scholarly journals A deep X-ray view of the bare AGN Ark 120

2018 ◽  
Vol 609 ◽  
pp. A42 ◽  
Author(s):  
D. Porquet ◽  
J. N. Reeves ◽  
G. Matt ◽  
A. Marinucci ◽  
E. Nardini ◽  
...  
Keyword(s):  
Spectral Analysis ◽  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Line Of Sight ◽  
Constant Density ◽  
High Flux ◽  
X Rays ◽  
X Ray ◽  
Intrinsic Absorption ◽  
The Continuum

Context. The physical characteristics of the material closest to supermassive black holes (SMBHs) are primarily studied through X-ray observations. However, the origins of the main X-ray components such as the soft X-ray excess, the Fe Kα line complex, and the hard X-ray excess are still hotly debated. This is particularly problematic for active galactic nuclei (AGN) showing a significant intrinsic absorption, either warm or neutral, which can severely distort the observed continuum. Therefore, AGN with no (or very weak) intrinsic absorption along the line of sight, so-called “bare AGN”, are the best targets to directly probe matter very close to the SMBH. Aims. We perform an X-ray spectral analysis of the brightest and cleanest bare AGN known so far, Ark 120, in order to determine the process(es) at work in the vicinity of the SMBH. Methods. We present spectral analyses of data from an extensive campaign observing Ark 120 in X-rays with XMM-Newton (4 × 120 ks, 2014 March 18–24), and NuSTAR (65.5 ks, 2014 March 22). Results. During this very deep X-ray campaign, the source was caught in a high-flux state similar to the earlier 2003 XMM-Newton observation, and about twice as bright as the lower-flux observation in 2013. The spectral analysis confirms the “softer when brighter” behavior of Ark 120. The four XMM-Newton/pn spectra are characterized by the presence of a prominent soft X-ray excess and a significant Fe Kα complex. The continuum is very similar above about 3 keV, while significant variability is present for the soft X-ray excess. We find that relativistic reflection from a constant-density, flat accretion disk cannot simultaneously produce the soft excess, broad Fe Kα complex, and hard X-ray excess. Instead, Comptonization reproduces the broadband (0.3–79 keV) continuum well, together with a contribution from a mildly relativistic disk reflection spectrum. Conclusions. During this 2014 observational campaign, the soft X-ray spectrum of Ark 120 below ~0.5 keV was found to be dominated by Comptonization of seed photons from the disk by a warm (kTe ~ 0.5 keV), optically-thick corona (τ ~ 9). Above this energy, the X-ray spectrum becomes dominated by Comptonization from electrons in a hot optically thin corona, while the broad Fe Kα line and the mild Compton hump result from reflection off the disk at several tens of gravitational radii.

scholarly journals Lifting the curtain: The Seyfert galaxy Mrk 335 emerges from deep low-state in a sequence of rapid flare events

2020 ◽  
Vol 643 ◽  
pp. L7
Author(s):  
S. Komossa ◽  
D. Grupe ◽  
L. C. Gallo ◽  
P. Poulos ◽  
D. Blue ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Spectral Energy Distribution ◽  
Galactic Nuclei ◽  
Seyfert Galaxy ◽  
Optical Emission ◽  
Line Of Sight ◽  
Spectral Energy ◽  
X Rays ◽  
X Ray ◽  
Partial Covering

Context. The narrow-line Seyfert 1 galaxy Mrk 335 was one of the X-ray brightest active galactic nuclei, but it has systematically faded since 2007. Aims. We report the discovery with Swift of a sequence of bright and rapid X-ray flare events that reveal the emergence of Mrk 335 from its ultra-deep multiyear low state. Methods. Results are based on our dedicated multiyear monitoring of Mrk 335 with Swift. Results. Unlike other bright active galactic nuclei, the optical–UV is generally not correlated with the X-rays in Mrk 335 on a timescale of days to months. This fact either implies the absence of a direct link between the two emission components; or else implies that the observed X-rays are significantly affected by (dust-free) absorption along our line of sight. The UV and optical, however, are closely correlated at the 99.99% confidence level. The UV is leading the optical by Δt = 1.5 ± 1.5 d. The Swift X-ray spectrum shows strong deviations from a single power law in all brightness states of the outbursts, indicating that significant absorption or reprocessing is taking place. Mrk 335 displays a softer-when-brighter variability pattern at intermediate X-ray count rates, which has been seen in our Swift data since 2007 (based on a total of 590 observations). This pattern breaks down at the highest and lowest count rates. Conclusions. We interpret the 2020 brightening of Mrk 335 as a decrease in column density and covering factor of a partial-covering absorber along our line of sight in the form of a clumpy accretion-disk wind that reveals an increasing portion of the intrinsic emission of Mrk 335 from the disk and/or corona region, while the optical emission-line regions receive a less variable spectral energy distribution. This then also explains why Mrk 335 was never seen to change its optical Seyfert type (not “changing look”) despite its factor ∼50 X-ray variability with Swift.

