A Multiepoch X-Ray Study of the Nearby Seyfert 2 Galaxy NGC 7479: Linking Column Density Variability to the Torus Geometry

Pizzetti, A.; Torres-Albà, N.; Marchesi, S.; Ajello, M.; Silver, R.; Zhao, X.

doi:10.3847/1538-4357/ac86c6

Cited by 8 publications

(12 citation statements)

References 47 publications

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“…Recent mid-infrared results (Leftley et al 2021) found evidence of the presence of polar warm dust at a distance r 1.5 pc, which is consistent with this scenario. The outer layer would also be clumpy, allowing for the observed long-term variability, a similar scenario to the one proposed for NGC 7479 by Pizzetti et al (2022).…”

Section: Ionized Absorberssupporting

confidence: 60%

“…In particular, in some cases the X-ray absorbing medium is variable on very short timescales (days/weeks), which implies that the obscuring medium is clumpy and located at much smaller distances than the torus, possibly consistent with the BLR (e.g., Risaliti et al 2007;Bianchi et al 2009;Maiolino et al 2010;Sanfrutos et al 2013;Marinucci et al 2013;Walton et al 2014). In other cases, the X-ray absorption variability timescale is of the order of months or years (e.g., Piconcelli et al 2007;Rivers et al 2011;Coffey et al 2014;Rivers et al 2015;Ricci et al 2016;Pizzetti et al 2022), suggesting an origin from the putative circumnuclear torus. However, these results strongly depend on the observation sampling time; frequently adopted monthly observational monitoring may lose the variations at lower timescales.…”

Section: Introductionmentioning

confidence: 99%

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The NuSTAR view of the changing look AGN ESO 323-G77

Serafinelli¹,

Braito²,

Reeves³

et al. 2023

Preprint

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The presence of an obscuring torus at parsec-scale distances from the central black hole is the main ingredient for the Unified Model of Active Galactic Nuclei (AGN), as obscured sources are thought to be seen through this structure. However, the Unified Model fails to describe a class of sources that undergo dramatic spectral changes, transitioning from obscured to unobscured and vice-versa through time. The variability in such sources, so-called Changing Look AGN (CLAGN), is thought to be produced by a clumpy medium at much smaller distances than the conventional obscuring torus. ESO 323-G77 is a CLAGN that was observed in various states through the years with Chandra, Suzaku, Swift-XRT and XMM-Newton, from unobscured (N H < 3×10 22 cm −2 ) to Compton-thin (N H ∼ 1 − 6 × 10 23 cm −2 ) and even Compton-thick (N H > 1 × 10 24 cm −2 ), with timescales as short as one month. We present the analysis of the first NuSTAR monitoring of ESO 323-G77, consisting of 5 observations taken at different timescales (1, 2, 4 and 8 weeks from the first one) in 2016-2017, in which the AGN was caught in a persistent Compton-thin obscured state (N H ∼ 2 − 4 × 10 23 cm −2 ). We find that a Compton-thick reflector is present (N H,refl = 5 × 10 24 cm −2 ), most likely associated with the presence of the putative torus. Two ionized absorbers are unequivocally present, located within maximum radii of r max,1 = 1.5 pc and r max,2 = 0.01 pc. In one of the observations, the inner ionized absorber is blueshifted, indicating the presence of a possible faster (v out = 0.2c) ionized absorber, marginally detected at 3σ. Finally, we are able to constrain the coronal temperature and the optical depth of ESO 323-G77, obtaining kT e = 38 keV or kT e = 36 keV, and τ = 1.4 or τ = 2.8, depending on the coronal geometry assumed.

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Section: Ionized Absorberssupporting

confidence: 60%

Section: Introductionmentioning

confidence: 99%

The NuSTAR view of the changing look AGN ESO 323-G77

Serafinelli¹,

Braito²,

Reeves³

et al. 2023

Preprint

View full text Add to dashboard Cite

show abstract

“…measurements when a source has multiepoch observations. This has been proven in recent works on sources such as NGC 7479 (Pizzetti et al 2022), NGC 1358 (Marchesi et al accepted), and in a sample of Compton-thin (Zhao et al 2021) and Compton-thick (N. Torres-Albà 2022, in preparation) sources. The three obscured AGN in our sample 9 (i.e., excluding 2MASX J02051994 −0233055) all lie away from the diagonal dashed line, thus further supporting this hypothesis.…”

Section: Observational Evidence For Nonhomogeneity Of the Obscuring M...mentioning

confidence: 56%

“…We note that while some AGN have shown line-of-sight N H variability (see, e.g., Risaliti et al 2010;Markowitz et al 2014;Laha et al 2020;Pizzetti et al 2022), no source has yet varied from a Compton-thick AGN state to an unobscured one. Therefore, it is much more likely that intrinsic luminosity variability is responsible for the change in spectral shape of 2MASX J02051994−0233055, as is supported statistically by our fits.…”

