67 research outputs found
The Constellation-X Mission
This viewgraph presentation reviews the goals, the instrumentation that will be aboard the Con-X spacecrafts, and the current status of the mission. Two science goals driving the need for this mission are: (1) Black Moles: precisions tests of GR in the strong field limit and determination of Black Hole spin in a large sample (2) Neutron Stars: Precision measurements of the mass-radius relation of neutron stars to determine the Equation of State (EOS) of ultra-dense matte
The Chandra Iron-L X-Ray Line Spectrum of Capella
An analysis of the iron L-shell emission in the publicly available spectrum
of the Capella binary system, as obtained by the High Energy Transmission
Grating Spectrometer on board the Chandra X-ray Observatory, is presented. The
atomic-state model, based on the HULLAC code, is shown to be especially
adequate for analyzing high-resolution x-ray spectra of this sort. Almost all
of the spectral lines in the 10 - 18 Angstrom wavelength range are identified.
It is shown that, for the most part, these lines can be attributed to emission
from L-shell iron ions in the Capella coronae. Possibilities for electron
temperature diagnostics using line ratios of Fe16+ are demonstrated. It is
shown that the observed iron-L spectrum can be reproduced almost entirely by
assuming a single electron temperature of kTe= 600 eV. This temperature is
consistent with both the measured fractional ion abundances of iron and with
the temperature derived from ratios of Fe16+ lines. A volume emission measure
of 1053 cm-3 is calculated for the iron L-shell emitting regions of the Capella
coronae indicating a rather small volume of 1029 cm3 for the emitting plasma if
an electron density of 1012 cm-3 is assumed.Comment: Accepted to Ap
High-Resolution X-Ray Spectroscopy of the Accretion Disk Corona Source 4U 1822-37
We present a preliminary analysis of the X-ray spectrum of the accretion disk
corona source, 4U 1822-37, obtained with the High Energy Transmission Grating
Spectrometer onboard the Chandra X-ray Observatory. We detect discrete emission
lines from photoionized iron, silicon, magnesium, neon, and oxygen, as well as
a bright iron fluorescence line. Phase-resolved spectroscopy suggests that the
recombination emission comes from an X-ray illuminated bulge located at the
predicted point of impact between the disk and the accretion stream. The
fluorescence emission originates in an extended region on the disk that is
illuminated by light scattered from the corona.Comment: 12 pages, 6 figures; Accepted for publication in ApJ Letter
High Resolution Spectroscopy of the X-ray Photoionized Wind in Cygnus X-3 with the Chandra High Energy Transmission Grating Spectrometer
We present a preliminary analysis of the 1--10 keV spectrum of the massive
X-ray binary Cyg X-3, obtained with the High Energy Transmission Grating
Spectrometer on the Chandra X-ray Observatory. The source reveals a richly
detailed discrete emission spectrum, with clear signatures of
photoionization-driven excitation.
Among the spectroscopic novelties in the data are the first astrophysical
detections of a number of He-like 'triplets' (Si, S, Ar) with emission line
ratios characteristic of photoionization equilibrium, fully resolved narrow
radiative recombination continua of Mg, Si, and S, the presence of the H-like
Fe Balmer series, and a clear detection of a ~ 800 km/s large scale velocity
field, as well as a ~1500 km/s FWHM Doppler broadening in the source. We
briefly touch on the implications of these findings for the structure of the
Wolf-Rayet wind.Comment: 11 pages, 3 figures; Accepted for publication in ApJ Letter
Atlas of Global Surface Water Dynamics
It is impossible to overstate the importance of freshwater in our daily lives – for proof, try going without it for any length of time. Surface waterbodies (lakes, ponds, rivers, creeks, estuaries… it doesn't matter what name they go under) are particularly important because they come into direct contact with us and our biophysical environment. But our knowledge concerning where and when waterbodies might be found was, until recently, surprisingly sparse. The paucity of information was because trying to map a moving target is actually very difficult – and waterbodies undeniably move, in both geographical space and time. By 2013 the U.S. Geological Survey and NASA were making petabyte scale archives of satellite imagery freely available, archives that covered the entire planet's surface and stretched back decades. Other's such as the European Commission / European Space Agency Copernicus programme were also putting full free and open data access policies into place, and Google's Earth Engine had become a mature, powerful cloud-based platform for processing very large geospatial datasets. Back in 2013 a small team working at the European Commission's Joint Research Centre were looking at ways satellite imagery could be used to capture surface waterbody dynamics, and create new maps that accurately incorporated time dimensions. Concurrently the Google Earth Engine team were focussing their massive computational capabilities on major issues facing humanity, such as deforestation, food security, climate change - and water management. The two teams came together in a partnership based not on financial transactions but on a mutual exchange of complementary capabilities, and devoted thousands of person hours and thousands of CPU years into turning petabytes of Landsat satellite imagery into unique, validated surface water maps, first published in 2016, and made available to everyone through a dedicated web portal, the Global Surface Water Explorer. Since then satellites have continued to image the Earth, surface water has continued to change and the JRC Goole Earth Engine partnership has continued to work on improving our knowledge of surface water dynamics and making sure this knowledge benefits as many people as possible. This Atlas is part of the outreach; it is not a guide to the Global Surface Water Explorer, it is not a Google Earth Engine tutorial (though if it inspires you to visit either of these resources then it has achieved one of its objectives), but it is a stand-alone window into how people and nature affect, and are affected by the 4.46 million km2 of the Earth's landmass that have been under water at some time over the past 35 years.JRC.D.5-Food Securit
