NuSTAR view of the Seyfert galaxy HE 0436-4717

We present the multi-epoch spectral analysis of HE 0436-4717, a bright Seyfert 1 galaxy serendipitously observed by the high energy satellite NuSTAR four times between December 2014 and December 2015. The source flux shows modest variability within each pointing and among the four observations. Spectra are well modelled in terms of a weakly variable primary power law with constant photon index (Γ = 2.01 ± 0.08). A constant narrow Fe Kα emission line suggests that this feature has an origin far from the central black hole, while a broad relativistic component is not required by the data. The Compton reflection component is also constant in flux with a corresponding reflection fraction R = 0.7+0.2−0.3. The iron abundance is compatible with solar (AFe = 1.2+1.4−0.4), and a lower limit for the high energy cut-off Ec > 280 keV is obtained. Adopting a self-consistent model accounting for a primary Comptonized continuum, we obtain a lower limit for the hot corona electron temperature kTe > 65 keV and a corresponding upper limit for the coronal optical depth of τe < 1.3. The results of the present analysis are consistent with the locus of local Seyfert galaxies in the kTe − τe and temperature-compactness diagrams.

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The soft excess of the NLS1 galaxy Mrk 359 studied with an XMM-Newton-NuSTAR monitoring campaign

Astronomy and Astrophysics ◽

10.1051/0004-6361/202038112 ◽

2020 ◽

Vol 640 ◽

pp. A99

Author(s):

R. Middei ◽

P.-O. Petrucci ◽

S. Bianchi ◽

F. Ursini ◽

M. Cappi ◽

...

Keyword(s):

Emission Spectrum ◽

Line Emission ◽

X Rays ◽

Multiple Exposures ◽

Reflection Model ◽

Photon Index ◽

The One ◽

Spectral Data Analysis ◽

Hot Corona ◽

Reflection Component

Context. Joint XMM-Newton and NuSTAR multiple exposures allow us to disentangle the different emission components of active galactic nuclei (AGNs) and to study the evolution of their different spectral features. In this work, we present the timing and spectral properties of five simultaneous XMM-NewtonandNuSTAR observations of the Narrow Line Seyfert 1 galaxy Mrk 359. Aims. We aim to provide the first broadband spectral modeling of Mrk 359 describing its emission spectrum from the UV up to the hard X-rays. Methods. We performed temporal and spectral data analysis, characterising the amplitude and spectral changes of the Mrk 359 time series and computing the 2–10 keV normalised excess variance. The spectral broadband modelling assumes the standard hot Comptonising corona and reflection component, while for the soft excess we tested two different models: a warm, optically thick Comptonising corona (the two-corona model) and a reflection model in which the soft-excess is the result of a blurred reflected continuum and line emission (the reflection model). Results. High and low flux states were observed during the campaign. The former state has a softer spectral shape, while the latter shows a harder one. The photon index is in the 1.75–1.89 range, and only a lower limit to the hot-corona electron temperature can be found. A constant reflection component, likely associated with distant matter, is observed. Regarding the soft excess, we found that among the reflection models we tested, the one providing the better fit (reduced χ2 = 1.14) is the high-density one. However, a significantly better fit (reduced χ2 = 1.08) is found by modelling the soft excess with a warm Comptonisation model. Conclusions. The present analysis suggests the two-corona model as the best scenario for the optical-UV to X-ray emission spectrum of Mrk 359.

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The inner view of NGC 1052 using multiple X-ray observations

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz2785 ◽

2019 ◽

Vol 491 (1) ◽

pp. 29-38 ◽

Cited By ~ 2

Author(s):

N Osorio-Clavijo ◽

O González-Martín ◽

I E Papadakis ◽

J Masegosa ◽

L Hernández-García

Keyword(s):

