Observations of the quasar PG 1211 + 143 are presented and its continuum is modelled in terms of an accretion disk and an underlying power law. The X-ray spectrum in the Einstein imaging proportional ...counter band is well described by a power law with the very steep spectral index 2.2 + or - 0.4. The overall continuum spectral energy distribution can be described as a power law with alpha roughly 1.2 from the infrared to about 1 keV, with the optical, ultraviolet, and soft X-rays forming a large excess above this power law. If the soft X-ray excess is attributed to emission from a physically thin, optically thick accretion disk, then the implied accretion rate is super-Eddington, from which it is concluded that the application of this simple model is not valid. The observed broad-line ratios in PG 1211 + 143 imply broad-line cloud densities that are somewhat higher than those usually derived for quasars.
Astron.Astrophys.409:57-64,2003 BeppoSAX observed the z=3.27 quasar PKS2126-158 on 1999 May 24-28 when its
2-10keV and 0.1-2.5keV fluxes were 1.1E-11 and 4.4E-12 cgs respectively, a
factor of 2 ...higher than in all previous ROSAT and ASCA observations and 40%
higher than in two more recent Chandra and XMM-Newton observations. The
shortest detected rest frame variability timescale is of a few months,
comparable to the causal timescale associated to an emission region of ~10
Schwarzschild radii around a few 1E10 solar masses black hole. The source is
detected with a signal to noise ratio S/N>=3 up to ~50 keV, 215 keV rest frame.
The BeppoSAX observations confirm the presence of low energy absorption along
the line of sight, independent on the continuum model adopted, at high
confidence level. Despite the limited spectral resolution of the BeppoSAX LECS
and MECS it is possible to put constraints on different absorption and
continuum models, but not to unambiguously determine the redshift of the
absorber. If the absorber is not significantly ionized the BeppoSAX data do
prefer an absorber at z<=2.7. Strong and complex metal line systems along the
line of sight to PKS2126-158 have been found at z=0.6631 and at 2.64<z<2.82.
They could well be associated to the X-ray absorption. Conversely, an ionized
(``warm'') absorber at the quasar redshift provides a good fit only if the iron
abundance is smaller than ~0.3 solar, while that of the other elements is fixed
to the solar value.
The high spatial resolution of the Chandra X-ray Observatory allows us to
study the environment of GPS/CSS sources to within an arcsec of the strong
compact core. We present the discovery of X-ray ...jets in two GPS quasars,
PKS1127-145 and B2 0738+393, indicating that X-ray emission associated with the
relativistic plasma is present at large distances from the GPS nucleus. We also
discuss first results from Chandra observations of our GPS/CSS sample. We find
that 6 out of 10 sources show intrinsic absorption at a level which may be
sufficient to confine the GPS source.
We present spectroscopic redshifts for the first 466 X-ray and radio-selected
AGN targets in the 2 deg^2 COSMOS field. Spectra were obtained with the IMACS
instrument on the Magellan (Baade) ...telescope, using the nod-and-shuffle
technique. We identify a variety of Type 1 and Type 2 AGN, as well as red
galaxies with no emission lines. Our redshift yield is 72% down to i_AB=24,
although the yield is >90% for i_AB<22. We expect the completeness to increase
as the survey continues. When our survey is complete and additional redshifts
from the zCOSMOS project are included, we anticipate ~1100 AGN with redshifts
over the entire COSMOS field. Our redshift survey is consistent with an
obscured AGN population that peaks at z~0.7, although further work is necessary
to disentangle the selection effects.
Astron.J.132:401-419,2006 We are conducting a large observing program with the Spitzer Space Telescope
to determine the mid-to-far infrared spectral energy distributions of a
well-defined sample of ...87 nearby, 12 micron-selected Seyfert galaxies. In this
paper we present the results of IRS low-resolution spectroscopy of a
statistically representative subsample of 51 of the galaxies (59%), with an
analysis of the continuum shapes and a comparison of the Seyfert types. We find
that the spectra clearly divide into groups based on their continuum shapes and
spectral features. Some spectral features are clearly related to a starburst
contribution to the IR spectrum, while the mechanisms producing observed
power-law continuum shapes, attributed to an AGN component, may be dust or
non-thermal emission. The infrared spectral types appear to be related to the
Seyfert types. Principal component analysis results suggest that the relative
contribution of starburst emission may be the dominant cause of variance in the
observed spectra. We find that Sy 1's have higher ratios of IR/radio emission
than Sy 2's, as predicted by the unified model if the torus is optically thick
in the mid-IR. However, smooth-density torus models predict a much larger
difference between type 1's and 2's than observed in our sample. Our
observations may be consistent with clumpy torus models containing a steep
radial distribution of optically thick dense clumps. (Abridged)
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