X-ray emission of radio-loud quasar SDSS J121426.52+140258.9: independent variations between optical/UV and X-ray emission

TL;DR

This study investigates the optical and X-ray variability of the radio-loud quasar J1214+1402, revealing independent variations and unusual emission epochs, challenging standard disk-corona models and suggesting a warm corona origin for soft X-ray excess.

Contribution

It provides multi-epoch observations showing independent optical and X-ray variability and identifies a potential warm corona as the source of soft X-ray excess in a RLQ.

Findings

Optical and X-ray emissions vary independently.

Unusual epochs with low optical but high X-ray flux.

Soft X-ray excess appears only during high optical states.

Abstract

To understand the X-ray emission of active galactic nuclei (AGNs), we explored the optical-to-X-ray variation correlation of a radio-loud quasar (RLQ) SDSS J121426.52+140258.9 (hereafter J1214+1402) with multi-epoch observations of Swift and XMM-Newton telescopes. With the historical multi-band data, we found that the infrared to X-ray flux of RLQ J1214+1402 should not be dominated by the beamed jet emission. The Swift optical/UV and X-ray light curves showed that J1214+1402 has two optical states with low flux before 2014 April 08 and high flux after 2014 June 11, but has no significant X-ray variations during the time range between 2007 March 09 and 2014 August 04. This result was supported by the XMM-Newton observations in the overlapped time with Swift. Interestingly, the early XMM-Newton data prior to the Swift time presents two unusual emission epochs when J1214+1402 has relatively low optical fluxes but has the brightest X-ray fluxes. The overall independence of optical-to-X-ray variation seems hard to be described by the disk-corona model. With the X-ray spectral fitting, we find that the soft X-ray excess in J1214+1402 appears only during the high optical state when the X-ray emission is at low state. The soft X-ray excess in J1214+1402 is difficult to be explained by the ionized accretion disk, instead, it may be related to the warm corona.