Search for X-ray occultations in active galactic nuclei

Torricelli‐Ciamponi, G.; Pietrini, P.; Risaliti, G.; Salvati, M.

doi:10.1093/mnras/stu969

Cited by 38 publications

(37 citation statements)

References 49 publications

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“…X-ray photoelectric absorption variability has also been found in many Seyfert 2s (e.g., Risaliti et al 2002Risaliti et al , 2007. Modeling of the observed absorption variations suggests this absorption originates in gas clouds in the BLR or torus orbiting the central source (e.g., Maiolino et al 2010;Markowitz et al 2014;Torricelli-Ciamponi et al 2014;Netzer 2015). X-ray absorption variability has also been widely investigated in warm absorbers, BAL quasar winds, and ultra fast outflows (UFOs), usefully characterizing wind properties (e.g., Chartas et al 2009;Matt et al 2011;Saez et al 2012;King & Pounds 2015;Scott et al 2015).…”

Section: Introductionmentioning

confidence: 93%

Long-Term X-Ray Variability of Typical Active Galactic Nuclei in the Distant Universe

Yang

Brandt

Luo

et al. 2016

ApJ

106

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We perform long-term (≈15 years, observed-frame) X-ray variability analyses of the 68 brightest radio-quiet active galactic nuclei (AGNs) in the 6 Ms Chandra Deep Field-South survey; the majority are in the redshift range of 0.6-3.1, providing access to penetrating rest-frame X-rays up to ≈10-30 keV. Of the 68 sources, 24 are optical spectral typeI AGNs, and the rest (44) are type II AGNs. The timescales probed in this work are among the longest for X-ray variability studies of distant AGNs. Photometric analyses reveal widespread photon flux variability: 90% of AGNs are variable above a 95% confidence level, including many X-ray obscured AGNs and several optically classified type II quasars. We characterize the intrinsic X-ray luminosity (L X ) and absorption (N H ) variability via spectral fitting. Most (74%) sources show L X variability; the variability amplitudes are generally smaller for quasars. A Compton-thick candidate AGN shows variability of its high-energy X-ray flux, indicating the size of reflecting material to be 0.3 pc. L X variability is also detected in a broad absorption line quasar. The N H variability amplitude for our sample appears to rise as time separation increases. About 16% of sources show N H variability. One source transitions from an X-ray unobscured to obscured state, while its optical classification remains type I; this behavior indicates the X-ray eclipsing material is not large enough to obscure the whole broadline region.

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Section: Introductionmentioning

confidence: 93%

Long-Term X-Ray Variability of Typical Active Galactic Nuclei in the Distant Universe

Yang

Brandt

Luo

et al. 2016

ApJ

106

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“…sources changing from being absorbed by a Compton thin to a Compton thick column density). From the pioneering works of Risaliti et al (Risaliti et al 2002) on a few interesting sources such as the Seyfert 1 NGC 1365, to detailed studies on an increasing number of sources and on systematic studies of larger samples (Markowitz et al 2014;Torricelli-Ciamponi et al 2014;Tatum et al 2013), evidence has accumulated for the importance of large, complex, and variable neutral absorption also in type 1 Seyfert galaxies. Current interpretations for this cold circumnuclear gas are clumpy molecular tori (Krolik & Begelman 1988, Markowitz et al 2014Hönig 2013), absorption from inner and/or outer BLR clouds (Risaliti et al 2009), or accretion disc outflows (Elitzur & Shlosman 2006;Proga 2007;Sim et al 2008).…”

Section: Introductionmentioning

confidence: 99%

Anatomy of the AGN in NGC 5548

Cappi

Marco

Ponti

et al. 2016

A&A

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In 2013, we conducted a large multi-wavelength campaign on the archetypical Seyfert 1 galaxy NGC 5548. Unexpectedly, this usually unobscured source appeared strongly absorbed in the soft X-rays during the entire campaign, and signatures of new and strong outflows were present in the almost simultaneous UV HST/COS data. Here we carry out a comprehensive spectral analysis of all available XMM-Newton observations of NGC 5548 (precisely 14 observations from our campaign plus three from the archive, for a total of ∼763 ks) in combination with three simultaneous NuSTAR observations. We obtain a best-fit underlying continuum model composed by i) a weakly varying flat (Γ ∼ 1.5-1.7) power-law component; ii) a constant, cold reflection (FeK + continuum) component; iii) a soft excess, possibly owing to thermal Comptonization; and iv) a constant, ionized scattered emission-line dominated component. Our main findings are that, during the 2013 campaign, the first three of these components appear to be partially covered by a heavy and variable obscurer that is located along the line of sight (LOS), which is consistent with a multilayer of cold and mildly ionized gas. We characterize in detail the short timescale (mostly ∼ks-to-days) spectral variability of this new obscurer, and find it is mostly due to a combination of column density and covering factor variations, on top of intrinsic power-law (flux and slope) variations. In addition, our best-fit spectrum is left with several (but marginal) absorption features at rest-frame energies ∼6.7−6.9 keV and ∼8 keV, as well as a weak broad emission line feature redwards of the 6.4 keV emission line. These could indicate a more complex underlying model, e.g. a P-Cygni-type emission profile if we allow for a large velocity and wide-angle outflow. These findings are consistent with a picture where the obscurer represents the manifestation along the LOS of a multilayer of gas, which is also in multiphase, and which is likely outflowing at high speed, and simultaneously producing heavy obscuration and scattering in the X-rays, as well as broad absorption features in the UV.

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“…The origin of such variability must be significantly closer to the central region. Recently, Torricelli-Ciamponi et al (2014) have shown that X-ray eclipses are common when the expected occultation time is compatible with the exposure and that these events may be responsible for most of the spectral variability at energies higher than 2 keV. They associated the origin of the eclipsing clouds to the broad line region (BLR) of AGNs.…”

Section: Introductionmentioning

confidence: 99%

An X-ray variable absorber within the broad line region in Fairall 51

Svoboda

Guainazzi

Longinotti

et al. 2015

A&A

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Context. Fairall 51 is a polar-scattered Seyfert 1 galaxy, a type of active galaxy believed to represent a bridge between unobscured type-1 and obscured type-2 objects. Fairall 51 has shown complex and variable X-ray absorption, but little is known about its origin. Aims. In our research, we observed Fairall 51 with the X-ray satellite Suzaku in order to constrain a characteristic time scale of its variability. Methods. We performed timing and spectral analysis of four observations separated by 1.5, 2, and 5.5 day intervals. Results. We found that the 0.5-50 keV broadband X-ray spectra are dominated by a primary power-law emission (with the photon index ∼2). This emission is affected by at least three absorbers with different ionisations (log ξ ≈ 1-4). The spectrum is shaped further by a reprocessed emission, possibly coming from two regions, the accretion disc and a more distant scattering region. The accretion disc emission is smeared by the relativistic effects, from which we measured the spin of the black hole as a ≈ 0.8 ± 0.2. We found that most of the spectral variability can be attributed to the least ionised absorber whose column density changed by a factor of two between the first (highest-flux) and the last (lowest-flux) observation. Conclusions. A week-long scale of the variability indicates that the absorber is located at the distance ≈0.05 pc from the centre, i.e., in the broad line region.

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Search for X-ray occultations in active galactic nuclei

Cited by 38 publications

References 49 publications

Long-Term X-Ray Variability of Typical Active Galactic Nuclei in the Distant Universe

Long-Term X-Ray Variability of Typical Active Galactic Nuclei in the Distant Universe

Anatomy of the AGN in NGC 5548

An X-ray variable absorber within the broad line region in Fairall 51

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