Power Law ◽

High Energy ◽

Spectral Slope ◽

X Ray ◽

Band Power ◽

Neutral Material ◽

Photon Index ◽

Epoch Analysis ◽

First Time ◽

Reflection Component

ABSTRACT In this paper, we present a multi-epoch analysis of NGC 1052, a prototypical low-luminisity active galactic nucleus, using XMM–Newton, Suzaku and NuSTAR observations taken from 2001 to 2017. This is the first time that results from NuSTAR observations have been reported for NGC 1052. Regarding technical aspects, we found a wavelength-dependent calibration issue between simultaneous XMM–Newton and NuSTAR spectra, characterized by a change in the photon index of $\rm { \Gamma _{NuSTAR}- \Gamma _{XMM-Newton}=0.17\pm 0.04}$. We use ancillary Chandra data to decontaminate the nuclear spectrum from circumnuclear contributors. We find that two baseline models can fit the broad (0.5–50 keV) X-ray spectrum of the source. One consists of a power-law-like continuum that is absorbed by a uniform absorber, and is reflected by neutral material, and a separate power-law component in the soft band. The second model consists of a clumpy absorber. The reflection component is still present, but not the soft-band power law. Instead, absorption by a warm absorber is necessary to fit the spectra. This is the first time that a reflection component has been established in this object, thanks to high-energy data from NuSTAR. This component is constant in flux and shape, supporting the idea that it is produced away from the central source (probably in the torus). We find flux, spectral slope and absorption variations on time-scales of months to years. We also find that a patchy absorber can explain the behaviour of this source better, as it is ∼200 times more likely than the uniform absorber and yields smaller intrinsic variations.

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Probing the circumnuclear environment of NGC 1275 with High-Resolution X-ray spectroscopy

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab2507 ◽

2021 ◽

Author(s):

Christopher S Reynolds ◽

Robyn N Smith ◽

Andrew C Fabian ◽

Yasushi Fukazawa ◽

Erin A Kara ◽

...

Keyword(s):

Seyfert Galaxies ◽

High Energy ◽

Emission Region ◽

Molecular Gas ◽

Cluster Galaxy ◽

X Ray ◽

Transmission Grating ◽

Photon Index ◽

Fluorescence Line ◽

Ngc 1275

Abstract NGC 1275 is the Brightest Cluster Galaxy (BCG) in the Perseus cluster and hosts the active galactic nucleus (AGN) that is heating the central 100 kpc of the intracluster medium (ICM) atmosphere via a regulated feedback loop. Here we use a deep (490 ks) Cycle-19 Chandra High-Energy Transmission Grating (HETG) observation of NGC 1275 to study the anatomy of this AGN. The X-ray continuum is adequately described by an unabsorbed power-law with photon index Γ ≈ 1.9, creating strong tension with the detected column of molecular gas seen via HCN and HCO+ line absorption against the parsec-scale core/jet. This tension is resolved if we permit a composite X-ray source; allowing a column of $N_H\sim 8\times 10^{22}\hbox{${\rm \, cm}^{-2}\, $}$ to cover ∼15 per cent of the X-ray emitter does produce a significant improvement in the statistical quality of the spectral fit. We suggest that the dominant unabsorbed component corresponds to the accretion disk corona, and the sub-dominant X-ray component is the jet working surface and/or jet cocoon that is expanding into clumpy molecular gas. We suggest that this may be a common occurence in BCG-AGN. We conduct a search for photoionized absorbers/winds and fail to detect such a component, ruling out columns and ionization parameters often seen in many other Seyfert galaxies. We detect the 6.4 keV iron-Kα fluorescence line seen previously by XMM-Newton and Hitomi. We describe an analysis methodology which combines dispersive HETG spectra, non-dispersive microcalorimeter spectra, and sensitive XMM-Newton/EPIC spectra in order to constrain (sub)arcsec-scale extensions of the iron-Kα emission region.

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Multi-wavelength campaign on NCG 7469

Astronomy and Astrophysics ◽

10.1051/0004-6361/201832726 ◽

2018 ◽

Vol 615 ◽

pp. A163 ◽

Cited By ~ 19

Author(s):

R. Middei ◽

S. Bianchi ◽

M. Cappi ◽

P.-O. Petrucci ◽

F. Ursini ◽

...

Keyword(s):

