262 research outputs found
Spectral analysis of a large sample of BeppoSAX Seyfert spectra with Comptonization models: Preliminary results
We present preliminary results of the spectral analysis of a large sample of
Seyfert galaxies observed by BeppoSAX. The only selection criterium was a
sufficiently large S/N ratio (>10) in the PDS band (12-200 keV) to allow good
detection up to the highest energy. The resulting sample is composed of 28
objects (17 Seyfert 1, 11 Seyfert 2) and 50 observations. Our main effort here
is to adopt Comptonization models to fit the different spectra on a truly broad
band basis (0.1-200 keV). We use two distinct disc-corona configurations, an
anisotropic slab and an isotropic spherical one. We discuss the distributions
of the physical parameters, like temperature and optical depth of the corona
and the reflection component, among this sample. We also discussed the
existence (or inexistence) of correlations between these parameters.Comment: 4 pages, 2 figures. Proc. of the meeting: "The Restless High-Energy
Universe" (Amsterdam, The Netherlands), E.P.J. van den Heuvel, J.J.M. in 't
Zand, and R.A.M.J. Wijers Ed
CIV and CIII] reverberation mapping of the luminous quasar PG 1247+267
So far the masses of about 50 active galactic nuclei have been measured
through the reverberation mapping technique (RM). Most measurements have been
performed for objects of moderate luminosity and redshift, based on H,
which is also used to calibrate the scaling relation which allows single-epoch
(SE) mass determination based on AGN luminosity and the width of different
emission lines. The SE mass obtained from CIV line shows a
large spread around mean values, due to complex structure and gas dynamics of
the relevant emission region. Direct RM measures of CIV exist for only 6 AGNs
of low luminosity and redshift, and only one luminous quasar (Kaspi et al
2007). We have collected since 2003 photometric and spectroscopic observations
of PG1247+267, the most luminous quasar ever analyzed for RM. We provide light
curves for the continuum and for CIV and
CIII], and measures of the reverberation time lags based on the
SPEAR method (Zu et al. 2011). The sizes of the line emission regions are in a
ratio , similar to the case of Seyfert galaxies,
indicating for the first time a similar ionization stratification in a luminous
quasar and low luminosity nuclei. Due to relatively small broad line region
size and relatively narrow line widths, we estimate a small mass and an
anomalously high Eddington ratio. We discuss the possibility that either the
shape of the emission region or an amplification of the luminosity caused by
gravitational lensing may be in part responsible of the result.Comment: 10 pagese, 6 figures, 3 tables, Accepted for publication in Ap
Have we detected the most luminous ULX so far?
We report the XMM-Newton detection of a moderately bright X-ray source
superimposed on the outer arms of the inactive spiral galaxy MCG-03-34-63
(z=0.0213). It is clearly offset from the nucleus (by about 19'') but well
within the D25 ellipse of the galaxy, just along its bar axis. The field has
also been observed with the HST enabling us to compute a lower limit of > 94 on
the X-ray to optical flux ratio which, together with the X-ray spectrum of the
source, argues against a background AGN. On the other hand, the detection of
excess X-ray absorption and the lack of a bright optical counterpart argue
against foreground contamination. Short-timescale variability is observed,
ruling out the hypothesis of a particularly powerful supernova. If it is
associated with the apparent host galaxy, the source is the most powerful ULX
detected so far with a peak luminosity of 1.35x10^41 erg/s in the 0.5-7 keV
band. If confirmed by future multi-wavelength observations, the inferred
bolometric luminosity (about 3x10^41 erg/s) requires a rather extreme beaming
factor (larger than 115) to accommodate accretion onto a stellar-mass black
hole of 20 solar masses and the source could represent instead one of the best
intermediate-mass black hole candidate so far. If beaming is excluded, the
Eddington limit implies a mass of >2300 solar masses for the accreting compact
object.Comment: MNRAS Letters in press; minor correction at the end of Section
Probing variability patterns of the Fe K line complex in bright nearby AGNs
The unprecedented sensitivity of current X-ray telescopes allows for the
first time to address the issue of the Fe K line complex variability patterns
in bright, nearby AGNs. We examine XMM-Newton observations of the brightest
sources of the FERO sample of radio-quiet type 1 AGNs with the aim of
characterizing the temporal behaviour of Fe K complex features. A systematic
mapping of residual flux above and below the continuum in the 4-9 keV range is
performed in the time vs energy domain, with the purpose of identifying
interesting spectral features in the three energy bands: 5.4-6.1 keV, 6.1-6.8
keV and 6.8-7.2 keV, corresponding respectively to the redshifted, rest frame
and blueshifted or highly ionized Fe Kalpha line bands. The variability
significance is assessed by extracting light curves and comparing them with
MonteCarlo simulations. The time-averaged profile of the Fe K complex revealed
spectral complexity in several observations. Red- and blue-shifted components
(either in emission or absorption) were observed in 30 out of 72 observations,
with an average ~90 eV for emission and ~ -30 eV for absorption
features. We detected significant line variability (with confidence levels
ranging between 90% and 99.7%) within at least one of the above energy bands in
26 out of 72 observations on time scales of ~6-30 ks. Reliability of these
features has been carefully calculated using this sample and has been assessed
at ~3sigma confidence level. This work increases the currently scanty number of
detections of variable, energy shifted, Fe lines and confirms the reliability
of the claimed detections. We found that the distribution of detected features
is peaked at high variability significances in the red- and blue-shifted energy
bands, suggesting an origin in a relativistically modified accretion flow.Comment: Accepted for publication in Astronomy & Astrophysic
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