74 research outputs found
On the relativistic iron line and soft excess in the Seyfert 1 galaxy Markarian 335
We report on a 133 ks XMM-Newton observation of the Seyfert 1 galaxy
Markarian 335. The 0.4-12 keV spectrum contains an underlying power law
continuum, a soft excess below 2 keV, and a double-peaked iron emission feature
in the 6-7 keV range. We investigate the possibility that the double-peaked
emission might represent the characteristic signature of the accretion disc.
Detailed investigations show that a moderately broad, accretion disc line is
most likely present, but that the peaks may be owing to narrower components
from more distant material. The peaks at 6.4 and 7 keV can be identified,
respectively, with the molecular torus in active galactic nucleus unification
schemes, and very highly ionized, optically thin gas filling the torus. The
X-ray variability spectra on both long (~100 ks) and short (~1 ks) timescales
disfavour the recent suggestion that the soft excess is an artifact of
variable, moderately ionized absorption.Comment: 6 pages, 2 figures, accepted for publication in MNRA
What is on Tap? The Role of Spin in Compact Objects and Relativistic Jets
We examine the role of spin in launching jets from compact objects across the
mass scale. Our work includes a total of 37 Seyferts, 11 stellar-mass black
holes, and 13 neutron stars. We find that when the Seyfert reflection lines are
modeled with Gaussian line features (a crude proxy for inner disk radius and
therefore spin), only a slight inverse correlation is found between the
Doppler-corrected radio luminosity at 5 GHz (a proxy for jet power) and line
width. When the Seyfert reflection features are fit with
relativistically-blurred disk reflection models that measure spin, there is a
tentative positive correlation between the Doppler-corrected radio luminosity
and the spin measurement. Further, when we include stellar-mass black holes in
the sample, to examine the effects across the mass scale, we find a slightly
stronger correlation with radio luminosity per unit mass and spin, at a
marginal significance (2.3 sigma confidence level). Finally, when we include
neutron stars, in order to probe lower spin values, we find a positive
correlation (3.3 sigma confidence level) between radio luminosity per unit mass
and spin. Although tentative, these results suggest that spin may have a role
in determining the jet luminosity. In addition, we find a slightly more
significant correlation (4.4 sigma confidence level) between radio luminosity
per Bolometric luminosity and spin, using our entire sample of black holes and
neutrons stars. Again, although tentative, these relations point to the
possibility that the mass accretion rate, i.e. Bolometric luminosity, is also
important in determining the jet luminosity, in addition to spin. Our analysis
suggests that mass accretion rate and disk or coronal magnetic field strength
may be the "throttle" in these compact systems, to which the Eddington limit
and spin may set the maximum jet luminosity that can be achieved.Comment: 14 pages, 13 Figures, ApJ Accepte
The relationship between X-ray variability amplitude and black hole mass in active galactic nuclei
We have investigated the relationship between the 2-10 keV X-ray variability
amplitude and black hole mass for a sample of 46 radio-quiet active galactic
nuclei observed by ASCA. Thirty-three of the objects in our sample exhibited
variability over a time-scale of ~40 ks, and we found a significant
anti-correlation between excess variance and mass. Unlike most previous
studies, we have quantified the variability using nearly the same time-scale
for all objects. Moreover, we provide a prescription for estimating the
uncertainties in excess variance which accounts both for measurement
uncertainties and for the stochastic nature of the variability. We also present
an analytical method to predict the excess variance from a model power spectrum
accounting for binning, sampling and windowing effects. Using this, we modelled
the variance-mass relation assuming all objects have a universal twice-broken
power spectrum, with the position of the breaks being dependent on mass. This
accounts for the general form of the relationship but there is considerable
scatter. We investigated this scatter as a function of the X-ray photon index,
luminosity and Eddington ratio. After accounting for the dependence of excess
variance on mass, we find no significant correlation with either luminosity or
X-ray spectral slope. We do find an anti-correlation between excess variance
and the Eddington ratio, although this relation might be an artifact owing to
the uncertainties in the mass measurements. It remains to be established that
enhanced X-ray variability is a property of objects with steep X-ray slopes or
large Eddington ratios.Comment: 13 pages, 5 figures, accepted for publication in MNRA
Intensive HST, RXTE and ASCA Monitoring of NGC 3516: Evidence Against Thermal Reprocessing
During 1998 April 13-16, NGC 3516 was monitored almost continuously with HST
for 10.3 hr in the UV and 2.8 d in the optical, and simultaneous RXTE and ASCA
monitoring covered the same period. The X-rays were strongly variable with the
soft (0.5-2 keV) showing stronger variations (~65% peak-to-peak) than the hard
(2-10 keV; ~50% peak-to-peak). The optical continuum showed much smaller but
highly significant variations: a slow ~2.5% rise followed by a faster ~3.5%
decline. The short UV observation did not show significant variability.
