Plants, property and trade

Brightman, Marc

doi:10.7761/9789738863279_6

Cited by 3 publications

(8 citation statements)

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“…A difference in the torus covering factor distribution between different types of AGN would also explain why the average hard X-ray spectrum of Compton-thin Seyfert 2s shows a larger reflection component than that of Seyfert 1s and Seyfert 1.5s (Ricci et al 2011). A similar result was found by Brightman & Ueda (2012): studying high-redshift AGN in the Chandra Deep Field South they found that more obscured objects appear to have tori with larger covering factors, although they did not find a clear luminosity dependence.…”

Section: Luminosity-dependent Unification Of Agnsupporting

confidence: 79%

“…torus. However, this kind of studies are still very scarce (e.g., Rivers et al 2011;Brightman & Ueda 2012), besides being largely geometry-dependent. Studies of AGN in the mid-IR band performed using the clumpy torus formalism of Nenkova et al (2008) have shown that the number of clouds along the equator is N 0 ∼ 5 −10 ( Mor et al 2009).…”

Section: The Equatorial Column Density Of the Torusmentioning

confidence: 99%

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Luminosity-dependent unification of active galactic nuclei and the X-ray Baldwin effect

Ricci

Paltani

Awaki

et al. 2013

A&A

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The existence of an anti-correlation between the equivalent width (EW) of the narrow core of the iron Kα line and the luminosity of the continuum (i.e., the X-ray Baldwin effect) in type I active galactic nuclei has been confirmed in recent years by several studies carried out with XMM-Newton, Chandra and Suzaku. However, no general consensus on the origin of this trend has been reached so far. Several works have proposed the decrease of the covering factor of the molecular torus with the luminosity (in the framework of the luminosity-dependent unification models) as a possible explanation for the X-ray Baldwin effect. Using the fraction of obscured sources measured by recent X-ray and infrared (IR) surveys as a proxy of the half-opening angle of the torus and recent Monte Carlo simulations of the X-ray radiation reprocessed by a structure with a spherical-toroidal geometry, we test the hypothesis that the X-ray Baldwin effect is related to the decrease of the half-opening angle of the torus with the luminosity. Simulating the spectra of an unabsorbed population with a luminosity-dependent covering factor of the torus as predicted by recent X-ray surveys, we find that this mechanism is able to explain the observed X-ray Baldwin effect. Fitting the simulated data with a log-linear L 2−10 keV −EW relation, we found that in the Seyfert regime (L 2−10 keV ≤ 10 44.2 erg s −1 ) luminosity-dependent unification produces a slope consistent with the observations for average values of the equatorial column densities of the torus of log N T

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Section: Luminosity-dependent Unification Of Agnsupporting

confidence: 79%

Section: The Equatorial Column Density Of the Torusmentioning

confidence: 99%

Luminosity-dependent unification of active galactic nuclei and the X-ray Baldwin effect

Ricci

Paltani

Awaki

et al. 2013

A&A

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“…The choice of the 0.5-8 keV band is motivated by recent results on the number density of Compton-thick AGN in that spectral band by Brightman & Ueda (2012). They used the 4 Ms Chandra Deep Field South data in combination with the spectral models of Brightman & Nandra (2011), which account for Compton-scattering and the geometry of the circumnuclear material, to identify Compton-thick AGN to the flux limit f X (0.5−8 keV) ≈ 10 −16 erg s −1 cm −2 .…”

Section: Predictions On the Properties Of Compton-thick Agnmentioning

confidence: 99%

“…We chose to compare our model predictions with the observed cumulative number count distribution of Comptonthick sources rather than their fraction relative to the overall AGN population. This is to avoid any uncertainties in the determination of the number density as a function of flux of the overall AGN population with L X (2 − 10 keV) > 10 42 erg s −1 adopted by Brightman & Ueda (2012) to normalise the Compton-thick number counts. In the context of our model the fraction f CT ≈ 25% implied by the Brightman & Ueda (2012) results is consistent at the 95% confidence level with the observed fraction of Comptonthick sources in the SWIFT/BAT AGN sample in the local Universe (see Figure 3).…”

Section: Predictions On the Properties Of Compton-thick Agnmentioning

confidence: 99%

“…This is to avoid any uncertainties in the determination of the number density as a function of flux of the overall AGN population with L X (2 − 10 keV) > 10 42 erg s −1 adopted by Brightman & Ueda (2012) to normalise the Compton-thick number counts. In the context of our model the fraction f CT ≈ 25% implied by the Brightman & Ueda (2012) results is consistent at the 95% confidence level with the observed fraction of Comptonthick sources in the SWIFT/BAT AGN sample in the local Universe (see Figure 3). This tentatively suggests a redshift dependence of the f CT , given the mean expected redshift, z ≈ 1, of the Brightman & Ueda (2012) Compton-thick AGN sample (see Figure 5).…”