scholarly journals Soft X-ray Variability and the Covering Fraction of Active Galactic Nuclei

1989 ◽  
Vol 134 ◽  
pp. 118-119
Author(s):  
Michael A. Strauss ◽  
Kenneth W. Wachter ◽  
Alexei V. Filippenko
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Line Of Sight ◽  
X Rays ◽  
Broad Line ◽  
X Ray ◽  
Broad Line Region ◽  
Line Region ◽  
Partial Covering

The variability of soft X-rays (0.2 – 2 keV) in some low-luminosity type 1 Seyferts may partly be due to an extrinsic mechanism: dense clouds of gas in the broad-line region, opaque to soft X-rays, move across our line of sight to the X-ray emitting portions of the accretion disk (Reichert, Mushotzky, and Holt 1986; Lawrence and Elvis 1982; Halpern 1984). As the clouds move, the covering fraction changes stochastically. Evidence for partial covering of the X-ray source in low-luminosity AGNs has been seen in soft X-ray spectra by Holt et al. (1980) and Reichert et al. (1985).

scholarly journals Compton-Thick AGN in the NuSTAR ERA VII. A joint NuSTAR, Chandra, and XMM-Newton Analysis of Two Nearby, Heavily Obscured Sources

2021 ◽  
Vol 922 (2) ◽  
pp. 159
Author(s):  
A. Traina ◽  
S. Marchesi ◽  
C. Vignali ◽  
N. Torres-Albà ◽  
M. Ajello ◽  
...  
Keyword(s):  
Spectral Analysis ◽  
Energy Range ◽  
Active Galactic Nuclei ◽  
Column Density ◽  
Galactic Nuclei ◽  
Seyfert Galaxies ◽  
Line Of Sight ◽  
Broad Energy Range ◽  
Larger Sample ◽  
Broad Energy

Abstract We present the joint Chandra, XMM-Newton, and NuSTAR analysis of two nearby Seyfert galaxies, NGC 3081 and ESO 565-G019. These are the only two having Chandra data in a larger sample of 10 low-redshift (z ≤ 0.05), candidates Compton-thick (CT) Active Galactic Nuclei selected in the 15–150 keV band with Swift-BAT that were still lacking NuSTAR data. Our spectral analysis, performed using physically motivated models, provides an estimate of both the line-of-sight (l.o.s.) and average (N H,S ) column densities of the two torii. NGC 3081 has a Compton-thin l.o.s. column density N H,z = [0.58–0.62] × 1024 cm−2, but the N H,S , beyond the CT threshold (N H,S = [1.41–1.78] × 1024 cm−2), suggests a “patchy” scenario for the distribution of the circumnuclear matter. ESO 565-G019 has both CT l.o.s. and N H,S column densities (N H,z > 2.31 × 1024 cm−2 and N H,S > 2.57 × 1024 cm−2, respectively). The use of physically motivated models, coupled with the broad energy range covered by the data (0.6–70 keV and 0.6–40 keV, for NGC 3081 and ESO 565-G019, respectively) allows us to constrain the covering factor of the obscuring material, which is C TOR = [0.63–0.82] for NGC 3081, and C TOR = [0.39–0.65] for ESO 565-G019.

scholarly journals Multifrequency Variability of AGN's: Continuum Variations from the Near IR to the X-rays

1994 ◽  
Vol 159 ◽  
pp. 131-143
Author(s):  
J. Clavel
Keyword(s):  
Active Galactic Nuclei ◽  
Temporal Evolution ◽  
Line Emission ◽  
Galactic Nuclei ◽  
The Other ◽  
X Rays ◽  
Optical Telescope ◽  
Emission Process ◽  
Near Ir ◽  
The Continuum

Because they emit copiously over more than 10 decades in frequency, Active Galactic Nuclei (AGN) cannot be understood without the help of multiwavelength observations. On the other hand, variability monitoring has also proven to be invaluable in understanding the continuum and line emission process as well as the geometry of the innermost regions in these objects. Indeed, at the heart of AGN's lies an object which is so compact that the only way to probe its structure is the study of the temporal evolution of its spectrum. The equivalent resolution which can be achieved in this way is of the order of 10 microarcsecs, far beyond the capability of any UV or optical telescope.

scholarly journals Non-equilibrium chemistry and destruction of CO by X-ray flares

