105 research outputs found
High-Energy Astrophysics in the 2020s and Beyond
With each passing decade, we gain new appreciation for the dynamic,
connected, and often violent nature of the Universe. This reality necessarily
places the study of high-energy processes at the very heart of modern
astrophysics. This White Paper illustrates the central role of high-energy
astrophysics to some of the most pressing astrophysical problems of our time,
the formation/evolution of galaxies, the origin of the heavy elements, star and
planet formation, the emergence of life on exoplanets, and the search for new
physics. We also highlight the new connections that are growing between
astrophysicists and plasma physicists. We end with a discussion of the
challenges that must be addressed to realize the potential of these
connections, including the need for integrated planning across physics and
astronomy programs in multiple agencies, and the need to foster the creativity
and career aspirations of individual scientists in this era of large projects.Comment: Astro2020 White Paper submissio
The Poplar-Poplar Rust Interaction: Insights from Genomics and Transcriptomics
Poplars are extensively cultivated worldwide, and their susceptibility to the leaf rust fungus Melampsora larici-populina leads to considerable damages in plantations. Despite a good knowledge of the poplar rust life cycle, and particularly the epidemics on poplar, the perennial status of the plant host and the obligate biotrophic lifestyle of the rust fungus are bottlenecks for molecular investigations. Following the completion of both M. larici-populina and Populus trichocarpa genome sequences, gene families involved in poplar resistance or in rust fungus virulence were investigated, allowing the identification of key genetic determinants likely controlling the outcome of the interaction. Specific expansions of resistance and defense-related genes in poplar indicate probable innovations in perennial species in relation with host-pathogen interactions. The genome of M. Larici-populina contains a strikingly high number of genes encoding small secreted proteins (SSPs) representing hundreds of candidate effectors. Transcriptome analyses of interacting partners in compatible and incompatible interactions revealed conserved set of genes involved in poplar defense reactions as well as timely regulated expression of SSP transcripts during host tissues colonisation. Ongoing functional studies of selected candidate effectors will be achieved mainly on the basis of recombinant protein purification and subsequent characterisation
A Broadband X-Ray Study of the Supernova Remnant 3C 397
We present an X-ray study of the radio bright supernova remnant (SNR) 3C 397
with ROSAT, ASCA, and RXTE. A central X-ray spot seen with the ROSAT
High-Resolution Imager hints at the presence of a pulsar-powered component, and
gives this SNR a composite X-ray morphology. Combined ROSAT and ASCA imaging
show that the remnant is highly asymmetric, with its hard X-ray emission
peaking at the western lobe. The spectrum of 3C 397 is heavily absorbed, and
dominated by thermal emission with emission lines evident from Mg, Si, S, Ar
and Fe. Single-component models fail to describe the spectrum, and at least two
components are required. We use a set of non-equilibrium ionization (NEI)
models (Borkowski et al. in preparation). The temperatures from the soft and
hard components are 0.2 keV and 1.6 keV respectively. The corresponding
ionization time-scales ( being the pre-shock hydrogen density) are
6 cm s and 6 10 cm s,
respectively. The spectrum obtained with the Proportional Counter Array (PCA)
of RXTE is contaminated by emission from the Galactic ridge, with only
15% of the count rate originating from 3C 397 in the 5-15 keV range. The PCA
spectrum allowed us to confirm the thermal nature of the hard X-ray emission. A
third component originating from a pulsar-driven component is possible, but the
contamination of the source signal by the Galactic ridge did not allow us to
find pulsations from any hidden pulsar. We discuss the X-ray spectrum in the
light of two scenarios: a young ejecta-dominated remnant of a core-collapse SN,
and a middle-aged SNR expanding in a dense ISM. Spatially resolved spectroscopy
(with CHANDRA and XMM) is needed to differentiate between the two scenarios,
and address the nature of the mysterious radio-quiet X-ray hot spot.Comment: 21 pages including 8 figures and 5 tables. Accepted for publication
in the Astrophysical journa
A dusty X-ray absorber in the Perseus Cluster ?
We have analyzed 0.35-7.5 keV X-ray spectra of the center of the Perseus
cluster collected using the Broad Band X-Ray Telescope (BBXRT) on the Astro-1
mission. These spectra are particularly useful for examining the nature of the
X-ray absorber in cooling flows because of BBXRT's sensitivity between 0.35 and
1.0 keV. We confirm that there is X-ray absorption above that expected from gas
in our own galaxy. Further, the absorbing medium is deficient in helium.
However, the energy of the K-edge of oxygen is consistent with neutral material
(at the redshift of the cluster) and is not consistent with any ionized state
of oxygen. It is not possible to completely ionize helium and have oxygen
neutral so the apparent helium deficiency cannot be due to ionization. We
propose that the X-ray absorption is due to dust grains that have condensed out
of a medium in which helium remains ionized. This model satisfies all the
observational constraints but is difficult to understand theoretically.Comment: 15 pages including 6 figures. Uses aaspp4 and psfig style
Highly ionized Fe K emission lines from the LINER galaxy M 81
We present spectral and timing results from a long (130 ks) XMM-NEWTON EPIC
observation of the nucleus of the Seyfert/LINER galaxy M 81. During the
observation the X-ray flux varied by 20%, but there was no significant change
in spectral shape. The 2-10 keV spectrum is well described by a power law
continuum and three narrow Fe K emission lines at 6.4, 6.7 and 6.96 keV. The
three emission lines have equivalent widths of 39, 47, and 37 eV respectively.
