THE 2-79 keV X-RAY SPECTRUM OF THE CIRCINUS GALAXY WITHNuSTAR,XMM-Newton, ANDCHANDRA: A FULLY COMPTON-THICK ACTIVE GALACTIC NUCLEUS

Arévalo, P.; Bauer, F. E.; Puccetti, S.; Walton, D. J.; Koss, Michael; Boggs, Steven E.; Brandt, W. N.; Brightman, Murray; Christensen, Finn Erland; Comastri, A.; Craig, William W.; Fuerst, F.; Gandhi, P.; Grefenstette, Brian W.; Hailey, Charles J.; Harrison, Fiona A.; Luo, Birong; Madejski, G.; Madsen, K. K.; Marinucci, Andrea; Matt, Giorgio; Saez, C.; Stern, Daniel; Stuhlinger, M.; Treister, Ezequiel; Urry, C. Megan; Zhang, W. W.

doi:10.1088/0004-637x/791/2/81

Cited by 133 publications

(167 citation statements)

References 59 publications

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“…Their results show that short-term variability (from hours to days) is not common in Seyfert 2s, in contrast to what is observed in Seyfert 1 (e.g., Nandra et al 1997). Because these galaxies are obscured by the torus, the lack of variations could come from these sources being reflection-dominated, as shown by some authors that studied Compton-thick sources (Awaki et al 1991;LaMassa et al 2011;Matt et al 2013;Arévalo et al 2014). However, a number of Seyfert 2s actually do show variations.…”

Section: Introductionmentioning

confidence: 87%

X-ray spectral variability of Seyfert 2 galaxies

Hernández-García

Masegosa

González‐Martín³

et al. 2015

A&A

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Context. Variability across the electromagnetic spectrum is a property of active galactic nuclei (AGN) that can help constrain the physical properties of these galaxies. Nonetheless, the way in which the changes happen and whether they occur in the same way in every AGN are still open questions. Aims. This is the third in a series of papers with the aim of studying the X-ray variability of different families of AGN. The main purpose of this work is to investigate the variability pattern(s) in a sample of optically selected Seyfert 2 galaxies. Methods. We use the 26 Seyfert 2s in the Véron-Cetty and Véron catalog with data available from Chandra and/or XMM-Newton public archives at different epochs, with timescales ranging from a few hours to years. All the spectra of the same source were simultaneously fitted, and we let different parameters vary in the model. Whenever possible, short-term variations from the analysis of the light curves and/or long-term UV flux variations were studied. We divided the sample into Compton-thick and Compton-thin candidates to account for the degree of obscuration. When transitions between Compton-thick and thin were obtained for different observations of the same source, we classified it as a changing-look candidate. Results. Short-term variability at X-rays was studied in ten cases, but variations are not found. From the 25 analyzed sources, 11 show long-term variations. Eight (out of 11) are Compton-thin, one (out of 12) is Compton-thick, and the two changing-look candidates are also variable. The main driver for the X-ray changes is related to the nuclear power (nine cases), while variations at soft energies or related to absorbers at hard X-rays are less common, and in many cases these variations are accompanied by variations in the nuclear continuum. At UV frequencies, only NGC 5194 (out of six sources) is variable, but the changes are not related to the nucleus. We report two changing-look candidates, MARK 273 and NGC 7319. Conclusions. A constant reflection component located far away from the nucleus plus a variable nuclear continuum are able to explain most of our results. Within this scenario, the Compton-thick candidates are dominated by reflection, which suppresses their continuum, making them seem fainter, and they do not show variations (except MARK 3), while the Compton-thin and changing-look candidates do.

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Section: Introductionmentioning

confidence: 87%

X-ray spectral variability of Seyfert 2 galaxies

Hernández-García

Masegosa

González‐Martín³

et al. 2015

A&A

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“…Considering the average travel time over the full body of the reflector, and/or intermediate inclinations angles, would push up the lower limit on R. While extended reflectors on scales of up to ∼150 pc have been observed in several CTAGN (e.g. NGC 4945: Marinucci et al 2012; Circinus, Arévalo et al 2014;NGC 1068, the studies so far find that these extended components make relatively minor flux contributions compared to the compact reflectors.…”

Section: The 'Switched-off' Agn Scenariomentioning

confidence: 99%

“…Indeed, most reflectiondominated CTAGN are observed to show little, or no flux variations at all [cf. two well-studied examples include Circinus (Arévalo et al 2014) andNGC 5643 (Annuar et al 2015), although sensitive observations have recently caught a transient column density change in NGC 1068 (Marinucci et al 2016)]. Sources where significant flux variability is observed (e.g.…”

