UBVRI simultaneous observations of the nucleus of Seyfert galaxy
NGC 5548 in 1993–1999

Observations of the optical polarization of NGC 4151 in 1997NGC 4151 in -2003 show variations of an order of magnitude in the polarized flux while the polarization position angle remains constant. The amplitude of variability of the polarized flux is comparable to the amplitude of variability of the total U -band flux, except that the polarized flux follows the total flux with a lag of 8 ± 3 days. The time lag and the constancy of the position angle strongly favor a scattering origin for the variable polarization rather than a non-thermal synchrotron origin. The orientation of the position angle of the polarized flux (parallel to the radio axis) and the size of the lag imply that the polarization arises from electron scattering in a flattened region within the low-ionization component of the broad-line-region. Polarization from dust scattering in the equatorial torus is ruled out as the source of the lag in polarized flux because it would produce a larger lag and, unless the half-opening angle of the torus is >53 • , the polarization would be perpendicular to the radio axis. We note a long-term change in the percentage of polarization at similar total flux levels and this could be due either to changing non-axisymmetry in the optical continuum emission, or a change in the number of scatterers on a timescale of years.

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“…This is shown in Fig. 5 of Merkulova (2002). In NGC 4151, as in other AGNs, the B-band and U -band fluxes vary essentially simultaneously.…”

mentioning

confidence: 69%

Discovery of Polarization Reverberation in NGC 4151

Gaskell

Goosmann

Меркулова

et al. 2012

ApJ

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“…In fact, this source has been shown to have long term optical and X-ray variability (e.g. 1993 to 1999 -Merkulova 2002and 1996to 2001-Uttley et al 2003. We searched the literature for optical measurements closer in time to the IRAS data campaign and found the specific flux at 4390 Å for this source measured in 1974 (de Bruyn & Sargent 1978).…”

Section: Infrared Observationsmentioning

confidence: 99%

Can we measure the accretion efficiency of active galactic nuclei?

Raimundo¹,

Fabian²,

Vasudevan³

et al. 2011

Monthly Notices of the Royal Astronomical Society

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The accretion efficiency for individual black holes is very difficult to determine accurately. There are many factors that can influence each step of the calculation, such as the dust and host galaxy contribution to the observed luminosity, the black hole mass and more importantly the uncertainties on the bolometric luminosity measurement. Ideally, we would measure the active galactic nuclei (AGNs) emission at every wavelength, remove the host galaxy and dust, reconstruct the AGN spectral energy distribution and integrate them to determine the intrinsic emission and the accretion rate. In reality, this is not possible due to observational limitations and our own galaxy line‐of‐sight obscuration. We have then to infer the bolometric luminosity from spectral measurements made in discontinuous wavebands and at different epochs. In this paper, we tackle this issue by exploring different methods to determine the bolometric luminosity. We first explore the trend of accretion efficiency with black hole mass (ε ∝ M∼0.5) found in recent work by Davis & Laor and discuss why this is most likely an artefact of the parameter space covered by their Palomar–Green quasar sample. We then target small samples of AGNs at different redshifts, luminosities and black hole masses to investigate the possible methods to calculate the accretion efficiency. For these sources we are able to determine the mass accretion rate and, with some assumptions, the accretion efficiency distributions. Even though we select the sources for which we are able to determine the parameters more accurately, there are still factors affecting the measurements that are hard to constrain. We suggest methods to overcome these problems based on contemporaneous multiwavelength data measurements and specifically targeted observations for AGNs in different black hole mass ranges.

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The International Cooperation of the Crimean Astrophysical Observatory on the Spectral and Photometric Monitoring of Active Galactic Nuclei

Pronik

2003

Astronomical & Astrophysical Transactions

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UBVRI simultaneous observations of the nucleus of Seyfert galaxy NGC 5548 in 1993–1999

Cited by 4 publications

References 31 publications

Discovery of Polarization Reverberation in NGC 4151

Discovery of Polarization Reverberation in NGC 4151

Can we measure the accretion efficiency of active galactic nuclei?

The International Cooperation of the Crimean Astrophysical Observatory on the Spectral and Photometric Monitoring of Active Galactic Nuclei

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