74 research outputs found
STROBE-X: X-Ray Timing and Spectroscopy on Dynamical Timescales from Microseconds to Years
The Spectroscopic Time-Resolving Observatory for Broadband Energy X-rays
(STROBE-X) probes strong gravity for stellar mass to supermassive black holes
and ultradense matter with unprecedented effective area, high time-resolution,
and good spectral resolution, while providing a powerful time-domain X-ray
observatory.Comment: Accepted for Publication in Results in Physic
ALFALFA HI Data Stacking I. Does the Bulge Quench Ongoing Star Formation in Early-Type Galaxies?
We have carried out an HI stacking analysis of a volume-limited sample of
~5000 galaxies with imaging and spectroscopic data from GALEX and the Sloan
Digital Sky Survey, which lie within the current footprint of the Arecibo
Legacy Fast ALFA (ALFALFA) Survey. Our galaxies are selected to have stellar
masses greater than 10^10 Msun and redshifts in the range 0.025<z<0.05. We
extract a sub-sample of 1833 "early-type" galaxies with inclinations less than
70deg, with concentration indices C>2.6 and with light profiles that are well
fit by a De Vaucouleurs model. We then stack HI line spectra extracted from the
ALFALFA data cubes at the 3-D positions of the galaxies from these two samples
in bins of stellar mass, stellar mass surface density, central velocity
dispersion, and NUV-r colour. We use the stacked spectra to estimate the
average HI gas fractions M_HI/M_* of the galaxies in each bin.
Our main result is that the HI content of a galaxy is not influenced by its
bulge. The average HI gas fractions of galaxies in both our samples correlate
most strongly with NUV-r colour and with stellar surface density. The relation
between average HI fraction and these two parameters is independent of
concentration index C. We have tested whether the average HI gas content of
bulge-dominated galaxies on the red sequence, differs from that of late-type
galaxies on the red sequence. We find no evidence that galaxies with a
significant bulge component are less efficient at turning their available gas
reservoirs into stars. This result is in contradiction with the "morphological
quenching" scenario proposed by Martig et al. (2009).Comment: 21 pages, 15 figures. Accepted for publication in MNRAS. Version with
high resolution figures available at
http://www.mpa-garching.mpg.de/GASS/pubs.ph
Reducing socio-economic inequalities in all-cause mortality: a counterfactual mediation approach.
Socio-economic inequalities in mortality are well established, yet the contribution of intermediate risk factors that may underlie these relationships remains unclear. We evaluated the role of multiple modifiable intermediate risk factors underlying socio-economic-associated mortality and quantified the potential impact of reducing early all-cause mortality by hypothetically altering socio-economic risk factors.
Data were from seven cohort studies participating in the LIFEPATH Consortium (total n = 179 090). Using both socio-economic position (SEP) (based on occupation) and education, we estimated the natural direct effect on all-cause mortality and the natural indirect effect via the joint mediating role of smoking, alcohol intake, dietary patterns, physical activity, body mass index, hypertension, diabetes and coronary artery disease. Hazard ratios (HRs) were estimated, using counterfactual natural effect models under different hypothetical actions of either lower or higher SEP or education.
Lower SEP and education were associated with an increase in all-cause mortality within an average follow-up time of 17.5 years. Mortality was reduced via modelled hypothetical actions of increasing SEP or education. Through higher education, the HR was 0.85 [95% confidence interval (CI) 0.84, 0.86] for women and 0.71 (95% CI 0.70, 0.74) for men, compared with lower education. In addition, 34% and 38% of the effect was jointly mediated for women and men, respectively. The benefits from altering SEP were slightly more modest.
These observational findings support policies to reduce mortality both through improving socio-economic circumstances and increasing education, and by altering intermediaries, such as lifestyle behaviours and morbidities
Large Observatory for x-ray Timing (LOFT-P): a Probe-class mission concept study
LOFT-P is a concept for a NASA Astrophysics Probe-Class (<$1B) X-ray timing
mission, based on the LOFT concept originally proposed to ESAs M3 and M4 calls.
