X-ray spectra of <i>XMM-Newton</i> serendipitous medium flux
 sources

Mateos, S.; Barcons, X.; Carrera, Francisco J.; Ceballos, M. T.; Caccianiga, A.; Lamer, G.; Maccacaro, T.; Page, M. J.; Schwope, A. D.; Watson, M. G.

doi:10.1051/0004-6361:20041340

Cited by 66 publications

(111 citation statements)

References 65 publications

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“…This is much harder than the typical intrinsic photon indices ( ∼ 1.9) seen in AGN X-ray spectra (cf. Nandra et al 1997;Mateos et al 2005;Piconcelli et al 2005) and is suggestive of heavy obscuration. Fitting the same model to the data from each mission separately, the observed 2-10 keV fluxes span the range of F 2-10 ≈ (7-14) × 10 −13 erg s −1 cm −2 between the missions (with the harder Swift photon index giving the highest flux), and are fully consistent with each other at 90 per cent confidence.…”

Section: Basic Characterizationmentioning

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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Section: Basic Characterizationmentioning

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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“…This should be done by calculating the intrinsic (before absorption) luminosity and absorption (N H ) function in order to obtain results free from selection effects. Since hard X-ray photons are less affected by absorption, absorbed AGN are more likely to be detected at energies above 2 keV and hence we have applied such method to the hard (2−10 keV) and ultrahard (4.5−7.5 keV) sources, for which we have detailed spectral data (photon index Γ and intrinsic absorbing column densities N H , Mateos et al 2005). With ∼25% of the XMS sources in the hard and ultrahard bands classified as type-2 AGN, we find that they typically log N H > 22, a value commonly used to separate absorbed AGN from the unabsorbed ones (see Fig.…”

Section: The N H Function Of Hard Sourcesmentioning

confidence: 99%

The XMM-Newton serendipitous survey

Ebrero

Carrera²,

Page³

et al. 2008

A&A

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125

215

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Aims. To study the cosmological evolution of active galactic nuclei (AGN) is one of the main goals of X-ray surveys. To accurately determine the intrinsic (before absorption) X-ray luminosity function, it is essential to constrain the evolutionary properties of AGN and therefore the history of the formation of supermassive black holes with cosmic time. Methods. In this paper we investigate the X-ray luminosity function of absorbed (log N H > 22) and unabsorbed AGN in three energy bands (soft: 0.5−2 keV, hard: 2−10 keV and ultrahard: 4.5−7.5 keV). For the hard and ultrahard sources we have also studied the N H function and the dependence of the fraction of absorbed AGN on luminosity and redshift. This investigation is carried out using the XMS survey along with other highly complete flux-limited deeper and shallower surveys in all three bands for a total of 1009, 435, and 119 sources in the soft, hard and ultrahard bands, respectively. We modelled the instrinsic absorption of the hard and ultrahard sources (N H function) and computed the X-ray luminosity function in all bands using two methods. The first makes use of a modified version of the classic 1/V a technique, while the second performs a maximum likelihood (ML) fit using an analytic model and all available sources without binning. Results. We find that the X-ray luminosity function (XLF) is best described by a luminosity-dependent density evolution (LDDE) model. Our results show good overall agreement with previous results in the hard band, although with slightly weaker evolution. Our model in the soft band present slight discrepancies with other works in this band, the shape of our present day XLF being significantly flatter. We find faster evolution in the AGN detected in the ultrahard band than those in the hard band. Conclusions. The results reported here show that the fraction of absorbed AGN in the hard and ultrahard bands is dependent on the X-ray luminosity. We find evidence that this fraction evolves with redshift in the hard band, whereas there is none in the ultrahard band, possibly due to the low statistics. Our best-fit XLF shows that the high-luminosity AGN, detected in all bands, exhibit a similar behaviours and are fully formed earlier than the less luminous AGN. The latter sources account for the vast majority of the accretion rate and mass density of the Universe, according to an anti-hierarchical black hole growth scenario.

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“…Excess X-ray absorption above the Galactic value and a soft excess emission were detected in ∼4% and ∼9% of the sources respectivelly. We used the recipe in Mateos et al (2005a) to obtain the intrinsic fraction of objects with detected soft excess and/or intrinsic absorption. The method takes into account the expected number of spurious detections (1% expected for the chosen F-test significance threshold) using Bayesian statistics.…”

Section: Spectral Fittingmentioning

confidence: 99%

“…Some authors claim an anti-correlation between the spectral photon index Γ and the X-ray luminosity (Young et al 2009;Saez et al 2008;Page et al 2005) while other studies suggest the opposite correlation (Dai et al 2004) or no correlation at all (Winter et al 2009;Mateos et al 2005b;George et al 2000;Reeves & Turner 2000). Studies of the X-ray spectra of AGN have generally shown no clear dependence of the AGN X-ray properties on the redshift (Mateos et al 2005a), although some exceptions have been found (Kelly et al 2007). …”

Section: Introductionmentioning

confidence: 99%

The XMM-NewtonWide Angle Survey (XWAS): the X-ray spectrum of type-1 AGN

Mateos¹,

Carrera

Page

et al. 2010

A&A

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Aims. We discuss the broad band X-ray properties of one of the largest samples of X-ray selected type-1 AGN to date (487 objects in total), drawn from the XMM-Newton Wide Angle Survey (XWAS). The objects presented in this work cover 2−10 keV (rest-frame) luminosities from ∼10 42 −10 45 erg s −1 and are detected up to redshift ∼4. We constrain the overall properties of the broad band continuum, soft excess and X-ray absorption, along with their dependence on the X-ray luminosity and redshift. We discuss the implications for models of AGN emission. Methods. We fitted the observed 0.2−12 keV broad band spectra with various models to search for X-ray absorption and soft excess. The F-test was used with a significance threshold of 99% to statistically accept the detection of additional spectral components. Results. We constrained the mean spectral index of the broad band X-ray continuum to Γ = 1.96 ± 0.02 with intrinsic dispersion σ Γ = 0.27 +0.01 −0.02 . The continuum becomes harder at faint fluxes and at higher redshifts and hard (2−10 keV) luminosities. The dependence of Γ with flux is likely due to undetected absorption rather than to spectral variation. We found a strong dependence of the detection efficiency of objects on the spectral shape. We expect this effect to have an impact on the measured mean continuum shapes of sources at different redshifts and luminosities. We detected excess absorption in > ∼ 3% of our objects, with rest-frame column densities ∼a few ×10 22 cm −2 . The apparent mismatch between the optical classification and X-ray properties of these objects is a challenge for the standard orientation-based AGN unification model. We found that the fraction of objects with detected soft excess is ∼36%. Using a thermal model, we constrained the soft excess mean rest-frame temperature and intrinsic dispersion to kT ∼ 100 eV and σ kT ∼ 34 eV. The origin of the soft excess as thermal emission from the accretion disk or Compton scattered disk emission is ruled out on the basis of the temperatures detected and the lack of correlation of the soft excess temperature with the hard X-ray luminosity over more than 2 orders of magnitude in luminosity. Furthermore, the high luminosities of the soft excess rule out an origin in the host galaxy.

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X-ray spectra of XMM-Newton serendipitous medium flux sources

Cited by 66 publications

References 65 publications

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

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

The XMM-Newton serendipitous survey

The XMM-NewtonWide Angle Survey (XWAS): the X-ray spectrum of type-1 AGN

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