539 research outputs found
Photometric Calibration of the Swift Ultraviolet/Optical Telescope
We present the photometric calibration of the Swift UltraViolet/Optical
Telescope (UVOT) which includes: optimum photometric and background apertures,
effective area curves, colour transformations, conversion factors for count
rates to flux, and the photometric zero points (which are accurate to better
than 4 per cent) for each of the seven UVOT broadband filters. The calibration
was performed with observations of standard stars and standard star fields that
represent a wide range of spectral star types. The calibration results include
the position dependent uniformity, and instrument response over the 1600-8000A
operational range. Because the UVOT is a photon counting instrument, we also
discuss the effect of coincidence loss on the calibration results. We provide
practical guidelines for using the calibration in UVOT data analysis. The
results presented here supersede previous calibration results.Comment: Minor improvements after referees report. Accepted for publication in
MNRA
Re-prioritizing traffic stops to reduce motor vehicle crash outcomes and racial disparities
Background: Law enforcement traffic stops are one of the most common entryways to the US justice system. Conventional frameworks suggest traffic stops promote public safety by reducing dangerous driving practices and non-vehicular crime. Law enforcement agencies have wide latitude in enforcement, including prioritization of stop types: (1) safety (e.g. moving violation) stops, (2) investigatory stops, or (3) economic (regulatory and equipment) stops. In order to prevent traffic crash fatalities and reduce racial disparities, the police department of Fayetteville, North Carolina significantly re-prioritized safety stops. Methods: Annual traffic stop, motor vehicle crash, and crime data from 2002 to 2016 were combined to examine intervention (2013-2016) effects. Fayetteville was compared against synthetic control agencies built from 8 similar North Carolina agencies by weighted matching on pre-intervention period trends and comparison against post-intervention trends. Results: On average over the intervention period as compared to synthetic controls, Fayetteville increased both the number of safety stops + 121% (95% confidence interval + 17%, + 318%) and the relative proportion of safety stops (+ 47%). Traffic crash and injury outcomes were reduced, including traffic fatalities - 28% (- 64%, + 43%), injurious crashes - 23% (- 49%, + 16%), and total crashes - 13% (- 48%, + 21%). Disparity measures were reduced, including Black percent of traffic stops - 7% (- 9%, - 5%) and Black vs. White traffic stop rate ratio - 21% (- 29%, - 13%). In contrast to the Ferguson Effect hypothesis, the relative de-prioritization of investigatory stops was not associated with an increase in non-traffic crime outcomes, which were reduced or unchanged, including index crimes - 10% (- 25%, + 8%) and violent crimes - 2% (- 33%, + 43%). Confidence intervals were estimated using a different technique and, given small samples, may be asymmetrical. Conclusions: The re-prioritization of traffic stop types by law enforcement agencies may have positive public health consequences both for motor vehicle injury and racial disparity outcomes while having little impact on non-traffic crime
Procedural Signaling, Party Loyalty, and Traceability in the U.S. House of Representatives
In this article, we take advantage of a new source of data providing updates from the Majority Leader’s Office that signal the leadership’s positions on floor votes. We offer a more nuanced explanation of voting in the U.S. House as our findings suggest that not all procedural votes are created equal. While the most liberal members of the party vote with the leadership on procedural votes at high rates and nearly 100 percent of the time when signaled by the majority leader, moderate members are significantly less likely to support the party and are not responsive to these signals.Yeshttps://us.sagepub.com/en-us/nam/manuscript-submission-guideline
Paper II: Calibration of the Swift ultraviolet/optical telescope
The Ultraviolet/Optical Telescope (UVOT) is one of three instruments onboard
the Swift observatory. The photometric calibration has been published, and this
paper follows up with details on other aspects of the calibration including a
measurement of the point spread function with an assessment of the orbital
variation and the effect on photometry. A correction for large scale variations
in sensitivity over the field of view is described, as well as a model of the
coincidence loss which is used to assess the coincidence correction in extended
regions. We have provided a correction for the detector distortion and measured
the resulting internal astrometric accuracy of the UVOT, also giving the
absolute accuracy with respect to the International Celestial Reference System.