The soft and hard X-ray light curves were strongly correlated with no
significant lag. Likewise, the optical continuum bands (3590 and 5510 A) were
also strongly correlated with no measurable lag above limits of <0.15 d.
However no significant correlation or simple relationship could be found for
the optical and X-ray light curves. These results appear difficult to reconcile
with previous reports of correlations between X-ray and optical variations and
of measurable lags within the optical band for some other Seyfert 1s.
These results also present serious problems for "reprocessing" models in
which the X-ray source heats a stratified accretion disk which then reemits in
the optical/ultraviolet: the synchronous variations within the optical would
suggest that the emitting region is <0.3 lt-d across, while the lack of
correlation between X-ray and optical variations would indicate, in the context
of this model, that any reprocessing region must be >1 lt-d in size. It may be
possible to resolve this conflict by invoking anisotropic emission or special
geometry, but the most natural explanation appears to be that the bulk of the
optical luminosity is generated by some other mechanism than reprocessing.Comment: 23 pages including 6 figures, accepted for publication in Ap
The Microchannel X-ray Telescope for the Gamma-Ray Burst mission SVOM
We present the Microchannel X-ray Telescope, a new light and compact
focussing telescope that will be flying on the Sino-French SVOM mission
dedicated to Gamma-Ray Burst science. The MXT design is based on the coupling
of square pore micro-channel plates with a low noise pnCCD. MXT will provide an
effective area of about 50 cmsq, and its point spread function is expected to
be better than 3.7 arc min (FWHM) on axis. The estimated sensitivity is
adequate to detect all the afterglows of the SVOM GRBs, and to localize them to
better then 60 arc sec after five minutes of observation.Comment: 12 pages, 8 figures, to be published in SPIE Astronomical Telescopes
+ Instrumentation, Montreal, June 201
An X-ray Bright Nucleus in the Low Surface Brightness Galaxy UGC 6614
We report a study of the X-ray emission from the nuclear region of the low
surface brightness (LSB) galaxy UGC 6614. Very little is known about the
central objects in LSB galaxies especially their X-ray properties and X-ray
spectra. In this study we have used XMM-Newton archival data to study the
characteristics of the X-ray spectrum and the X-ray flux variability of the AGN
in the LSB galaxy UGC 6614. The nucleus of UGC 6614 is very bright in X-ray
emission with an absorption corrected 0.2-10.0 keV luminosity of ~1.1 x 10^{42}
erg s^{-1}. The X-ray spectrum is found to be power-law type with a moderate
column density. A short time scale of intensity variation and large X-ray flux
is indicative of the presence of a black hole at the centre of this galaxy.
Using the method of excess variance, we have determined the black hole mass to
be ~0.12 x 10^{6} solar mass. The X-ray spectral properties are similar to that
of the Seyfert I type AGNs. Our study thus demonstrates that although LSB
galaxies are poor in star formation, they may harbour AGNs with X-ray
properties comparable to that seen in more luminous spiral galaxies.Comment: 5 pages, 4 figures, Accepted for publication in MNRA
Discovery of Water Maser Emission in Five AGN and a Possible Correlation Between Water Maser and Nuclear 2-10 keV Luminosities
We report the discovery of water maser emission in five active galactic
nuclei (AGN) with the 100-m Green Bank Telescope (GBT). The positions of the
newly discovered masers, measured with the VLA, are consistent with the optical
positions of the host nuclei to within 1 sigma (0.3 arcsec radio and 1.3 arcsec
optical) and most likely mark the locations of the embedded central engines.
