Betriebserfahrungen

Winkler, Wolfgang

doi:10.1007/978-3-662-06169-5_6

Cited by 19 publications

(41 citation statements)

References 3 publications

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“…Two of the assumptions made when applying this model are that the discrepancy in slope between the difference spectra and a ν 1/3 slope is due to extinction from our own Galaxy and within the central regions of the AGN, and also that the variable component of the AGN spectra does not change shape between the bright and the faint state. To test these assumptions, we use the flux variation gradient method of Winkler et al (1992) and Winkler (1997). In this method, when comparing the flux through one filter with the flux through another filter at corresponding times, a very strong linear relationship is seen.…”

Section: Accretion Disc Modelmentioning

confidence: 99%

Testing thermal reprocessing in active galactic nuclei accretion discs

Cackett¹,

Horne²,

Winkler³

2007

Monthly Notices of the Royal Astronomical Society

281

351

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The thermal reprocessing hypothesis in active galactic nuclei (AGN), where extreme ultraviolet/X‐ray photons are reprocessed by the accretion disc into optical/UV photons, predicts wavelength‐dependent time‐delays between the optical continuum at different wavelengths. Recent photometric monitoring by Sergeev et al. has shown that the time‐delay is observed in 14 AGN, and generally seen to increase with increasing wavelength, as predicted in the reprocessing scenario. We fit the observed time‐delays and optical spectral energy distribution using a disc reprocessing model. The model delivers estimates for the nuclear reddening, the product of black hole mass and accretion rate, and the distance to each object. However, the distances at face value give H0= 44 ± 5 km s−1 Mpc−1– a factor of 1.6 smaller than generally accepted. We discuss the implications of this on the reprocessing model.

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Section: Accretion Disc Modelmentioning

confidence: 99%

Testing thermal reprocessing in active galactic nuclei accretion discs

Cackett¹,

Horne²,

Winkler³

2007

Monthly Notices of the Royal Astronomical Society

281

351

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“…Akn 120 has been monitored in the visible region at SAAO by Winkler et al (1992), Winkler (1997) and in a service observing programme at SAAO under the control of Dr D. Kilkenny.…”

Section: Comments On Individual Galaxiesmentioning

confidence: 99%

“…Visible‐region photometry from Winkler et al (1992) and Winkler (1997) is also shown. The U data are insufficient for cross‐correlation purposes.…”

Section: Comments On Individual Galaxiesmentioning

confidence: 99%

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Long-term infrared photometry of Seyferts

Glass

2004

Monthly Notices of the Royal Astronomical Society

103

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Long‐term (up to 10 000 d) monitoring has been undertaken for 41 Seyferts in the near‐infrared (1.25–3.45 μm). All but two showed variability, with amplitudes at K in the range <0.1 to >1.1 mag. The time‐scale for detectable change is from about one week to a few years. Where contemporary observations of variability in X‐rays, ultraviolet (UV) or visible light exist, it is found that the near‐infrared varies in a similar way, though in some cases the shorter‐wavelength infrared (IR) bands are diluted by underlying galaxy radiation. A simple cross‐correlation study indicates that there is evidence for delays of up to several hundred d between the variations seen at the shortest wavelengths (U or J) and the longest (L) in many galaxies. In particular, the data for Fairall 9 now extend to twice the interval covered in earlier publications and the delay between its UV and IR outputs is seen to persist. An analysis of the fluxes shows that, for any given galaxy, the colours of the variable component of its nucleus are usually independent of the level of activity. The state of activity of the galaxy can be parameterized. Taken over the whole sample, the colours of the variable components fall within moderately narrow ranges. In particular, the H−K colour is appropriate to a blackbody of temperature 1600 K. The H−K excess for a heavily reddened nucleus can be determined and used to find EB−V, which can be compared to the values found from the visible region broad line ratios. Using flux–flux diagrams, the flux within the aperture from the underlying galaxies can often be determined without the need for model surface brightness profiles. In many galaxies it is apparent that there must be an additional constant contribution from warm dust.

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“…Fig. 4 shows the position of the optical points – from Winkler (1997) and the OM, as circle and star symbols respectively – in relation to the X‐ray data, together with the radio measurement obtained from Bicay et al (1995) and four infrared (IR) data points, obtained from the IRAS Faint Source Catalogue, version 2.0 (Moshir et al 1990).…”

Section: Spectral Analysismentioning

confidence: 99%

An XMM--Newton observation of the narrow-line Seyfert 1 galaxy Markarian 896

Page¹,

O’Brien²,

Reeves³

et al. 2003

Monthly Notices of the Royal Astronomical Society

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We present XMM–Newton observations of the narrow‐line Seyfert 1 galaxy Markarian 896. Over the 2–10 keV band, an iron emission line, close to 6.4 keV, is seen. The line is just resolved and has an equivalent width of ∼170 eV. The broad‐band spectrum is well modelled by a power‐law slope of Γ∼ 2.03, together with two blackbody components to fit the soft X‐ray excess. Using a more physical two‐temperature Comptonization model, a good fit is obtained for an input photon distribution of kT∼ 60 eV and Comptonizing electron temperatures of ∼0.3 and 200 keV. The soft excess cannot be explained purely through the reprocessing of a hard X‐ray continuum by an ionized disc reflector.

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Betriebserfahrungen

Cited by 19 publications

References 3 publications

Testing thermal reprocessing in active galactic nuclei accretion discs

Testing thermal reprocessing in active galactic nuclei accretion discs

Long-term infrared photometry of Seyferts

An XMM--Newton observation of the narrow-line Seyfert 1 galaxy Markarian 896

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