812 research outputs found
Snowball: strain aware gene assembly of metagenomes
Gregor I, Schönhuth A, McHardy AC. Snowball: strain aware gene assembly of metagenomes. Bioinformatics. 2016;32(17):i649-i657
Implications of the X-ray Variability for the Mass of MCG-6-30-15
The bright Seyfert 1 galaxy \mcg shows large variability on a variety of time
scales. We study the \aproxlt 3 day time scale variability using a set of
simultaneous archival observations that were obtained from \rxte and the {\it
Advanced Satellite for Cosmology and Astrophysics} (\asca). The \rxte\
observations span nearly sec and indicate that the X-ray Fourier Power
Spectral Density has an rms variability of 16%, is flat from approximately
10^{-6} - 10^{-5} Hz, and then steepens into a power law
with \alpha\aproxgt 1. A further steepening to occurs
between 10^{-4}-10^{-3} Hz. The shape and rms amplitude are comparable to what
has been observed in \ngc and \cyg, albeit with break frequencies that differ
by a factor of 10^{-2} and 10^{4}, respectively. If the break frequencies are
indicative of the central black hole mass, then this mass may be as low as
. An upper limit of ks for the relative lag
between the 0.5-2 keV \asca band compared to the 8-15 keV \rxte band was also
found. Again by analogy with \ngc and \cyg, this limit is consistent with a
relatively low central black hole mass.Comment: 5 pages, 3 figures, LaTeX, uses emulateapj.sty and apjfonts.sty,
revised version, accepted for publication in ApJ Letter
Heating of the Intracluster Gas in the Triangulum Australis Cluster
ASCA and ROSAT X-ray data are used to obtain two-dimensional maps of the gas
temperature, pressure and specific entropy in the Triangulum Australis cluster
of galaxies. We find that this hot (T_e=10.3+-0.8 keV) system probably has a
temperature peak (T_e>12 keV) at the cluster core, which approximately
corresponds to the adiabatic relation. An underdense gas sector, found in the
ROSAT cluster image eastward of the core, has a higher temperature than average
at that radius. At this higher temperature, the gas pressure in this region is
equal to that of the rest of the cluster at the same radius, but the specific
entropy of this gas is significantly higher (although the temperature
difference itself is only marginally significant). We speculate that the
existence of this region of underdense high-entropy gas, as well as the
adiabatic central temperature peak, indicate recent or ongoing heating of the
intergalactic medium in this cluster. The most probable source of such heating
is a subcluster merger, for which the hydrodynamic simulations predict a
qualitatively similar temperature structure. We point out that entropy maps can
provide a physically meaningful way of diagnosing merging clusters and
comparing the predictions of merger simulations to the data.Comment: Text revised to give more technical details and clarify discussion.
Accepted for ApJ Letters. Latex, 5 pages incl. figures, macros include
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
Large Scale Fluctuations in the X-Ray Background
We present an attempt to measure the large angular scale fluctuations in the
X-Ray Background (XRB) from the HEAO1-A2 data, expressed in terms of spherical
harmonics. We model the harmonic coefficients assuming a power spectrum and an
epoch-dependent bias parameter, and using a phenomenological scenario
describing the evolution of the X-ray sources. From the few low-order
multipoles detected above shot noise, we estimate the power-spectrum
normalization on scales intermediate between those explored by local galaxy
redshift surveys (~ 100 Mpc) and by the COBE Microwave Background measurements
(~ 1000 Mpc). We find that the HEAO1 harmonics are consistent with present
epoch rms fluctuations of the X-ray sources bx(0)sigma8 ~ 1-2 in 8 Mpc spheres.
