The X-ray spectra of high-luminosity active galactic nuclei observed by Ginga

Williams, O. R.; Turner, Martin; Stewart, G. C.; Saxton, R. D.; Ohashi, T.; Makishima, Kazuo; Kii, T.; Inoue, H.; Makino, F.; Hayashida, Kentaro; Koyama, K.

doi:10.1086/171194

Cited by 95 publications

(64 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…However, stacking the unabsorbed AGN in four different luminosity bins with equal numbers of objects per bin (Figure 4) shows no trend for luminosity-dependent reflection (for log L 2-10 keV < 44.4). This remains a debated issue: such a trend has been observed to varying degrees in smaller samples of high-luminosity quasars (Williams et al 1992;Page et al 2005), but our sample does not extend to such luminosities to test this.…”

Section: Parameterizing the Hard Excess Using Reflectionmentioning

confidence: 84%

Can We Reproduce the X-Ray Background Spectral Shape Using Local Active Galactic Nuclei?

Vasudevan

Mushotzky

Gandhi

2013

ApJ

View full text Add to dashboard Cite

The X-ray background (XRB) is due to the aggregate of active galactic nuclei (AGNs), which peak in activity at z ∼ 1 and is often modeled as the sum of different proportions of unabsorbed, moderately, and heavily absorbed AGN. We present the summed spectrum of a complete sample of local AGN (the Northern Galactic Cap of the 58 month Swift/BAT catalog, z < 0.2) using 0.4-200 keV data and directly determine the different proportions of unabsorbed, moderately and heavily absorbed AGN that make up the summed spectrum. This stacked low redshift AGN spectrum is remarkably similar in shape to the XRB spectrum (when shifted to z ∼ 1), but the observed proportions of different absorption populations differ from most XRB synthesis models. AGN with Compton-thick absorption account for only ∼12% of the sample, but produce a significant contribution to the overall spectrum. We confirm that Compton reflection is more prominent in moderately absorbed AGN and that the photon index differs intrinsically between unabsorbed and absorbed AGN. The AGN in our sample account for only ∼1% of the XRB intensity. The reproduction of the XRB spectral shape suggests that strong evolution in individual AGN properties is not required between z ∼ 0 and 1.

show abstract

Section: Parameterizing the Hard Excess Using Reflectionmentioning

confidence: 84%

Can We Reproduce the X-Ray Background Spectral Shape Using Local Active Galactic Nuclei?

Vasudevan

Mushotzky

Gandhi

2013

ApJ

View full text Add to dashboard Cite

show abstract

“…The detector background was subtracted by the now standard ''universal'' technique (see, e.g., Williams et al 1992). Detectors 5 and 6 were excluded due to instrumental problems; we use only the top layer data in the remaining detectors.…”

Section: Gingamentioning

confidence: 99%

NGC 4945: The Brightest Seyfert 2 Galaxy at 100 keV

Done

Madejski

Smith

1996

The Astrophysical Journal

View full text Add to dashboard Cite

Seyfert 2 galaxies are generally heavily absorbed in soft X-rays, plausibly because of obscuration of the Seyfert nucleus by a thick molecular torus. With a high torus column, 10 23 Ն N H Ն 10 25 cm Ϫ2 , the observed flux in the ''classical'' 2-10 keV X-ray band can be strongly suppressed, while at higher energies the photoelectric absorption becomes less important and the true nuclear luminosity can be seen. The high-energy bandpass of the Ginga X-ray telescope, extending to 20 keV, allowed several such objects to be discovered, and an extrapolation of the obscured nuclear spectra out to 100 keV suggested that NGC 4945 should be among the very brightest radio-quiet Seyferts in the sky at 100 keV, second only to NGC 4151. OSSE data reported here confirm this prediction, and we analyze these, together with archival Ginga and ASCA data, in order to present a broadband spectrum from 0.6 -500 keV of this object.

show abstract

“…For example, does the shape of the intrinsic spectrum depend on the luminosity of the source? Other QSO studies have not found a significant correlation between Γ and L X except for the general trend that RLQs have smaller X-ray indices than RQQs [11,12,14]. Table 2 also shows no correlation between Γ and L X , but Γ depends on how the 1) Not necessarily a complete sample.…”

Section: Photoelectric Absorptionmentioning

confidence: 91%

X-ray observations of AGN at intermediate to high redshift

Weaver¹

1999

The 9th Astrophysics Conference: After the Dark Ages, When Galaxies Were Young (The Universe at 2

0
0
0
0

View full text Add to dashboard Cite

Abstract.The cores of active galactic nuclei (AGN) harbor some of the most extreme conditions of matter and energy in the Universe. One of the major goals of high-energy astrophysics is to probe these extreme environments in the vicinity of supermassive black holes, which are intimately linked to the mechanisms that produce the continuum emission in AGN. X-ray studies seek to understand the physics responsible for the continuum emission, its point of origin, how nuclear activity is fueled, and how supermassive black holes evolve. The key to finding answers to these questions lies in measuring the intrinsic luminosities and spectral shapes, the relation of these properties to other wavebands, and how the source properties change with redshift. This article reviews X-ray observations of AGN from redshifts of ∼ 0.1 − 3 with the goal of summarizing our current knowledge of their X-ray spectral characteristics. Results are evaluated in terms of their robustness and are examined in the light of current theoretical predictions of energy release via processes associated with the accretion mechanism. A possible evolutionary scenario is discussed, along with the importance of AGN studies at high redshift as they relate to the total energetics of the Universe.

show abstract

The X-ray spectra of high-luminosity active galactic nuclei observed by Ginga

Cited by 95 publications

References 0 publications

Can We Reproduce the X-Ray Background Spectral Shape Using Local Active Galactic Nuclei?

Can We Reproduce the X-Ray Background Spectral Shape Using Local Active Galactic Nuclei?

NGC 4945: The Brightest Seyfert 2 Galaxy at 100 keV

X-ray observations of AGN at intermediate to high redshift

Contact Info

Product

Resources

About