LOFT-P requires very large collecting area (>6 m^2, >10x RXTE), high time
resolution, good spectral resolution, broad-band spectral coverage (2-30 keV),
highly flexible scheduling, and an ability to detect and respond promptly to
time-critical targets of opportunity. It addresses science questions such as:
What is the equation of state of ultra dense matter? What are the effects of
strong gravity on matter spiraling into black holes? It would be optimized for
sub-millisecond timing to study phenomena at the natural timescales of neutron
star surfaces and black hole event horizons and to measure mass and spin of
black holes. These measurements are synergistic to imaging and high-resolution
spectroscopy instruments, addressing much smaller distance scales than are
possible without very long baseline X-ray interferometry, and using
complementary techniques to address the geometry and dynamics of emission
regions. A sky monitor (2-50 keV) acts as a trigger for pointed observations,
providing high duty cycle, high time resolution monitoring of the X-ray sky
with ~20 times the sensitivity of the RXTE All-Sky Monitor, enabling
multi-wavelength and multi-messenger studies. A probe-class mission concept
would employ lightweight collimator technology and large-area solid-state
detectors, technologies which have been recently greatly advanced during the
ESA M3 study. Given the large community interested in LOFT (>800 supporters,
the scientific productivity of this mission is expected to be very high,
similar to or greater than RXTE (~2000 refereed publications). We describe the
results of a study, recently completed by the MSFC Advanced Concepts Office,
that demonstrates that LOFT-P is feasible within a NASA probe-class mission
budget.Comment: Proc. SPIE 9905, Space Telescopes and Instrumentation 2016:
Ultraviolet to Gamma Ray, 99054Y (July 18, 2016
Fermi Large Area Telescope Constraints on the Gamma-ray Opacity of the Universe
The Extragalactic Background Light (EBL) includes photons with wavelengths
from ultraviolet to infrared, which are effective at attenuating gamma rays
with energy above ~10 GeV during propagation from sources at cosmological
distances. This results in a redshift- and energy-dependent attenuation of the
gamma-ray flux of extragalactic sources such as blazars and Gamma-Ray Bursts
(GRBs). The Large Area Telescope onboard Fermi detects a sample of gamma-ray
blazars with redshift up to z~3, and GRBs with redshift up to z~4.3. Using
photons above 10 GeV collected by Fermi over more than one year of observations
for these sources, we investigate the effect of gamma-ray flux attenuation by
the EBL. We place upper limits on the gamma-ray opacity of the Universe at
various energies and redshifts, and compare this with predictions from
well-known EBL models. We find that an EBL intensity in the optical-ultraviolet
wavelengths as great as predicted by the "baseline" model of Stecker et al.
(2006) can be ruled out with high confidence.Comment: 42 pages, 12 figures, accepted version (24 Aug.2010) for publication
in ApJ; Contact authors: A. Bouvier, A. Chen, S. Raino, S. Razzaque, A.
Reimer, L.C. Reye
STROBE-X: X-Ray Timing and Spectroscopy on Dynamical Timescales from Microseconds to Years
No abstract availabl
Exploring the dating of âdirtyâ speleothems and cave sinters using radiocarbon dating of preserved organic matter
Speleothems and other carbonate deposits such as tufa containing high proportions of detrital material can be difficult to chemically date due to detrital thorium levels causing a high level of error in conventional U-Th disequilibrium dating. Here we investigate the use of an alternative technique centring on radiocarbon dating of organic matter preserved within the detrital fraction. Non-acid soluble humic, particulate and detritally absorbed organic matter was recovered from eight samples from a flowstone sinter formed within a roman aqueduct at Trento in Italy with a maximum age of 100 CE (1850 cal yr BP), and two repeat samples from a dripstone formed within the 20th Century on a wire fence at Lilly-Pilly Cave, Buchan Caves Reserve in Victoria, Australia. In the aqueduct samples the median calibrated 14C ages ranged from 2232 to 2889 cal yr BP, with 95.4% probability age range in the youngest and oldest samples of 2153â2337 and 2342â3449 cal yr BP respectively. The median age of the more modern dripstone was 336 cal yr BP, with a 95.4% probability age range of 148â486 cal yr BP. These results provide very approximate ball-park estimates of the age of the sample, but are consistently too old when compared to the known maximum ages of formation. It is hypothesised that this offset is due to a combination of the nature of the organic carbon transported from the source organic matter pools, and reworking of both modern and old organic carbon by in situ microbial communities
STROBE-X: A probe-class mission for x-ray spectroscopy and timing on timescales from microseconds to years
We describe the Spectroscopic Time-Resolving Observatory for Broadband Energy X-rays (STROBE-X), a probeclass mission concept that will provide an unprecedented view of the X-ray sky, performing timing and spectroscopy over both a broad energy band (0.2-30 keV) and a wide range of timescales from microseconds to years. STROBE-X comprises two narrow-field instruments and a wide field monitor. The soft or low-energy band (0.2-12 keV) is covered by an array of lightweight optics (3-m focal length) that concentrate incident photons onto small solid-state detectors with CCD-level (85-175 eV) energy resolution, 100 ns time resolution, and low background rates. This technology has been fully developed for NICER and will be scaled up to take advantage of the longer focal length of STROBE-X. The higher-energy band (2-30 keV) is covered by large-area, collimated silicon drift detectors that were developed for the European LOFT mission concept. Each instrument will provide an order of magnitude improvement in effective area over its predecessor (NICER in the soft band and RXTE in the hard band). Finally, STROBE-X offers a sensitive wide-field monitor (WFM), both to act as a trigger for pointed observations of X-ray transients and also to provide high duty-cycle, high time-resolution, and high spectral-resolution monitoring of the variable X-ray sky. The WFM will boast approximately 20 times the sensitivity of the RXTE All-Sky Monitor, enabling multi-wavelength and multi-messenger investigations with a large instantaneous field of view. This mission concept will be presented to the 2020 Decadal Survey for consideration
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