X-ray spectral and temporal analysis of Narrow Line Seyfert 1 galaxy Was 61

TL;DR

This study analyzes the X-ray spectrum and variability of the Narrow Line Seyfert 1 galaxy Was 61, revealing stable spectral index, variable Fe Kα lines, and soft excess correlated with hard flux, suggesting a warm Comptonization origin.

Contribution

It provides detailed spectral and temporal analysis of Was 61, highlighting the variability of Fe Kα lines and supporting a warm Comptonization model for soft excess.

Findings

Detection of a broad Fe Kα line at 6.7 keV in low flux segments.

Observation of a narrow Fe Kα line at 6.4 keV in higher flux segments.

Correlation between soft X-ray excess and hard flux, favoring Comptonization model.

Abstract

We present an analysis of spectrum and variability of the bright reddened narrow line Seyfert 1 galaxy Was~61 using 90 ks archival {\it XMM-Newton} data. The X-ray spectrum in 0.2-10 keV can be characterized by an absorbed power-law plus soft excess and an Fe K$\alpha$ emission line. The power-law spectral index remains constant during the flux variation. The absorbing material is mildly ionized, with a column density of 3.2$\times$10$^{21}$ cm$^{-2}$, and does not appear to vary during the period of the X-ray observation. If the same material causes the optical reddening (E(B-V)$\simeq$0.6 mag), it must be located outside the narrow line region with a dust-to-gas ratio similar to the average Galactic value. We detect significant variations of the Fe K$\alpha$ line during the observational period. A broad Fe K$\alpha$ line at $\simeq$6.7 keV with a width of $\sim$0.6 keV is detected in the low flux segment of the first 40 ks exposure, and is absent in the spectra of other segments; a narrow Fe K$\alpha$ emission line $\sim$6.4 keV with a width of $\sim$0.1 keV is observed in the subsequent 20 ks segment, which has a count rate of 35% higher and is in the next day. We believe this is due to the change in geometry and kinematics of the X-ray emitting corona. The temperature and flux of soft X-ray excess appear to correlate with the flux of the hard power-law component. Comptonization of disc photons by a warm and optically thick inner disk is preferred to interpret the soft excess, rather than the ionized reflection.