2018/07/08 by S. Gasparyan, N. Sahakyan, V. Baghmanyan +1 · 1 citation
Physics and Astronomy · #astro-ph.HE
paper · pdf · doi:10.3847/1538-4357/aad234
Accepted for publication in ApJ
arxiv created 2018/07/08 · arxiv updated 2018/08/22
We report on broadband observations of CTA 102 (z=1.037) during the active states in 2016-2017. In the γ-ray band, Fermi LAT observed several prominent flares which followed a harder-when-brighter behavior: the hardest photon index Γ=1.61± 0.10 being unusual for FSRQs. The peak γ-ray flux above 100 MeV (3.55±0.55)×10-5 \rm photon cm-2 s-1 observed on MJD 57738.47 within 4.31 minutes, corresponds to an isotropic γ-ray luminosity of Lγ=3.25×1050 \rm erg s-1, comparable with the highest values observed from blazars so far. The analyses of the Swift UVOT/XRT data show an increase in the UV/optical and X-ray bands which is contemporaneous with the bright γ-ray periods. The X-ray spectrum observed by Swift XRT and NuSTAR during the γ-ray flaring period is characterized by a hard photon index of ∼1.30. The shortest e-folding time was 4.08±1.44 hours, suggesting a very compact emission region R≤δ×2.16×1014 cm. We modeled the spectral energy distribution of CTA 102 in several periods (having different properties in UV/optical, X-ray and γ-ray bands) assuming a compact blob inside and outside the BLR. We found that the high-energy data are better described when the infrared thermal radiation of the dusty torus is considered. In the flaring periods when the correlation between the γ-ray and UV/optical/X-ray bands is lacking, the γ-ray emission can be produced from the interaction of fresh electrons in a different blob, which does not make a dominant contribution at lower energies.