Signature of Seyfert-like component in a blazar 3C 273 and its reflection-based explanation

TL;DR

This study analyzes multi-epoch X-ray and UV observations of blazar 3C 273, revealing Seyfert-like features such as soft excess and reflection components, and models these with reflection and jet emission models to understand their origin.

Contribution

It demonstrates the presence of Seyfert-like thermal and reflection features in a blazar's X-ray spectra and models these features with relativistic reflection, providing new insights into blazar emission mechanisms.

Findings

Detection of soft X-ray excess and reflection hump.

Presence of faint iron line indicating disk reflection.

Additional Seyfert-like thermal component needed for low state spectra.

Abstract

We present the results of blazar 3C 273 obtained from simultaneous observations obtained using 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 Compton reflection hump which might be a weak component arising from dense and cold material. The presence of a faint iron line is present in XMM-Newton observations. We interpret such features as attributed to the coronal emission plus those arising from reflection from an accretion disk. We model the SEDs with the single zone inverse Compton jet model based on Synchrotron Self Compton and External Compton phenomena. It is found that a one-zone synchrotron plus IC model explains quite well the SEDs but the jet component alone fails to fit the multiband X-ray emission for the low state of this object in 2018 and 2019 which arises due 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/ultraviolet band in all SEDs. Finally, we analyzed all the epochs using relxill model to incorporate relativistic reflection to model those residuals of soft excess and Compton hump in the X-ray bands.