Constraints on quasar accretion disks from the optical/ultraviolet/soft X-ray big bump

Czerny, B.; Elvis, M.

doi:10.1086/165630

Cited by 262 publications

(244 citation statements)

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“…In the optical-UV, the SED comprises a 'big blue bump', which is broadly consistent with that expected from an optically thick, geometrically thin Shakura & Sunyaev (1973) accretion disc (AD; see also Novikov & Thorne 1973;Czerny & Elvis 1987). At infrared (IR) wavelengths, a significant contribution from a hot, dusty torus is observed (e.g.…”

Section: Introductionsupporting

confidence: 74%

Reaching the peak of the quasar spectral energy distribution – II. Exploring the accretion disc, dusty torus and host galaxy

Collinson

Ward

Landt

et al. 2016

Mon. Not. R. Astron. Soc.

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Section: Introductionsupporting

confidence: 74%

Reaching the peak of the quasar spectral energy distribution – II. Exploring the accretion disc, dusty torus and host galaxy

Collinson

Ward

Landt

et al. 2016

Mon. Not. R. Astron. Soc.

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“…The first composite that suggests a softening in the far-ultraviolet (blueward of Ly α) was reported by Zheng et al (1997, Z97 hereafter) who analysed 101 quasars from the Hubble Space Telescope (HST ) in the redshift range 0.33 < z < 3.6, covering the wavelengths between 350 and 3000Å. This softening was interpreted as Comptonization of the thermal disc emission in a hot corona above the disc (Czerny & Elvis 1987), due to the similarity between the slope of −1.8 found by Z97 at λ < 1216Å and the one measured by Laor et al (1997) for a sample of radio quiet X-ray selected quasars (αν ∼ −1.7), for which simple accretion disc+X-ray corona models were utilised. The break would thus indicate the peak of the BBB.…”

Section: Introductionmentioning

confidence: 94%

The first ultraviolet quasar-stacked spectrum at z ≃ 2.4 from WFC3

Lusso

Worseck

Hennawi

et al. 2015

Monthly Notices of the Royal Astronomical Society

260

355

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The ionising continuum from active galactic nuclei (AGN) is fundamental for interpreting their broad emission lines and understanding their impact on the surrounding gas. Furthermore, it provides hints on how matter accretes onto supermassive black holes. Using HST's Wide Field Camera 3 we have constructed the first stacked ultraviolet (rest-frame wavelengths 600-2500Å) spectrum of 53 luminous quasars at z 2.4, with a state-of-the-art correction for the intervening Lyman forest and Lyman continuum absorption. The continuum slope (f ν ∝ ν αν ) of the full sample shows a break at ∼912Å with spectral index α ν = −0.61 ± 0.01 at λ > 912Å and a softening at shorter wavelengths (α ν = −1.70 ± 0.61 at λ 912Å). Our analysis proves that a proper intergalactic medium absorption correction is required to establish the intrinsic continuum emission of quasars. We interpret our average ultraviolet spectrum in the context of photoionisation, accretion disk models, and quasar contribution to the ultraviolet background. We find that observed broad line ratios are consistent with those predicted assuming an ionising slope of α ion =−2.0, similar to the observed ionising spectrum in the same wavelength range. The continuum break and softening are consistent with accretion disk plus X-ray corona models when black hole spin is taken into account. Our spectral energy distribution yields a 30% increase to previous estimates of the specific quasar emissivity, such that quasars may contribute significantly to the total specific Lyman limit emissivity estimated from the Lyα forest at z < 3.2.

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“…Many of these models ignore the vertical structure in the accretion disk and the radiation transfer. More sophisticated treatments of these corrections indeed do Ðnd that the accretion disks can emit strongly in soft X-rays, especially when the accretion rate is high and/or the black hole mass is low (e.g., Czerny & Elvis 1987 ;Ross et al 1992 ;Shimura & Takahara 1993). A shifted and strengthened accretion disk spectrum can explain the steeper ROSAT spectra observed in NLS1s, and therefore this was interpreted as evidence for a high accretion rate (e.g., Boller, Brandt, & Fink 1996 ;Laor et al 1997a ;Grupe et al 1999a).…”

Section: Models Of the Soft Excessmentioning

confidence: 99%

A Comprehensive Spectral and Variability Study of Narrow‐Line Seyfert 1 Galaxies Observed by ASCA . II. Spectral Analysis and Correlations

Leighly

1999

ASTROPHYS J SUPPL S

310

197

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I present a comprehensive and uniform analysis of 25 ASCA observations from 23 narrow-line Seyfert 1 galaxies (NLS1s). The spectral analysis and correlations are presented in this paper ; the reduction and time series analysis are presented in the companion paper. A maximum likelihood analysis conÐrms that the hard X-ray photon index is signiÐcantly steeper at more than 90% conÐdence in this sample of NLS1s compared with a random sample of Seyfert galaxies with broad optical lines. Soft excess emission was detected in 17 of the 19 objects that had no signiÐcant absorption, a result that demonstrates that soft excesses appear considerably more frequently in NLS1s than in Seyfert 1 galaxies with broad optical lines. The strength of the soft excess, parameterized using a Ñux ratio obtained from the blackbody plus power-law model, has a wide range of values in these objects (a factor of 50). The photon index was found to be correlated with the Hb FWHM, despite the small range of the latter parameter ; however, neither parameter is correlated with the strength of the soft excess or ROSAT slope. Therefore, assuming that an excess of soft photons causes the steep photon index and narrow Hb FWHM, that excess may lie primarily in the unobservable EUV. The strength of the soft excess is correlated with the variability parameters, so that objects with strong soft excesses show higher amplitude variability ; this potentially important result is not easily explained. While a range of 2 orders of magnitude in luminosity is represented, the temperature of the soft excess is approximately consistent throughout the sample, in contrast with expectations of simple accretion disk models. The presence of ionized absorption was sought using a two-edge model. It was found that this component appears to be typically less common in NLS1s and some evidence was found that the typical ionization state is lower compared with broad-line Seyfert galaxies. This fact, plus evidence for a correlation between the presence of the warm absorber and signiÐcant optical polarization, may imply that the inner warm absorber is missing or is too highly ionized to be detected, and only the outer, dusty, less ionized warm absorber is present in many cases. The iron line equivalent width appears to be similar among narrow and broad-line Seyfert galaxies. This could mean that reprocessing occurs with similar geometry in both classes of objects ; however, the detection of ionized iron lines in a few objects, implying possibly altered Ñuorescence yields, and poor statistics, makes this conclusion tentative. Constraints on physical processes and models based on extreme values of orientation and accretion rate for NLS1s are examined in light of the observational results.

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Constraints on quasar accretion disks from the optical/ultraviolet/soft X-ray big bump

Cited by 262 publications

References 0 publications

Reaching the peak of the quasar spectral energy distribution – II. Exploring the accretion disc, dusty torus and host galaxy

Reaching the peak of the quasar spectral energy distribution – II. Exploring the accretion disc, dusty torus and host galaxy

The first ultraviolet quasar-stacked spectrum at z ≃ 2.4 from WFC3

A Comprehensive Spectral and Variability Study of Narrow‐Line Seyfert 1 Galaxies Observed by ASCA . II. Spectral Analysis and Correlations

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