675 research outputs found
Discovery of multiple Lorentzian components in the X-ray timing properties of the Narrow Line Seyfert 1 Ark 564
We present a power spectral analysis of a 100 ksec XMM-Newton observation of
the narrow line Seyfert 1 galaxy Ark~564. When combined with earlier RXTE and
ASCA observations, these data produce a power spectrum covering seven decades
of frequency which is well described by a power law with two very clear breaks.
This shape is unlike the power spectra of almost all other AGN observed so far,
which have only one detected break, and resemble Galactic binary systems in a
soft state. The power spectrum can also be well described by the sum of two
Lorentzian-shaped components, the one at higher frequencies having a hard
spectrum, similar to those seen in Galactic binary systems. Previously we have
demonstrated that the lag of the hard band variations relative to the soft band
in Ark 564 is dependent on variability time-scale, as seen in Galactic binary
sources. Here we show that the time-scale dependence of the lags can be
described well using the same two-Lorentzian model which describes the power
spectrum, assuming that each Lorentzian component has a distinct time lag. Thus
all X-ray timing evidence points strongly to two discrete, localised, regions
as the origin of most of the variability. Similar behaviour is seen in Galactic
X-ray binary systems in most states other than the soft state, i.e. in the
low-hard and intermediate/very high states. Given the very high accretion rate
of Ark 564 the closest analogy is with the very high (intermediate) state
rather than the low-hard state. We therefore strengthen the comparison between
AGN and Galactic binary sources beyond previous studies by extending it to the
previously poorly studied very high accretion rate regime.Comment: 11 pages, 11 figures, accepted for publication in MNRA
Tumour antigenicity in ovarian cancer.
The blastogenic response to a crude cell extract of ovarian cancer cells has been studied in 48 patients with ovarian cancer (9, autologous, 39 allogeneic), in 26 female controls matched for age and in 18 female patients with other types of cancer in remission from disease. The responses in ovarian cancer patients in remission and relapse were considered separately. The blastogenic responses to cell extracts of foetal ovary, foetal lung, foetal liver and normal adult ovary were also assessed in a proportion of all 3 groups. The blastogenic responses to ovarian cancer and foetal ovary cell extracts were found to be significantly greater in the ovarian cancer patients in remission than in the controls, but the responses to ovarian cancer extract were not greater in the relapse group or in patients with other cancers. As a blastogenic response to normal ovarian extract was also present in some of these patients, the data so far do not support the hypothesis of a tumour specific antigen. This tumour associated response may be occurring to determinants in foetal or adult ovarian tissue to which the patient becomes sensitized in malignant disease. The response is complex and the nature of the antigen requires further analysis
The HST Survey of BL Lacertae Objects. I. Surface Brightness Profiles, Magnitudes, and Radii of Host Galaxies
We report on a large HST imaging survey of BL Lac objects, at spatial
resolution ~10 times better than previous ground-based surveys. We focus on
data reduction and analysis, describing the procedures used to model the host
galaxy surface brightness radial profiles. A total of 69 host galaxies were
resolved out of 110 objects observed, including almost all sources at z < 0.5.
We classify them morphologically by fitting with either an exponential disk or
a de~Vaucouleurs profile; when one fit is preferred over the other, in 58 of 69
cases, it is invariably the elliptical morphology. This is a very strong result
given the large number of BL Lac objects, the unprecedented spatial resolution,
and the homogeneity of the data set. With the present reclassification of the
host galaxy of 1418+546 as an elliptical, there remain no undisputed examples
of a disk galaxy hosting a BL Lac nucleus. This implies that, at 99%
confidence, fewer than 7% of BL Lacs can be in disk galaxies. The apparent
magnitude of the host galaxies varies with distance as expected if the absolute
magnitudes are approximately the same, with a spread of +-1 mag, out to
redshift z < 0.5. At larger redshifts, only 6 of 23 BL Lacs are resolved so the
present data do not constrain possible luminosity evolution of the host
galaxies. The collective Hubble diagram for BL Lac host galaxies and radio
galaxies strongly supports their unification.Comment: Accepted for publication on ApJS. 43 pages. 10 figures. Figure 1 can
also be downloaded from http://icarus.stsci.edu/~scarpa/tmp/hst_figure1.ta
The warm absorber in NGC 5548: The lean years
We study the variability of the warm absorber and the gas responsible for the
emission lines in the Seyfert 1 galaxy NGC 5548, in order to constrain the
location and physical properties of these components. Using X-ray spectra taken
with the \textit{Chandra}LETGS in 2002 and 2005, we study variability in the
ionic column densities and line intensities. We find a lower \ion{O}{vii}
forbidden emission line flux in 2005, while the Fe K line flux stays
constant. The warm absorber is less ionized in 2005, allowing us to constrain
