1,111 research outputs found
The Locus of Highly Accreting AGNs on the M_BH--sigma Plane: Selections, Limitations, and Implications
We re-examine the locus of narrow line Seyfert 1 galaxies on the M_BH--sigma
(black hole mass--bulge velocity dispersion) plane in the light of the results
from large new optically selected samples. We find that (1) soft X-ray selected
NLS1s have a lower ratio of BH mass to \sigma^{4}_{[OIII]} than broad line
Seyfert 1 galaxies; this remains a robust statistical result contrary to recent
claims otherwise; (2) optically selected NLS1s have systematically lower
Eddington luminosity ratio compared to X-ray selected NLS1s; and (3) as a
result, the locus of NLS1s on the M_BH--sigma plane is affected by selection
effects. We argue that there is no single explanation for the origin of the
M_BH--sigma relation; instead tracks of galaxies on the M_BH--sigma plane
differ with redshift, consistent with the downsizing of AGN activity. If these
results at face value are incorrect, then the data imply that AGNs with high
Eddington accretion reside preferentially in relatively late type galaxies at
the present epoch, perhaps a more interesting result and a challenge to
theoretical models.Comment: To appear in Ap
A high velocity ionised outflow and XUV photosphere in the narrow emission line quasar PG1211+143
We report on the analysis of a ~60 ksec XMM observation of the bright, narrow
emission line quasar PG 1211+143. Absorption lines are seen in both EPIC and
RGS spectra corresponding to H- and He-like ions of Fe, S, Mg, Ne, O, N and C.
The observed line energies indicate an ionised outflow velocity of ~24000 km
s^-1. The highest energy lines require a column density of N_H ~ 5 x 10^23
cm^-2, at an ionisation parameter of log(xi) ~ 3.4. If the origin of this high
velocity outflow lies in matter being driven from the inner disc, then the flow
is likely to be optically thick within a radius ~130 Schwarzschild radii,
providing a natural explanation for the Big Blue Bump (and strong soft X-ray)
emission in PG 1211+143.Comment: Accepted by MNRAS; Table 1 correcte
Discovery of close companions to the nearby young stars HD 199143 and HD 358623
Young stellar systems in the solar neighborhood provide valuable laboratories
for detailed studies of star and planet formation. The bright F8V star HD
199143 and the Li-rich late-type emission line star HD 358623 are among the
nearest young stars identified to date, and may be members of a young
association in Capricornus. We present high-resolution near-infrared images of
these two sources, obtained using the adaptive optics system on the 3.6-meter
telescope at the European Southern Observatory in La Silla, Chile. Our
observations reveal that both are in fact close binary systems. The newly
discovered companion at a separation of 1'' may account for the unusual
characteristics of HD 199143 --rapid rotation, emission lines, ultraviolet
variability, and excess infrared emission-- recently discussed by van den
Ancker and co-workers. HD 199143 may be a rare example of a close binary with
only a circum{\it secondary} disk. With the detection of a 2'' companion,
HD 358623 is now possibly one of the closest known T Tauri binaries. Both
binary systems are prime targets for follow-up spectroscopic and astrometric
observations.Comment: 9 pages, 1 PostScript figure, to appear in The Astrophysical Journal
Letter
The XMM-Newton Iron Line Profile of NGC 3783
We report on observations of the iron K line in the nearby Seyfert 1 galaxy,
NGC 3783, obtained in a long, 2 orbit (240 ks) XMM-Newton observation. The line
profile obtained exhibits two strong narrow peaks at 6.4 keV and at 7.0 keV,
with measured line equivalent widths of 120 and 35 eV respectively. The 6.4 keV
emission is the K-alpha line from near neutral Fe, whilst the 7.0 keV feature
probably originates from a blend of the neutral Fe K-beta line and the H-like
line of Fe at 6.97 keV. The relatively narrow velocity width of the K-alpha
line (<5000 km/s), its lack of response to the continuum emission on short
timescales and the detection of a neutral Compton reflection component are all
consistent with a distant origin in Compton-thick matter such as the putative
molecular torus. A strong absorption line from highly ionized iron (at 6.67
keV) is detected in the time-averaged iron line profile, whilst the depth of
the feature appears to vary with time, being strongest when the continuum flux
is higher. The iron absorption line probably arises from the highest ionization
component of the known warm absorber in NGC 3783, with an ionization of logxi=3
and column density of 5x10^{22}cm{-2} and may originate from within 0.1pc of
the nucleus. A weak red-wing to the iron K line profile is also detected below
6.4 keV. However when the effect of the highly ionized warm absorber on the
underlying continuum is taken into account, the requirement for a relativistic
iron line component from the inner disk is reduced.Comment: 34 pages, including 11 figures. Accepted for publication in Ap
Variable iron-line emission near the black hole of Markarian 766