We have compiled statistics on the background count rates, and discuss the
sources of the background, including instrumental scattered light. In each case
we describe any impact on UVOT measurements, whether any correction is applied
in the standard pipeline data processing or whether further steps are
recommended.Comment: Accepted for publication in MNRAS. 15 pages, 21 figures, 4 table
Ultraviolet number counts of galaxies from Swift UV/Optical Telescope deep imaging of the Chandra Deep Field South
Deep Swift UV/Optical Telescope (UVOT) imaging of the Chandra Deep Field
South is used to measure galaxy number counts in three near ultraviolet (NUV)
filters (uvw2: 1928 A, uvm2: 2246 A, uvw1: 2600 A) and the u band (3645 A).
UVOT observations cover the break in the slope of the NUV number counts with
greater precision than the number counts by the Hubble Space Telescope (HST)
Space Telescope Imaging Spectrograph (STIS) and the Galaxy Evolution Explorer
(GALEX), spanning a range from 21 < m_AB < 25. Number counts models confirm
earlier investigations in favoring models with an evolving galaxy luminosity
function.Comment: 20 pages, 6 figures, accepted to Ap
GRB 081203A: Swift UVOT captures the earliest ultraviolet spectrum of a gamma-ray burst
We present the earliest ultraviolet (UV) spectrum of a gamma-ray burst (GRB) as observed with the Swift Ultra-Violet/Optical Telescope (UVOT). The GRB 081203A spectrum was observed for 50 s with the UV-grism starting 251 s after the Swift-Burst-Alert-Telescope (BAT) trigger. During this time, the GRB was ≈13.4 mag (u filter) and was still rising to its peak optical brightness. In the UV-grism spectrum, we find a damped Lyα line, Lyβ and the Lyman continuum break at a redshift z= 2.05 ± 0.01. A model fit to the Lyman absorption implies a gas column density of log NH i= 22.0 ± 0.1 cm−2, which is typical of GRB host galaxies with damped Lyα absorbers. This observation of GRB 081203A demonstrates that for brighter GRBs (v≈ 14 mag) with moderate redshift (0.5 < z < 3.5) the UVOT is able to provide redshifts, and probe for damped Lyα absorbers within 4–6 min from the time of the Swift-BAT trigger
A statistical study of gamma-ray burst afterglows measured by the Swift Ultra-violet Optical Telescope
We present the first statistical analysis of 27 UVOT optical/ultra-violet
lightcurves of GRB afterglows. We have found, through analysis of the
lightcurves in the observer's frame, that a significant fraction rise in the
first 500s after the GRB trigger, that all lightcurves decay after 500s,
typically as a power-law with a relatively narrow distribution of decay
indices, and that the brightest optical afterglows tend to decay the quickest.
We find that the rise could either be produced physically by the start of the
forward shock, when the jet begins to plough into the external medium, or
geometrically where an off-axis observer sees a rising lightcurve as an
increasing amount of emission enters the observers line of sight, which occurs
as the jet slows. We find that at 99.8% confidence, there is a correlation, in
the observed frame, between the apparent magnitude of the lightcurves at 400s
and the rate of decay after 500s. However, in the rest frame a Spearman Rank
test shows only a weak correlation of low statistical significance between
luminosity and decay rate. A correlation should be expected if the afterglows
were produced by off-axis jets, suggesting that the jet is viewed from within
the half-opening angle theta or within a core of uniform energy density
theta_c. We also produced logarithmic luminosity distributions for three rest
frame epochs. We find no evidence for bimodality in any of the distributions.