Spectral Analysis ◽

Optical Depth ◽

Spherical Geometry ◽

Relativistic Effects ◽

Seyfert Galaxy ◽

High Energy ◽

Joint Analysis ◽

Photon Index ◽

Multi Wavelength ◽

Average Flux

We conducted a multi-wavelength 6-month campaign to observe the Seyfert Galaxy NGC 7469, using the space-based observatories HST, Swift, XMM-Newton and NuSTAR. We report the results of the spectral analysis of the seven simultaneous XMM-Newton and NuSTAR observations. The source shows significant flux variability within each observation, but the average flux is less variable among the different pointings of our campaign. Our spectral analysis reveals a prominent narrow neutral Fe Kα emission line in all the spectra and weaker contributions from Fe Kβ, neutral Ni Kα, and ionized iron. We find no evidence for variability or relativistic effects acting on the emission lines, which indicates that they originate from distant material. In the joint analysis of XMM-Newton and NuSTAR data, a constant photon index is found (Γ = 1.78 ± 0.02) together with a high energy cut-off Ecut = 170−40+60 keV. Adopting a self-consistent Comptonization model, these values correspond to an average coronal electron temperature of kT = 45−12+15 keV and, assuming a spherical geometry, an optical depth τ = 2.6 ± 0.9. The reflection component is consistent with being constant and the reflection fraction is in the range R = 0.3−0.6. A prominent soft excess dominates the spectra below 4 keV. This is best fit with a second Comptonization component, arising from a warm corona with an average kT = 0.67 ± 0.03 keV and a corresponding optical depth τ = 9.2 ± 0.2.

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NuSTAR observations of heavily obscured Swift/BAT AGNs: Constraints on the Compton-thick AGNs fraction

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833038 ◽

2019 ◽

Vol 621 ◽

pp. A28 ◽

Cited By ~ 11

Author(s):

I. Georgantopoulos ◽

A. Akylas

Keyword(s):

High Energy ◽

Selection Function ◽

Number Density ◽

Local Universe ◽

X Ray ◽

Photon Index ◽

Very High Energy ◽

History Of ◽

X Ray Background ◽

Reflection Component

The evolution of the accretion history of the Universe has been studied in unprecedented detail owing to recent X-ray surveys performed by Chandra and XMM-Newton. A focus on the most heavily obscured or Compton-thick active galactic nuclei (AGNs) is missing in these studies. These AGNs evade detection even in X-ray surveys owing to their extreme hydrogen column densities, which exceed 1024 cm−2. Recently, the all-sky hard X-ray survey performed by Swift/BAT brought a breakthrough, allowing the detection of many of these AGNs. This is because of the very high energy bandpass (14–195 keV) of this instrument, which helps to minimise attenuation effects. In our previous work, we identified more than 50 candidate Compton-thick AGNs in the local Universe, corresponding to an observed fraction of about 7% of the total AGNs population. This number can only be converted to the intrinsic Compton-thick AGNs number density if we know their exact selection function. This function sensitively depends on the form of the Compton-thick AGN spectrum, that is the energy of their absorption turnover, photon-index and its cut-off energy at high energies, and the strength of the reflection component on the matter surrounding the nucleus. For example, the reflection component at hard energies 20–40 keV antagonises the number density of missing Compton-thick AGNs in the sense that the stronger the reflection the easier these sources are detected in the BAT band. In order to constrain their number density, we analysed the spectra of 19 Compton-thick AGNs that have been detected with Swift/BAT and have been subsequently observed with NuSTAR in the 3–80 keV band. We analysed their X-ray spectra using the MYTORUS models which properly take into account the Compton scattering effects. These were combined with physically motivated Comptonisation models, which accurately describe the primary coronal X-ray emission. We derived absorbing column densities that are consistent with those derived by the previous Swift/BAT analyses. We estimate the coronal temperatures to be roughly between 25 and 80 keV corresponding to high energy cut-offs roughly between 75 and 250 keV. Furthermore, we find that the majority of our AGNs lack a strong reflection component in the 20–40 keV band placing tighter constraints on the intrinsic fraction of Compton-thick AGNs. Combining these results with our X-ray background synthesis models, we estimate a percentage of Compton-thick AGNs in the local Universe of ≈20 ± 3 % relative to the type-II AGNs population.

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NuSTAR observation of Ark 564 reveals the variation of coronal temperature with flux

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa067 ◽

2020 ◽

Vol 492 (2) ◽

pp. 3041-3046 ◽

Cited By ~ 2

Author(s):

Samuzal Barua ◽

V Jithesh ◽

Ranjeev Misra ◽

Gulab C Dewangan ◽

Rathin Sarma ◽

...