2019 ◽  
Vol 486 (1) ◽  
pp. 1094-1122 ◽  
Author(s):  
Jonathan Mackey ◽  
Stefanie Walch ◽  
Daniel Seifried ◽  
Simon C O Glover ◽  
Richard Wünsch ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Thermal Evolution ◽  
Galactic Nuclei ◽  
Galactic Centre ◽  
X Rays ◽  
X Ray ◽  
Uv Emission ◽  
Sgr A ◽  
X Ray Binaries ◽  
Fractal Cloud

ABSTRACT Sources of X-rays such as active galactic nuclei and X-ray binaries are often variable by orders of magnitude in luminosity over time-scales of years. During and after these flares the surrounding gas is out of chemical and thermal equilibrium. We introduce a new implementation of X-ray radiative transfer coupled to a time-dependent chemical network for use in 3D magnetohydrodynamical simulations. A static fractal molecular cloud is irradiated with X-rays of different intensity, and the chemical and thermal evolution of the cloud are studied. For a simulated $10^5\, \mathrm{M}_\odot$ fractal cloud, an X-ray flux <0.01 erg cm−2 s−1 allows the cloud to remain molecular, whereas most of the CO and H2 are destroyed for a flux of ≥1 erg cm−2 s−1. The effects of an X-ray flare, which suddenly increases the X-ray flux by 105×, are then studied. A cloud exposed to a bright flare has 99 per cent of its CO destroyed in 10–20 yr, whereas it takes >103 yr for 99 per cent of the H2 to be destroyed. CO is primarily destroyed by locally generated far-UV emission from collisions between non-thermal electrons and H2; He+ only becomes an important destruction agent when the CO abundance is already very small. After the flare is over, CO re-forms and approaches its equilibrium abundance after 103–105 yr. This implies that molecular clouds close to Sgr A⋆ in the Galactic Centre may still be out of chemical equilibrium, and we predict the existence of clouds near flaring X-ray sources in which CO has been mostly destroyed but H is fully molecular.

scholarly journals X-Rays from Active Galactic Nuclei

1983 ◽  
Vol 6 ◽  
pp. 491-498 ◽  
Author(s):  
A.C. Fabian
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Seyfert Galaxies ◽  
X Rays ◽  
Bl Lac Objects ◽  
X Ray ◽  
Bl Lac

Recent X-ray observations of active galactic nuclei and Seyfert galaxies in particular are briefly reviewed. The application of the efficiency limit to rapidly varying luminous sources such as NGC 6814 is discussed. It is argued that the variability and probable MeV spectral turnover imply that most of the electrons which radiate the observed flux are only mildly relativistic. A possible link between the steep soft X-ray spectra and featureless optical continua of BL Lac objects is considered.

scholarly journals Sources of X-rays from galaxies

2011 ◽  
Vol 7 (S284) ◽  
pp. 183-192
Author(s):  
Q. Daniel Wang
Keyword(s):  
Active Galactic Nuclei ◽  
Galaxy Evolution ◽  
Supernova Remnants ◽  
Large Scale ◽  
Formation Rate ◽  
Galactic Nuclei ◽  
High Energy ◽  
High Mass ◽  
X Rays ◽  
X Ray

AbstractGalactic X-ray emission is a manifestation of various high-energy phenomena and processes. The brightest X-ray sources are typically accretion-powered objects: active galactic nuclei and low- or high-mass X-ray binaries. Such objects with X-ray luminosities of ≳ 1037 ergs s−1 can now be detected individually in nearby galaxies. The contributions from fainter discrete sources (including cataclysmic variables, active binaries, young stellar objects, and supernova remnants) are well correlated with the star formation rate or stellar mass of galaxies. The study of discrete X-ray sources is essential to our understanding of stellar evolution, dynamics, and end-products as well as accretion physics. With the subtraction of the discrete source contributions, one can further map out truly diffuse X-ray emission, which can be used to trace the feedback from active galactic nuclei, as well as from stars, both young and old, in the form of stellar winds and supernovae. The X-ray emission efficiency, however, is only about 1% of the energy input rate of the stellar feedback alone. The bulk of the feedback energy is most likely gone with outflows into large-scale galactic halos. Much is yet to be investigated to comprehend the role of such outflows in regulating the ecosystem, hence the evolution of galaxies. Even the mechanism of the diffuse X-ray emission remains quite uncertain. A substantial fraction of the emission cannot arise directly from optically-thin thermal plasma, as commonly assumed, and most likely originates in its charge exchange with neutral gas. These uncertainties underscore our poor understanding of the feedback and its interplay with the galaxy evolution.

