750 research outputs found
A direct limit on the turbulent velocity of the intracluster medium in the core of Abell 1835 from XMM-Newton
We examine deep XMM-Newton Reflection Grating Spectrometer (RGS) observations
of the X-ray luminous galaxy cluster A1835. For the first time in a galaxy
cluster we place direct limits on turbulent broadening of the emission lines.
This is possible because the coolest X-ray emitting gas in the cluster, which
is responsible for the lines, occupies a small region within the core. The most
conservative determination of the 90 per cent upper limit on line-of-sight,
non-thermal, velocity broadening is 274 km/s, measured from the emission lines
originating within 30 kpc radius. The ratio of turbulent to thermal energy
density in the core is therefore less than 13 per cent. There are no emission
lines in the spectrum showing evidence for gas below ~3.5 keV. We examine the
quantity of gas as a function of temperature and place a limit of 140 Msun/yr
(90 per cent) for gas cooling radiatively below 3.85 keV.Comment: 5 pages, accepted by MNRAS, includes minor change suggested by
refere
The large-scale shock in the cluster of galaxies Hydra A
We analyzed a deep XMM-Newton observation of the cluster of galaxies Hydra A,
focusing on the large-scale shock discovered as a surface brightness
discontinuity in Chandra images. The shock front can be seen both in the
pressure map and in temperature profiles in several sectors. The Mach numbers
determined from the temperature jumps are in good agreement with the Mach
numbers derived from EPIC/pn surface brightness profiles and previously from
Chandra data and are consistent with M~1.3. The estimated shock age in the
different sectors using a spherically symmetric point explosion model ranges
between 130 and 230 Myr and the outburst energy between 1.5 and 3e61 ergs. The
shape of the shock seen in the pressure map can be approximated with an ellipse
centered 70 kpc towards the NE from the cluster center. We aimed to develop a
better model that can explain the offset between the shock center and the AGN
and give a consistent result on the shock age and energy. To this end, we
performed 3D hydrodynamical simulations in which the shock is produced by a
symmetrical pair of AGN jets launched in a spherical galaxy cluster. As an
explanation of the observed offset of the shock center, we consider large-scale
bulk flows in the intracluster medium. The simulation successfully reproduces
the size, ellipticity, and average Mach number of the observed shock front. The
predicted age of the shock is 160 Myr and the total input energy 3e61 erg. Both
values are within the range determined by the spherically symmetric model.
Matching the observed 70 kpc offset of the shock ellipse from the cluster
center requires large-scale coherent motions with a high velocity of 670 km/s.
We discuss the feasibility of this scenario and offer alternative ways to
produce the offset and to further improve the simulation.Comment: 14 pages, accepted for publication in A&A, minor revision compared to
previous versio
Multi-Player Quantum Games
Recently the concept of quantum information has been introduced into game
theory. Here we present the first study of quantum games with more than two
players. We discover that such games can possess a new form of equilibrium
strategy, one which has no analogue either in traditional games or even in
two-player quantum games. In these `pure' coherent equilibria, entanglement
shared among multiple players enables new kinds of cooperative behavior: indeed
it can act as a contract, in the sense that it prevents players from
successfully betraying one-another.Comment: 5 pages, 2 figs. Substantial revisons inc. new result
Alkali and Alkaline Earth Metal Compounds: Core-Valence Basis Sets and Importance of Subvalence Correlation
Core-valence basis sets for the alkali and alkaline earth metals Li, Be, Na,
Mg, K, and Ca are proposed. The basis sets are validated by calculating
spectroscopic constants of a variety of diatomic molecules involving these
elements. Neglect of correlation in K and Ca compounds will lead to
erratic results at best, and chemically nonsensical ones if chalcogens or
halogens are present. The addition of low-exponent functions to the K and
Ca basis sets is essential for smooth convergence of molecular properties.