Keyword(s):

Active Galactic Nuclei ◽

Galactic Nuclei ◽

High Energy ◽

Quality Data ◽

X Rays ◽

Coronal Temperature ◽

High Quality Data ◽

Photon Index ◽

Reflection Component ◽

Shed Light

ABSTRACT The hard X-ray spectral index of some active galactic nuclei (AGN) has been observed to steepen with the source flux. This has been interpreted in a Comptonization scenario, where an increase in the soft flux decreases the temperature of the corona, leading to steepening of the photon index. However, the variation of the coronal temperature with flux has been difficult to measure due to the presence of complex reflection component in the hard X-rays and the lack of high-quality data at that energy band. Recently, a 200 ks Nuclear Spectroscopic Telescope Array(NuSTAR) observation of Ark 564 in 3–50 keV band revealed the presence of one of the coolest coronae with temperature kTe ∼ 15 keV in the time-averaged spectrum. Here, we reanalyse the data and examined the spectra in four flux levels. Our analysis shows that the coronal temperature decreased from ∼17 to ∼14 keV as the flux increased. The high energy photon index Γ ∼ 2.3 varied by less than 0.1, implying that the optical depth of the corona increased by about 10 per cent as the flux increased. This first reporting of coronal temperature variation with flux shows that further long observation by NuSTAR of this and other sources would shed light on the geometry and dynamics of the inner regions of the accretion flow.

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A NuSTAR census of coronal parameters in Seyfert galaxies

Astronomy and Astrophysics ◽

10.1051/0004-6361/201732382 ◽

2018 ◽

Vol 614 ◽

pp. A37 ◽

Cited By ~ 30

Author(s):

A. Tortosa ◽

S. Bianchi ◽

A. Marinucci ◽

G. Matt ◽

P. O. Petrucci

Keyword(s):

Black Hole ◽

Active Galactic Nuclei ◽

Optical Depth ◽

Galactic Nuclei ◽

Seyfert Galaxies ◽

Black Hole Mass ◽

Significance Level ◽

X Ray ◽

Photon Index ◽

Hot Corona

Context. We discuss the results of the hot corona parameters of active galactic nuclei (AGN) that have been recently measured with NuSTAR. The values taken from the literature of a sample of 19 bright Seyfert galaxies are analysed. Aims. The aim of this work is to look for correlations between coronal parameters, such as the photon index and cut-off energy (when a phenomenological model is adopted) or the optical depth and temperature (when a Comptonization model is used), and other parameters of the systems, such as the black hole mass or the Eddington ratio. Methods. We analysed the coronal parameters of the 19 unobscured, bright Seyfert galaxies that are present in the Swift/BAT 70-month catalogue and that have been observed by NuSTAR, alone or simultaneously with others X-ray observatories, such as Swift, Suzaku, or XMM-Newton. Results. We found an anti-correlation with a significance level >98% between the coronal optical depth and the coronal temperature of our sample. On the other hand, no correlation between the above parameters and the black hole mass, the accretion rate, and the intrinsic spectral slope of the sources is found.

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Relations between phenomenological and physical parameters in the hot coronae of AGNs computed with the MoCA code

Astronomy and Astrophysics ◽

10.1051/0004-6361/201935881 ◽

2019 ◽

Vol 630 ◽

pp. A131 ◽

Cited By ~ 5

Author(s):

R. Middei ◽

S. Bianchi ◽

A. Marinucci ◽

G. Matt ◽

P.-O. Petrucci ◽

...

Keyword(s):

Power Law ◽

High Energy ◽

Physical Parameters ◽

Monte Carlo Code ◽

X Ray ◽

Accretion Rates ◽

Energy Cutoff ◽

Photon Index ◽

Hot Corona ◽

Black Hole Masses

Context. The primary X-ray emission in active galactic nuclei (AGNs) is widely believed to be due to Comptonisation of the thermal radiation from the accretion disc in a corona of hot electrons. The resulting spectra can, in first approximation, be modelled with a cut-off power law, the photon index and the high-energy roll-over encoding information on the physical properties of the X ray emitting region. The photon index and the high-energy curvature of AGNs (Γ, Ec) have been largely studied since the launch of X-ray satellites operating above 10 keV. However, high-precision measurements of these two observables have only been obtained in recent years thanks to the unprecedented sensitivity of NuSTAR up to 79 keV. Aims. We aim at deriving relations between Γ, Ec phenomenological parameters and the intrinsic properties of the X-ray-emitting region (the hot corona), namely the optical depth and temperature. Methods. We use MoCA (Monte Carlo code for Comptonisation in Astrophysics) to produce synthetic spectra for the case of an AGN with MBH = 1.5 × 108 M⊙ and ṁ = 0.1 and then compared them with the widely used power-law model with an exponential high-energy cutoff. Results. We provide phenomenological relations relating Γ and Ec with the opacity and temperature of the coronal electrons for the case of spherical and slab-like coronae. These relations give origin to a well defined parameter space which fully contains the observed values. Exploiting the increasing number of high-energy cut-offs quoted in the literature, we report on the comparison of physical quantities obtained using MoCA with those estimated using commonly adopted spectral Comptonisation models. Finally, we discuss the negligible impact of different black hole masses and accretion rates on the inferred relations.

