X-ray Timing and Spectral studies of bare AGN Mrk 110

TL;DR

This paper investigates the origin of the soft X-ray excess in the bare AGN Mrk 110 by combining timing and spectral analyses of six XMM-Newton observations. Using frequency- and energy-dependent lag analyses along with cross-correlation functions, the study detects a soft lag at $\nu \sim 7$–$9\times10^{-5}$ Hz with amplitudes up to a few thousand seconds, though with modest significance ($\sim$80%) due to variability and noise. Spectrally, the data are best described by a persistent warm corona ($kT_{\rm w} \sim 0.21$–$0.33$ keV, $\tau_{\rm w} \sim 14$–$15$) and a compact hot corona ($R_{\rm h} \sim 7$–$15\,R_{\rm g}$) with a low reflection fraction ($R_{\rm f} \lesssim 1$), across epochs; the warm corona dominates the soft X-ray emission and the reflection signatures are weak. Interpreting the soft lag in the light-travel time framework suggests $R \sim 4.5\,R_{\rm g}$ for $M_{\rm BH} = 1.4\times10^{8}\,M_{\odot}$, favoring a reflection origin, whereas for $M_{\rm BH} = 2\times10^{7}\,M_{\odot}$ the inferred radius ($\sim 31\,R_{\rm g}$) allows a hybrid contribution from both reverberation and warm corona variability. The results support an outflowing coronal geometry with a possible link to the detected jet activity, and show that the warm corona can naturally explain the soft excess in a broad, physically self-consistent framework (AGNSED) with relatively weak disk reflection.

Abstract

The origin of the soft X-ray excess below 2 keV in active galactic nuclei (AGNs) remains debated, with relativistic reflection from the inner accretion disk and warm Comptonization in an optically thick corona being the leading explanations. We investigate the timing and spectral properties of the Seyfert galaxy Mrk 110 using six XMM-Newton observations. A frequency-dependent lag analysis in the 7-9 $\times 10^{-5}$ Hz range reveals a soft X-ray lag of 889-3000s in the combined 2019 data, detected with a significance of 80%. The cross-correlation function analysis, supported by simulations, also detects lags of similar nature. Spectral modeling performed by adopting both proposed black hole masses in the literature for Mrk 110 confirms the presence of a warm corona in all observations, along with a weak relativistic reflection component and the reflection fraction remains low (Rf < 1). Interpreting the measured soft lag in terms of light travel time implies an emission radius 4.5 Rg for a supermassive black hole mass of $M = 1.4 \times 10^8$ solar mass , favoring a reflection scenario. However, if a lower mass of $M = 2 \times 10^7$ solar mass is adopted, the inferred radius increases, and both relativistic reflection and warm Comptonization can plausibly contribute to the observed soft lag. The warm corona radius appears larger in the high accretion state and smaller in a lower accretion state, although no trend can be established. The persistently low reflection fraction suggests an outflowing inner corona in Mrk 110, consistent with the recent detection of jet activity in this source.

Figures (8)

• Figure 1: EPIC-pn X-ray light curves for all observations in 0.3 -- 10 keV energy bands with a time bin of 500 s. /// Alt text:Plot showing all the x-ray light curve for the source
• Figure 2: Hardness-intensity plot for all the observations along with a linear fit (f(x)), see text for more details./// Alt text:Plot of all the hardness ratio along with the fit in shown.
• Figure 3: Power density spectra in 0.3 -- 10 keV energy band of Mrk 110 for different observations. The dotted line shows the best fit powerlaw+constant model for three of the observations with the same color as the dataset for clarity (Obs. 1, Obs. 2b, and Obs. 3)./// Alt text: All the power density spectra are over-plotted along with the fitting
• Figure 4: Top three panel displays the frequency-lag spectra (0.3 -- 1 keV versus 1 -- 5 keV) of the respective observations. The dashed line displays the zero lag. The bottom panel displays the coherence with 1$\sigma$ error bars./// Alt text: The top three panels shows the frequency-lag spectra and the bottom panel shows the coherence plot for all the observations.
• Figure 5: The merit of lag $\chi$ for all the simulated frequency-lag spectra for all the 2019 observation combined to obtain the soft-lag significance is plotted. The red-dotted line represents real $\chi$ value of the observation./// Alt text: Histogram plot for the merit of lag and the real merit value