13,840 research outputs found
Double lenses
The analysis of the shear induced by a single cluster on the images of a
large number of background galaxies is all centered around the curl-free
character of a well-known vector field that can be derived from the data. Such
basic property breaks down when the source galaxies happen to be observed
through two clusters at different redshifts, partially aligned along the line
of sight. In this paper we address the study of double lenses and obtain five
main results. (i) First we generalize the procedure to extract the available
information, contained in the observed shear field, from the case of a single
lens to that of a double lens. (ii) Then we evaluate the possibility of
detecting the signature of double lensing given the known properties of the
distribution of clusters of galaxies. (iii) As a different astrophysical
application, we demonstrate how the method can be used to detect the presence
of a dark cluster that might happen to be partially aligned with a bright
cluster studied in terms of statistical lensing. (iv) In addition, we show that
the redshift distribution of the source galaxies, which in principle might also
contribute to break the curl-free character of the shear field, actually
produces systematic effects typically two orders of magnitude smaller than the
double lensing effects we are focusing on. (v) Remarkably, a discussion of
relevant contributions to the noise of the shear measurement has brought up an
intrinsic limitation of weak lensing analyses, since one specific contribution,
associated with the presence of a non-vanishing two-galaxy correlation
function, turns out not to decrease with the density of source galaxies (and
thus with the depth of the observations).Comment: 40 pages, 15 figures. Accepted for publication in ApJ main journa
Parametric Strong Gravitational Lensing Analysis of Abell 1689
(Abridged) We measure the mass distribution of galaxy cluster Abell 1689
within 0.3 Mpc/h_70 of the cluster centre using its strong lensing effect on 32
background galaxies. The multiple images are based on those of Broadhurst et
al. 2005 with some modifications. The cluster profile is explored further out
to ~2.5 Mpc/h_70 with weak lensing shear measurements from Broadhurst et al.
2005b. The masses of ~200 cluster galaxies are measured with Fundamental Plane
in order to accurately model the small scale mass structure in the cluster. The
galaxies are modelled as elliptical truncated isothermal spheres. The dark
matter component of the cluster is described by either non-singular isothermal
ellipsoids (NSIE) or elliptical versions of the universal dark matter profile
(ENFW). We use two dark matter haloes to model the smooth DM in the cluster.
The total mass profile is well described by either an NSIS profile with
sigma=1514+-18 km/s and core radius of r_c=71+-5kpc/h_70, or an NFW profile
with C=6.0+-0.5 and r_200=2.82+-0.11 Mpc/h_70. The errors are assumed to be due
to the error in assigning masses to the individual galaxies in the galaxy
component. The derived total mass is in good agreement with the mass profile of
Broadhurst et al. 05. Using also weak lensing we can constrain the profile
further out to r~2.5 Mpc/h_70. The best fit parameters are then sigma=1499+-15
km/s and r_c=66+-5 kpc/h_70 for the NSIS profile and C=7.6+-0.5 and
r_200=2.55+-0.07 Mpc/h_70 for the NFW profile. Using the same image
configuration as Broadhurst et al. 2005 we obtain a strong lensing model that
is superior to that of Broadhurst et al. 2005 (rms of 2.7'' compared to 3.2'').Comment: 43 pages, 22 figures, submitted to the Monthly Notices of the Royal
Astronomical Society after the first referee report. Full resolution paper
available from http://www.usm.uni-muenchen.de/~halkola/A1689
Implementation of robust image artifact removal in SWarp through clipped mean stacking
We implement an algorithm for detecting and removing artifacts from
astronomical images by means of outlier rejection during stacking. Our method
is capable of addressing both small, highly significant artifacts such as
cosmic rays and, by applying a filtering technique to generate single frame
masks, larger area but lower surface brightness features such as secondary
(ghost) images of bright stars. In contrast to the common method of building a
median stack, the clipped or outlier-filtered mean stacked point-spread
function (PSF) is a linear combination of the single frame PSFs as long as the
latter are moderately homogeneous, a property of great importance for weak
lensing shape measurement or model fitting photometry. In addition, it has
superior noise properties, allowing a significant reduction in exposure time
compared to median stacking. We make publicly available a modified version of
SWarp that implements clipped mean stacking and software to generate single
frame masks from the list of outlier pixels.Comment: PASP accepted; software for download at
http://www.usm.uni-muenchen.de/~dgruen
Strong Lensing Reconstruction
We present a general linear algorithm for measuring the surface mass density
1-\kappa from the observable reduced shear g=\gamma/(1-\kappa) in the strong
lensing regime. We show that in general, the observed polarization field can be
decomposed into ``electric'' and ``magnetic'' components, which have
independent and redundant solutions, but perfectly orthogonal noise properties.
By combining these solutions, one can increase the signal-to-noise ratio by
\sqrt{2}. The solutions allow dynamic optimization of signal and noise, both in
real and Fourier space (using arbitrary smoothing windows). Boundary conditions
have no effect on the reconstructions, apart from its effect on the
signal-to-noise. Many existing reconstruction techniques are recovered as
special cases of this framework. The magnetic solution has the added benefit of
yielding the global and local parity of the reconstruction in a single step.Comment: final accepted version for ApJ
The noise of cluster mass reconstructions from a source redshift distribution
The parameter-free reconstruction of the surface-mass density of clusters of
galaxies is one of the principal applications of weak gravitational lensing.
