219 research outputs found
SGR 1806−20 distance and dust properties in molecular clouds by analysis of flare X-ray echoes
The soft gamma repeater SGR 1806−20 is most famous for its giant flare from 2004, which yielded the highest gamma-ray flux ever observed on Earth. The flare emphasized the importance of determining the distance to the SGR, thus revealing the flare’s energy output, with implications on SGRs energy budget and giant flare rates. We analyse X-ray scattering echoes observed by Swift/X-Ray Telescope (XRT) following the 2006 August 6 intermediate burst of SGR 1806−20. Assuming positions and opacities of the molecular clouds along the line of sight from previous works, we derive direct constraints on the distance to SGR 1806−20, setting a lower limit of 9.4 kpc and an upper limit of 18.6 kpc (90 per cent confidence), compared with a 6–15 kpc distance range by previous works. This distance range matches an energy output of ≈10^(46) erg for the 2004 giant flare. We further use, for the first time, the X-ray echoes in order to study the dust properties in molecular clouds. Analysing the temporal evolution of the observed flux using a dust-scattering model, which assumes a power-law size distribution of the dust grains, we obtain a power-law index of −3.3^(+0.6)_(−0.7) (1σ) and a lower limit of 0.1. µm (2σ) on the dust maximal grain size, both conforming to measured dust properties in the diffused interstellar medium (ISM). We advocate future burst follow-up observations with Swift, Chandra and the planned NuSTAR telescopes, as means of obtaining much superior results from such an analysis
An audit of discharge summaries
Background: In the continuum of patient care, admission to the department of medicine constitutes a brief yet critical period. Subsequent patient care depends on the discharge summary (DS) and its implementation. Aim: To evaluate the department of medicine -family physician interface by a discharge summaries audit. Method: A retrospective study analyzing all admissions and discharges between a department of medicine and a primary care clinic over a period of ten months. Results: 129 DS were evaluated and compared to 97 available primary care medical charts. Most admissions were due to a medical emergency (95%), the patients were often elderly and 23% lived alone. Hospital stay averaged 4.0±2.4 days, readmission rate was 15.8%. In 73% of the DS at least one new drug was prescribed. The family physician was the one expected to continue treatment in most of the cases, but in over a third of the patients, a referral to further consultation was deemed necessary. The DS was found in 82% of the primary care charts. Median time interval between discharge and consultation with the family physician was three days (range 1-30). Home visits by physicians were documented in eight cases only. Conclusion: Most discharged patients require further evaluation and newly prescribed medications, making a timely and coordinated continuous care in the community mandatory. A high quality, rapidly available DS is therefore important for the family physician. Whether improved communication will reduce readmissions and improve patient prognosis and quality of care should be clarified by further study.peer-reviewe
An Observational Limit on the Earliest GRBs
We predict the redshift of the first observable (i.e., in our past light
cone) Gamma Ray Burst (GRB) and calculate the GRB-rate redshift distribution of
the Population III stars at very early times (z=20-60). Using the last 2 years
of data from Swift we place an upper limit on the efficiency (\eta_{GRB}) of
GRB production per solar mass from the first generation of stars. We find that
the first observable GRB is most likely to have formed at redshift 60. The
observed rate of extremely high redshift GRBs (XRGs) is a subset of a group of
15 long GRBs per year, with no associated redshift and no optical afterglow
counterparts, detected by Swift. Taking this maximal rate we get that
\eta_{GRB}<1.1~10^{-4} GRBs per solar mass in stars. A more realistic
evaluation, e.g., taking a subgroup of 5% of the total sample of Swift gives an
upper limit of \eta_{GRB}<3.2~10^{-5} GRBs per solar mass.Comment: 6 Pages, 3 figures, submitted to MNRA
An outburst from a massive star 40 days before a supernova explosion
Various lines of evidence suggest that very massive stars experience extreme
mass-loss episodes shortly before they explode as a supernova. Interestingly,
several models predict such pre-explosion outbursts. Establishing a causal
connection between these mass-loss episodes and the final supernova explosion
will provide a novel way to study pre-supernova massive-star evolution. Here we
report on observations of a remarkable mass-loss event detected 40 days prior
to the explosion of the Type IIn supernova SN 2010mc (PTF 10tel). Our
photometric and spectroscopic data suggest that this event is a result of an
energetic outburst, radiating at least 6x10^47 erg of energy, and releasing
about 0.01 Solar mass at typical velocities of 2000 km/s. We show that the
temporal proximity of the mass-loss outburst and the supernova explosion
implies a causal connection between them. Moreover, we find that the outburst
luminosity and velocity are consistent with the predictions of the wave-driven
pulsation model and disfavor alternative suggestions.Comment: Nature 494, 65, including supplementary informatio
Superluminal motion of a relativistic jet in the neutron star merger GW170817
The binary neutron star merger GW170817 was accompanied by radiation across
the electromagnetic spectrum and localized to the galaxy NGC 4993 at a distance
of 41+/-3 Mpc. The radio and X-ray afterglows of GW170817 exhibited delayed
onset, a gradual rise in the emission with time as t^0.8, a peak at about 150
days post-merger, followed by a relatively rapid decline. To date, various
models have been proposed to explain the afterglow emission, including a
choked-jet cocoon and a successful-jet cocoon (a.k.a. structured jet). However,
the observational data have remained inconclusive as to whether GW170817
launched a successful relativistic jet. Here we show, through Very Long
Baseline Interferometry, that the compact radio source associated with GW170817
exhibits superluminal motion between two epochs at 75 and 230 days post-merger.
