354 research outputs found
Unveiling the environment surrounding LMXB SAX J1808.4-3658
Low-mass X-ray binaries (LMXBs) are a natural workbench to study accretion
disk phenomena and optimal background sources to measure elemental abundances
in the Interstellar medium (ISM). In high-resolution XMM-Newton spectra, the
LMXB SAX J1808.4-3658 showed in the past a neon column density significantly
higher than expected given its small distance, presumably due to additional
absorption from a neon-rich circumstellar medium (CSM). It is possible to
detect intrinsic absorption from the CSM by evidence of Keplerian motions or
outflows. For this purpose, we use a recent, deep (100 ks long),
high-resolution Chandra/LETGS spectrum of SAX J1808.4-3658 in combination with
archival data. We estimated the column densities of the different absorbers
through the study of their absorption lines. We used both empirical and
physical models involving photo- and collisional-ionization in order to
determine the nature of the absorbers. The abundances of the cold interstellar
gas match the solar values as expected given the proximity of the X-ray source.
For the first time in this source, we detected neon and oxygen blueshifted
absorption lines that can be well modeled with outflowing photoionized gas. The
wind is neon rich (Ne/O>3) and may originate from processed, ionized gas near
the accretion disk or its corona. The kinematics (v=500-1000 km/s) are indeed
similar to those seen in other accretion disks. We also discovered a system of
emission lines with very high Doppler velocities (v~24000 km/s) originating
presumably closer to the compact object. Additional observations and UV
coverage are needed to accurately determine the wind abundances and its
ionization structure.Comment: 12 pages, 10 figures, accepted for publication on A&
Abundance and temperature distributions in the hot intra-cluster gas of Abell 4059
Using the EPIC and RGS data from a deep (~200 ks) XMM-Newton observation, we
investigate the temperature structure (kT and sigma_T ) and the abundances of 9
elements (O, Ne, Mg, Si, S, Ar, Ca, Fe and Ni) of the intra-cluster medium
(ICM) in the nearby (z=0.046) cool-core galaxy cluster Abell 4059. Next to a
deep analysis of the cluster core, a careful modelling of the EPIC background
allows us to build radial profiles up to 12' (~650 kpc) from the core. Probably
because of projection effects, the temperature ICM is found not to be in single
phase, even in the outer parts of the cluster. The abundances of Ne, Si, S, Ar,
Ca and Fe, but also O are peaked towards the core. Fe and O are still
significantly detected in the outermost annuli; suggesting that the enrichment
by both type Ia and core-collapse SNe started in the early stages of the
cluster formation. However, the particularly high Ca/Fe ratio that we find in
the core is not well reproduced by the standard SNe yield models. Finally, 2-D
maps of temperature and Fe abundance are presented and confirm the existence of
a denser, colder, and Fe-rich ridge southwest of the core, previously observed
by Chandra. The origin of this asymmetry in the hot gas of the cluster core is
still unclear, but might be explained by a past intense ram-pressure stripping
event near the central cD galaxy.Comment: 17 pages, 13 figures, accepted for publication in A&
X-ray variability with WFXT: AGNs, transients and more
The Wide Field X-ray Telescope (WFXT) is a proposed mission with a high
survey speed, due to the combination of large field of view (FOV) and effective
area, i.e. grasp, and sharp PSF across the whole FOV. These characteristics
make it suitable to detect a large number of variable and transient X-ray
sources during its operating lifetime. Here we present estimates of the WFXT
capabilities in the time domain, allowing to study the variability of thousand
of AGNs with significant detail, as well as to constrain the rates and
properties of hundreds of distant, faint and/or rare objects such as X-ray
Flashes/faint GRBs, Tidal Disruption Events, ULXs, Type-I bursts etc. The
planned WFXT extragalactic surveys will thus allow to trace variable and
transient X-ray populations over large cosmological volumes.Comment: Proceedings of "The Wide Field X-ray Telescope Workshop", held in
Bologna, Italy, Nov. 25-26 2009 (arXiv:1010.5889). To appear in Memorie della
Societ\`a Astronomica Italiana 2010 - Minor corrections to text
Chemical Enrichment RGS cluster sample (CHEERS): Constraints on turbulence
Feedback from AGN, galactic mergers, and sloshing are thought to give rise to
turbulence, which may prevent cooling in clusters. We aim to measure the
turbulence in clusters of galaxies and compare the measurements to some of
their structural and evolutionary properties. It is possible to measure the
turbulence of the hot gas in clusters by estimating the velocity widths of
their X-ray emission lines. The RGS Spectrometers aboard XMM-Newton are
currently the only instruments provided with sufficient effective area and
spectral resolution in this energy domain. We benefited from excellent 1.6Ms
new data provided by the CHEERS project. The new observations improve the
quality of the archival data and allow us to place constraints for some
clusters, which were not accessible in previous work. One-half of the sample
shows upper limits on turbulence less than 500km/s. For several sources, our
data are consistent with relatively strong turbulence with upper limits on the
velocity widths that are larger than 1000km/s. The NGC507 group of galaxies
shows transonic velocities, which are most likely associated with the merging
phenomena and bulk motions occurring in this object. Where both low- and
high-ionization emission lines have good enough statistics, we find larger
upper limits for the hot gas, which is partly due to the different spatial
extents of the hot and cool gas phases. Our upper limits are larger than the
Mach numbers required to balance cooling, suggesting that dissipation of
turbulence may prevent cooling, although other heating processes could be
dominant. The systematics associated with the spatial profile of the source
continuum make this technique very challenging, though still powerful, for
current instruments. The ASTRO-H and Athena missions will revolutionize the
velocity estimates and discriminate between different spatial regions and
