Anatomy of the AGN in NGC 5548

Abstract

During an extensive multiwavelength campaign that we performed in 2013−2014, we found the prototypical Seyfert 1 galaxy NGC 5548 in an unusual condition of heavy and persistent obscuration. The newly discovered "obscurer" absorbs most of the soft X-ray continuum along our line of sight and lowers the ionizing luminosity received by the classical warm absorber. We present the analysis of the high resolution X-ray spectra collected with XMM-Newton and Chandra throughout the campaign, which are suitable to investigate the variability of both the obscurer and classical warm absorber. The time separation between these X-ray observations range from two days to eight months. On these timescales the obscurer is variable both in column density and in covering fraction. This is consistent with the picture of a patchy wind. The most significant variation occurred in September 2013 when the source brightened for two weeks. A higher and steeper intrinsic continuum and a lower obscurer covering fraction are both required to explain the spectral shape during the flare. We suggest that a geometrical change of the soft X-ray source behind the obscurer causes the observed drop in the covering fraction. Because of the higher soft X-ray continuum level, the September 2013 Chandra spectrum is the only X ray spectrum of the campaign in which individual features of the warm absorber could be detected. The spectrum shows absorption from Fe-UTA, O , and O , consistent with belonging to the lower-ionization counterpart of the historical NGC 5548 warm absorber.Hence, we confirm that the warm absorber has responded to the drop in the ionizing luminosity caused by the obscurer.

Anatomy of the AGN in NGC 5548

“…We note that during the first three archival observations, when the source was unobscured, the best-fit parameters of our Cloudy models converged into a two-component warm absorber solution that is consistent with the values reported by the Suzaku data , and which were considered a good approximation, at low energy resolution, of the multi-temperature warm absorber detected in grating Chandra and XMM-Newton spectra (Andrade-Velazquez et al 2010;Steenbrugge et al 2005;Paper VI). During the campaign, our best-fit values are overall in agreement with the average values found by Paper 0 and the independent measurements from Di Gesu et al (2015), except for the much larger value of ξ 1 found here with respect to Paper 0 and Paper IV, who found a log ξ 1 = −1.2 ± 0.08. There are multiple possible reasons for this apparent discrepancy.…”

“…Another obvious explanation could be the presence of an additional outflowing absorption component, at such a high ionization state to contribute only/mostly with FeXXV (He-α and He-β) and FeXXVI (Ly-α and Ly-β) absorption lines. Alternatively, both these remaining blueshifted absorption features and red-shifted emission features could be signatures of a Fe PCygni type emission and absorption profile originating in an outflowing, highly ionized wind (Dorodnitsyn 2010;Hagino et al 2015;Gardner & Done 2015;Nardini et al 2015). Finally, another possibility for the 6 keV emission line could be a (yet unmodelled) contribution from a weak, and significantly redshifted and broadened reflection component.…”

“…The shadowing effects of this UV BAL and X-ray obscurer on the larger-scale "historical" UV narrow absorption lines and WA are presented in Arav et al (2015; hereafter Paper II). The high energy properties of the source during, and before, the campaign are shown in Ursini et al (2015; hereafter Paper III), while the study of a short-timescale flaring event that happened in September 2013 and which triggered a Chandra LETG observation is addressed in Di Gesu et al (2015; hereafter Paper IV), together with the analysis of the WA short-term variability during this event. The time-averaged soft X-ray linedominated RGS spectrum is presented and modeled in detail in Whewell et al (2015;hereafter Paper V).…”

A Deep X-Ray View of the Bare Agn Ark 120. I. Revealing the Soft X-Ray Line Emission

“…A turbulence velocity of σ=300 km s −1 was chosen to account for any narrow absorption lines. The ionization parameter of the absorption table was varied between x = log 0 3 -9 to allow for the typical range in ionization seen toward other Seyfert 1s, with prominent warm absorption components (Kaspi et al 2002;Blustin et al 2005;Detmers et al 2011;Reeves et al 2013;Di Gesu et al 2015). The total N H column was recorded for each value of the ionization parameter, in increments of 0.1 in x log space.…”

High‐energy monitoring of Seyfert galaxies: The case of NGC 4593

“…The properties of this obscuring outflow are consistent with those of a disc wind (Kaastra et al 2014). The detailed description of the campaign is given by Mehdipour et al (2015), while the physical and temporal properties of the outflows are described in Arav et al (2015) and Di Gesu et al (2015 INTEGRAL data from the campaign, Ursini et al (2015) studied the broad-band (0.3-400 keV) X-ray spectrum of NGC 5548. A high-energy cut-off of 70 +40 −10 keV, attributed to thermal Comptonization, is found in one observation out of seven, while a lower limit ranging from 50 to 250 keV is found in the other six observations.…”