Section: Comparison With Previous Resultsmentioning

confidence: 86%

Compton-thick AGN in the NuSTAR Era. IX. A Joint NuSTAR and XMM-Newton Analysis of Four Local AGN

Silver

Torres-Albà

Zhao

et al. 2022

ApJ

Self Cite

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We present the results of the broadband X-ray spectral analysis of simultaneous NuSTAR and XMM-Newton observations of four nearby Compton-thick active galactic nuclei (AGN) candidates selected from the Swift Burst Alert Telescope 150 month catalog. This work is part of a larger effort to identify and characterize all Compton-thick (N H ≥ 1024 cm−2) AGN in the local universe (z ≤ 0.05). We used three physically motivated models—MYTorus, borus02, and UXClumpy—to fit and characterize these sources. Of the four candidates analyzed, 2MASX J02051994-0233055 was found to be an unobscured (N H < 1022 cm−2) AGN, 2MASX J04075215-6116126 and IC 2227 to be Compton-thin (1022 cm−2 < N H < 1024 cm−2) AGN, and one, ESO 362−8, was confirmed to be a Compton-thick AGN. Additionally, every source was found to have a statistically significant difference between their line-of-sight and average torus hydrogen column density, further supporting the idea that the obscuring material in AGN is inhomogeneous. Furthermore, half of the sources in our sample (2MASX J02051994-0233055 and 2MASX J04075215-6116126) exhibited significant luminosity variation in the last decade, suggesting that this might be a common feature of AGN.

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“…In particular, in some cases, the X-ray absorbing medium is variable on relatively very short timescales (days to weeks), which implies that the obscuring medium is clumpy and located at much smaller distances than the torus, possibly consistent with the BLR (e.g., Risaliti et al 2007;Bianchi et al 2009;Maiolino et al 2010;Sanfrutos et al 2013;Marinucci et al 2013;Walton et al 2014). In other cases, the X-ray absorption variability timescale is of the order of months or years (e.g., Piconcelli et al 2007;Rivers et al 2011Rivers et al , 2015Coffey et al 2014;Ricci et al 2016;Pizzetti et al 2022), suggesting an origin from the putative circumnuclear torus. However, these results strongly depend on the observation sampling time; frequently adopted monthly observational monitoring may lose the variations at lower timescales.…”

Section: Introductionmentioning

confidence: 99%

The NuSTAR view of the changing-look AGN ESO 323-G77

Serafinelli

Braito

Reeves

et al. 2023

A&A

View full text Add to dashboard Cite

The presence of an obscuring torus at parsec-scale distances from the central black hole is the main ingredient for the Unified Model of active galactic nuclei (AGN), as obscured sources are thought to be seen through this structure. However, the Unified Model fails to describe a class of sources that undergo dramatic spectral changes, transitioning from obscured to unobscured and vice versa through time. The variability in these sources, which are known as changing-look AGN (CLAGN), is thought to be produced by a clumpy medium at much smaller distances than the conventional obscuring torus. ESO 323-G77 is a CLAGN that was observed in various states through the years with Chandra, Suzaku, Swift-XRT, and XMM-Newton, from unobscured (NH < 3 × 1022 cm−2) to Compton-thin (NH ∼ 1 − 6 × 1023 cm−2) and even Compton-thick (NH > 1 × 1024 cm−2), on timescales as short as one month. We present an analysis of the first NuSTAR monitoring of ESO 323-G77, consisting of five observations taken at different timescales (1, 2, 4, and 8 weeks from the first one) in 2016–2017, in which the AGN was caught in a persistent Compton-thin obscured state (NH ∼ 2 − 4 × 1023 cm−2). We find that a Compton-thick reflector is present (NH, refl = 5 × 1024 cm−2), most likely associated with the presence of the putative torus. Two ionized absorbers are unequivocally present, located within maximum radii of rmax, 1 = 1.5 pc and rmax, 2 = 0.01 pc. In one of the observations, the inner ionized absorber is blueshifted, indicating the presence of a possible faster (vout = 0.2c) ionized absorber, marginally detected at 3σ. Finally, we are able to constrain the coronal temperature and the optical depth of ESO 323-G77, obtaining kTe = 38 keV or kTe = 36 keV, and τ = 1.4 or τ = 2.8, depending on the coronal geometry assumed.

show abstract

A Multiepoch X-Ray Study of the Nearby Seyfert 2 Galaxy NGC 7479: Linking Column Density Variability to the Torus Geometry

Cited by 8 publications

References 47 publications

The NuSTAR view of the changing look AGN ESO 323-G77

The NuSTAR view of the changing look AGN ESO 323-G77

Compton-thick AGN in the NuSTAR Era. IX. A Joint NuSTAR and XMM-Newton Analysis of Four Local AGN

The NuSTAR view of the changing-look AGN ESO 323-G77

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