Excess hard X-ray emission from the obscured low luminosity AGN in the nearby galaxy M 51 (NGC 5194)

Fukazawa, Yasushi; Iyomoto, Naoko; Kubota, Aya; Matsumoto, Y; Makishima, Kazuo

doi:10.1051/0004-6361:20010708

Cited by 44 publications

(36 citation statements)

References 53 publications

(69 reference statements)

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“…This result agrees with ours. Fukazawa et al (2001) did not find any short-term variability from BeppoSAX data. We studied six Chandra light curves and did not find short-term variations either.…”

Section: B15 Ngc 5194mentioning

confidence: 73%

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: B15 Ngc 5194mentioning

confidence: 73%

X-ray spectral variability of Seyfert 2 galaxies

Hernández-García

Masegosa

González‐Martín³

et al. 2015

A&A

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“…A bright hard X-ray excess above 10 keV had been reported from the BeppoSAX observation of M51 (Fukazawa et al 2001), and an absorption column density ∼ 10 24 cm −2 was inferred. The lack of spatial information of BeppoSAX, however, makes the inference uncertain.…”

Section: Introductionmentioning

confidence: 74%

X-ray fluorescent lines from the Compton-thick AGN in M51

Gou

et al. 2015

Monthly Notices of the Royal Astronomical Society: Letters

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The cold disk/torus gas surrounding active galactic nuclei (AGN) emits fluorescent lines when irradiated by hard X-ray photons. The fluorescent lines of elements other than Fe and Ni are rarely detected due to their relative faintness. We report the detection of Kα lines of neutral Si, S, Ar, Ca, Cr, and Mn, along with the prominent Fe Kα, Fe Kβ, and Ni Kα lines, from the deep Chandra observation of the low-luminosity Compton-thick AGN in M51. The Si Kα line at 1.74 keV is detected at ∼ 3σ, the other fluorescent lines have a significance between 2 and 2.5 σ, while the Cr line has a significance of ∼ 1.5σ. These faint fluorescent lines are made observable due to the heavy obscuration of the intrinsic spectrum of M51, which is revealed by NuSTAR observation above 10 keV. The hard X-ray continuum of M51 from Chandra and NuSTAR can be fitted with a power-law spectrum with an index of 1.8, reprocessed by a torus with an equatorial column density of N H ∼ 7 × 10 24 cm −2 and an inclination angle of 74 degrees. This confirms the Compton-thick nature of the nucleus of M51. The relative element abundances inferred from the fluxes of the fluorescent lines are similar to their solar values, except for Mn, which is about 10 times overabundant. It indicates that Mn is likely enhanced by the nuclear spallation of Fe.

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“…References. Maiolino et al 1998;(16) Della Ceca et al 2002;(17) Ballo et al 2004;(18) Braito et al 2004;(19) Guainazzi et al 2000;(20) Fukazawa et al 2001;(21) Matt et al 1999;(22) Iwasawa et al 1997;(23) Comastri et al 2007;(24) Vignati et al 1999;(25) Turner et al 2000;(26) Malaguti et al 1998;(27) Braito et al 2009. Upper panel: low-resolution (R ∼ 57-127) Spitzer-IRS spectroscopy of all 20 bona fide Compton-thick AGNs in the nearby universe with highenergy (E > 10 keV) spectroscopic constraints.…”

Section: Spitzer-irs Spectral Decomposition and Silicate Absorption Mmentioning

confidence: 99%

Deep Silicate Absorption Features in Compton-Thick Active Galactic Nuclei Predominantly Arise Due to Dust in the Host Galaxy

Goulding

Alexander

Bauer

et al. 2012

ApJ

148

172

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We explore the origin of mid-infrared (mid-IR) dust extinction in all 20 nearby (z < 0.05) bona fide Compton-thick (N H > 1.5×10 24 cm −2 ) active galactic nuclei (AGNs) with hard energy (E > 10 keV) X-ray spectral measurements. We accurately measure the silicate absorption features at λ ∼ 9.7 μm in archival low-resolution (R ∼ 57-127) Spitzer Infrared Spectrograph spectroscopy, and show that only a minority (≈45%) of nearby Compton-thick AGNs have strong Si-absorption features (S 9.7 = ln(f int /f obs ) 0.5) which would indicate significant dust attenuation. The majority (≈60%) are star formation dominated (AGN:SB < 0.5) at mid-IR wavelengths and lack the spectral signatures of AGN activity at optical wavelengths, most likely because the AGN emission lines are optically extinguished. Those Compton-thick AGNs hosted in low-inclination-angle galaxies exhibit a narrow range in Si-absorption (S 9.7 ∼ 0-0.3), which is consistent with that predicted by clumpy-torus models. However, on the basis of the IR spectra and additional lines of evidence, we conclude that the dominant contribution to the observed mid-IR dust extinction is dust located in the host galaxy (i.e., due to disturbed morphologies, dust lanes, galaxy inclination angles) and not necessarily a compact obscuring torus surrounding the central engine.

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Excess hard X-ray emission from the obscured low luminosity AGN in the nearby galaxy M 51 (NGC 5194)

Cited by 44 publications

References 53 publications

X-ray spectral variability of Seyfert 2 galaxies

X-ray spectral variability of Seyfert 2 galaxies

X-ray fluorescent lines from the Compton-thick AGN in M51

Deep Silicate Absorption Features in Compton-Thick Active Galactic Nuclei Predominantly Arise Due to Dust in the Host Galaxy

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