85 research outputs found
The environment of weak emission-line quasars
The nature of weak emission-line quasars (WLQs) is probed by comparing the Baldwin effect (BEff) in WLQs and normal quasars [quasi-stellar objects (QSOs)]. We selected 81 high-redshift (z > 2.2) and two intermediate-redshift (z= 1.66 and 1.89) WLQs. Their rest-frame equivalent widths (EWs) of the C iv emission line and their Eddington ratio were obtained from the Sloan Digital Sky Survey Data Release 7 (SDSS DR7) quasar catalogue or from Diamond-Stanic et al. We compare the parameters of WLQs with those of 81 normal quasars from Bright Quasar Survey and 155 radio-quiet and radio-intermediate quasars detected by SDSS and Chandra. The influence of the Eddington ratio, LBol/LEdd, and the X-ray to optical luminosity ratio, αox, on the BEff is analysed. We find that WLQs follow a different relationship on the EW(C iv)-LBol/LEdd plane than normal quasars. This relationship disagrees with the super-Eddington hypothesis. The weakness/absence of emission lines in WLQs does not seem to be caused by their extremely soft ionizing continuum but by low covering factor (Ω/4π) of their broad-line region. Comparison of emission-line intensities indicates that the ratios of high-ionization line and low-ionization line regions (i.e. ΩHIL/ΩLIL) are lower in WLQs than in normal QSOs. The covering factors of the regions producing C iv and Lyα emission lines are similar in both WLQs and QSO
The mass of the black hole in RE J1034+396
The black hole mass measurement in active galaxies is a challenge,
particularly in sources where the reverberation method cannot be applied. We
aim to determine the black hole mass in a very special object, RE J1034+396,
one of the two AGN with QPO oscillations detected in X-rays, and a single
bright AGN with optical band totally dominated by starlight. We fit the stellar
content using the code starlight, and the broad band disk contribution to
optical/UV/X-ray emission is modeled with optxagnf. We also determine the black
hole mass using several other independent methods. Various methods give
contradictory results. Most measurements of the blacc hole mass are in the
range 1.e6-1.e7 Msun, and the measurements based on dynamics give higher values
than measurements based on Hbeta and Mg II emission lines.Comment: A&A, in pres
The flare model for X-ray variability of NGC 4258
We study the variability mechanism of active galactic nuclei (AGN) within the
framework of the flare model. To this end we examine the case of Seyfert/LINER
galaxy NGC 4258, which is observed at high inclination angle and exhibits rapid
fluctuations of the X-ray light curve. We construct a model light curve based
on the assumption of magnetic flares localized in the equatorial plane and
orbiting with Keplerian speed at each given radius. We calculate the level of
variability as a function of the inclination of an observer, taking into
account all effects of general relativity near a rotating supermassive black
hole. The variability level is a monotonic function of the source inclination.
It rises more rapidly for larger values of the black hole spin (Kerr parameter)
and for steeper emissivity (index beta of the radial profile). We compare the
expected level of variability for the viewing angle 81.6 deg, as inferred for
NGC 4258, with the case of moderate viewing angles about 30 deg, typical for
Seyfert type-1 galaxies. Highly inclined sources such as this one are
particularly suitable to test the flare model because the effects of orbital
motion, Doppler boosting and light bending are all expected to have maximum
when the accretion disk is seen almost edge-on. The model is consistent with
the NGC 4258 variability, where the obscuring material is thought to be
localized mainly towards the equatorial plane rather than forming a
geometrically thick torus. Once the intrinsic time-scales of the flare duration
are determined to better precision, this kind of highly inclined objects with a
precisely known mass of the black hole can be used to set independent
constraints on the spin parameter.Comment: 7 pages, 3 figures; Astronomy & Astrophysics (this version includes
minor language corrections
RT Crucis: A look into the X-ray emission of a peculiar symbiotic star
