1,177 research outputs found
Strong support for the millisecond pulsar origin of the Galactic center GeV excess
Using gamma-ray data from the Fermi Large Area Telescope, various groups have
identified a clear excess emission in the Inner Galaxy, at energies around a
few GeV. This excess resembles remarkably well a signal from dark-matter
annihilation. One of the most compelling astrophysical interpretations is that
the excess is caused by the combined effect of a previously undetected
population of dim gamma-ray sources. Because of their spectral similarity, the
best candidates are millisecond pulsars. Here, we search for this hypothetical
source population, using a novel approach based on wavelet decomposition of the
gamma-ray sky and the statistics of Gaussian random fields. Using almost seven
years of Fermi-LAT data, we detect a clustering of photons as predicted for the
hypothetical population of millisecond pulsar, with a statistical significance
of 10.0 sigma. For plausible values of the luminosity function, this population
explains 100% of the observed excess emission. We argue that other
extragalactic or Galactic sources, a mismodeling of Galactic diffuse emission,
or the thick-disk population of pulsars are unlikely to account for this
observation.Comment: 6+10 pages, 3+10 figures, 1 table; v2 updated to pass 8 Fermi data,
additional supplemental material with extended discussion (conclusions
unchanged); v3 matches PRL version with further checks (conclusions
unchanged
Enhancing Electroretinogram Classification with Multi-Wavelet Analysis and Visual Transformer
The electroretinogram (ERG) is a clinical test that records the retina's electrical response to light. Analysis of the ERG signal offers a promising way to study different retinal diseases and disorders. Machine learning-based methods are expected to play a pivotal role in achieving the goals of retinal diagnostics and treatment control. This study aims to improve the classification accuracy of the previous work using the combination of three optimal mother wavelet functions. We apply Continuous Wavelet Transform (CWT) on a dataset of mixed pediatric and adult ERG signals and show the possibility of simultaneous analysis of the signals. The modern Visual Transformer-based architectures are tested on a time-frequency representation of the signals. The method provides 88% classification accuracy for Maximum 2.0 ERG, 85% for Scotopic 2.0, and 91% for Photopic 2.0 protocols, which on average improves the result by 7.6% compared to previous work
A FIRST DETERMINATION OF THE SURFACE DENSITY OF GALAXY CLUSTERS AT VERY LOW X--RAY FLUXES
We present the first results of a serendipitous search for clusters of
galaxies in deep ROSAT-PSPC pointed observations at high galactic latitude. The
survey is being carried out using a Wavelet based Detection Algorithm which is
not biased against extended, low surface brightness sources. A new
flux--diameter limited sample of 10 cluster candidates has been created from
surveyed area. Preliminary CCD observations have revealed
that a large fraction of these candidates correspond to a visible enhancement
in the galaxy surface density, and several others have been identified from
other surveys. We believe these sources to be either low--moderate redshift
groups or intermediate to high redshift clusters. We show X-ray and optical
images of some of the clusters identified to date. We present, for the first
time, the derived number density of the galaxy clusters to a flux limit of (0.5--2.0 keV). This extends the -- of previous cluster surveys by more than one decade in flux.
Results are compared to theoretical predictions for cluster number counts.Comment: uuencoded compressed Postscript, 7 pages including 4 figures.
Accepted for publication in Ap. J. Letters
A Chandra Study of Temperature Substructures in Intermediate-Redshift Galaxy Clusters
By analyzing the gas temperature maps created from the Chandra archive data,
we reveal the prevailing existence of temperature substructures on ~100 kpc
scales in the central regions of nine intermediate-redshift (z~0.1) galaxy
clusters, which resemble those found in the Virgo and Coma Clusters. Each
substructure contains a clump of hot plasma whose temperature is about 2-3 keV
higher than the environment, corresponding to an excess thermal energy of
~1E58-1E60 erg per clump. Since if there were no significant non-gravitational
heating sources, these substructures would have perished in 1E8-1E9 yrs due to
thermal conduction and turbulent flows, whose velocity is found to range from
about 200 to 400 km/s, we conclude that the substructures cannot be created and
sustained by inhomogeneous radiative cooling. We also eliminate the
possibilities that the temperature substructures are caused by supernova
explosions, or by the non-thermal X-ray emission due to the
inverse-Comptonization of the CMB photons. By calculating the rising time of
AGN-induced buoyant bubbles, we speculate that the intermittent AGN outbursts
(~ 1E60 erg per burst) may have played a crucial role in the forming of the
high temperature substructures. Our results are supported by recent study of
McNamara & Nulsen (2007), posing a tight observational constraint on future
theoretical and numerical studies.Comment: 31 pages, 7 figures, ApJ accepte
Scale-Dependent Functions, Stochastic Quantization and Renormalization
We consider a possibility to unify the methods of regularization, such as the
renormalization group method, stochastic quantization etc., by the extension of
the standard field theory of the square-integrable functions to the theory of functions that depend on coordinate
and resolution . In the simplest case such field theory turns out to be a
theory of fields defined on the affine group ,
, which consists of dilations and translation of
Euclidean space. The fields are constructed using the
continuous wavelet transform. The parameters of the theory can explicitly
depend on the resolution . The proper choice of the scale dependence
makes such theory free of divergences by construction.Comment: Published in SIGMA (Symmetry, Integrability and Geometry: Methods and
Applications) at http://www.emis.de/journals/SIGMA
The Brera Multi-scale Wavelet (BMW) ROSAT HRI source catalog. II: application to the HRI and first results
The wavelet detection algorithm (WDA) described in the accompanying paper by
Lazzati et al. is made suited for a fast and efficient analysis of images taken
with the High Resolution Imager (HRI) instrument on board the ROSAT satellite.
