In-depth investigation of the physical origin of the soft X-ray excess in PG 1448+273

Abstract

We present systematic X-ray spectral and variability analyses for the narrow-line Seyfert 1 galaxy (NLsy1), PG 1448+273, using the data from two long-exposure XMM-Newton observations of the source in the different flux states. These X-ray spectral analyses indicate that the two main-stream models of soft X-ray excess, the relativistically smeared reflection scenario and the warm corona scenario, show a similar statistical fit to the data sets. However, the warm corona scenario requires a black hole mass that is much larger than that estimated by the single-epoch optical spectroscopy and the X-ray variability scaling technology to alleviate the conflict between the X-ray and optical/ultraviolet data. The time-varying analyses reveal that PG 1448+273 has significant X-ray variability, especially in the low state. The features of X-ray spectra and variability show significant differences between the high and low states. At the low state, a highly variable ultra-fast outflow feature appears in the X-ray spectra, and the X-ray spectra show a very significant soft X-ray excess. At the high state, a ‘dip’, or oscillation, feature with ∼3.2σ confidence level emerges in the power spectral density at ν ∼ 103.6 Hz, which is a unique time signature of the reflected X-ray reprocessing. Meanwhile, we also detect a tentative soft lag. It is shown that these unique spectral features and variation behaviours can be explained self-consistently in the relativistically smeared reflection scenario, in which the geometric position of the corona changes. Our results suggest that PG 1448-273 can be used as an ideal object to further study the details of the relativistic reflection process.

The variability and soft X-ray excess properties of narrow-line Seyfert 1 galaxies: TheSwiftview

“…the height of corona) is highly variable. Indeed, Ding et al (2021) conducted an in-depth study on the nature of soft X-ray excess and variability of this source by using the multi-epoch XMM-Newton observation data. The results show that the soft X-ray excess of the source is most likely to be originated by the relativistically smeared reflection scenario.…”

“…For NLSy1s, which occupy extreme physical parameters, most of the current research is dedicated to individual sources with extremely significant and special variability, such as Mrk 335, I Zw 1, and PG 1148+273 (see e.g. Wilkins & Gallo 2015;Ding et al 2021;Wilkins et al 2021). These studies have successfully revealed that the corona of NLSy1s is highly dynamic and that the structure of the corona undergoes significant changes in a short time (such as a few weeks to several years), resulting in extreme multi-band variation and even X-ray-weak special characteristics.…”