Inclusion of inner-shell correlation is important for accurate spectroscopic
constants and binding energies of all the compounds. In basis set
extrapolation/convergence calculations, the explicit inclusion of alkali and
alkaline earth metal subvalence correlation at all steps is essential for K and
Ca, strongly recommended for Na, and optional for Li and Mg, while in Be
compounds, an additive treatment in a separate `core correlation' step is
probably sufficient. Consideration of inner-shell correlation energy in
first-row elements requires inclusion of `deep core' correlation
energy in K and Ca for consistency. The latter requires special CCVZ `deep
core correlation' basis sets. For compounds involving Ca bound to
electronegative elements, additional functions in the basis set are
strongly recommended. For optimal basis set convergence in such cases, we
suggest the sequence CV(D+3d)Z, CV(T+2d)Z, CV(Q+)Z, and CV5Z on calcium.Comment: Molecular Physics, in press (W. G. Richards issue); supplementary
material (basis sets in G98 and MOLPRO formats) available at
http://theochem.weizmann.ac.il/web/papers/group12.htm
XMM-Newton Spectroscopy of the Cluster of Galaxies 2A 0335+096
We present here the results of a deep (130 ks) XMM-Newton observation of the
cluster of galaxies 2A 0335+096. The deep exposure allows us to study in detail
its temperature structure and its elemental abundances. We fit three different
thermal models and find that the multi-temperature wdem model fits our data
best. We find that the abundance structure of the cluster is consistent with a
scenario where the relative number of Type Ia supernovae contributing to the
enrichment of the intra-cluster medium is ~25%, while the relative number of
core collapse supernovae is ~75%. Comparison of the observed abundances to the
supernova yields does not allow us to put any constrains on the contribution of
Pop III stars to the enrichment of the ICM. Radial abundance profiles show a
strong central peak of both Type Ia and core collapse supernova products. Both
the temperature and iron abundance maps show an asymmetry in the direction of
the elongated morphology of the surface brightness. In particular the
temperature map shows a sharp change over a brightness edge on the southern
side of the core, which was identified as a cold front in the Chandra data.
This suggests that the cluster is in the process of a merger with a subcluster.
Moreover, we find that the blobs or filaments discovered in the core of the
cluster by Chandra are, contrary to the previous results, colder than the
ambient gas and they appear to be in pressure equilibrium with their
environment.Comment: Accepted for publication in A&A, 19 page
Metal transport by gas sloshing in M87
We present the results of an XMM-Newton mosaic covering the central ~200 kpc
of the nearby Virgo cluster. We focus on a strong surface brightness
discontinuity in the outskirts of the brightest cluster galaxy, M87. Using both
XMM-Newton and Suzaku, we derive accurate temperature and metallicity profiles
across this feature and show that it is a cold front probably due to sloshing
of the Virgo ICM. It is also associated with a discontinuity in the chemical
composition. The gas in the inner, bright region of the front is ~40% more
abundant in Fe than the gas outside the front, suggesting the important role of
sloshing in transporting metals through the ICM. For the first time, we provide
a quantitative estimate of the mass of Fe transported by a cold front. This
amounts to ~6% of the total Fe mass within the radial range affected by
sloshing, significantly more than the amount of metals transported by the AGN
in the same cluster core. The very low Fe abundance of only ~0.2 solar
immediately outside the cold front at a radius of 90 kpc suggests we are
witnessing first-hand the transport of higher metallicity gas into a pristine
region, whose abundance is typical of the cluster outskirts. The Mg/Fe and O/Fe
abundance ratios remain approximately constant over the entire radial range
between the centre of M87 and the faint side of the cold front, which requires
the presence of a centrally peaked distribution not only for Fe but also for
core-collapse type supernova products. This peak may stem from the star
formation triggered as the BCG assembled during the protocluster phase.Comment: accepted for publication in MNRA
Extreme AGN Feedback and Cool Core Destruction in the X-ray Luminous Galaxy Cluster MACS J1931.8-2634
We report on a deep, multiwavelength study of the galaxy cluster MACS
J1931.8-2634 using Chandra X-ray, Subaru optical, and VLA 1.4 GHz radio data.