This measurement breaks the degeneracy between the models and indicates that,
while the early-time radio emission was powered by a wider-angle outflow
(cocoon), the late-time emission was most likely dominated by an energetic and
narrowly-collimated jet, with an opening angle of <5 degrees, and observed from
a viewing angle of about 20 degrees. The imaging of a collimated relativistic
outflow emerging from GW170817 adds substantial weight to the growing evidence
linking binary neutron star mergers and short gamma-ray bursts.Comment: 42 pages, 4 figures (main text), 2 figures (supplementary text), 2
tables. Referee and editor comments incorporate
SGR 1806-20 distance and dust properties in molecular clouds by analysis of a flare x-ray echoes
The soft gamma repeater SGR 1806-20 is most famous for its giant flare from
2004, which yielded the highest gamma-ray flux ever observed on Earth. The
flare emphasized the importance of determining the distance to the SGR, thus
revealing the flare's energy output, with implications on SGRs energy budget
and giant flare rates. We analyze x-ray scattering echoes observed by Swift/XRT
following the 2006 August 6 intermediate burst of SGR 1806-20. Assuming
positions and opacities of the molecular clouds along the line-of-sight from
previous works, we derive direct constrains on the distance to SGR 1806-20,
setting a lower limit of 9.4 kpc and an upper limit of 18.6 kpc (90%
confidence), compared with a 6-15 kpc distance range by previous works. This
distance range matches an energy output of ~10^46 erg/s for the 2004 giant
flare. We further use, for the first time, the x-ray echoes in order to study
the dust properties in molecular clouds. Analyzing the temporal evolution of
the observed flux using a dust scattering model, which assumes a power-law size
distribution of the dust grains, we find a power-law index of
-3.3_{-0.7}^{+0.6} (1 sigma) and a lower limit of 0.1 micron (2 sigma) on the
dust maximal grain size, both conforming to measured dust properties in the
diffused interstellar medium (ISM). We advocate future burst follow-up
observations with Swift, Chandra and the planned NuSTAR telescopes, as means of
obtaining much superior results from such an analysis.Comment: 12 pages, 7 figures, 3 tables, submitted to MNRA
A Strong Jet Signature in the Late-Time Lightcurve of GW170817
We present new 0.6-10 GHz observations of the binary neutron star merger
GW170817 covering the period up to 300 days post-merger, taken with the Karl G.
Jansky Very Large Array, the Australia Telescope Compact Array, the Giant
Metrewave Radio Telescope and the MeerKAT telescope. We use these data to
precisely characterize the decay phase of the late-time radio light curve. We
find that the temporal decay is consistent with a power-law slope of t^-2.2,
and that the transition between the power-law rise and decay is relatively
sharp. Such a slope cannot be produced by a quasi-isotropic (cocoon-dominated)
outflow, but is instead the classic signature of a relativistic jet. This
provides strong observational evidence that GW170817 produced a successful jet,
and directly demonstrates the link between binary neutron star mergers and
short-hard GRBs. Using simple analytical arguments, we derive constraints on
the geometry and the jet opening angle of GW170817. These results are
consistent with those from our companion Very Long Baseline Interferometry
(VLBI) paper, reporting superluminal motion in GW170817.Comment: 11 pages, 3 figures, 3 tables. Accepted for publication in ApJ
Letter
A Revised View of the Transient Radio Sky
We report on a re-analysis of archival data from the Very Large Array for a
sample of ten long duration radio transients reported by Bower and others.
These transients have an implied all-sky rate that would make them the most
common radio transient in the sky and yet most have no quiescent counterparts
at other wavelengths and therefore no known progenitor (other than Galactic
neutron stars). We find that more than half of these transients are due to rare
data artifacts. The remaining sources have lower signal-to-noise ratio (SNR)
than initially reported by 1 to 1.5-sigma. This lowering of SNR matters greatly
since the sources are at the threshold. We are unable to decisively account for
the differences. By two orthogonal criteria one source appears to be a good
detection. Thus the rate of long duration radio transients without optical
counterparts is, at best, comparable to that of the class of recently
discovered Swift J1644+57 nuclear radio transients. We revisit the known and
expected classes of long duration radio transients and conclude that the
dynamic radio sky remains a rich area for further exploration. Informed by the
experience of past searches for radio transients, we suggest that future
surveys pay closer attention to rare data errors and ensure that a wealth of
sensitive multi-wavelength data be available in advance of the radio
observations and that the radio searches should have assured follow-up
resources.Comment: ApJ, submitte
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