The ratios of the three lines are thus more similar to those observed from the
Galactic Centre region than to those typically observed from Seyfert galaxies.
The high ionization lines most likely originate either from photoionized gas
within 0.1 pc of the nucleus of M 81, or from a non-thermal distribution of
cosmic-ray electrons interacting with the 0.2-0.6 keV thermal plasma which is
found in the bulge of M 81.Comment: Accepted for publication in A&
XMM-Newton observations of the supernova remnant IC 443: II. evidence of stellar ejecta in the inner regions
We investigate the spatial distribution of the physical and chemical
properties of the hot X-ray emitting plasma of the supernova remnant IC 443, in
order to get important constraints on its ionization stage, on the progenitor
supernova explosion, on the age of the remnant, and its physical association
with a close pulsar wind nebula.
The hard X-ray thermal emission (1.4-5.0 keV) of IC 443 displays a
centrally-peaked morphology, its brightness peaks being associated with hot
(kT>1 keV) X-ray emitting plasma. A ring-shaped structure, characterized by
high values of equivalent widths and median photon energy, encloses the PWN.
Its hard X-ray emission is spectrally characterized by a collisional ionization
equilibrium model, and strong emission lines of Mg, Si, and S, requiring
oversolar metal abundances. Dynamically, the location of the ejecta ring
suggests an SNR age of ~4,000 yr.
The presence of overionized plasma in the inner regions of IC 443, addressed
in previous works, is much less evident in our observations.Comment: 9 pages, 7 figures, accepted for publication in A&A. For hi-res
figures, see
http://www.astropa.unipa.it/Library/OAPA_preprints/aa20079123.pd
The Youngest Galactic Supernova Remnant: G1.9+0.3
Our 50 ks Chandra observation of the small radio supernova remnant (SNR)
G1.9+0.3 shows a complete shell structure with strong bilateral symmetry, about
in diameter. The radio morphology is also shell-like, but only about
in diameter, based on observations made in 1985. We attribute the size
difference to expansion between 1985 and our Chandra observations of 2007.
Expansion is confirmed in comparing radio images from 1985 and 2008. We deduce
that G1.9+0.3 is of order 100 years old -- the youngest supernova remnant in
the Galaxy. Based on a very high absorbing column density of cm, we place G1.9+0.3 near the Galactic Center, at a distance
of about 8.5 kpc, where the mean remnant radius would be about 2 pc, and the
required expansion speed about km s. The X-ray spectrum is
featureless and well-described by the exponentially cut off synchrotron model
{\tt srcut}. With the radio flux at 1 GHz fixed at 0.9 Jy, we find a spectral
index of 0.65 and a rolloff frequency of Hz. The implied
characteristic rolloff electron energy of about
TeV is the highest ever reported for a shell supernova remnant. It can easily
be reached by standard diffusive shock acceleration, given the very high shock
velocities; it can be well described by either age-limited or
synchrotron-loss-limited acceleration. Not only is G1.9+0.3 the youngest known
Galactic remnant, it is also only the fourth Galactic X-ray
synchrotron-dominated shell supernova remnant.Comment: 4 pages, 5 figures; revised to include new radio data and accepted
for ApJ
High-Energy Astrophysics in the 2020s and Beyond
With each passing decade, we gain new appreciation for the dynamic, connected, and often violent nature of the Universe. This reality necessarily places the study of high-energy processes at the very heart of modern astrophysics. This White Paper illustrates the central role of high-energy astrophysics to some of the most pressing astrophysical problems of our time, the formation/evolution of galaxies, the origin of the heavy elements, star and planet formation, the emergence of life on exoplanets, and the search for new physics. We also highlight the new connections that are growing between astrophysicists and plasma physicists. We end with a discussion of the challenges that must be addressed to realize the potential of these connections, including the need for integrated planning across physics and astronomy programs in multiple agencies, and the need to foster the creativity and career aspirations of individual scientists in this era of large projects
An XMM-Newton view of the `bare' nucleus of Fairall 9
We present the spectral results from a 130 ks observation, obtained from the
X-ray Multi-Mirror Mission-Newton (XMM-Newton) observatory, of the type I
Seyfert galaxy Fairall 9. An X-ray hardness-ratio analysis of the light-curves,
reveals a `softer-when-brighter' behaviour which is typical for radio-quiet
type I Seyfert galaxies. Moreover, we analyse the high spectral-resolution data
of the reflection grating spectrometer and we did not find any significant
evidence supporting the presence of warm-absorber in the low X-ray energy part
of the source's spectrum. This means that the central nucleus of Fairall 9 is
`clean' and thus its X-ray spectral properties probe directly the physical
conditions of the central engine. The overall X-ray spectrum in the 0.5-10 keV
energy-range, derived from the EPIC data, can be modelled by a relativistically
blurred disc-reflection model. This spectral model yields for Fairall 9 an
intermediate black-hole best-fit spin parameter of
.Comment: Accepted for publication in MNRAS. The paper contains 11 figures and
1 tabl
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