Non-Detection of Gravitationally Redshifted Absorption Lines in the X-ray Burst Spectra of GS 1826-24
During a 200 ks observation with the XMM-Newton Reflection Grating
Spectrometer, we detected 16 type-I X-ray bursts from GS 1826-24. We combined
the burst spectra in an attempt to measure the gravitational redshifts from the
surface of the neutron star. We divided the composite GS 1826-24 burst spectrum
into three groups based on the blackbody temperature during the bursts. The
spectra do not show any obvious discrete absorption lines. We compare our
observations with those of EXO 0748-676.Comment: 4 pages, 4 figures; accepted for publication in ApJ
High-resolution X-ray spectroscopy of the ultracompact LMXB pulsar 4U 1626-67
[abridged] We report results from four recent observations of the
ultracompact LMXB pulsar 4U 1626-67. All the observations obtained
high-resolution X-ray spectra of the system, two from the Chandra X-ray
Observatory using the HETGS, and two from the XMM-Newton Observatory using the
RGS as well as the EPIC PN and MOS. These data allow us to study in detail the
prominent Ne and O emission line complexes which make 4U 1626-67 unique among
LMXBs. The observations were spaced over a period of 3 years for a total
observing time of 238 ks, allowing us to monitor the line regions as well as
the overall source flux, continuum spectrum, and timing properties. The
structure of the emission lines and the ratios of the components of the
helium-like Ne IX and O VII triplets support the hypothesis that they are
formed in the high-density environment of the accretion disk. We do not find
any significant changes in the line widths or ratios over this time period,
though we note that the line equivalent widths decrease. We are able to place
constraints on the strengths of the Ne K, Fe L, and O K photoelectric
absorption edges, and find that the data do not require an overabundance of Ne
or O in the system relative to the expected ISM values. We find that the pulsar
is still spinning down, and note that the pulse profile has changed
significantly from what was found prior to the torque reversal in 1990,
suggesting that this event may be linked to a change in the geometry of the
accretion column. The flux of 4U 1626-67 continues to decrease, in keeping with
the trend of the last approximately 30 years over which it has been observed.
Taking into consideration current theory on disk stability, we expect that 4U
1626-67 will enter a period of quiescence in 2-15 years.Comment: 10 pages, 7 figures, submitted to Ap
X-Ray and Near-Infrared Observations of GX 339-4 in the Low/Hard State with Suzaku and IRSF
X-ray and near-infrared (--) observations of the Galactic
black hole binary GX 339--4 in the low/hard state were performed with Suzaku
and IRSF in 2009 March. The spectrum in the 0.5--300 keV band is dominated by
thermal Comptonization of multicolor disk photons, with a small contribution
from a direct disk component, indicating that the inner disk is almost fully
covered by hot corona with an electron temperature of 175 keV. The
Comptonizing corona has at least two optical depths, .
Analysis of the iron-K line profile yields an inner disk radius of
( represents the gravitational
radius ), with the best-fit inclination angle of .
This radius is consistent with that estimated from the continuum fit by
assuming the conservation of photon numbers in Comptonization. Our results
suggest that the standard disk of GX 339--4 is likely truncated before reaching
the innermost stable circular orbit (for a non rotating black hole) in the
low/hard state at 1% of the Eddington luminosity. The one-day averaged
near-infrared light curves are found to be correlated with hard X-ray flux with
. The flatter near infrared
spectrum than the radio one suggests that the optically thin synchrotron
radiation from the compact jets dominates the near-infrared flux. Based on a
simple analysis, we estimate the magnetic field and size of the jet base to be
G and cm, respectively. The synchrotron self
Compton component is estimated to be approximately 0.4% of the total X-ray
flux.Comment: 17pages, 15 figures, accepted for publication in PASJ (Suzaku and
MAXI Special Issue
An introduction to the Digital Observatory for Protected Areas (DOPA) and the DOPA Explorer (Beta)
The Digital Observatory for Protected Areas (DOPA) is conceived around a set of interacting Critical Biodiversity Informatics Infrastructures (databases, web modelling services, broadcasting services, ...) hosted at different institutions, including the Joint Research Centre of the European Commission, the World Conservation Monitoring Centre (UNEP-WCMC), the International Union for Conservation of Nature (IUCN), the Global Biodiversity Information Facility (GBIF) and BirdLife International. The current services of DOPA provide to a large variety of end-users, ranging from park managers, funding agencies to researchers, with means to assess, monitor and possibly forecast the state and pressure of protected areas at the local, national and global scales.
With an introduction to the DOPA, the readers will find here a user manual of the beta version of DOPA Explorer, a first web based assessment tool where information on 9 000 protected areas covering almost 90% of the global protected surface has been processed automatically to generate a set of indicators on ecosystems, climate, phenology, species, ecosystem services and pressures. DOPA Explorer can so help identify the protected areas with most unique ecosystems and species and assess the pressures they are exposed to because of human development. Ecological data derived from and near real-time earth observations are also made available for the African continent. Inversely, DOPA Explorer indirectly highlights the protected areas for which the information is incomplete.JRC.H.5-Land Resources Managemen
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