Supermassive black holes in the nuclei of active galaxies expel large amounts of matter through powerful winds of ionized gas. The archetypal active galaxy NGC 5548 has been studied for decades, and ...high-resolution x-ray and ultraviolet (UV) observations have previously shown a persistent ionized outflow. An observing campaign in 2013 with six space observatories shows the nucleus to be obscured by a long-lasting, clumpy stream of ionized gas not seen before. It blocks 90% of the soft x-ray emission and causes simultaneous deep, broad UV absorption troughs. The outflow velocities of this gas are up to five times faster than those in the persistent outflow, and, at a distance of only a few light days from the nucleus, it may likely originate from the accretion disk.
Aims. We observed the Seyfert 1 galaxy NGC 985 on several occasions to search for variability in its UV and X-ray absorption features to establish their location and physical properties. Methods. We ...used XMM-Newton to obtain X-ray spectra using the EPIC-pn camera, and the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope (HST) to obtain UV spectra. Our observations were simultaneous and span timescales of days to years. Results. We find that the soft X-ray obscuration that absorbed the low energy continuum of NGC 985 in August 2013 diminished greatly by January 2015. The total X-ray column density decreased from 2.1 × 1022 cm-2 to ~6 × 1021 cm-2. We also detect broad, fast UV absorption lines in COS spectra obtained during the 2013 obscuration event. Lines of C iii*, Lyα, Si iv, and C iv with outflow velocities of −5970 km s-1 and a full-width at half-maximum of 1420 km s-1 are prominent in the 2013 spectrum, but have disappeared in all but Lyα in the 2015 spectra. The ionization state and the column density of the UV absorbing gas is compatible with arising in the same gas as that causing the X-ray obscuration. The high velocity of the UV-absorbing gas suggests that the X-ray obscurer and the associated UV outflow are manifestations of an accretion disk wind.
In 2016 we carried out a Swift monitoring programme to track the X-ray hardness variability of eight type-I AGN over a year. The purpose of this monitoring was to find intense obscuration events in ...AGN, and thereby study them by triggering joint XMM-Newton, NuSTAR, and HST observations. We successfully accomplished this for NGC 3783 in December 2016. We found heavy X-ray absorption produced by an obscuring outflow in this AGN. As a result of this obscuration, interesting absorption features appear in the UV and X-ray spectra, which are not present in the previous epochs. Namely, the obscuration produces broad and blue-shifted UV absorption lines of Lyα, C iv, and N v, together with a new high-ionisation component producing Fe xxv and Fe xxvi absorption lines. In soft X-rays, only narrow emission lines stand out above the diminished continuum as they are not absorbed by the obscurer. Our analysis shows that the obscurer partially covers the central source with a column density of few 1023 cm-2, outflowing with a velocity of few thousand km s-1. The obscuration in NGC 3783 is variable and lasts for about a month. Unlike the commonly seen warm-absorber winds at pc-scale distances from the black hole, the eclipsing wind in NGC 3783 is located at about 10 light days. Our results suggest that the obscuration is produced by an inhomogeneous and clumpy medium, consistent with clouds in the base of a radiatively driven disk wind at the outer broad-line region of the AGN.
Our Swift monitoring program triggered two joint XMM-Newton, NuSTAR, and HST observations on 11 and 21 December 2016 targeting NGC 3783 because its soft X-ray continuum was heavily obscured. ...Consequently, emission features, including the O VII radiative recombination continuum, stand out above the diminished continuum. We focus on the photoionized emission features in the December 2016 Reflection Grating Spectrometer (RGS) spectra, and compare them to the time-averaged RGS spectrum obtained in 2000–2001 when the continuum was unobscured. A two-phase photoionized plasma is required to account for the narrow emission features. These narrow emission features are weakly varying between 2000–2001 and December 2016. We also find a statistically significant broad emission component in the time-averaged RGS spectrum in 2000–2001. This broad emission component is significantly weaker in December 2016, suggesting that the obscurer is farther away than the X-ray broad-line region. In addition, by analyzing the archival high-resolution X-ray spectra, we find that nine photoionized absorption components with different ionization parameters and kinematics are required for the warm absorber in X-rays.
Recurring obscuration in NGC 3783 Kaastra, J. S.; Mehdipour, M.; Behar, E. ...