We investigate the link between ionised Fe X-ray line emission and continuum
emission in the bright nearby AGN, Mrk 766. A new long (433 ks) XMM-Newton
observation is analysed, together with archival data from 2000 and 2001. The
contribution from ionised line emission is measured and its time variations on
short (5-20 ks) timescales are correlated with the continuum emission. The
ionised line flux is found to be highly variable and to be strongly correlated
with the continuum flux, demonstrating an origin for the ionised line emission
that is co-located with the continuum emission. Most likely the emission is
ionised reflection from the accretion disc within a few A.U. of the central
black hole, and its detection marks the first time that such an origin has been
identified other than by fitting to spectral line profiles. Future observations
may be able to measure a time lag and hence achieve reverberation mapping of
AGN at X-ray energies.Comment: Accepted for publication, Astronomy and Astrophysics letter
Phase-resolved far-ultraviolet HST spectroscopy of the peculiar magnetic white dwarf RE J0317-853
We present phase resolved FUV HST FOS spectra of the rapidly rotating, highly
magnetic white dwarf RE J0317-853. Using these data, we construct a new model
for the magnetic field morphology across the stellar surface. From an expansion
into spherical harmonics, we find the range of magnetic field strengths present
is 180-800MG. For the first time we could identify an absorption feature
present at certain phases at 1160A as a ``forbidden'' 1s_0 -> 2s_0 component,
due to the combined presence of an electric and magnetic field.Comment: 15 pages including 4 figures. Accepted for publication in ApJ Letter
A Multi-Cloud Warm-Absorber Model for NGC 4051
A multi-cloud model is presented which explains the soft X-ray excess in NGC
4051 and, consistently, the optical line spectrum and the SED of the continuum.
The clouds are heated and ionized by the photoionizing flux from the active
center and by shocks. Diffuse radiation, partly absorbed throughout the clouds,
nicely fits the bump in the soft X-ray domain, while bremsstrahlung radiation
from the gaseous clouds contribute to the fit of the continuum SED. Debris of
high density fragmented clouds are necessary to explain the absorption oxygen
throats observed at 0.87 keV and 0.74 keV. The debris are heated by shocks of
about 200-300 km/s. Low velocity (100 km/s)-density (100 cm-3) clouds
contribute to the line and continuum spectra, as well as high velocity (1000
km/s)-density (8000 cm-3) clouds which are revealed by the FWHM of the line
profiles. The SED in the IR is explained by reradiation of dust, however, the
dust-to-gas ratio is not particularly high. Radio emission is well fitted by
synchrotron radiation created at the shock front by Fermi mechanism.Comment: 19 pages + 3 figures PostScrip
XMM-Newton observations of seven soft X-ray excess QSOs
XMM-Newton observations of seven QSOs are presented and the EPIC spectra
analysed. Five of the AGN show evidence for Fe K-alpha emission, with three
being slightly better fitted by lines of finite width; at the 99 per cent level
they are consistent with being intrinsically narrow, though. The broad-band
spectra can be well modelled by a combination of different temperature
blackbodies with a power-law, with temperatures between kT ~ 100-300 eV. On the
whole, these temperatures are too high to be direct thermal emission from the
accretion disc, so a Comptonization model was used as a more physical
parametrization. The Comptonizing electron population forms the soft excess
emission, with an electron temperature of ~ 120-680 eV. Power-law, thermal
plasma and disc blackbody models were also fitted to the soft X-ray excess. Of
the sample, four of the AGN are radio-quiet and three radio-loud. The
radio-quiet QSOs may have slightly stronger soft excesses, although the
electron temperatures cover the same range for both groups.Comment: 13 pages, 7 figures, accepted for publication in MNRA
The X-ray spectrum of NGC 7213 and the Seyfert--LINER connection
We present an XMM-Newton observation of the Seyfert-LINER galaxy NGC 7213.
The RGS soft X-ray spectrum is well fitted with a power law plus soft X-ray
collisionally ionised thermal plasma (kT = 0.18 +0.03/-0.01 keV). We confirm
the presence of Fe I, XXV and XXVI K-alpha emission in the EPIC spectrum and
set tighter constraints on their equivalent widths of 82 +10/-13, 24 +9/-11 and
24 +10/-13 eV respectively. We compare the observed properties together with
the inferred mass accretion rate of NGC 7213, to those of other Seyfert and
LINER galaxies. We find that NGC 7213 has intermediate X-ray spectral
properties lying between those of the weak AGN found in the LINER M81 and
higher luminosity Seyfert galaxies. There appears to be a continuous sequence
of X-ray properties from the Galactic Centre through LINER galaxies to
Seyferts, likely determined by the amount of material available for accretion
in the central regions.Comment: 8 pages, 3 figures. Accepted for MNRA
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