This cluster (z=0.352) harbors one of the most X-ray luminous cool cores yet
discovered, with an equivalent mass cooling rate within the central 50 kpc is
approximately 700 solar masses/yr. Unique features observed in the central core
of MACSJ1931.8-2634 hint to a wealth of past activity that has greatly
disrupted the original cool core. We observe a spiral of relatively cool,
dense, X-ray emitting gas connected to the cool core, as well as highly
elongated intracluster light (ICL) surrounding the cD galaxy. Extended radio
emission is observed surrounding the central AGN, elongated in the east-west
direction, spatially coincident with X-ray cavities. The power input required
to inflate these `bubbles' is estimated from both the X-ray and radio emission
to reside between 4 and 14e45 erg/s, putting it among the most powerful jets
ever observed. This combination of a powerful AGN outburst and bulk motion of
the cool core have resulted in two X-ray bright ridges to form to the north and
south of the central AGN at a distance of approximately 25 kpc. The northern
ridge has spectral characteristics typical of cool cores and is consistent with
being a remnant of the cool core after it was disrupted by the AGN and bulk
motions. It is also the site of H-alpha filaments and young stars. The X-ray
spectroscopic cooling rate associated with this ridge is approximately 165
solar masses/yr, which agrees with the estimate of the star formation rate from
broad-band optical imaging (170 solar masses/yr). MACS J1931.8-2634 appears to
harbor one of most profoundly disrupted low entropy cores observed in a
cluster, and offers new insights into the survivability of cool cores in the
context of hierarchical structure formation.Comment: 19 pages, 15 figures, 5 tables. Accepted by MNRAS for publication
September 30 201
High-Redshift SDSS Quasars with Weak Emission Lines
We identify a sample of 74 high-redshift quasars (z>3) with weak emission
lines from the Fifth Data Release of the Sloan Digital Sky Survey and present
infrared, optical, and radio observations of a subsample of four objects at
z>4. These weak emission-line quasars (WLQs) constitute a prominent tail of the
Lya+NV equivalent width distribution, and we compare them to quasars with more
typical emission-line properties and to low-redshift active galactic nuclei
with weak/absent emission lines, namely BL Lac objects. We find that WLQs
exhibit hot (T~1000 K) thermal dust emission and have rest-frame 0.1-5 micron
spectral energy distributions that are quite similar to those of normal
quasars. The variability, polarization, and radio properties of WLQs are also
different from those of BL Lacs, making continuum boosting by a relativistic
jet an unlikely physical interpretation. The most probable scenario for WLQs
involves broad-line region properties that are physically distinct from those
of normal quasars.Comment: Updated to match version published in ApJ. 20 pages, 12 figure
Mid-Infrared Properties of the Swift Burst Alert Telescope Active Galactic Nuclei Sample of the Local Universe. I. Emission-Line Diagnostics
We compare mid-infrared emission-line properties, from high-resolution
Spitzer spectra of a hard X-ray (14 -- 195 keV) selected sample of nearby (z <
0.05) AGN detected by the Burst Alert Telescope (BAT) aboard Swift. The
luminosity distribution for the mid-infrared emission-lines, [O IV] 25.89
micron, [Ne II] 12.81 micron, [Ne III] 15.56 micron and [Ne V] 14.32/24.32
micron, and hard X-ray continuum show no differences between Seyfert 1 and
Seyfert 2 populations, however six newly discovered BAT AGNs are under-luminous
in [O IV], most likely the result of dust extinction in the host galaxy. The
overall tightness of the mid-infrared correlations and BAT fluxes and
luminosities suggests that the emission lines primarily arise in gas ionized by
the AGN. We also compare the mid-infrared emission-lines in the BAT AGNs with
those from published studies of ULIRGs, PG QSOs, star-forming galaxies and
LINERs. We find that the BAT AGN sample fall into a distinctive region when
comparing the [Ne III]/[Ne II] and the [O IV]/[Ne III] ratios. These line
ratios are lower in sources that have been previously classified in the
mid-infrared/optical as AGN than those found for the BAT AGN, suggesting that,
in our X-ray selected sample, the AGN represents the main contribution to the
observed line emission. These ratios represent a new emission line diagnostic
for distinguishing between AGN and star forming galaxies.Comment: 54 pages, 9 Figures. Accepted for publication in The Astrophysical
Journal
Entangled state quantum cryptography: Eavesdropping on the Ekert protocol
Using polarization-entangled photons from spontaneous parametric
downconversion, we have implemented Ekert's quantum cryptography protocol. The
near-perfect correlations of the photons allow the sharing of a secret key
between two parties. The presence of an eavesdropper is continually checked by
measuring Bell's inequalities. We investigated several possible eavesdropper
strategies, including pseudo-quantum non-demolition measurements. In all cases,
the eavesdropper's presence was readily apparent. We discuss a procedure to
increase her detectability.Comment: 4 pages, 2 encapsulated postscript files, PRL (tentatively) accepte
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