© 2016 ESO.Symbiotic stars are a heterogeneous class of interacting binaries. Among them, RT Cru has been classified as prototype of a subclass that is characterised by hard X-ray spectra that extend past ∼20 keV. We analyse ∼8.6 Ms of archival INTEGRAL data collected during the period 2003-2014, ∼ 140 ks of Swift/XRT data, and a Suzaku observation of 39 ks, to study the spectral X-ray emission and investigate the nature of the compact object. Based on the 2MASS photometry, we estimate the distance to the source of 1.2-2.4 kpc. The X-ray spectrum obtained with Swift/XRT, JEM-X, IBIS/ISGRI, and Suzaku data is well fitted by a cooling flow model modified by an absorber that fully covers the source and two partially covering absorbers. Assuming that the hard X-ray emission of RT Cru originates from an optically thin boundary layer around a non-magnetic white dwarf, we estimated a mass of the white dwarf of MWD ≈ 1.2M⊙. The mass accretion rate obtained for this source might be too high for the optically thin boundary layer scenario. Therefore we investigate other plausible scenarios to model its hard X-ray emission. We show that, alternatively, the observed X-ray spectrum can be explained with the X-ray emission from the post-shock region above the polar caps of a magnetised white dwarf with mass MWD ≈ 0.9-1.1M⊙
SDSS J094533.99+100950.1 - the remarkable weak emission line quasar
Weak emission line quasars are a rare and puzzling group of objects. In this
paper we present one more object of this class found in the Sloan Digital Sky
Survey (SDSS). The quasar SDSS J094533.99+100950.1, lying at z = 1.66, has
practically no C IV emission line, a red continuum very similar to the second
steepest of the quasar composite spectra of Richards et al., is not strongly
affected by absorption and the Mg II line, although relatively weak, is strong
enough to measure the black hole mass. The Eddington ratio in this object is
about 0.45, and the line properties are not consistent with the trends expected
at high accretion rates. We propose that the most probable explanation of the
line properties in this object, and perhaps in all weak emission line quasars,
is that the quasar activity has just started. A disk wind is freshly launched
so the low ionization lines which form close to the disk surface are already
observed but the wind has not yet reached the regions where high ionization
lines or narrow line components are formed. The relatively high occurrence of
such a phenomenon may additionally indicate that the quasar active phase
consists of several sub-phases, each starting with a fresh build-up of the
Broad Line Region.Comment: 10 pages, 3 figures, 5 tables; accepted for publication in MNRA
The final verdict by XMM-Newton: the X-ray obscured Seyfert galaxy NGC5506 has a broad Fe K-alpha line
We present the first unambiguous evidence of a broad (Gaussian width ~330 eV)
component of the iron K-alpha fluorescent emission line in the X-ray obscured
Narrow Line Seyfert 1 Galaxy NGC5506. This is the main results of a
spectroscopic monitoring campaign on this source performed with the XMM-Newton
observatory between February 2001 and January 2009. The broad line lacks
extreme redwards skewness. If modelled with a relativistic component, the
profile of the line is consistent with a flat emissivity radial dependence
(alpha~1.9). The disk inclination (~40 degrees) is nominally larger then
typically observed in unobscured AGN, in agreement with most measurements of
broadened iron lines in Seyfert 2 galaxies. The quality of the data allows us
to decompose the full iron emission line complex, and to study its long-term
(timescales of weeks to years) variability pattern. The intensity of the
neutral and narrow iron K-alpha core remains constant during the monitoring
campaign. This indicates that the optically thick gas responsible for the
non-relativistic reprocessing of the primary AGN continuum in NGC5506 is
probably located in the torus rather than in the optical Broad Line Region.Comment: 11 pages, 8 figures, accepted for publication in MNRA
The environment of weak emission-line quasars
The nature of weak emission-line quasars (WLQs) is probed by comparing the
Baldwin effect (BEff) in WLQs and normal quasars (QSOs). We selected 81
high-redshift (z>2.2) and 2 intermediate-redshift (z=1.66 and 1.89) WLQs. Their
rest-frame equivalent widths (EWs) of the C IV emission-line and their
Eddington ratio were obtained from the Sloan Digital Sky Survey Data Release 7
(SDSS DR7) Quasar Catalogue or from Diamond-Stanic et al. We compare the
parameters of WLQs with these of 81 normal quasars from Bright Quasar Survey
(BQS) and 155 radio-quiet and radio-intermediate quasars detected by SDSS and
Chandra. The influence of the Eddington ratio, Lbol/Ledd, and the X-ray to
optical luminosity ratio,alpha_ox, on the BEff is analysed. We find that WLQs
follow a different relationship on the EW(CIV)-Lbol/Ledd plane than normal
quasars. This relationship disagrees with the super-Eddington hypothesis. The
weakness/absence of emission-lines in WLQs does not seem to be caused by their
extremely soft ionizing continuum but by low covering factor (Omega) of their
broad line region (BLR). Comparing emission-line intensities indicates that the
ratios of high-ionization line and low-ionization line regions (i.e.
