Photoionisation modelling of the X-ray emission line regions within the Seyfert 2 AGN NGC 1068

Abstract

Aims. We investigate the photoionised X-ray emission line regions (ELRs) within the Seyfert 2 galaxy NGC 1068 to determine if there are any characteristic changes between observations taken 14 years apart. Methods. We compared XMM-Newton observations collected in 2000 and 2014, simultaneously fitting the reflection grating spectrometer and EPIC-pn spectra of each epoch, for the first time, with the photoionisation model, PION, in SPEX. Results. We find that four PION components are required to fit the majority of the emission lines in the spectra of NGC 1068, with log ξ = 1−4, log NH > 26 m−2, and vout = −100 to −600 km s−1 for both epochs. Comparing the ionisation state of the components shows almost no difference between the two epochs, while there is an increase in the total equivalent column density. To estimate the locations of these plasma regions from the central black hole, we compare distance methods, excluding the variability arguments as there is no spectral change between observations. Although the methods are unable to constrain the distances for each plasma component, the locations are consistent with the narrow line region, with the possibility of the higher ionised component being part of the broad line region; we cannot conclude this for certain, but the photoionisation modelling does suggest this is possible. In addition, we find evidence for emission from collisionally ionised plasma, while previous analysis had suggested that collisional plasma emission was unlikely. However, although PION is unable to account for the Fe XVII emission lines at 15 and 17 Å, we do not rule out that photoexcitation is a valid processes to produce these lines as well. Conclusions. NGC 1068 has not changed, both in terms of the observed spectra or from our modelling, within the 14 year time period between observations. This suggests that the ELRs are fairly static relative to the 14 year time frame between observations, or there is no dramatic change in the spectral energy distribution, resulting from a lack of black hole variability.

The Long Stare at Hercules X-1. I. Emission Lines from the Outer Disk, the Magnetosphere Boundary, and the Accretion Curtain

“…The findings above suggest a gain inaccuracy in the EPIC pn Timing mode. A similar gain issue, but in other EPIC pn observing modes, was previously discussed by multiple authors, including Ponti et al (2013), Cappi et al (2016, Zoghbi et al (2019), Grafton-Waters et al (2021), and Costanzo et al (2022, but with a significantly lower value of about 50 eV (in the same "blueshift" direction as found here). The shift could be caused by uncorrected charge transfer inefficiency evolution in EPIC pn or alternatively by optical loading, and appears to be significantly worse in Timing mode spectra.…”

The long stare at Hercules X-1 -- I. Emission lines from the outer disk, the magnetosphere boundary and the accretion curtain

“…The findings above suggest a gain inaccuracy in the EPIC pn Timing mode. A similar gain issue, but in other EPIC pn observing modes was previously discussed by multiple authors, including Ponti et al (2013), Cappi et al (2016), Zoghbi et al (2019), Grafton-Waters et al (2021 and Costanzo et al (2021) but with a significantly lower value of about 50 eV (in the same 'blueshift' direction as found here). The shift could be caused by uncorrected charge transfer inefficiency (CTI) evolution in EPIC pn or alternatively by optical loading, and appears to be significantly worse in Timing mode spectra.…”

Multiwavelength Observations of the Obscuring Wind in the Radio-quiet Quasar MR 2251-178

“…The warm emitter features are not prominent though, partly due to the relatively short exposure time. To reduce the number of free parameters, based on experience (e.g., Mao et al 2018Mao et al , 2019Grafton-Waters et al 2021), we fix the emission covering factor C em = Ω/4π, where Ω is the solid angle subtended by the warm emitter with respect to the central engine. The emission covering factors of the two warm emitter components are 0.005 and 0.10, respectively.…”