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

Middei, R.; Bianchi, S.; Marinucci, Andrea; Matt, Giorgio; Petrucci, P.-O.; Tamborra, F.; Tortosa, A.

doi:10.1051/0004-6361/201935881

Cited by 46 publications

(56 citation statements)

References 59 publications

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“…The energy cutoff was usually estimated by the temperature of the hot corona with a relation, E cut ∼ (2-3)kT e (Petrucci et al 2001). Although Middei et al (2019) reported that this relationship works only for low temperatures, this correction should therefore be appropriate for the warm corona model. Given that the Eddington ratio of ESO 362-G18 is not very large ( m 0.015), the low electron temperature derived with Model A is in conflict with the trend found by Ricci et al (2018), while our result of a higher coronal temperature in the relativistic reflection scenario (Model B) is compatible with their analysis.…”

Section: Physical Properties Of the Warm Corona Modelmentioning

confidence: 99%

The Nature of Soft Excess in ESO 362-G18 Revealed by XMM-Newton and NuSTAR Spectroscopy

García

Walton

et al. 2021

ApJ

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We present a detailed spectral analysis of the joint XMM-Newton and NuSTAR observations of the active galactic nuclei (AGNs) in the Seyfert 1.5 Galaxy ESO 362-G18. The broadband (0.3-79 keV) spectrum shows the presence of a power-law continuum with a soft excess below 2 keV, iron Kα emission (∼6.4 keV), and a Compton hump (peaking at ∼20 keV). We find that the soft excess can be modeled by two different possible scenarios: a warm (kT e ∼ 0.2 keV) and optically thick (τ ∼ 34) Comptonizing corona, or with a relativistically blurred reflection off a high-density ( [ ]>n log cm 18.3 e 3) inner disk. These two models cannot be easily distinguished solely from their fit statistics. However, the low temperature (kT e ∼ 20 keV) and the thick optical depth (τ ∼ 5) of the hot corona required by the warm corona scenario are uncommon for AGNs. We also fit a "hybrid" model, which includes both disk reflection and a warm corona. Unsurprisingly, as this is the most complex of the models considered, this provides the best fit, and more reasonable coronal parameters. In this case, the majority of the soft excess flux arises in the warm corona component. However, based on recent simulations of warm coronae, it is not clear whether such a structure can really exist at the low accretion rates relevant for ESO 362-G18 ( m 0.015). This may therefore argue in favor of a scenario in which the soft excess is instead dominated by the relativistic reflection. Based on this model, we find that the data would require a compact hot corona (h ∼ 3 R Horizon ) around a rapidly spinning (a å > 0.927) black hole.Unified Astronomy Thesaurus concepts: Supermassive black holes (1663); X-ray astronomy (1810); Seyfert galaxies (1447); High energy astrophysics (739); Active galactic nuclei (16); Astrophysical black holes (98); Spectroscopy (1558); X-ray active galactic nuclei (2035)

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Section: Physical Properties Of the Warm Corona Modelmentioning

confidence: 99%

The Nature of Soft Excess in ESO 362-G18 Revealed by XMM-Newton and NuSTAR Spectroscopy

García

Walton

et al. 2021

ApJ

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“…We construct the continuous relation above based on two commonly assumed limiting cases for kT e , E cut 2 for t  1 e and E cut 3 for t 1 e  (e.g., Shapiro et al 1976), noting that more realistic coronal models cover a wider range of scaling factors (Middei et al 2019). kT e , Γ, and τ e are related via an approximate expression derived for a plane-parallel corona and formally valid for t  1 e (Zdziarski 1985;Petrucci et al 2001):…”

Section: Exclusion Of Potentially Degenerate Constraintsmentioning

confidence: 99%

“…However, it is not an accurate representation of the AGN coronal spectrum (e.g., Fabian et al 2015;Lubiński et al 2016;Niedźwiecki et al 2019). Although the phenomenological parameter E cut may be approximately converted to a coronal temperature under certain assumptions (Middei et al 2019), the proper way to characterize the physical parameters of obscured AGN coronae is to directly employ more parameter and is likely spurious. From fits with R pex fixed at 0, 1, and 2, they derive E cut in the range of 40-90 keV, all of which correspond to τ e >3.…”