scholarly journals Compton-thick active galactic nuclei from the 7 Ms observation in the Chandra Deep Field South

2019 ◽  
Vol 629 ◽  
pp. A133 ◽  
Author(s):  
A. Corral ◽  
I. Georgantopoulos ◽  
A. Akylas ◽  
P. Ranalli
Keyword(s):  
Spectral Analysis ◽  
Data Quality ◽  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Photometric Redshifts ◽  
X Ray ◽  
Spectral Fitting ◽  
Fitting Procedure ◽  
Bayesian Monte Carlo ◽  
X Ray Background

We present the X-ray spectroscopic study of the Compton-thick (CT) active galactic nuclei (AGN) population within the Chandra Deep Field South (CDF-S) by using the deepest X-ray observation to date, the Chandra 7 Ms observation of the CDF-S. We combined an optimized version of our automated selection technique and a Bayesian Monte Carlo Markov chains (MCMC) spectral fitting procedure, to develop a method to pinpoint and then characterize candidate CT AGN as less model dependent and/or data-quality dependent as possible. To obtain reliable automated spectral fits, we only considered the sources detected in the hard (2−8 keV) band from the CDF-S 2 Ms catalog with either spectroscopic or photometric redshifts available for 259 sources. Instead of using our spectral analysis to decide if an AGN is CT, we derived the posterior probability for the column density, and then we used it to assign a probability of a source being CT. We also tested how the model-dependence of the spectral analysis, and the spectral data quality, could affect our results by using simulations. We finally derived the number density of CT AGN by taking into account the probabilities of our sources being CT and the results from the simulations. Our results are in agreement with X-ray background synthesis models, which postulate a moderate fraction (25%) of CT objects among the obscured AGN population.

scholarly journals X-ray spectral and eclipsing model of the clumpy obscurer in active galactic nuclei

2019 ◽  
Vol 629 ◽  
pp. A16 ◽  
Author(s):  
Johannes Buchner ◽  
Murray Brightman ◽  
Kirpal Nandra ◽  
Robert Nikutta ◽  
Franz E. Bauer
Keyword(s):  
Active Galactic Nuclei ◽  
Column Density ◽  
Galactic Nuclei ◽  
Line Of Sight ◽  
Broad Line ◽  
X Ray ◽  
Line Region ◽  
Self Consistent ◽  
Multi Wavelength ◽  
Table Model

We present a unification model for a clumpy obscurer in active galactic nuclei (AGN) and investigate the properties of the resulting X-ray spectrum. Our model is constructed to reproduce the column density distribution of the AGN population and cloud eclipse events in terms of their angular sizes and frequency. We developed and released a generalised Monte Carlo X-ray radiative transfer code, XARS, to compute X-ray spectra of obscurer models. The geometry results in strong Compton scattering, causing soft photons to escape also along Compton-thick sight lines. This makes our model spectra very similar to our TORUS previous model. However, only if we introduce an additional Compton-thick reflector near the corona, we achieve good fits to NuSTAR spectra. This additional component in our model can be interpreted as part of the dust-free broad-line region, an inner wall or rim, or a warped disk. It cannot be attributed to a simple disk because the reflector must simultaneously block the line of sight to the corona and reflect its radiation. We release our model as an Xspec table model and present corresponding CLUMPY infrared spectra, paving the way for self-consistent multi-wavelength analyses.

scholarly journals Hot Accretion Disks and the High Energy Background

1983 ◽  
Vol 104 ◽  
pp. 345-346
Author(s):  
M. Kafatos ◽  
Jean A. Eilek
Keyword(s):  
Active Galactic Nuclei ◽  
Accretion Disks ◽  
Spectral Range ◽  
Gamma Rays ◽  
Gamma Ray ◽  
Galactic Nuclei ◽  
Seyfert Galaxies ◽  
High Energy ◽  
X Rays ◽  
X Ray

The origin of the high energy (X-ray and gamma-ray) background may be attributed to discrete sources, which are usually thought to be active galactic nuclei (AGN) (cf. Rothschild et al. 1982, Bignami et al. 1979). At X-rays a lot of information has been obtained with HEAO-1 in the spectral range 2–165 keV. At gamma-rays the background has been estimated from the Apollo 15 and 16 (Trombka et al. 1977) and SAS-2 (Bignami et al. 1979) observations. A summary of some of the observations (Rothschild et al. 1982) is shown in Figure 1. The contribution of AGN to the diffuse high energy background is uncertain at X-rays although it is generally estimated to be in the 20–30% range (Rothschild et al. 1982). At gamma-rays, in the range 1–150 MeV, AGN (specifically Seyfert galaxies) could account for all the emission.

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