Signature of a Seyfert-like Component in Blazar 3C 273 and Its Reflection-based Explanation

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Abstract
We present the results of blazar 3C 273 from simultaneous observations obtained using the XMM-Newton and NuSTAR satellites during the period 2015–2019 in five epochs. When the spectra are modeled with a power law, significant residuals arise below ∼2 keV and in the energy range of 30–78 keV in NuSTAR data. Residuals in the lower energy band represent soft X-ray excess, while at higher energies it likely represents a Compton reflection hump, which might be a weak component arising from dense and cold material. A faint iron line is present in XMM-Newton observations. We interpret such features as being attributed to the coronal emission plus those produced through reflection from an accretion disk. We model the spectral energy distributions (SEDs) with the single-zone inverse Compton (IC) jet model based on synchrotron self-Compton and external Compton phenomena. It is found that a one-zone synchrotron+IC model explains the SEDs quite well, but the jet component alone fails to fit the multiband X-ray emission for the low flux state of this object in 2018 and 2019, which arises owing to spectral flattening at low-energy X-rays, indicating that an additional Seyfert-like thermal component must be present at X-rays. This is further supported by a big blue bump present in the optical/UV band in all SEDs. Finally, we analyzed all the epochs using the relxill model to incorporate relativistic reflection and to model those residuals of soft excess and Compton hump in the X-ray bands.

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