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Date and Time of the Query: 2019-08-24 T01:10:32 PDT
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For refcode 2001ApJ...550..655K:
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Copyright by American Astronomical Society. Reproduced by permission
2001ApJ...550..655K Modeling the X-Ray-Optical Correlations in NGC 3516 Demosthenes Kazanas and Sergei Nayakshin Received 2000 June 28; accepted 2000 November 17 ABSTRACT We test the "reprocessing paradigm" of optical-UV active galactic nucleus (AGN) variability, according to which the variations in this wavelength range are driven by a variable X-ray component, by detailed modeling of the correlated X-ray-optical (3590 and 5510 A) variability of the recent multiwavelength campaign of NGC 3516. To this end we produce model optical light curves by convolving the observed X-ray flux with the response function of an infinite, thin accretion disk, illuminated by a pointlike X-ray source located at a given height h_X_ above the compact object (the lamppost model). We also produce the ionized X-ray reflection and Fe K{alpha} line spectra that result from the reprocessing of the same X-rays on the disk surface. Then we compare the properties of the model light curves (amplitude, morphology, lags) as well as those of the Fe K{alpha} line profiles to those observed. Our calculations improve on those of similar past treatments by including the effects of an X-ray -heated ionized layer in hydrostatic equilibrium on its surface, which greatly affects its X-ray timing and spectral properties. The results of our calculations do not provide a clear-cut picture that would either support or refute the reprocessing paradigm: despite the large (~=50%) amplitude excursions of the X-ray flux, the model optical light curves exhibit variability amplitudes of only 3%-4% and vary in synchrony in the two bands, in agreement with observations. However, the model light curves, when viewed in detail, do not have a direct correspondence to those observed. Futhermore, while the observed intraband synchrony generally points toward smaller values for the black hole mass (M = 10^7^ M_sun_), the X-ray Fe K{alpha} line, X-ray reflection, and optical-UV spectra seem to favor larger mass values (M = 10^8^ M_sun_). Generally, no combination of the model parameters seems to produce agreement with the ensemble of the constraints imposed by optical/UV/X-ray spectral and timing observations; we are thus led to believe that the simplest version of the lamppost model geometry is inconsistent with the NGC 3516 observations. Subject headings: accretion, accretion disks-galaxies: active -galaxies: individual (NGC 3516)-galaxies: Seyfert-ultraviolet: galaxies-X-rays: galaxies
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