7,825 research outputs found
The cluster M-T relation from temperature profiles observed with ASCA and ROSAT
We calibrate the galaxy cluster mass - temperature relation using the
temperature profiles of intracluster gas observed with ASCA (for hot clusters)
and ROSAT (for cool groups). Our sample consists of apparently relaxed clusters
for which the total masses are derived assuming hydrostatic equilibrium. The
sample provides data on cluster X-ray emission-weighted cooling flow-corrected
temperatures and total masses up to r_1000. The resulting M-T scaling in the
1-10 keV temperature range is M_1000 = (1.23 +- 0.20)/h_50 10^15 Msun (T/10
keV)^{1.79 +- 0.14} with 90% confidence errors, or significantly (99.99%
confidence) steeper than the self-similar relation M propto T^{3/2}. For any
given temperature, our measured mass values are significantly smaller compared
to the simulation results of Evrard et al. (1996) that are frequently used for
mass-temperature scaling. The higher-temperature subsample (kT > 4 keV) is
consistent with M propto T^{3/2}, allowing the possibility that the
self-similar scaling breaks down at low temperatures, perhaps due to heating by
supernovae that is more important for low-temperature groups and galaxies as
suggested by earlier works.Comment: 8 pages, 2 figures, accepted by Ap
Security of practical private randomness generation
Measurements on entangled quantum systems necessarily yield outcomes that are
intrinsically unpredictable if they violate a Bell inequality. This property
can be used to generate certified randomness in a device-independent way, i.e.,
without making detailed assumptions about the internal working of the quantum
devices used to generate the random numbers. Furthermore these numbers are also
private, i.e., they appear random not only to the user, but also to any
adversary that might possess a perfect description of the devices. Since this
process requires a small initial random seed, one usually speaks of
device-independent randomness expansion.
The purpose of this paper is twofold. First, we point out that in most real,
practical situations, where the concept of device-independence is used as a
protection against unintentional flaws or failures of the quantum apparatuses,
it is sufficient to show that the generated string is random with respect to an
adversary that holds only classical-side information, i.e., proving randomness
against quantum-side information is not necessary. Furthermore, the initial
random seed does not need to be private with respect to the adversary, provided
that it is generated in a way that is independent from the measured systems.
The devices, though, will generate cryptographically-secure randomness that
cannot be predicted by the adversary and thus one can, given access to free
public randomness, talk about private randomness generation.
The theoretical tools to quantify the generated randomness according to these
criteria were already introduced in [S. Pironio et al, Nature 464, 1021
(2010)], but the final results were improperly formulated. The second aim of
this paper is to correct this inaccurate formulation and therefore lay out a
precise theoretical framework for practical device-independent randomness
expansion.Comment: 18 pages. v3: important changes: the present version focuses on
security against classical side-information and a discussion about the
significance of these results has been added. v4: minor changes. v5: small
typos correcte
Dark Matter and Baryon Fraction at the Virial Radius in Abell 2256
We combine ASCA and ROSAT X-ray data to constrain the radial dark matter
distribution in the primary cluster of A2256, free from the isothermality
assumption. Both instruments indicate that the temperature declines with
radius. The region including the central galaxy has a multicomponent spectrum,
which results in a wide range of allowed central temperatures. We find that the
secondary subcluster has a temperature and luminosity typical of a rich
cluster; however, the ASCA temperature map shows no signs of an advanced
merger. It is therefore assumed that the primary cluster is in hydrostatic
equilibrium. The data then require dark matter density profiles steeper than
rho ~ r^-2.5 in its outer part. Acceptable models have a total mass within
r=1.5 Mpc (the virial radius) of 6.0+-1.5 10^14 Msun at the 90% confidence,
about 1.6 times smaller than the mass derived assuming isothermality. Near the
center, dark matter profiles with and without central cusps are consistent with
the data. Total mass inside the X-ray core (r=0.26 Mpc) is 1.28+-0.08 10^14
Msun, which exceeds the isothermal value by a factor of 1.4. Although the
confidence intervals above may be underestimates since they do not include
possible asymmetry and departures from hydrostatic equilibrium, the behavior of
the mass distribution, if applicable to other clusters, can bring into better
agreement X-ray and lensing mass estimates, but aggravate the ``baryon
catastrophe''. The observed considerable increase in the gas content with
radius, not anticipated by simulations, may imply that a significant fraction
of thermal gas energy comes from sources other than gravity and merger shocks.Comment: Added dynamic argument against advanced merger. Latex, 10 pages, 3
figures; uses emulateapj.sty. ApJ in pres
Simulations of galactic winds and starbursts in galaxy clusters
We present an investigation of the metal enrichment of the intra-cluster
medium (ICM) by galactic winds and merger-driven starbursts. We use combined
N-body/hydrodynamic simulations with a semi-numerical galaxy formation model.
The mass loss by galactic winds is obtained by calculating transonic solutions
of steady state outflows, driven by thermal, cosmic ray and MHD wave pressure.
The inhomogeneities in the metal distribution caused by these processes are an
ideal tool to reveal the dynamical state of a galaxy cluster. We present
surface brightness, X-ray emission weighted temperature and metal maps of our
model clusters as they would be observed by X-ray telescopes like XMM-Newton.
We show that X-ray weighted metal maps distinguish between pre- or post-merger
galaxy clusters by comparing the metallicity distribution with the
galaxy-density distribution: pre-mergers have a metallicity gap between the
subclusters, post-mergers a high metallicity between subclusters. We apply our
approach to two observed galaxy clusters, Abell 3528 and Abell 3921, to show
whether they are pre- or post-merging systems. The survival time of the
inhomogeneities in the metallicity distribution found in our simulations is up
to several Gyr. We show that galactic winds and merger-driven starbursts enrich
the ICM very efficiently after z=1 in the central (~ 3 Mpc radius) region of a
galaxy cluster.Comment: 18 pages, 25 figures, 2 tables, accepted for publication in A&A, more
technical details added - results are unaffected, high resolution PDF version
is available at http://astro.uibk.ac.at/Kapferer.pd
Ultra-short silicon-organic hybrid (SOH) modulator for bidirectional polarization-independent operation
We propose a bidirectional, polarization-independent, recirculating IQ-modulator scheme based on the silicon-organic hybrid (SOH) platform. We demonstrate the viability of the concept by using an SOH Mach-Zehnder modulator, operated at 10 GBd BPSK and 2ASK-2PSK
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