Astronomy and astrophysics (Berlin),
11/2018, Letnik:
619
Journal Article
Recenzirano
Odprti dostop
Context. Obscuration of the continuum emission from active galactic nuclei by streams of gas with relatively high velocity (>1000 km s−1) and column density (>3 × 1025 m−2) has been seen in a few ...Seyfert galaxies. This obscuration has a transient nature. In December 2016 we witnessed such an event in NGC 3783. Aims. The frequency and duration of these obscuration events is poorly known. Here we study archival data of NGC 3783 in order to constrain this duty cycle. Methods. We use archival Chandra/NuSTAR spectra taken in August 2016. We also study the hardness ratio of all Swift XRT spectra taken between 2008 and 2017. Results. In August 2016, NGC 3783 also showed evidence of obscuration. While the column density of the obscuring material is ten times lower than in December 2016, the opacity is still sufficient to block a significant fraction of the ionising X-ray and extreme ultraviolet photons. From the Swift hardness ratio behaviour we find several other epochs with obscuration. Obscuration with columns >1026 m−2 may take place about half of the time. Also, in archival X-ray data taken by the Advanced Satellite for Cosmology and Astrophysics (ASCA) in 1993 and 1996 we find evidence of obscuration. Conclusions. Obscuration of the ionising photons in NGC 3783 occurs more frequently than previously thought. This may not always have been recognised due to low-spectral-resolution observations, overly limited spectral bandwidth or confusion with underlying continuum variations.
Context.
NGC 985 was observed by
XMM-Newton
twice in 2015, revealing that the source was coming out from a soft X-ray obscuration event that took place in 2013. These kinds of events are possibly ...recurrent since a previous
XMM-Newton
archival observation in 2003 also showed signatures of partial obscuration.
Aims.
We have analyzed the high-resolution X-ray spectra of NGC 985 obtained by the Reflection Grating Spectrometer onboard
XMM-Newton
in 2003, 2013, and 2015 in order to characterize the ionized absorbers superimposed to the continuum and to study their response as the ionizing flux varies.
Methods.
The spectra were analyzed with the SPEX fitting package and the photoionization code CLOUDY.
Results.
We found that up to four warm absorber (WA) components were present in the grating spectra of NGC 985, plus a mildy ionized (log
ξ
∼ 0.2−0.5) obscuring (
N
H
∼ 2 × 10
22
cm
−2
) wind outflowing at ∼ − 6000 km s
−1
. The absorbers have a column density that ranges from ∼10
21
to a few times 10
22
cm
−2
, and ionization parameters ranging from log
ξ
∼ 1.6 to ∼2.9. The most ionized component is also the fastest, moving away at ∼ − 5100 km s
−1
, while the others outflow in two kinematic regimes, ∼ − 600 and ∼ − 350 km s
−1
. These components showed variability at different time scales in response to changes in the ionizing continuum. Assuming that these changes are due to photoionization and recombination mechanisms, we have obtained upper and lower limits on the density of the gas. We used these limits to pinpoint the location of the warm absorbers, finding that the closest two components are at parsec-scale distances, while the rest may extend up to tens of parsecs from the central source. With these constraints on the density and location, we found that the fastest, most ionized WA component accounts for the bulk of the kinetic luminosity injected back into the interstellar medium of the host galaxy, which is on the order of 0.8% of the bolometric luminosity of NGC 985. According to the models, this amount of kinetic energy per unit time would be sufficient to account for cosmic feedback.
Conclusions.
Observations of the onset and conclusion of transient obscuring events in active galactic nuclei are a key tool to understand both the dynamics and physics of the gas in their innermost regions, and also to study the response of the surrounding gas as the ionizing continuum varies.
Aims. To understand the nature of transient obscuring outflows in active galactic nuclei, we use simultaneous multiwavelength observations with XMM-Newton, NuSTAR, the Hubble Space Telescope (HST), ...and the Max Planck Gesellschaft/European Southern Observatory (ESO) 2.2 m telescope triggered by soft X-ray absorption detected by Swift. Methods. We obtained ultraviolet spectra on 2016-12-12 and 2016-12-21 using the Cosmic Origins Spectrograph (COS) on HST simultaneously with X-ray spectra obtained with XMM-Newton and NuSTAR. We modeled the ultraviolet spectra to measure the strength and variability of the absorption, and used photoionization models to obtain its physical characteristics. Results. We find new components of broad, blue-shifted absorption associated with Lyα, N V, Si IV, and C IV in our COS spectra. The absorption extends from near-zero velocities in the rest-frame of the host galaxy to −6200 km s−1. These features appear for the first time in NGC 3783 at the same time as heavy soft X-ray absorption seen in the XMM-Newton X-ray spectra. The X-ray absorption has a column density of ∼1023 cm−2, and it partially covers the X-ray continuum source. Combining the X-ray column densities with the UV spectral observations yields an ionization parameter for the obscuring gas of log ξ = 1.84−0.2+0.4 erg cm s−1 log ξ = 1 . 84 − 0.2 + 0.4 erg cm s −1 $ \log \xi = 1.84_{ - 0.2}^{ + 0.4}{\rm{erg}}\,{\rm{cm}}\,{{\rm{s}}^{ - 1}}\ $ . Despite the high intensity of the UV continuum in NGC 3783, F(1470 Å) = 8 × 10−14 erg cm−2 s−1 Å−1>, the well known narrow UV absorption lines are deeper than in earlier observations in unobscured states, and low ionization states such as C III appear, indicating that the narrow-line gas is more distant from the nucleus and is being shadowed by the gas producing the obscuration. Despite the high continuum flux levels in our observations of NGC 3783, moderate velocities in the UV broad line profiles have substantially diminished. Conclusions.We suggest that a collapse of the broad line region has led to the outburst and triggered the obscuring event.