An extensive testing is carried out on the detection pipeline: HRI fields with
different exposure times are simulated and analysed in the same fashion as the
real data. Positions are recovered with few arcsecond errors, whereas fluxes
are within a factor of two from their input values in more than 90% of the
cases in the deepest images. At variance with the ``sliding-box'' detection
algorithms, the WDA provides also a reliable description of the source
extension, allowing for a complete search of e.g. supernova remnant or cluster
of galaxies in the HRI fields. A completeness analysis on simulated fields
shows that for the deepest exposures considered (~120 ks) a limiting flux of
\~3x10^{-15} erg/cm2/s can be reached over the entire field of view. We test
the algorithm on real HRI fields selected for their crowding and/or presence of
extended or bright sources (e.g. cluster of galaxies and of stars, supernova
remnants). We show that our algorithm compares favorably with other X-ray
detection algorithms such as XIMAGE and EXSAS. A complete catalog will result
from our analysis: it will consist of the Brera Multi-scale Wavelet Bright
Source Catalog (BMW-BSC) with sources detected with a significance >4.5 sigma
and of the Faint Source Catalog (BMW-FSC) with sources at >3.5 sigma. A
conservative estimate based on the extragalactic log(N)-log(S) indicates that
at least 16000 sources will be revealed in the complete analysis of the whole
HRI dataset.Comment: 6 pages, 11 PostScript figures, 1 gif figure, ApJ in pres
The Brera Multi-scale Wavelet Chandra Survey. I. Serendipitous source catalogue
We present the BMW-Chandra source catalogue drawn from essentially all
Chandra ACIS-I pointed observations with an exposure time in excess of 10ks
public as of March 2003 (136 observations). Using the wavelet detection
algorithm developed by Lazzati et al. (1999) and Campana et al. (1999), which
can characterise both point-like and extended sources, we identified 21325
sources. Among them, 16758 are serendipitous, i.e. not associated with the
targets of the pointings, and do not require a non-automated analysis. This
makes our catalogue the largest compilation of Chandra sources to date. The
0.5--10 keV absorption corrected fluxes of these sources range from ~3E-16 to
9E-12 erg cm^-2 s^-1 with a median of 7E-15 erg cm^-2 s^-1. The catalogue
consists of count rates and relative errors in three energy bands (total,
0.5-7keV; soft, 0.5-2keV; and hard, 2-7keV), and source positions relative to
the highest signal-to-noise detection among the three bands. The wavelet
algorithm also provides an estimate of the extension of the source. We include
information drawn from the headers of the original files, as well, and
extracted source counts in four additional energy bands, SB1 (0.5-1keV), SB2
(1-2keV), HB1 (2-4keV), and HB2 (4-7keV). We computed the sky coverage for the
full catalogue and for a subset at high Galactic latitude (|b|> 20deg). The
complete catalogue provides a sky coverage in the soft band (0.5-2keV, S/N =3)
of ~8 deg^2 at a limiting flux of 1E-13 erg cm^-2 s^-1, and ~2 deg^2 at a
limiting flux of ~1E-15 erg cm^-2 s^-1.Comment: Accepted by A&A, Higher res. Figs 4 and 5 at
http://www.ifc.inaf.it/~romano/BMC/Docs/aapaper/9601f4.eps
http://www.ifc.inaf.it/~romano/BMC/Docs/aapaper/9601f5.eps, Catalog Web
pages: http://www.brera.inaf.it/BMC/bmc_home.html
http://www.ifc.inaf.it/~romano/BMC/bmc_home.html (Mirror
The Burst Cluster: Dark Matter in a Cluster Merger Associated with the Short Gamma Ray Burst, GRB 050509B
We have identified a merging galaxy cluster with evidence of two distinct
sub-clusters. The X-ray and optical data suggest that the subclusters are
moving away from each other after closest approach. This cluster merger was
discovered from observations of the well localized short-duration gamma-ray
burst (GRB), GRB 050509B. The Swift/Burst Alert Telescope (BAT) source position
is coincident with a cluster of galaxies ZwCl 1234.0+02916. The subsequent
Swift/X-Ray Telescope (XRT) localization of the X-ray afterglow found the GRB
coincident with 2MASX J12361286+2858580, a giant red elliptical galaxy in the
cluster. Deep multi-epoch optical images were obtained to constrain the
evolution of the GRB afterglow, including a 27480s exposure in the F814W band
with Hubble Space Telescope Advanced Camera for Surveys (ACS), among the
deepest imaging ever obtained towards a known galaxy cluster in a single
passband. We perform a weak gravitational lensing analysis, including mapping
the total mass distribution of the merger system. Combined with Chandra X-ray
Observatory and Swift/XRT observations, we investigate the dynamical state of
the merger to probe the nature of the dark matter component. Our weak
gravitational lensing measurements reveal a separation of the X-ray centroid of
the western subcluster from the center of the mass and galaxy light
distributions, similar to that of the famous "Bullet cluster". We conclude that
the "Burst cluster" is another candidate merger system for determining the
nature of dark matter and for studying the environment of short GRBs. We
discuss connections between the cluster dynamical state and/or matter
composition and compact object mergers, the leading model for the origin of
short GRBs. Finally, we present results from a weak lensing survey based on
archival Very Large Telescope (VLT) images in the areas of 5 other short GRBs.Comment: 17 pages, 7 figures, accepted by Ap
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