167 research outputs found
Nonthermal hard X-ray excess in the cluster Abell 2256 from two epoch observations
After confirmation of the presence of a nonthermal hard X-ray excess with
respect to the thermal emission in the Coma cluster from two independent
observations, obtained using the Phoswich Detection System onboard BeppoSAX, we
present in this Letter also for Abell 2256 the results of two observations
performed with a time interval of about 2.5 yr. In both spectra a nonthermal
excess is present at a confidence level of ~3.3sigma and ~3.7sigma,
respectively. The combined spectrum obtained by adding up the two spectra
allows to measure an excess at the level of ~4.8sigma in the 20-80 keV energy
range. The nonthermal X-ray flux is in agreement with the published value of
the first observation (Fusco-Femiano et al. 2000) and with that measured by a
Rossi X-Ray Timing Explorer observation (Rephaeli & Gruber 2003).Comment: 12 pages, 3 figures, 1 table - ApJL, in pres
On the ICS interpretation of the Hard X-Ray Excesses in Galaxy Clusters: the case of Ophiuchus
(Abridged) High-E electrons produce Hard X-Ray (HXR) emission in galaxy
clusters by via Inverse Compton Scattering (ICS) of CMB photons. We derive the
ICS HXR emission of Ophiuchus under various scenarios: primary cosmic ray
model, secondary cosmic rays model and neutralino DM annihilation scenario. We
further discuss the predictions of the Warming Ray model for the cluster
atmosphere. Under the assumption to fit the observed HXR emission, we find that
the high-E electrons induce various consequences on the cluster atmosphere: i)
primary electrons can be marginally consistent with the data provided that
their spectrum is cutoff at E~30(90) MeV for spectral index of 3.5 (4.4); ii)
secondary electron models from pp collisions are inconsistent with gamma-ray
limits, cosmic ray protons produce too much heating of the IC gas and their
pressure at the cluster center largely exceeds the thermal one; iii) secondary
electron models from DM annihilation are inconsistent with gamma-ray and radio
limits and electrons produce too much heating of the IC gas at the cluster
center, unless the neutralino annihilation cross section is much lower than the
proposed value. We conclude that ICS by secondary electrons from both
neutralino DM annihilation and pp collisions cannot be the mechanism
responsible for the HXR excess emission; primary electrons are still a
marginally viable solution provided that their spectrum has a low-energy cutoff
at E~30-90 MeV. The WR model offers, so far, the best description of the
cluster in terms of temperature distribution, heating, pressure and spectral
energy distribution. Fermi observations of Ophiuchus will set further
constraints to this model.Comment: 10 pages, 9 figures, A&A in pres
Solving the Cooling Flow Problem of Galaxy Clusters by Dark Matter Neutralino Annihilation
Recent X-ray observations revealed that strong cooling flow of intracluster
gas is not present in galaxy clusters, even though predicted theoretically if
there is no additional heating source. I show that relativistic particles
produced by dark matter neutralino annihilation in cluster cores provide a
sufficient heating source to suppress the cooling flow, under reasonable
astrophysical circumstances including adiabatic growth of central density
profile, with appropriate particle physics parameters for dark matter
neutralinos. In contrast to other astrophysical heat sources such as AGNs, this
process is a steady and stable feedback over cosmological time scales after
turned on.Comment: 4 pages, no figure. Accepted to Phys. Rev. Lett. A few minor
revisions and references adde
Orthodontic management of a mandibular double-tooth incisor: A case report
The presence of a double-tooth requires specific complex management due to the need for differential diagnosis and following treatment choices. The aim of this report was to present a rare case of a geminated mandibular lateral incisor, treated with an orthodontic approach. A Caucasian 10.9-year-old girl presented a lower right double-tooth incisor, with a class 1 molar and a class 2 cuspid tendency on both sides. The upper arch was constricted as shown by bilaterally tendencies to cross-bite, a slightly lower midline deviation was reported and a lack of space for all four permanent cuspids was confirmed also by the panoramic X-ray. In the lower arch, there was a severe crowding of about 14 mm and a buccally ectopic left canine. Overbite was normal and Overjet minimally increased. The double-tooth was identified like a geminated tooth, for the presence of one root and one pulp canal of increased size, as shown by the radiographic examinations. The anomalous tooth was managed with an orthodontic approach associated with a progressive stripping to reshape the crown. A two-phase treatment plan was performed, based on first maxillary expansion and lip bumper and then fixed appliances, in order to achieve a proper occlusion and a better aesthetic
Galaxy Clusters in the Swift/BAT era II: 10 more Clusters detected above 15 keV
We report on the discovery of 10 additional galaxy clusters detected in the
ongoing Swift/BAT all-sky survey. Among the newly BAT-discovered clusters there
are: Bullet, Abell 85, Norma, and PKS 0745-19. Norma is the only cluster, among
those presented here, which is resolved by BAT. For all the clusters we perform
a detailed spectral analysis using XMM-Newton and Swift/BAT data to investigate
the presence of a hard (non-thermal) X-ray excess. We find that in most cases
the clusters' emission in the 0.3-200keV band can be explained by a
multi-temperature thermal model confirming our previous results. For two
clusters (Bullet and Abell 3667) we find evidence for the presence of a hard
X-ray excess. In the case of the Bullet cluster, our analysis confirms the
presence of a non-thermal, power-law like, component with a 20-100 keV flux of
3.4 \times 10-12 erg cm-2 s-1 as detected in previous studies. For Abell 3667
the excess emission can be successfully modeled as a hot component (kT=~13keV).