ABSTRACT
We present joint XMM–Newton and NuSTAR observations of the ‘bare’ narrow-line Seyfert 1 Ton S180 (z = 0.062), carried out in 2016 and providing the first hard X-ray view of this luminous ...galaxy. We find that the 0.4–30 keV band cannot be self-consistently reproduced by relativistic reflection models, which fail to account simultaneously for the soft and hard X-ray emission. The smooth soft excess prefers extreme blurring parameters, confirmed by the nearly featureless nature of the Reflection Grating Spectrometer (RGS) spectrum, while the moderately broad Fe K line and the modest hard excess above 10 keV appear to arise in a milder gravity regime. By allowing a different origin of the soft excess, the broad-band X-ray spectrum and overall spectral energy distribution (SED) are well explained by a combination of (a) direct thermal emission from the accretion disc, dominating from the optical to the far/extreme UV; (b) Comptonization of seed disc photons by a warm (kTe ∼ 0.3 keV) and optically thick (τ ∼ 10) corona, mostly contributing to the soft X-rays; (c) Comptonization by a standard hot ($kT_{\rm \mathrm{ e}}\gtrsim 100$ keV) and optically thin (τ < 0.5) corona, responsible for the primary X-ray continuum; and (d) reflection from the mid/outer part of the disc. The two coronae are suggested to be rather compact, with $R_{\rm hot}\lesssim R_{\rm warm}\lesssim 10\, r_{\rm g}$. Our SED analysis implies that Ton S180 accretes at super-Eddington rates. This is a key condition for the launch of a wind, marginal (i.e. 3.1σ significance) evidence of which is indeed found in the RGS spectrum.
Context.
Obscuration events in type I active galactic nuclei (AGN) have been detected more frequently in recent years. The strong flux decrease in the soft X-ray band between observations has been ...caused by clouds with large column densities transiting our line of sight (LOS) and covering the central AGN. Another event has been captured in NGC 3227 at the end of 2019, which was observed with
XMM-Newton
,
NuSTAR
, and the
Hubble
Space Telescope.
Aims.
We aim to determine the nature and origin of the observed spectral variability in the 2019 obscuration event.
Methods.
We study the evolution of the obscurer by splitting the two
XMM-Newton
observations from 2019 into timing bins of length ∼10 ks. We used the
SPEX
code to analyse the 0.35–10 keV EPIC-PN spectra of each timing bin.
Results.
In the first observation (Obs 1), there is a strong anti-correlation between the column density (
N
H
) of the obscurer and the continuum normalisations of the X-ray power law and soft Comptonisation components (
N
pow
and
N
comt
, respectively). The power-law continuum models the hard X-rays produced by the corona, and the Comptonisation component models the soft X-ray excess and emission from the accretion disk. Through further testing, we conclude that the continuum is likely to drive the observed variability, but we cannot rule out a possible contribution from
N
H
of the obscurer if it fully transverses across the ionising source within our LOS during the observation. The ionisation parameter (
ξ
) of the obscurer is not easily constrained, and therefore it is not clear whether it varies in response to changes in the ionising continuum. The second observation (Obs 2) displays a significantly lower count rate due to the combination of a high
N
H
and covering fraction of the obscurer, and a lower continuum flux.
Conclusions.
The observed variability seen during the obscuration event of NGC 3227 in 2019 is likely driven by the continuum, but the obscurer varies at the same time, making it difficult to distinguish between the two possibilities with full certainty.
Anatomy of the AGN in NGC 5548 Ebrero, J; Kaastra, J S; Kriss, G A ...
Astronomy and astrophysics (Berlin),
03/2016, Letnik:
587
Journal Article
Recenzirano
Odprti dostop
We observed the archetypal Seyfert 1 galaxy NGC 5548 in 2013-2014 in the context of an extensive multi-wavelength campaign involving several satellites, which revealed the source to be in an ...extraordinary state of persistent heavy obscuration. We re-analyzed the archival grating spectra obtained by XMM-Newton and Chandra between 1999 and 2007 in order to characterize the classic warm absorber (WA) using consistent models and up-to-date photoionization codes and atomic physics databases and to construct a baseline model that can be used as a template for the physical state of the WA in the 2013 observations. We find that the WA in NGC 5548 is composed of six distinct ionization phases outflowing in four kinematic regimes. The total kinetic luminosity injected into the surrounding medium is a small fraction (~0.03%) of the bolometric luminosity of the source. After adding the contribution of the UV absorbers, this value augments to ~0.2% of the bolometric luminosity, well below the minimum amount of energy required by current feedback models to regulate galaxy evolution.
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