11,103 research outputs found
XMM-Newton unveils the type 2 nature of the BLRG 3C 445
We present an observation of XMM-Newton that unambiguously reveals the
``Seyfert 2'' nature of the Broad Line Radio Galaxy 3C 445. For the first time
the soft excess of this source has been resolved. It consists of unobscured
scattered continuum flux and emission lines, likely produced in a warm
photoionized gas near the pole of an obscuring torus. The presence of
circumnuclear (likely stratified) matter is supported by the complex
obscuration of the nuclear region. Seventy percent of the nuclear radiation
(first component) is indeed obscured by a column density ~4*10^{23} cm^{-2},
and 30 % (second component) is filtered by ~7* 10^{22} cm^{-2}. The first
component is nuclear radiation directly observed by transmission through the
thicker regions. The second one is of more uncertain nature. If the observer
has a deep view into the nucleus but near the edge of the torus, it could be
light scattered by the inner wall of the torus and/or by photoionized gas
within the Broad Line Region observed through the thinner rim of the
circumnuclear matter.Comment: MNRAS Letters, in pres
The structure of Abell 1351: a bimodal galaxy cluster with peculiar diffuse radio emission
We aim to review the internal structure and dynamics of the Abell 1351
cluster, shown to host a radio halo with a quite irregular shape. Our analysis
is based on radial velocity data for 135 galaxies obtained at the Telescopio
Nazionale Galileo. We combine galaxy velocities and positions to select 95
cluster galaxy members and analyse the internal dynamics of the whole cluster.
We also examine X-ray data retrieved from Chandra and XMM archives. We measure
the cluster redshift, =0.325, the line-of-sight (LOS) velocity dispersion,
\sigma_v~1500 km/s, and the X-ray temperature, kT~9 keV. From both X-ray and
optical data independently, we estimate a large cluster mass, in the 1--4
M range. We attribute the extremely high value of \sigma_v to
the bimodality in the velocity distribution. We find evidence of a significant
velocity gradient and optical 3D substructure. The X-ray analysis also shows
many features in favour of a complex cluster structure, probably supporting an
ongoing merger of substructures in Abell 1351. The observational scenario
agrees with the presence of two main subclusters in the northern region, each
with its brightest galaxy (BCG1 and BCG2), detected as the two most important
X-ray substructures with a rest-frame LOS velocity difference of \Delta v~2500
km/s (in the rest frame) and probably being in large part aligned with the LOS.
We conclude that Abell 1351 is a massive merging cluster. The details of the
cluster structure allow us to interpret the quite asymmetric radio halo as a
`normal' halo plus a southern relic, strongly supporting a previous suggestion
based only on inspection of radio and preliminary X-ray data.Comment: 13 pages, 13 figures, 1 tabl
Topological properties of the bond-modulated honeycomb lattice
We study the combined effects of lattice deformation, e-e interaction and
spin-orbit coupling in a two-dimensional (2D) honeycomb lattice. We adopt
different kinds of hopping modulation--generalized dimerization and a Kekule
distortion--and calculate topological invariants for the non-interacting system
and for the interacting system. We identify the parameter range (Hubbard U,
hopping modulation, spin-orbit coupling) where the 2D system behaves as a
trivial insulator or Quantum Spin Hall Insulator.Comment: 8 pages, 4 figures: discussion improved, typos corrected, references
updated. Matches version published in PR
Smart technologies: useful tools to assess the exposure to solar ultraviolet radiation for general population and outdoor workers
Beside some documented benefits attributed to ultraviolet solar radiation (solar UVR), a lot of adverse effects are a consequence of a chronic exposure, including the occurrence of photo-induced skin cancer. Improvement in risks perception, due to UVR overexposure, in the case of occupational or recreational exposure, is of great importance for public health. The amount of exposure to UVR has to be assessed as accurately as possible, with the aim to characterize different exposure conditions and, by their appropriate management, to prevent adverse health effects attributed to prolonged exposure to solar radiation (SR). The available technology allows to acquire such information, either using miniaturized and wearable sensors, or through devices who exploit radiative transfer models by integrating satellite-based radiometric data with meteorological data. We proceeded to an intercomparison to evaluate the performance of different devices in three commonly exposure conditions. Applications using satellite data, developed for preventing sunburn during recreational exposure, are adeguate for that purpose, while for a more accurate exposure assessment, only those which evaluate the irradiance in near real-time provide acceptable results. Unlike earlier, the low-cost devices that use wearable sensors showed inadequate performance for our purpose
Topological invariants in interacting Quantum Spin Hall: a Cluster Perturbation Theory approach
Using Cluster Perturbation Theory we calculate Green's functions,
quasi-particle energies and topological invariants for interacting electrons on
a 2-D honeycomb lattice, with intrinsic spin-orbit coupling and on-site e-e
interaction. This allows to define the parameter range (Hubbard U vs spin-orbit
coupling) where the 2D system behaves as a trivial insulator or Quantum Spin
Hall insulator. This behavior is confirmed by the existence of gapless
quasi-particle states in honeycomb ribbons. We have discussed the importance of
the cluster symmetry and the effects of the lack of full translation symmetry
typical of CPT and of most Quantum Cluster approaches. Comments on the limits
of applicability of the method are also provided.Comment: 7 pages, 7 figures: discussion improved, one figure added, references
updated. Matches version published in New J. Phy
Where does the gas fueling star formation in BCGs originate?
We investigate the relationship between X-ray cooling and star formation in
brightest cluster galaxies (BCGs). We present an X-ray spectral analysis of the
inner regions, 10-40 kpc, of six nearby cool core clusters (z<0.35) observed
with Chandra ACIS. This sample is selected on the basis of the high star
formation rate (SFR) observed in the BCGs. We restrict our search for cooling
gas to regions that are roughly cospatial with the starburst. We fit single-
and multi-temperature mkcflow models to constrain the amount of isobarically
cooling intracluster medium (ICM). We find that in all clusters, below a
threshold temperature ranging between 0.9 and 3 keV, only upper limits can be
obtained. In four out of six objects, the upper limits are significantly below
the SFR and in two, namely A1835 and A1068, they are less than a tenth of the
SFR. Our results suggests that a number of mechanisms conspire to hide the
cooling signature in our spectra. In a few systems the lack of a cooling
signature may be attributed to a relatively long delay time between the X-ray
cooling and the star burst. However, for A1835 and A1068, where the X-ray
cooling time is shorter than the timescale of the starburst, a possible
explanation is that the region where gas cools out of the X-ray phase extends
to very large radii, likely beyond the core of these systems.Comment: to appear in A&
3C 33: another case of photoionized soft X-ray emission in radio galaxies
All the observations available in the Chandra and XMM-Newton archives have
been used to investigate the X-ray spectral properties of 3C 33. In this paper
is presented a complete X-ray analysis of the nuclear emission of this narrow
line radio galaxy. The broad band spectrum of 3C 33 is complex. The hard part
resembles that of Seyfert 2 galaxies, with a heavily obscured nuclear continuum
(N_H~10^23 cm^-2) and a prominent Fe Kalpha line. This represents the nuclear
radiation directly observed in transmission through a cold circumnuclear gas.
On the other hand an unabsorbed continuum plus emission lines seem to fit well
the soft part of the spectrum (0.5-2 keV) suggesting that the jet does not
significantly contribute to the X-ray emission. We discuss the possible
collisional or photoionized origin of the gas that emits the soft X-ray lines.
Our results, strengthened by optical spectroscopy favor the photoionization
scenario.Comment: 7 pages, 5 figures, accepted for publication in A&
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