temperature phases.Comment: 16 pages, 18 figures, 3 tables, accepted for publications in
Astronomy and Astrophysic
A high-density relativistic reflection origin for the soft and hard X-ray excess emission from Mrk 1044
We present the first results from a detailed spectral-timing analysis of a
long (130 ks) XMM-Newton observation and quasi-simultaneous NuSTAR and
Swift observations of the highly-accreting narrow-line Seyfert 1 galaxy Mrk
1044. The broadband (0.350 keV) spectrum reveals the presence of a strong
soft X-ray excess emission below 1.5 keV, iron K emission
complex at 67 keV and a `Compton hump' at 1530 keV. We find
that the relativistic reflection from a high-density accretion disc with a
broken power-law emissivity profile can simultaneously explain the soft X-ray
excess, highly ionized broad iron line and the Compton hump. At low frequencies
( Hz), the power-law continuum dominated 1.55 keV band
lags behind the reflection dominated 0.31 keV band, which is explained with
a combination of propagation fluctuation and Comptonization processes, while at
higher frequencies ( Hz), we detect a soft lag which is
interpreted as a signature of X-ray reverberation from the accretion disc. The
fractional root-mean-squared (rms) variability of the source decreases with
energy and is well described by two variable components: a less variable
relativistic disc reflection and a more variable direct coronal emission. Our
combined spectral-timing analyses suggest that the observed broadband X-ray
variability of Mrk~1044 is mainly driven by variations in the location or
geometry of the optically thin, hot corona.Comment: 23 pages, 19 figures, 4 tables, Published in MNRA
Influence of abiotic factors on the resistance of plants to insects
Abstract. Plant resistance is considered as an important pillar of Integrated Pest Management (IPM), being a highly targeted method since is a less harmful method to the environment, if compared to other tactics such as chemical control. Abiotic factors are those related to the environment and have a direct influence on the dynamics of interaction between insects and plants. The abiotic factors such as altitude, temperature, humidity, luminosity, wind and soil fertility, among others, do not act alone, but in a complex net that leads insect population dynamics in agroecosystems. How the variations of these factors can be studied in the same context? First, it is important to consider how each abiotic factors act separately and then in a coexistence influence over the populations dynamics of insects and plants. In this study, the literature about the influence of abiotic factors on insect herbivory has been reviewed, focusing mainly on the mechanisms in which the plants use in the defense against insects.
Influência de fatores abióticos na resistência de plantas a insetos
Resumo. A resistência de plantas é considerada um importante pilar no contexto do Manejo Integrado de Pragas (MIP), sendo um método bastante visado por ser menos nocivo ao meio ambiente, quando comparado a outras táticas como o controle quÃmico. Os fatores abióticos são aqueles relacionados ao ambiente e têm influência direta na dinâmica de interação entre insetos e plantas. Os fatores abióticos como altitude, temperatura, umidade, luminosidade, ventos e fertilidade do solo, por exemplo, não atuam sozinhos, mais sim em um complexo de fatores coexistentes que regem as dinâmicas populacionais nos diversos agroecosistemas. Como as variações destes fatores podem ser estudadas em um mesmo contexto? Primeiramente, é importante conhecer como cada uma atua individualmente para então contextualizar em uma situação de coexistência sobre as dinâmicas populacionais de insetos e plantas. Neste artigo, a literatura sobre a influência de fatores abióticos na herbivoria de insetos foi revisada, focando principalmente nos mecanismos em que as plantas utilizam na defesa contra insetos
Searching for cool and cooling X-ray emitting gas in 45 galaxy clusters and groups
We present a spectral analysis of cool and cooling gas in 45 cool-core
clusters and groups of galaxies obtained from Reflection Grating Spectrometer
(RGS) XMM- observations. The high-resolution spectra show FeXVII
emission in many clusters, which implies the existence of cooling flows. The
cooling rates are measured between the bulk Intracluster Medium (ICM)
temperature and 0.01 keV and are typically weak, operating at less than a few
tens of in clusters, and less than 1 in groups of galaxies. They are 10-30% of the classical
cooling rates in the absence of heating, which suggests that AGN feedback has a
high level of efficiency. If cooling flows terminate at 0.7 keV in clusters,
the associated cooling rates are higher, and have a typical value of a few to a
few tens of . Since the soft X-ray emitting region,
where the temperature keV, is spatially associated with H
nebulosity, we examine the relation between the cooling rates above 0.7 keV and
the H nebulae. We find that the cooling rates have enough energy to
power the total UV-optical luminosities, and are 5 to 50 times higher than the
observed star formation rates for low luminosity objects. In 4 high luminosity
clusters, the cooling rates above 0.7 keV are not sufficient and an inflow at a
higher temperature is required. Further residual cooling below 0.7 keV
indicates very low complete cooling rates in most clusters.Comment: 17 pages, 10 figures, accepted for publication in MNRA
The inner gas mass-temperature profile in the core of nearby galaxy clusters
We present a mass-temperature profile of gas within the central 10 kpc of a small sample of cool core clusters. The mass of the hottest gas phases, at 1.5 and 0.7 keV, is determined from X-ray spectra from the XMM Reflection Grating Spectrometers. The masses of the partially ionized atomic and the molecular phases are obtained from published H α and CO measurements. We find that the mass of gas at 0.7 keV in a cluster is remarkably similar to that of the molecular gas. Assuming pressure equilibrium between the phases, this means that they occupy volumes differing by 105. The molecular gas is located within the H α nebula which is often filamentary and coincides radially and in position angle with the soft X-ray emitting gas
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