its location to within 7 pc of the central source. Using both the observed
variability and the limit on the FWHM of the \ion{O}{vii} f line, we have
constrained the location of the narrow line region to a distance of 1 pc from
the central source. The apparent lack of variability of the Fe K line
flux does not allow for a unique explanation.Comment: 6 pages, 6 figures, accepted by A&
Fourier-resolved energy spectra of the Narrow Line Seyfert 1 Mkn 766
We compute Fourier-resolved X-ray spectra of the Seyfert 1 Markarian 766 to
study the shape of the variable components contributing to the 0.3-10 keV
energy spectrum and their time-scale dependence. The fractional variability
spectra peak at 1-3 keV, as in other Seyfert 1 galaxies, consistent with either
a constant contribution from a soft excess component below 1 keV and Compton
reflection component above 2 keV, or variable warm absorption enhancing the
variability in the 1-3 keV range. The rms spectra, which shows the shape of the
variable components only, is well described by a single power law with an
absorption feature around 0.7 keV, which gives it an apparent soft excess. This
spectral shape can be produced by a power law varying in normalisation,
affected by an approximately constant (within each orbit) warm absorber, with
parameters similar to those found by Turner et al. for the warm-absorber layer
covering all spectral components in their scattering scenario. The total soft
excess in the average spectrum can therefore be produced by a combination of
constant warm absorption on the power law plus an additional less variable
component. On shorter time-scales, the rms spectrum hardens and this evolution
is well described by a change in power law slope, while the absorption
parameters remain the same. The frequency dependence of the rms spectra can be
interpreted as variability arising from propagating fluctuations through an
extended emitting region, whose emitted spectrum is a power law that hardens
towards the centre. This scenario reduces the short time-scale variability of
lower energy bands making the variable spectrum harder on shorter time-scales
and at the same time explains the hard lags found in these data by Markowitz et
al.Comment: accepted for publication in MNRA
Novel experimental setup for MHz X-ray diffraction in the Diamond Anvil Cell at the High Energy Density (HED) Instrument of the European X-ray Free Electron Laser
Dating COINS: Kinematic Ages for Compact Symmetric Objects
We present multi-epoch VLBA observations of Compact Symmetric Objects (CSOs)
from the COINS sample (CSOs Observed In the Northern Sky). These observations
allow us to make estimates of, or place limits on, the kinematic ages for those
sources with well-identified hot spots. This study significantly increases the
number of CSOs with well-determined ages or limits. The age distribution is
found to be sharply peaked under 500 years, suggesting that many CSOs die
young, or are episodic in nature, and very few survive to evolve into FR II
sources like Cygnus A. Jet components are found to have higher velocities than
hot spots which is consistent with their movement down cleared channels. We
also report on the first detections of significant polarization in two CSOs,
J0000+4054 (2.1%) and J1826+1831 (8.8%). In both cases the polarized emission
is found in jet components on the stronger side of the center of activity.Comment: 34 pages including 7 figures, Accepted to ApJ on Dec 7, 200
Frenkel line and solubility maximum in supercritical fluids
This research utilised Queen Maryâs MidPlus computational
facilities, supported by QMUL Research-IT and funded
by EPSRC Grant EP/K000128/1. K.T. is grateful to EPSRC,
C.Y. to CSC. V.V.B. is grateful to RSF (14-2200093) for
financial support
Chandra Observations of Galaxy Cluster Abell 2218
We present results from two observations (combined exposure of ~17 ks) of
galaxy cluster A2218 using the Advanced CCD Imaging Spectrometer on board the
Chandra X-ray Observatory that were taken on October 19, 1999. Using a
Raymond-Smith single temperature plasma model corrected for galactic absorption
we find a mean cluster temperature of kT = 6.9+/-0.5 keV, metallicity of
0.20+/-0.13 (errors are 90 % CL) and rest-frame luminosity in the 2-10 keV
energy band of 6.2x10^{44} erg/s in a LambdaCDM cosmology with H_0=65 km/s/Mpc.
The brightness distribution within 4'.2 of the cluster center is well fit by a
simple spherical beta model with core radius 66".4 and beta = 0.705 . High
resolution Chandra data of the inner 2' of the cluster show the x-ray
brightness centroid displaced ~22" from the dominant cD galaxy and the presence
of azimuthally asymmetric temperature variations along the direction of the
cluster mass elongation. X-ray and weak lensing mass estimates are in good
agreement for the outer parts (r > 200h^{-1}) of the cluster; however, in the
core the observed temperature distribution cannot reconcile the x-ray and
strong lensing mass estimates in any model in which the intracluster gas is in
thermal hydrostatic equilibrium. Our x-ray data are consistent with a scenario
in which recent merger activity in A2218 has produced both significant
non-thermal pressure in the core and substructure along the line of sight; each
of these phenomena probably contributes to the difference between lensing and
x-ray core mass estimates.Comment: 33 pages, 6 figures, uses AASTeX 5.02, ApJ submitte
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