The spectra of three sources, 2MASX J08362280+3327383, NGC 6264, and UGC 09618
NED02, display the characteristic spectral signature of emission from an
edge-on accretion disk with maximum orbital velocity of ~700, ~800, and ~1300
km s^-1, respectively. We also present a GBT spectrum of a previously known
source MRK 0034 and interpret the narrow Doppler components reported here as
indirect evidence that the emission originates in an edge-on accretion disk
with orbital velocity of ~500 km s^-1. We obtained a detection rate of 12
percent (5 out of 41) among Seyfert 2 and LINER systems with 10000 km s^-1 <
v_sys < 15000 km s^-1. For the 30 nuclear water masers with available hard
X-ray data, we report a possible relationship between unabsorbed X-ray
luminosity (2-10 keV) and total isotropic water maser luminosity, L_{2-10}
proportional to L_{H2O}^{0.5+-0.1}, consistent with the model proposed by
Neufeld and Maloney in which X-ray irradiation and heating of molecular
accretion disk gas by the central engine excites the maser emission.Comment: 16 pages, 5 tables, 3 figures, to appear in the November 10, 2006,
v651n2 issue of the Astrophysical Journa
Hard X-ray spectral variability of the brightest Seyfert AGN in the Swift/BAT sample
Aims: We used data from the 58 month long, continuous Swift/Burst Alert
Telescope (BAT) observations of the five brightest Seyfert galaxies at hard
X-rays, to study their flux and spectral variability in the 20-100 keV energy
band. The column density in these objects is less than 10^24 cm-2, which
implies that the Swift/BAT data allow us to study the "true" variability of the
central source. Results: All objects show significant variations, with an
amplitude which is similar to the AGN variability amplitude at energies below
10 keV. We found evidence for an anti-correlation between variability amplitude
and black hole mass. The light curves in both bands are well correlated, with
no significant delays on time scales as short as 2 days. NGC 4151 and NGC 2110
do not show spectral variability, but we found a significant anti-correlation
between hardness ratios and source flux in NGC 4388 (and NGC 4945, IC 4329, to
a lesser extent). This "softer when brighter" behaviour is similar to what has
been observed at energies below 10 keV, and cannot be explained if the
continuum varies only in flux; the intrinsic shape should also steepen with
increasing flux. Conclusions: The presence of significant flux variations
indicate that the central source in these objects is intrinsically variable on
time scales as short as 1-2 days. The intrinsic slope of the continuum varies
with the flux (at least in NGC 4388). The positive "spectral slope-flux"
correlation can be explained if the temperature of the hot corona decreases
with increasing flux. The lack of spectral variations in two objects, could be
due to the fact that they may operate in a different "state", as their
accretion rate is less than 1% of the Eddington limit (significantly smaller
than the rate of the other three objects in the sample).Comment: Accepted (29/10/11) for publication in A&A (12 pages, containing 14
figures and 2 tables). (Abstract shortened --see link for the complete one
The Sloan Digital Sky Survey Reverberation Mapping Project: the XMM-Newton X-ray source catalog and multi-band counterparts
The XMM-RM project was designed to provide X-ray coverage of the Sloan
Digital Sky Survey Reverberation Mapping (SDSS-RM) field. 41 XMM-Newton
exposures, placed surrounding the Chandra AEGIS field, were taken, covering an
area of 6.13 deg^2 and reaching a nominal exposure depth of ~15 ks. We present
an X-ray catalog of 3553 sources detected in these data, using a PSF-fitting
algorithm and a sample selection threshold that produces a ~5% fraction of
spurious sources. In addition to the PSF-fitting likelihood, we calculate a
second source reliability measure based on Poisson theory using source and
background counts within an aperture. Using the Poissonian likelihood, we
select a sub-sample with a high purity and find that it has similar number
count profiles to previous X-ray surveys. The Bayesian method "NWAY" was
employed to identify counterparts of the X-ray sources from the optical Legacy
and the IR unWISE catalogs, using a 2-dimensional unWISE magnitude-color prior
created from optical/IR counterparts of Chandra X-ray sources. A significant
number of the optical/IR counterparts correspond to sources with low detection
likelihoods, proving the value of retaining the low-likelihood detections in
the catalog. 932 of the XMM-RM sources are covered by SDSS spectroscopic
observations. 89% of them are classified as AGN, and 71% of these AGN are in
the SDSS-RM quasar catalog. Among the SDSS-RM quasars, 80% are detectable at
the depth of the XMM observations.Comment: ApJS accepted. 20 pages, 16 figure
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