermassive black holes at cosmological distances can be powerful emitters of -rays. However, the precise mechanisms and locations responsible for the dissipation of energy within these jets, leading to observable -ray radiation, remain elusive. We detect evidence for an intrinsic absorption feature in the -ray spectrum at energies exceeding GeV, presumably due to the photon-photon pair production of -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 1424418. The feature can be discriminated from the turnover at higher energies resulting from -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 -ray emitting zones outside the BLR, possibly associated with the moving VLBI radio knots. The inferred location of -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 location of -ray emission of blazars remains a contested topic, inspiring the development of numerous investigative techniques to address this issue.
In this work, we analyzed \textit{Fermi} -ray lightcurves in the GeV and MeV bands, employing the discrete cross-correlation function (DCF) method to discern time lags between the two bands.
For 4C +21.35, Ton 599, B2 1420+32, and PKS 1510-089, we identified a time lag spanning several days, while for PKS 1441+25, the time lag was not statistically found.
The results imply that the soft photons necessary for inverse Compton scattering predominantly originate from the dusty torus (DT) in the first four sources, whereas for PKS 1441+25, they seem to be sourced mainly from the BLR.
Further analysis of the opacity () and the GeV spectra study supports the conclusion that the location of the dissipation region must be beyond the BLR to avoid significant absorption.
Notably, for PKS 1441+25, the emission region is also posited to lie outside yet proximate to the BLR.
The parameters of describing the emission region were obtained by fitting broadband spectral energy distribution (SED) with contemporaneous observation data.
Our findings suggest that for the five TeV FSRQs, during TeV flaring events, the jet appears to maintain an equilibrium between the energy density of the magnetic field and that of the particles for all investigated sources, with the exceptions of 4C +21.35 and PKS 1441+25.
In terms of the overall jet power, particle energy is the dominant contributor, and the observed blazar radiation cannot be solely attributed to the magnetic field, except in the case of 4C +21.35.
Consequently, magnetic reconnection is unlikely to be the primary mechanism behind particle acceleration in these systems.
OT 081 is a low-synchrotron-peaked (LSP) frequency blazar target, and has strong emission in the γ-ray band. In July 2016, a significant short-term flare was observed in the optical, X-ray and γ-ray bands. In addition, a long-term orphan flare was observed in the X-ray band from 2009 to 2012. Using the multiwavelength data, we investigate the origin of these two flares and the emission mechanism of γ-ray photons. According to the correlation analysis, we suggest that both flares may have originated from the formation of the new dissipation zones within the jet rather than the change of Doppler factor. The 2016 short-term flare happens on small-scale dissipation zone, while the long-term X-ray flare originates from large scale dissipation zone. Furthermore, we study the spectral energy distribution (SED) to investigate whether the broad-line region (BLR) and the dust torus can provide enough external photons to explain the γ-ray emission of the 2016 flare within the leptonic scenario. We find that the 2016 flare can be explained when the scale of the newly formed dissipation zone is comparable to that of BLR. For the 2009–2012 orphan X-ray flare, we suggest that it may be dominated by the synchrotron self-Compton (SSC) process in a newly formed dissipation zone at pc scale, since both the magnetic field and the external soft photon field energy density are small enough at this region. In summary, the emission mechanism of OT 081 could be explained in the leptonic scenario.