From the observable ellipticities of images of background galaxies, the tidal
gravitational field (shear) of the mass distribution is estimated, and the
corresponding surface mass density is constructed. The noise of the resulting
mass map is investigated here, generalizing previous work which included mainly
the noise due to the intrinsic galaxy ellipticities. Whereas this dominates the
noise budget if the lens is very weak, other sources of noise become important,
or even dominant, for the medium-strong lensing regime close to the center of
clusters. In particular, shot noise due to a Poisson distribution of galaxy
images, and increased shot noise owing to the correlation of galaxies in
angular position and redshift, can yield significantly larger levels of noise
than that from the intrinsic ellipticities only. We estimate the contributions
from these various effects for two widely used smoothing operations, showing
that one of them effectively removes the Poisson and the correlation noises
related to angular positions of galaxies. Noise sources due to the spread in
redshift of galaxies are still present in the optimized estimator and are shown
to be relevant in many cases. We show how (even approximate) redshift
information can be profitably used to reduce the noise in the mass map. The
dependence of the various noise terms on the relevant parameters (lens
redshift, strength, smoothing length, redshift distribution of background
galaxies) are explicitly calculated and simple estimates are provided.Comment: 18 pages, A&A in pres
On the Reverse Engineering of the Citadel Botnet
Citadel is an advanced information-stealing malware which targets financial
information. This malware poses a real threat against the confidentiality and
integrity of personal and business data. A joint operation was recently
conducted by the FBI and the Microsoft Digital Crimes Unit in order to take
down Citadel command-and-control servers. The operation caused some disruption
in the botnet but has not stopped it completely. Due to the complex structure
and advanced anti-reverse engineering techniques, the Citadel malware analysis
process is both challenging and time-consuming. This allows cyber criminals to
carry on with their attacks while the analysis is still in progress. In this
paper, we present the results of the Citadel reverse engineering and provide
additional insight into the functionality, inner workings, and open source
components of the malware. In order to accelerate the reverse engineering
process, we propose a clone-based analysis methodology. Citadel is an offspring
of a previously analyzed malware called Zeus; thus, using the former as a
reference, we can measure and quantify the similarities and differences of the
new variant. Two types of code analysis techniques are provided in the
methodology, namely assembly to source code matching and binary clone
detection. The methodology can help reduce the number of functions requiring
manual analysis. The analysis results prove that the approach is promising in
Citadel malware analysis. Furthermore, the same approach is applicable to
similar malware analysis scenarios.Comment: 10 pages, 17 figures. This is an updated / edited version of a paper
appeared in FPS 201
Optimizing weak lensing mass estimates for cluster profile uncertainty
Weak lensing measurements of cluster masses are necessary for calibrating
mass-observable relations (MORs) to investigate the growth of structure and the
properties of dark energy. However, the measured cluster shear signal varies at
fixed mass M_200m due to inherent ellipticity of background galaxies,
intervening structures along the line of sight, and variations in the cluster
structure due to scatter in concentrations, asphericity and substructure. We
use N-body simulated halos to derive and evaluate a weak lensing circular
aperture mass measurement M_ap that minimizes the mass estimate variance <(M_ap
- M_200m)^2> in the presence of all these forms of variability. Depending on
halo mass and observational conditions, the resulting mass estimator improves
on M_ap filters optimized for circular NFW-profile clusters in the presence of
uncorrelated large scale structure (LSS) about as much as the latter improve on
an estimator that only minimizes the influence of shape noise. Optimizing for
uncorrelated LSS while ignoring the variation of internal cluster structure
puts too much weight on the profile near the cores of halos, and under some
circumstances can even be worse than not accounting for LSS at all. We briefly
discuss the impact of variability in cluster structure and correlated
structures on the design and performance of weak lensing surveys intended to
calibrate cluster MORs.Comment: 11 pages, 5 figures; accepted by MNRA
The hyaluronan-binding serine protease from human plasma cleaves HMW and LMW kininogen and releases bradykinin
The influence of the hyaluronanbinding protease (PHBSP), a plasma enzyme with FVII- and pro-urokinase-activating potency, on components of the contact phase (kallikrein/kinin) system was investigated. No activation or cleavage of the proenzymes involved in the contact phase system was observed. The procofactor high molecular weight kininogen (HK), however, was cleaved in vitro by PHBSP in the absence of any charged surface, releasing the activated cofactor and the vasoactive nonapeptide bradykinin. Glycosoaminoglycans strongly enhanced the reaction. The cleavage was comparable to that of plasma kallikrein, but clearly different from that of coagulation factor FXIa. Upon extended incubation with PHBSP, the light chain was further processed, partially removing about 60 amino acid residues from the Nterminus of domain D5 of the light chain. These cleavage site(s) were distinct from plasma kallikrein or FXIa cleavage sites. PHBSP and, more interestingly, also plasma kallikrein could cleave low molecular weight kininogen in vitro, indicating that domains D5(H) and D6(H) are no prerequisite for kininogen cleavage. PHBSP was also able to release bradykinin from HK in plasma where the pro-cofactor circulates predominantly in complex with plasma kallikrein or FXI. In conclusion, PHBSP represents a novel kininogen-cleaving and bradykinin-releasing enzyme in plasma that shares significant catalytic similarities with plasma kallikrein. Since they are structurally unrelated in their heavy chains (propeptide), their similar in vivo catalytic activities might be directed at distinct sites where PHBSP could induce processes that are related to the kallikrein/kinin system
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