2,156 research outputs found
Detection of Pulsed X-ray Emission from XMM-Newton Observations of PSR J0538+2817
We report on the XMM-Newton observations of the 143 ms pulsar PSR J0538+2817.
We present evidence for the first detections of pulsed X-rays from the source
at a frequency which is consistent with the predicted radio frequency. The
pulse profile is broad and asymmetric, with a pulse fraction of 18 +/- 3%. We
find that the spectrum of the source is well-fit with a blackbody with
T^{infty} = (2.12^{+0.04}_{-0.03}) x 10^6 K and N_{H} = 2.5 x 10^21 cm^{-2}.
The radius determined from the model fit of 1.68 +/- 0.05 km suggests that the
emission is from a heated polar cap. A fit to the spectrum with an atmospheric
model reduces the inferred temperature and hence increases the radius of the
emitting region, however the pulsar distance determined from the fit is then
smaller than the dispersion distance.Comment: 24 pages, 6 figures, 3 tables, accepted for publication in ApJ. Error
in radius calculation corrected, discussion and conclusions remain unchange
A rapid synthesis of evidence on whole systems approaches to obesity prevention to inform policy
© 2023 The Author(s) . Published by Oxford University Press on behalf of the European Public Health Association. This is an open-access meeting abstract distributed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International License (CC BY-NC), https://creativecommons.org/licenses/by-nc/4.0/Peer reviewe
XMM-Newton Observations of PSR B1706-44
We report on the XMM-Newton observations of the young, 102 ms pulsar PSR
B1706-44. We have found that both a blackbody plus power-law and a magnetized
atmospheric model plus power-law provide an excellent fit to the EPIC spectra.
The two scenarios are therefore indistinguishable on a statistical basis,
although we are inclined to prefer the latter on physical grounds. In this
case, assuming a source distance of ~2.3 kpc, the size of the region
responsible for the thermal emission is R~13 km, compatible with the surface of
a neutron star. A comparison of the surface temperature of PSR B1706-44
obtained from this fit with cooling curves favor a medium mass neutron star
with M~1.45 solar masses or M~1.59 solar masses, depending on two different
models of proton superfluidity in the interior. The large collecting area of
XMM-Newton allows us to resolve a substructure in the broad soft X-ray
modulation detected by Chandra, revealing the presence of two separate peaks
with pulsed fractions of 7 +/- 4% and 15 +/- 3%, respectively.Comment: 21 pages, 5 figures, 2 tables, accepted for publication in Ap
On the Correlated X-ray and Optical Evolution of SS Cygni
We have analyzed the variability and spectral evolution of the prototype
dwarf nova system SS Cygni using RXTE data and AAVSO observations. A series of
pointed RXTE/PCA observations allow us to trace the evolution of the X-ray
spectrum of SS Cygni in unprecedented detail, while 6 years of optical AAVSO
and RXTE/ASM light curves show long-term patterns. Employing a technique in
which we stack the X-ray flux over multiple outbursts, phased according to the
optical light curve, we investigate the outburst morphology. We find that the
3-12 keV X-ray flux is suppressed during optical outbursts, a behavior seen
previously, but only in a handful of cycles. The several outbursts of SS Cygni
observed with the more sensitive RXTE/PCA also show a depression of the X-rays
during optical outburst. We quantify the time lags between the optical and
X-ray outbursts, and the timescales of the X-ray recovery from outburst. The
optical light curve of SS Cygni exhibits brief anomalous outbursts. During
these events the hard X-rays and optical flux increase together. The long-term
data suggest that the X-rays decline between outburst. Our results are in
general agreement with modified disk instability models (DIM), which invoke a
two-component accretion flow consisting of a cool optically thick accretion
disk truncated at an inner radius, and a quasi-spherical hot corona-like flow
extending to the surface of the white dwarf. We discuss our results in the
framework of one such model, involving the evaporation of the inner part of the
optically thick accretion disk, proposed by Meyer & Meyer-Hofmeister (1994).Comment: 24 pages, 8 figures, 2 tables, accepted for publication in Ap
Detection statistics in the micromaser
We present a general method for the derivation of various statistical
quantities describing the detection of a beam of atoms emerging from a
micromaser. The user of non-normalized conditioned density operators and a
linear master equation for the dynamics between detection events is discussed
as are the counting statistics, sequence statistics, and waiting time
statistics. In particular, we derive expressions for the mean number of
successive detections of atoms in one of any two orthogonal states of the
two-level atom. We also derive expressions for the mean waiting times between
detections. We show that the mean waiting times between de- tections of atoms
in like states are equivalent to the mean waiting times calculated from the
uncorrelated steady state detection rates, though like atoms are indeed
correlated. The mean waiting times between detections of atoms in unlike states
exhibit correlations. We evaluate the expressions for various detector
efficiencies using numerical integration, reporting re- sults for the standard
micromaser arrangement in which the cavity is pumped by excited atoms and the
excitation levels of the emerging atoms are measured. In addition, the atomic
inversion and the Fano-Mandel function for the detection of de-excited atoms is
calculated for compari- son to the recent experimental results of Weidinger et
al. [1], which reports the first observation of trapping states.Comment: 26 pages, 11 figure
Increasing healthy life expectancy equitably in England by 5 years by 2035: could it be achieved?
In 2018, the UK Government’s Secretary of State for Health and Social Care articulated an ambition to increase healthy life expectancy by five years by 2035 for England, while also reducing the gap in this between the rich and the poor1. While we doubt that England – or indeed any high-income country – could achieve this ambition, we describe a set of policies with the potential to make a significant contribution
The ROTSE-III Robotic Telescope System
The observation of a prompt optical flash from GRB990123 convincingly
demonstrated the value of autonomous robotic telescope systems. Pursuing a
program of rapid follow-up observations of gamma-ray bursts, the Robotic
Optical Transient Search Experiment (ROTSE) has developed a next-generation
instrument, ROTSE-III, that will continue the search for fast optical
transients. The entire system was designed as an economical robotic facility to
be installed at remote sites throughout the world. There are seven major system
components: optics, optical tube assembly, CCD camera, telescope mount,
enclosure, environmental sensing & protection and data acquisition. Each is
described in turn in the hope that the techniques developed here will be useful
in similar contexts elsewhere.Comment: 19 pages, including 4 figures. To be published in PASP in January,
2003. PASP Number IP02-11
Electron Transmission Spectroscopy in Atomic Hydrogen
An electron transmission experiment is used to study the resonances in the total scattering cross section of atomic hydrogen below the threshold of the first excited state. The three lowest resonances, designated 1S, 3P, and 1D, are observed and their energies and decay widths are found to be in good agreement with the values predicted theoretically using close coupling with correlation
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