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A Lower Limit to the Excess of Companions Among Seyfert Galaxies

Symposium - International Astronomical Union ◽

10.1017/s0074180900176909 ◽

1994 ◽

Vol 159 ◽

pp. 519-519

Author(s):

P. Rafanelli ◽

M. Violato

Keyword(s):

Lower Limit ◽

Visual Inspection ◽

Control Sample ◽

Seyfert Galaxy ◽

Seyfert Galaxies ◽

Cumulative Number ◽

Normal Galaxies ◽

Statistical Procedures ◽

Upper Limit ◽

Statistical Results

It is not yet clear which is the role played by interaction on Seyfert activity. Presently there are on this topic contradictory statistical results, based on the study of more or less rich samples of Seyfert galaxies. Petrosian (1982), Dahari (1985) and Mac Kenty (1989, 1990) found an excess of Seyferts among galaxies which have nearby companions and an excess of galaxies with nearby neighbors among Seyfert galaxies. The contrary result was found by Bushouse (1987) and by Fuentes Williams & Stocke (1988). In order to find more reliable conclusions, taking advantage of the increased number of Seyfert galaxies identified in the last years, we have applied the statistical procedures used by Dahari (1985) to a sample of 287 Seyfert-1 (S1) and 195 Seyfert-2 (S2) (namely to all known S1 and S2 galaxies with z ≤ 0.11 and δ ≥ −23°). A subsample has been extracted carefully excluding objects, identified as Seyfert on the basis of their morphology (e.g. on the basis of the presence of a companion) and brighter than mB = 15.5, the magnitude at which the cumulative number of S1 and S2 galaxies becomes flat. The possible companions of our Seyfert galaxies have been identified on the blue POSS prints by visual inspection looking for objects not more distant than 3 diameters from the Seyfert galaxy and not more than 3 magnitudes fainter. It results that ∼35% of both the S1 and S2 galaxies have a neighbor. This percentage is reduced to ∼14% for both classes of galaxies excluding the possible optical companions, the upper limit to the number of which has been derived starting from the counts of galaxies published by Shane and Wirtanen (1967), assuming that the probability of finding an optical companion is a Poisson probability. The same procedure applied to a control sample of 281 normal galaxies indicates that only ∼3% of the galaxies have a close companion. In conclusion Seyfert galaxies show a larger percentage (14%) of objects with companion than normal galaxies do (3%). This excess, which is the same for S1 and S2 galaxies, has been derived overestimating the number of optical companions and its value is then a lower limit.

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High-energy Neutrinos from Magnetized Coronae of Active Galactic Nuclei and Prospects for Identification of Seyfert Galaxies and Quasars in Neutrino Telescopes

The Astrophysical Journal ◽

10.3847/1538-4357/ac1c77 ◽

2021 ◽

Vol 922 (1) ◽

pp. 45

Author(s):

Ali Kheirandish ◽

Kohta Murase ◽

Shigeo S. Kimura

Keyword(s):

Galactic Nuclei ◽

Seyfert Galaxy ◽

Seyfert Galaxies ◽

High Energy ◽

X Rays ◽

Neutrino Telescopes ◽

Neutrino Detectors ◽

Ngc 1068 ◽

High Energy Neutrinos ◽

Promising Source

Abstract Particles may be accelerated in magnetized coronae via magnetic reconnections and/or plasma turbulence, leading to high-energy neutrinos and soft γ-rays. We evaluate the detectability of neutrinos from nearby bright Seyfert galaxies identified by X-ray measurements. In the disk-corona model, we find that NGC 1068 is the most promising Seyfert galaxy in the Northern sky, where IceCube is the most sensitive, and show prospects for the identification of aggregated neutrino signals from Seyfert galaxies bright in X-rays. Moreover, we demonstrate that nearby Seyfert galaxies are promising targets for the next generation of neutrino telescopes such as KM3NeT and IceCube-Gen2. For KM3NeT, Cen A can be the most promising source in the Southern sky if a significant fraction of the observed X-rays come from the corona, and it could be identified in few years of KM3NeT operation. Our results reinforce the idea that hidden cores of supermassive black holes are the dominant sources of the high-energy neutrino emission and underlines the necessity of better sensitivity to medium-energy ranges in future neutrino detectors for identifying the origin of high-energy cosmic neutrinos.

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