In:
The Astrophysical Journal, American Astronomical Society, Vol. 939, No. 2 ( 2022-11-01), p. 76-
Abstract:
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 reprocessed disk emission. We study the connection between the optical continuum, H γ line, and γ -ray emissions from the FSRQ PKS 1222+216, using long-term (∼2011–2018) optical spectroscopic data from Steward Observatory and γ -ray observations from Fermi Large Area Telescope (LAT). We measured the continuum ( F C,opt ) and H γ ( F H γ ) fluxes by performing a systematic analysis of the 6029–6452 Å optical spectra. We observed stronger variability in F C,opt than F H γ , an inverse correlation between the H γ equivalent width and F C,opt , and a redder-when-brighter trend. Using discrete cross-correlation analysis, we found a positive correlation (DCF ∼ 0.5) between the F γ ‐ray 〉 100 MeV and F C,opt (6024–6092 Å) light curves with a time lag consistent with zero at the 2 σ level. We found no correlation between the F γ ‐ray 〉 100 MeV and F H γ light curves, probably dismissing the disk contribution to the optical and γ -ray variability. The observed strong variability in the Fermi-LAT flux and F γ ‐ray 〉 100 MeV − F C,opt correlation could be due to the changes in the particle acceleration at various epochs. We derived the optical-to- γ -ray spectral energy distributions during the γ -ray flaring and quiescent epochs that show a dominant disk component with no variability. Our study suggests that the γ -ray emission zone is likely located at the edge of the BLR or in the radiation field of the torus.
Type of Medium:
Online Resource
ISSN:
0004-637X
,
1538-4357
DOI:
10.3847/1538-4357/ac9627
Language:
Unknown
Publisher:
American Astronomical Society
Publication Date:
2022
detail.hit.zdb_id:
2207648-7
detail.hit.zdb_id:
1473835-1
SSG:
16,12
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