Finally, we compare our sample of UVOT lightcurves with the XRT lightcurve
canonical model. The range in decay indices seen in UVOT lightcurves at any
epoch is most similar to the range in decay of the shallow decay segment of the
XRT canonical model. However, in the XRT canonical model there is no indication
of the rising behaviour observed in the UVOT lightcurves.Comment: 16 pages, 9 figures, accepted MNRA
Swift panchromatic observations of the bright gamma-ray burst GRB050525a
The bright gamma-ray burst GRB050525a has been detected with the Swift
observatory, providing unique multiwavelength coverage from the very earliest
phases of the burst. The X-ray and optical/UV afterglow decay light curves both
exhibit a steeper slope ~0.15 days after the burst, indicative of a jet break.
This jet break time combined with the total gamma-ray energy of the burst
constrains the opening angle of the jet to be 3.2 degrees. We derive an
empirical `time-lag' redshift from the BAT data of z_hat = 0.69 +/- 0.02, in
good agreement with the spectroscopic redshift of 0.61.
Prior to the jet break, the X-ray data can be modelled by a simple power law
with index alpha = -1.2. However after 300 s the X-ray flux brightens by about
30% compared to the power-law fit. The optical/UV data have a more complex
decay, with evidence of a rapidly falling reverse shock component that
dominates in the first minute or so, giving way to a flatter forward shock
component at later times.
The multiwavelength X-ray/UV/Optical spectrum of the afterglow shows evidence
for migration of the electron cooling frequency through the optical range
within 25000 s. The measured temporal decay and spectral indices in the X-ray
and optical/UV regimes compare favourably with the standard fireball model for
Gamma-ray bursts assuming expansion into a constant density interstellar
medium.Comment: 31 pages, 7 figures, referee comments implemented, typo corrected in
author list, accepted by Ap
Comparing Breast Cancer Multiparameter Tests in the OPTIMA Prelim Trial: No Test Is More Equal Than the Others
Background: Previous reports identifying discordance between multiparameter tests at the individual patient level have been largely attributed to methodological shortcomings of multiple in silico studies. Comparisons between tests, when performed using actual diagnostic assays, have been predicted to demonstrate high degrees of concordance. OPTIMA prelim compared predicted risk stratification and subtype classification of different multiparameter tests performed directly on the same population.
Methods: Three hundred thirteen women with early breast cancer were randomized to standard (chemotherapy and endocrine therapy) or test-directed (chemotherapy if Oncotype DX recurrence score >25) treatment. Risk stratification was also determined with Prosigna (PAM50), MammaPrint, MammaTyper, NexCourse Breast (IHC4-AQUA), and conventional IHC4 (IHC4). Subtype classification was provided by Blueprint, MammaTyper, and Prosigna.
Results: Oncotype DX predicted a higher proportion of tumors as low risk (82.1%, 95% confidence interval [CI] = 77.8% to 86.4%) than were predicted low/intermediate risk using Prosigna (65.5%, 95% CI = 60.1% to 70.9%), IHC4 (72.0%, 95% CI = 66.5% to 77.5%), MammaPrint (61.4%, 95% CI = 55.9% to 66.9%), or NexCourse Breast (61.6%, 95% CI = 55.8% to 67.4%). Strikingly, the five tests showed only modest agreement when dichotomizing results between high vs low/intermediate risk. Only 119 (39.4%) tumors were classified uniformly as either low/intermediate risk or high risk, and 183 (60.6%) were assigned to different risk categories by different tests, although 94 (31.1%) showed agreement between four of five tests. All three subtype tests assigned 59.5% to 62.4% of tumors to luminal A subtype, but only 121 (40.1%) were classified as luminal A by all three tests and only 58 (19.2%) were uniformly assigned as nonluminal A. Discordant subtyping was observed in 123 (40.7%) tumors.
Conclusions: Existing evidence on the comparative prognostic information provided by different tests suggests that current multiparameter tests provide broadly equivalent risk information for the population of women with estrogen receptor (ER)–positive breast cancers. However, for the individual patient, tests may provide differing risk categorization and subtype information
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