Therefore the observed fluctuations in the XRB are roughly as expected from
interpolating between the local galaxy surveys and the COBE CMB experiment. We
predict that an X-ray all-sky surface brightness survey resolving sources a
factor of 10 fainter than HEAO1, may reveal fluctuations to significantly
larger angular scales and therefore more strongly constrain the large scale
structure of the Universe on scales of hundreds of Mpcs.Comment: 14 pages, 3 Postscript figures, uses aaspp4.sty and psfig. Revised
following referee's report. Accepted for publication in Ap
Analysis of attitudes of Turkish citizens towards the effect of European Union membership on the economic, political, and cultural environment
Author's OriginalPrevious studies on Turkeyâs possible accession to the European Union have mostly focused on the level of support for membership as expressed by Turkish citizens. The purpose of this paper is to shed some light on the specific expectations and perceptions of the Turks about the EU membership process, focusing on economic development, democratic progress, economic and political stability, and cultural influence. In both the focus group studies and the final survey, the authors targeted people who have some knowledge about the EU accession process and EU membership, namely, academics and business people.Aybar, C., Mergen, A., Perotti, V., & Reid, D. (2007). Analysis of Attitudes of Turkish Citizens towards the Effect of European Union Membership on the Economic, Political, and Cultural Environment. Turkish Studies, 8(3), 329-348. doi:10.1080/1468384070148908
Redshifts and Neutral Hydrogen Observations of Compact Symmetric Objects in the COINS Sample
Compact Symmetric Objects (CSOs) are young radio galaxies whose jet axes lie
close to the plane of the sky, and whose appearance is therefore not dominated
by relativistic beaming effects. The small linear sizes of CSOs make them
valuable for studies of both the evolution of radio galaxies and testing
unified schemes for active galactic nuclei (AGN). A parsec-scale region of gas
surrounding the central engine is predicted by both accretion and obscuration
scenarios. Working surfaces, or ``hot spots,'' and the radio jets of CSOs are
close enough to the central engines that this circumnuclear gas can be seen in
absorption.
The CSOs Observed in the Northern Sky (COINS) sample is comprised of 52 CSO
candidates identified in three VLBI surveys. Of these, 27 have now been
confirmed as CSOs. Optical redshifts are available in the literature for 28 of
the CSO candidates, and HI absorption has been detected toward four. We present
new optical spectroscopic redshifts for three of the candidates and summarize
the current status of optical identifications. We further report on the
discovery of HI in absorption towards the CSO J1816+3457 and summarize the
results of neutral hydrogen absorption studies of the sources in this sample.Comment: 12 pages, Accepted for publication in Ap
The swan song: the disappearance of the nucleus of NGC 4051 and the echo of its past glory
BeppoSAX observed the low-luminous Seyfert 1 Galaxy NGC4051 in a ultra-dim
X-ray state. The 2-10 keV flux (1.26 x 10^{-12} erg/cm^2/s) was about 20 times
fainter than its historical average value, and remained steady along the whole
observation (~2.3 days). The observed flat spectrum (\Gamma ~ 0.8) and intense
iron line (EW ~600 eV) are best explained assuming that the active nucleus has
switched off, leaving only a residual reflection component visible.Comment: 5 pages, Latex, 3 Postscript figures, accepted for publication in
MNRA
Near-infrared and X-ray obscuration to the nucleus of the Seyfert 2 galaxy NGC 3281
We present the results of a near-infrared and X-ray study of the Seyfert 2
galaxy NGC 3281. Emission from the Seyfert nucleus is detected in both regions
of the electromagnetic spectrum, allowing us to infer both the equivalent line
of sight hydrogen column density, N_H = 71.0(+11.3,-12.3)e26/m^2 and the
extinction due to dust, A_V = 22+/-11 magnitudes (90% confidence intervals). We
infer a ratio of N_H/A_V which is an order of magnitude larger than that
determined along lines of sight in the Milky Way and discuss possible
interpretations. We consider the most plausible explanation to be a dense cloud
in the foreground of both the X-ray and infrared emitting regions which
obscures the entire X-ray source but only a fraction of the much larger
infrared source.Comment: 23 pages including 9 figure
X-ray Fluctuation Power Spectral Densities of Seyfert 1 Galaxies
By combining complementary monitoring observations spanning long, medium and
short time scales, we have constructed power spectral densities (PSDs) of six
Seyfert~1 galaxies. These PSDs span 4 orders of magnitude in temporal
frequency, sampling variations on time scales ranging from tens of minutes to
over a year. In at least four cases, the PSD shows a "break," a significant
departure from a power law, typically on time scales of order a few days. This
is similar to the behavior of Galactic X-ray binaries (XRBs), lower mass
compact systems with breaks on time scales of seconds. NGC 3783 shows tentative
evidence for a doubly-broken power law, a feature that until now has only been
seen in the (much better-defined) PSDs of low-state XRBs. It is also
interesting that (when one previously-observed object is added to make a small
sample of seven), an apparently significant correlation is seen between the
break time scale and the putative black hole mass , while none
is seen between break time scale and luminosity. The data are consistent with
the linear relation T = M_{\rm BH}/10^{6.5} \Msun; extrapolation over 6--7
orders of magnitude is in reasonable agreement with XRBs. All of this
strengthens the case for a physical similarity between Seyfert~1s and XRBs.Comment: 27 pages, 13 figures. Accepted for publication in ApJ. Typo correcte
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