Omega_(HIL)/Omega_(LIL)) are lower in WLQs than in normal QSOs. The covering
factor of the regions producing C IV and Lyalpha emission-lines are similar in
both WLQs and QSOs.Comment: 9 pages, 3 figures, 2 tables. Accepted for publication in MNRAS.
Minor changes (corrected typos) to match published versio
Universal spectral shape of high accretion rate AGN
The spectra of quasars and NLS1 galaxies show surprising similarity in their
spectral shape. They seem to scale only with the accretion rate. This is in
contradiction with the simple expectations from the standard disk model which
predicts lower disk temperature for higher black hole mass. Here we consider
two mechanisms modifying the disk spectrum: the irradiation of the outer disk
due to the scattering of the flux by the extended ionized medium (warm absorber
and the development of the warm Comptonizing disk skin under the effect of the
radiation pressure instability. Those two mechanisms seem to lead to a spectrum
which indeed roughly scales, as observed, only with the accretion rate. The
scenario applies only to objects with relatively high luminosity to the
Eddington luminosity ratio for which disk evaporation is inefficient.Comment: 14 pages, 14 figures, 1 table, accepted for publication in A&
Consistency of the black hole mass determination in AGN from the reverberation and the X-ray excess variance method
Values of black hole masses are frequently determined with the help of the
reverberation method. This method requires a specific geometrical factor
related to the distribution of the orbits of the Broad Line Region clouds.
Onken et al. determined the value f^2= 1.37+/-0.45 from the black hole mass -
dispersion relation. In this paper we determine this factor using an
independent mass determination from the X-ray variance method for a number of
Seyfert 1 galaxies and comparing them with the reverberation results by
Peterson et al. We obtain mean value f^2 = 1.12 +/- 0.54, consistent with Onken
et al. Both values are larger than the value 0.75 corresponding to a spherical
geometry. It indicates that most probably all values of the black hole masses
obtained with the use of the Kaspi et al. formulae should be multiplied by a
factor of \sim 1.7. This also shows that the Broad Line Region is rather flat,
and hints for a dependence of the factor f^2 on a source inclination seem to be
present in the data.Comment: 7 pages, 4 figures, 1 table; accepted for publication in MNRA
Constraints on the black hole spin in the quasar SDSS J094533.99+100950.1
The spin of the black hole is an important parameter which may be responsible
for the properties of the inflow and outflow of the material surrounding a
black hole. Broad band IR/optical/UV spectrum of the quasar SDSS
J094533.99+100950.1 is clearly disk-dominated, with the spectrum peaking up in
the observed frequency range. Therefore, disk fitting method usually used for
Galactic black holes can be used in this object to determine the black hole
spin. We develop the numerical code for computing disk properties, including
radius-dependent hardening factor, and we apply the ray-tracing method to
incorporate all general relativity effects in light propagation. We show that
the simple multicolor disk model gives a good fit, without any other component
required, and the disk extends down to the marginally stable orbit. The best
fit accretion rate is 0.13, well below the Eddington limit, and the black hole
spin is moderate, 0.3. The contour error for the fit combined with the
constraints for the black hole mass and the disk inclination gives a constraint
that the spin is lower than 0.8. We discuss the sources of possible systematic
errors in the parameter determinations
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