Section: Limitations and Future Workmentioning

confidence: 99%

“…The high-energy cutoff (E cut ) is a parameter of the commonly used approximation to the coronal continuum (e.g., Rothschild et al 1983;Gondek et al 1996;Dadina 2008): the power law with an exponential cutoff, µ -G -E e E E cut , where E is photon energy and Γ is the photon index. Spectral parameters of this phenomenological model correspond to the physical parameters of the corona (e.g., Poutanen & Svensson 1996;Petrucci et al 2001;Fabian et al 2015), and E cut is a proxy for the coronal temperature (Middei et al 2019). However, it has been difficult to constrain it observationally even in the brightest AGN, since it additionally requires high-quality data above 10 keV.…”

Section: Introductionmentioning

confidence: 99%

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NuSTAR Survey of Obscured Swift/BAT-selected Active Galactic Nuclei. II. Median High-energy Cutoff in Seyfert II Hard X-Ray Spectra

Baloković

Harrison

Madejski

et al. 2020

ApJ

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Broadband X-ray spectroscopy of the X-ray emission produced in the coronae of active galactic nuclei (AGNs) can provide important insights into the physical conditions very close to their central supermassive black holes. The temperature of the Comptonizing plasma that forms the corona is manifested through a high-energy cutoff that has been difficult to directly constrain even in the brightest AGN because it requires high-quality data at energies above 10 keV. In this paper we present a large collection of coronal cutoff constraints for obscured AGNs based on a sample of 130AGNs selected in the hard X-ray band with Swift/BAT and observed nearly simultaneously with NuSTAR and Swift/XRT. We find that under a reasonable set of assumptions regarding partial constraints the median cutoff is well constrained to 290±20 keV, where the uncertainty is statistical and given at the 68% confidence level. We investigate the sensitivity of this result to our assumptions and find that consideration of various known systematic uncertainties robustly places the median cutoff between 240 and 340 keV. The central 68% of the intrinsic cutoff distribution is found to be between about 140 and 500 keV, with estimated uncertainties of 20 and 100 keV, respectively. In comparison with the literature, we find no clear evidence that the cutoffs in obscured and unobscured AGNs are substantially different. Our analysis highlights the importance of carefully considering partial and potentially degenerate constraints on the coronal high-energy cutoff in AGNs.Unified Astronomy Thesaurus concepts: Active galactic nuclei (16); X-ray active galactic nuclei (2035); Seyfert galaxies (1447); High energy astrophysics (739); X-ray surveys (1824)

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“…These high energy cut-offs can then be used to estimate the coronal temperature (e.g. Middei et al 2019) which in turn allows for testing whether pair-production is important for these systems or not (Fabian et al 2015). For a thermal plasma, there is a maximum threshold temperature beyond which a pair cascade would occur and this threshold depends on the compactness parameter l = Lσ T /Rm e c 3 , where L is the luminosity and R is the size of the corona (Svensson 1984;Zdziarski 1985).…”

Section: Introductionmentioning

confidence: 99%

Evidence for coronal temperature variation in Seyfert 2 ESO 103--035 using NuSTAR observations

Barua,

Jithesh,

Misra

et al. 2021

Preprint

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We report flux-resolved spectroscopic analysis of the active galactic nucleus (AGN) ESO 103-035 using NuSTAR observations. Following an earlier work, we fit the spectra using a thermal Comptonization model with a relativistic reflection component to obtain estimates of the coronal temperature for two flux levels. The coronal temperature was found to increase from 24.0 +6.8 −3.4 to 55.3 +54.6 −7.2 keV (errors at 1-σ confidence level) as the flux increased from 9.8 to 11.9 × 10 −11 erg cm −2 s −1 in the 3-78 keV band. A marginal variation in the high energy photon index allows for both, a non-varying optical depth and for the optical depth to have varied by a factor of ∼2. This is in contrast to a previous work on NuSTAR flux resolved spectroscopy of the AGN, Ark 564, where the temperature was found to decrease with flux along with a 10% variation in the optical depth. The results maybe understood in a framework where AGN variability is either dominated by coronal heating variation leading to correlated increase of temperature with flux and the opposite effect being seen when the variability is dominated by changes in the seed photon flux.

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

Cited by 46 publications

References 59 publications

The Nature of Soft Excess in ESO 362-G18 Revealed by XMM-Newton and NuSTAR Spectroscopy

The Nature of Soft Excess in ESO 362-G18 Revealed by XMM-Newton and NuSTAR Spectroscopy

NuSTAR Survey of Obscured Swift/BAT-selected Active Galactic Nuclei. II. Median High-energy Cutoff in Seyfert II Hard X-Ray Spectra

Evidence for coronal temperature variation in Seyfert 2 ESO 103--035 using NuSTAR observations

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