Section: Predictions On the Properties Of Compton-thick Agnmentioning

confidence: 99%

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Constraining the fraction of Compton-thick AGN in the Universe by modelling the diffuse X-ray background spectrum

Akylas

Georgakakis

Georgantopoulos

et al. 2012

A&A

120

186

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This paper investigates which constraints can be placed on the fraction of Compton-thick active galactic nuclei (AGN) in the Universe from modelling the spectrum of the diffuse X-ray background (XRB). We present a model for the synthesis of the XRB that uses as input a library of AGN X-ray spectra generated by Monte Carlo simulations. This is essential to account for the Compton scattering of X-ray photons in a dense medium and the impact of that process on the spectra of heavily obscured AGN. We identify a small number of input parameters to the XRB synthesis code that encapsulate the minimum level of uncertainty in reconstructing the XRB spectrum. These are the power-law index and high-energy cutoff of the intrinsic X-ray spectra of AGN, the level of the reflection component in AGN spectra, and the fraction of Compton-thick AGN in the Universe. We then map the volume of the space allowed to these parameters by current observational determinations of the XRB spectrum in the range 3−100 keV. One of the least-constrained parameters is the fraction of Compton-thick AGN. Statistically acceptable fits to the XRB spectrum at the 68% confidence level can be obtained for Compton-thick AGN fractions in the range 5−50%. This is because of degeneracies among input parameters to the XRB synthesis code and uncertainties in the modelling of AGN spectra (e.g. level of reflection fraction). The most promising route for constraining the fraction of Compton-thick AGN in the Universe is via the direct detection of those sources in high-energy ( > ∼ 10 keV) surveys. We show that the observed fraction of Compton-thick sources identified in the Swift/BAT serendipitous survey limits the intrinsic fraction of Compton-thick AGN, at least at low redshift, to 10−20% (68% confidence level). We also make predictions on the number density of Compton-thick sources that current and future X-ray missions are expected to discover. Testing those predictions with data will place tight constraints on the intrinsic fraction of Compton-thick AGN as a function of redshift.

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The Wealth of the Body: Trade Relations, Objects, and Personhood in Northeastern Amazonia

Grotti

2013

J Latin Amer Carib Anth

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This article is an analysis of trade among the Trio (Suriname), and their relationship with objects and persons in their quest for manufactured goods. Based on data mostly collected in the Trio village of Tëpu in southern Suriname, it discusses trade from the point of view of Amerindian sociality, with regard to the nature of the interpersonal relations involved. I examine trade through the prism of an Amerindian understanding of personhood, the body and materiality, and show how these relationships tend to be fabricated over a lifetime, eventually becoming an integral and material part of the actors involved. This is manifested in the way Trio social space is constructed and inhabited as an extension of the body, and how objects acquired through trade come to elicit narratives of past exploits and travels to distant spheres of alterity. [Brazil, Guyana, indigenous people, social anthropology, Surinam]They found a Nation of Indians, which never had seene white men, or Christians before, and could not be drawne to any familiar commerce, or conversation, not so much as with our Indians, because they were strangers to them, and of another Nation (Harris 1928:111).1 WHEN EXPLORER AND COLONIZER Robert Harcourt reports the first inland journey that his brother Michael organized with Captain Harvey, a few of their own men, and sixty Amerindian helpers, he dwells on this surprising encounter with a group of indigenous inhabitants who refuse to trade with them. It is the first time since their landing on the northeastern shores of the Guiana region in the early 17th century that the party of English adventurers have come across Amerindians who refuse to engage with them in any form of social interaction; the incident is so remarkable that it is deemed worthy of a detailed description. Elsewhere, Harcourt recounts with satisfaction the ease with which the "friendly" nations of Indians have engaged in commerce since the English landed by the mouth of the river Wiapoco in May 1609.2 In his dry prose he repeatedly emphasizes that the riches of this new land are to be found in its commercial exploitation and the extraction of its natural resources such as timber rather than in the deluded search for gold mines. These attainable riches are readily provided by the local inhabitants in exchange for "toies, and such like trifeling things " (1928:106). Laden with the long lists that became a regular feature of early explorers' accounts (see Stedman 1806:(I) 417-9, (II) 197; Williamson

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Plants, property and trade

Cited by 3 publications

References 0 publications

Luminosity-dependent unification of active galactic nuclei and the X-ray Baldwin effect

Luminosity-dependent unification of active galactic nuclei and the X-ray Baldwin effect

Constraining the fraction of Compton-thick AGN in the Universe by modelling the diffuse X-ray background spectrum

The Wealth of the Body: Trade Relations, Objects, and Personhood in Northeastern Amazonia

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