Section: Clumpy Compton-thick Obscurer Scenariomentioning

confidence: 99%

The weak Fe fluorescence line and long-term X-ray evolution of the Compton-thick active galactic nucleus in NGC 7674

Gandhi

Annuar

Lansbury

et al. 2017

Monthly Notices of the Royal Astronomical Society

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We present NuSTAR X-ray observations of the active galactic nucleus (AGN) in NGC 7674. The source shows a flat X-ray spectrum, suggesting that it is obscured by Compton-thick gas columns. Based upon long-term flux dimming, previous work suggested the alternate possibility that the source is a recently switched-off AGN with the observed X-rays being the lagged echo from the torus. Our high-quality data show the source to be reflection-dominated in hard X-rays, but with a relatively weak neutral Fe Kα emission line (equivalent width [EW] of ≈ 0.4 keV) and a strong Fe XXVI ionised line (EW ≈ 0.2 keV). We construct an updated longterm X-ray light curve of NGC 7674 and find that the observed 2-10 keV flux has remained constant for the past ≈ 20 years, following a high flux state probed by Ginga. Light travel time arguments constrain the minimum radius of the reflector to be ∼ 3.2 pc under the switchedoff AGN scenario, ≈ 30 times larger than the expected dust sublimation radius, rendering this possibility unlikely. A patchy Compton-thick AGN (CTAGN) solution is plausible, requiring a minimum line-of-sight column density (N H ) of 3 × 10 24 cm −2 at present, and yields an intrinsic 2-10 keV luminosity of (3-5) × 10 43 erg s −1 . Realistic uncertainties span the range of ≈ (1-13) × 10 43 erg s −1 . The source has one of the weakest fluorescence lines amongst bona fide CTAGN, and is potentially a local analogue of bolometrically luminous systems showing complex neutral and ionised Fe emission. It exemplifies the difficulty of identification and proper characterisation of distant CTAGN based on the strength of the neutral Fe Kα line.

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“…Indeed, most of our knowledge about the circumnuclear reprocessing matter, at least as far as their X-ray properties are concerned, is based on the brightest Compton-thick sources, like NGC 1068 (Kinkhabwala et al 2002;Matt et al 2004;Bauer et al 2015;Marinucci et al 2016), Circinus (e.g. Molendi, Bianchi & Matt 2003;Arévalo et al 2014) and Mrk 3 (e.g. Bianchi et al 2005b;Pounds & Page 2005;Guainazzi et al 2012Guainazzi et al , 2016.…”

Section: Introductionmentioning

confidence: 99%

Spatially resolved Fe K spectroscopy of NGC 4945

Marinucci

Bianchi

Fabbiano

et al. 2017

Monthly Notices of the Royal Astronomical Society

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We present the imaging and spectroscopic analysis of the combined Chandra ACIS-S observations of the Compton-thick Seyfert 2 galaxy NGC 4945. We performed a spatially-resolved spectroscopy of the circumnuclear environment of the source, picturing the innermost 200 parsecs around the highly absorbed nucleus. The additional 200 ks ACIS-S data with respect to the previous campaign allowed us to map with even greater detail the central structure of this source and to discover an enhanced iron emission in the innermost nuclear region, with respect to the associated Compton reflection continuum. We revealed that the Equivalent Width of the iron Kα line is spatially variable (ranging from 0.5 to 3 keV), on scales of tens of parsecs, likely due to the ionization state and orientation effects of the reprocessing material, with respect to the central X-ray illuminating source. A clump of highly ionized Fe xxv He-α is also detected, 40 parsecs east to the nucleus. When observations taken years apart are considered, the central unresolved reflected emission is found to remain constant.

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THE 2-79 keV X-RAY SPECTRUM OF THE CIRCINUS GALAXY WITHNuSTAR,XMM-Newton, ANDCHANDRA: A FULLY COMPTON-THICK ACTIVE GALACTIC NUCLEUS

Cited by 133 publications

References 59 publications

X-ray spectral variability of Seyfert 2 galaxies

X-ray spectral variability of Seyfert 2 galaxies

The weak Fe fluorescence line and long-term X-ray evolution of the Compton-thick active galactic nucleus in NGC 7674

Spatially resolved Fe K spectroscopy of NGC 4945

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