{
  "id": "2209.13574",
  "version": "v1",
  "published": "2022-09-27T17:48:32.000Z",
  "updated": "2022-09-27T17:48:32.000Z",
  "title": "Long-term optical and $γ-$ray variability of the blazar PKS~1222+216",
  "authors": [
    "Savithri H. Ezhikode",
    "Amit Shukla",
    "Gulab C. Dewangan",
    "Pramod K. Pawar",
    "Sushmita Agarwal",
    "Blesson Mathew",
    "Akhil Krishna R"
  ],
  "comment": "15 pages, 8 figures; Accepted for publication in ApJ",
  "categories": [
    "astro-ph.HE"
  ],
  "abstract": "The $\\gamma-$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$\\gamma$ line, and $\\gamma-$ray emissions from the FSRQ PKS~1222+216, using long-term ($\\sim$2011-2018) optical spectroscopic data from Steward Observatory and $\\gamma-$ray observations from $Fermi$-LAT. We measured the continuum ($F_{C,opt}$) and H$\\gamma$ ($F_{H\\gamma}$) fluxes by performing a systematic analysis of the 6029-6452 \\r{A} optical spectra. We observed stronger variability in $F_{C,opt}$ than $F_{H\\gamma}$, an inverse correlation between H$\\gamma$ equivalent width and $F_{C,opt}$, and a redder-when-brighter trend. Using discrete cross-correlation analysis, we found a positive correlation (DCF$\\sim$0.5) between $F_{\\gamma-ray>100MeV}$ and $F_{C,opt}$ (6024-6092 \\r{A}) light curves with time-lag consistent with zero at 2$\\sigma$ level. We found no correlation between $F_{\\gamma-ray>100MeV}$ and $F_{H\\gamma}$ light curves, probably dismissing the disk contribution to the optical and $\\gamma$-ray variability. The observed strong variability in the $Fermi$-LAT flux and $F_{\\gamma-ray>100MeV}-F_{C,opt}$ correlation could be due to the changes in the particle acceleration at various epochs. We derived the optical-to-$\\gamma$-ray spectral energy distributions (SEDs) during the $\\gamma$-ray flaring and quiescent epochs that show a dominant disk component with no variability. Our study suggests that the $\\gamma$-ray emission zone is likely located at the edge of the BLR or in the radiation field of the torus.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2022-09-27T17:48:32.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "ray variability",
      "long-term optical",
      "light curves",
      "ray spectral energy distributions",
      "dominant disk component"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 15,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}