6,448 research outputs found
Reverberation Mapping of High-z, High-luminosity Quasars
We present Reverberation Mapping results after monitoring a sample of 17
high-z, high-luminosity quasars for more than 10 years using photometric and
spectroscopic capabilities. Continuum and line emission flux variability is
observed in all quasars. Using cross-correlation analysis we successfully
determine lags between the variations in the continuum and broad emission lines
for several sources. Here we present a highlight of our results and the
determined radius--luminosity relations for Ly_alpha and CIV.Comment: Contributed talk at conference "Quasars at all cosmic epochs", held
in Padova 2-7 April 2017, published in Frontiers in Astronomy and Space
Science
Locally Optimally Emitting Clouds and the Origin of Quasar Emission Lines
The similarity of quasar line spectra has been taken as an indication that
the emission line clouds have preferred parameters, suggesting that the
environment is subject to a fine tuning process. We show here that the observed
spectrum is a natural consequence of powerful selection effects. We computed a
large grid of photoionization models covering the widest possible range of
cloud gas density and distance from the central continuum source. For each line
only a narrow range of density and distance from the continuum source results
in maximum reprocessing efficiency, corresponding to ``locally
optimally-emitting clouds'' (LOC). These parameters depend on the ionization
and excitation potentials of the line, and its thermalization density. The mean
QSO line spectrum can be reproduced by simply adding together the full family
of clouds, with an appropriate covering fraction distribution. The observed
quasar spectrum is a natural consequence of the ability of various clouds to
reprocess the underlying continuum, and can arise in a chaotic environment with
no preferred pressure, gas density, or ionization parameter.Comment: 9 pages including 1 ps figure. LaTeX format using aaspp4.st
Complex Optical-X-ray Correlations in the Narrow-Line Seyfert 1 Galaxy NGC 4051
This paper presents the results of a dense and intensive X-ray and optical
monitoring of the narrow-line Seyfert 1 galaxy NGC 4051 carried out in 2000.
Results of the optical analysis are consistent with previous measurements. The
amplitude of optical emission line variability is a factor of two larger than
that of the underlying optical continuum, but part or all of the difference can
be due to host-galaxy starlight contamination or due to the lines being driven
by the unseen UV continuum, which is more variable than the optical continuum.
We measured the lag between optical lines and continuum and found a lower, more
accurate broad line region size of 3.0+-1.5 light days in this object. The
implied black hole mass is M_BH=5(+6,-3)x10^5 M_sun; this is the lowest mass
found, so far, for an active nucleus. We find significant evidence for an
X-ray-optical (XO) correlation with a peak lag of about <1 day, although the
centroid of the asymmetric correlation function reveals that part of the
optical flux varies in advance of the X-ray flux by 2.4+-1.0 days. This complex
XO correlation is explained as a possible combination of X-ray reprocessing and
perturbations propagating from the outer (optically emitting) parts of the
accretion disc into its inner (X-ray emitting) region.Comment: 8 pages, 4 figures included, LaTeX mn.sty, accepted for publication
in MNRA
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