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 &gt;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

Finding a moral homeground: appropriately critical religious education and transmission of spiritual values

Values-inspired issues remain an important part of the British school curriculum. Avoiding moral relativism while fostering enthusiasm for spiritual values and applying them to non-curricular learning such as school ethos or children's home lives are challenges where spiritual, moral, social and cultural (SMSC) development might benefit from leadership by critical religious education (RE). Whether the school's model of spirituality is that of an individual spiritual tradition (schools of a particular religious character) or universal pluralistic religiosity (schools of plural religious character), the pedagogy of RE thought capable of leading SMSC development would be the dialogical approach with examples of successful implementation described by Gates, Ipgrave and Skeie. Marton's phenomenography, is thought to provide a valuable framework to allow the teacher to be appropriately critical in the transmission of spiritual values in schools of a particular religious character as evidenced by Hella's work in Lutheran schools