We thus conclude that the hard X-ray emission from galaxy clusters (except the
Bullet) has most likely thermal origin.Comment: Accepted for publication by Ap
An X-ray and optical study of the cluster A33
We report the first detailed X-ray and optical observations of the
medium-distant cluster A33 obtained with the Beppo-SAX satellite and with the
UH 2.2m and Keck II telescopes at Mauna Kea. The information deduced from X-ray
and optical imaging and spectroscopic data allowed us to identify the X-ray
source 1SAXJ0027.2-1930 as the X-ray counterpart of the A33 cluster. The faint,
F_{2-10 keV} \approx 2.4 \times 10^{-13} \ergscm2, X-ray source
1SAXJ0027.2-1930, arcmin away from the optical position of the cluster
as given in the Abell catalogue, is identified with the central region of A33.
Based on six cluster galaxy redshifts, we determine the redshift of A33,
; this is lower than the value derived by Leir and Van Den Bergh
(1977). The source X-ray luminosity, L_{2-10 keV} = 7.7 \times 10^{43} \ergs,
and intracluster gas temperature, keV, make this cluster interesting
for cosmological studies of the cluster relation at intermediate
redshifts. Two other X-ray sources in the A33 field are identified. An AGN at
z0.2274, and an M-type star, whose emission are blended to form an extended
X-ray emission arcmin north of the A33 cluster. A third possibly
point-like X-ray source detected arcmin north-west of A33 lies close
to a spiral galaxy at z0.2863 and to an elliptical galaxy at the same
redshift as the cluster.Comment: 9 pages, 6 Figures, Latex (using psfig,l-aa), to appear in Astronomy
and Astrophysics S. (To get better quality copies of Figs.1-3 send an email
to: [email protected]). A&AS, in pres
Where does the hard X-ray diffuse emission in clusters of galaxies come from?
The surface brightness produced by synchrotron radiation in Clusters of
Galaxies with a radio-halo sets a degenerate constraint on the magnetic field
strength, the relativistic electron density and their spatial distributions.
Using the Coma radio-halo as a case-study, predictions are made for the
brightness profile expected in the 20-80 keV band due to ICS by the
relativistic electrons on the CMB, for a range of central values of the
magnetic field B_0 and models of its radial dependence. We show that the
presence of B-field scalar fluctuations on small scales tends to systematically
depress the electron density required by the radio data, hence to decrease the
ICS brightness expected. These predictions are useful to evaluate the
sensitivity required in future imaging HXR instruments, in order to obtain
direct information on the spatial distribution and content of relativistic
electrons, hence on the magnetic field properties. If compared with the flux in
the Coma HXR tail - interpreted as ICS from within the radius R_h - the
predictions lead to values of B_0 which are lower than those obtained from
Faraday Rotation measurements. The discrepancy is somewhat reduced if the
radio-halo profile is extrapolated out to R_{vir}, i.e. about 3 R_h, or if it
is assumed that B(r) \propto n_{th}(r) (Dolag et al. 2002). Note that in the
latter case, n_{rel}(r) has its minimum value at the center of the cluster. If
real and from ICS, the bulk of the HXR tail should then be contributed by
electrons other than those responsible for the bulk of the radio-halo emission.
This case illustrates the need for spatially resolved spectroscopy in the HXR,
in order to obtain solid information on the non-thermal content of Clusters of
Galaxies.Comment: 11 pages, 13 figures, A&A in pres
The Intragroup versus the Intracluster Medium
Galaxy groups differ from clusters primarily by way of their lower masses, M~10^14 M_sun vs. M~10^15 M_sun. We discuss how mass affects the thermal state of the intracluster or the intragroup medium, specifically as to their entropy levels and radial profiles. We show that entropy is produced in both cases by the continuing inflow of intergalactic gas across the system boundary into the gravitational potential well. The inflow is highly supersonic in clusters, but weakly so in groups. The former condition implies strong accretion shocks with substantial conversion of a large inflow kinetic into thermal energy, whereas the latter condition implies less effective conversion of lower energies. These features produce a conspicuous difference in entropy deposition at the current boundary. Thereafter, adiabatic compression of the hot gas into the potential well converts such time histories into radial profiles throughout a cluster or a group. In addition, in both cases a location of the system at low z in the accelerating universe or in a poor environment will starve out the inflow and the entropy production, and produce flattening or even bending down of the outer profile. We analyze in detail the sharp evidence provided by the two groups ESO 3060170 and RXJ1159+5531 that have been recently observed in X rays out to their virial radii, and find a close and detailed match with our expectations. \ua9 2016. The American Astronomical Society. All rights reserved
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