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Space Telescope Science Center

Baltimore, MD, United States
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Roming P.W.A.,Southwest Research Institute | Roming P.W.A.,Pennsylvania State University | Pritchard T.A.,Pennsylvania State University | Prieto J.L.,Princeton University | And 20 more authors.
Astrophysical Journal | Year: 2012

We present very early UV to optical photometric and spectroscopic observations of the peculiar TypeIIn supernova (SN) 2011ht in UGC5460. The UV observations of the rise to peak are only the second ever recorded for a TypeIIn SN and are by far the most complete. The SN, first classified as an SN impostor, slowly rose to a peak of MV -17 in 55days. In contrast to the 2mag increase in the v-band light curve from the first observation until peak, the UV flux increased by >7mag. The optical spectra are dominated by strong, Balmer emission with narrow peaks (FWHM 600kms-1), very broad asymmetric wings (FWHM 4200kms-1), and blueshifted absorption (300kms-1) superposed on a strong blue continuum. The UV spectra are dominated by Fe II, Mg II, Si II, and Si III absorption lines broadened by 1500kms-1. Merged X-ray observations reveal a L 0.2-10 = (1.0 ± 0.2) × 1039ergs-1. Some properties of SN 2011ht are similar to SN impostors, while others are comparable to TypeIIn SNe. Early spectra showed features typical of luminous blue variables at maximum and during giant eruptions. However, the broad emission profiles coupled with the strong UV flux have not been observed in previous SN impostors. The absolute magnitude and energetics (2.5 × 1049erg in the first 112days) are reminiscent of normal TypeIIn SN, but the spectra are of a dense wind. We suggest that the mechanism for creating this unusual profile could be a shock interacting with a shell of material that was ejected a year before the discovery of the SN. © 2012. The American Astronomical Society. All rights reserved..


Brown P.J.,University of Utah | Brown P.J.,Mitchell Institute | Dawson K.S.,University of Utah | De Pasquale M.,University of Nevada, Las Vegas | And 11 more authors.
Astrophysical Journal | Year: 2012

We present the earliest ultraviolet (UV) observations of the bright Type Ia supernova SN 2011fe/PTF11kly in the nearby galaxy M101 at a distance of only 6.4 Mpc. It was discovered shortly after explosion by the Palomar Transient Factory and first observed by Swift/UVOT about a day after explosion. The early UV light is well defined, with 20 data points per filter in the five days after explosion. These early and well-sampled UV observations form new template light curves for comparison with observations of other SNe Ia at low and high redshift. We report fits from semiempirical models of the explosion and find the time evolution of the early UV flux to be well fitted by the superposition of two parabolic curves. Finally, we use the early UV flux measurements to examine a possible shock interaction with a non-degenerate companion. From models predicting the measurable shock emission, we find that even a solar mass companion at a distance of a few solar radii is unlikely at more than 95% confidence. © 2012. The American Astronomical Society. All rights reserved.


Oates S.R.,University College London | Page M.J.,University College London | De Pasquale M.,University of Nevada, Las Vegas | Schady P.,Max Planck Institute for Extraterrestrial Physics | And 4 more authors.
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2012

We examine a sample of 48 Swift/UVOT long gamma-ray burst light curves and find a correlation between the logarithmic luminosity at 200 s and average decay rate determined from 200 s onwards, with a Spearman rank coefficient of -0.58 at a significance of 99.998 per cent (4.2σ).We discuss the causes of the log L200s-α>200 s correlation, finding it to be an intrinsic property of long gamma-ray bursts, and not resulting from the selection criteria. We find two ways to produce the correlation. One possibility is that there is some property of the central engine, outflow or external medium that affects the rate of energy release so that the bright afterglows release their energy more quickly and decay faster than the fainter afterglows. Alternatively, the correlation may be produced by variation of the observer's viewing angle, with observers at large viewing angles observing fainter and slower decaying light curves. © 2012 The Authors Monthly Notices of the Royal Astronomical Society. © 2012 RAS.


Oates S.R.,University College London | Page M.J.,University College London | De Pasquale M.,University of Nevada, Las Vegas | Schady P.,Max Planck Institute for Extraterrestrial Physics | And 4 more authors.
EAS Publications Series | Year: 2013

We examine 48 Swift/UVOT long Gamma-ray Burst light curves and find a correlation between the logarithmic luminosity at 200 s and average decay rate determined from 200 s onwards, with a Spearman rank coefficient of -0.58 at a significance of 99.998% (4.2σ). We determine the log L200s - α>200s correlation to be intrinsic and discuss two possible causes: there is a property of the central engine, outflow or external medium that effects the rate of energy release so that the bright afterglows release their energy more quickly and decay faster than the fainter afterglows; alternatively, the observers viewing angle may produce the correlation, with observers at large viewing angles observing fainter and slower decaying light curves. © EAS, EDP Sciences 2013.


Brown P.J.,Texas A&M University | Kuin P.,University College London | Scalzo R.,Australian National University | Smitka M.T.,Texas A&M University | And 5 more authors.
Astrophysical Journal | Year: 2014

Among Type Ia supernovae (SNe Ia), a class of overluminous objects exist whose ejecta mass is inferred to be larger than the canonical Chandrasekhar mass. We present and discuss the UV/optical photometric light curves, colors, absolute magnitudes, and spectra of three candidate Super-Chandrasekhar mass SNe - 2009dc, 2011aa, and 2012dn - observed with the Swift Ultraviolet/Optical Telescope. The light curves are at the broad end for SNe Ia, with the light curves of SN 2011aa being among the broadest ever observed. We find all three to have very blue colors which may provide a means of excluding these overluminous SNe from cosmological analysis, though there is some overlap with the bluest of "normal" SNe Ia. All three are overluminous in their UV absolute magnitudes compared to normal and broad SNe Ia, but SNe 2011aa and 2012dn are not optically overluminous compared to normal SNe Ia. The integrated luminosity curves of SNe 2011aa and 2012dn in the UVOT range (1600-6000 Å) are only half as bright as SN 2009dc, implying a smaller 56Ni yield. While it is not enough to strongly affect the bolometric flux, the early time mid-UV flux makes a significant contribution at early times. The strong spectral features in the mid-UV spectra of SNe 2009dc and 2012dn suggest a higher temperature and lower opacity to be the cause of the UV excess rather than a hot, smooth blackbody from shock interaction. Further work is needed to determine the ejecta and 56Ni masses of SNe 2011aa and 2012dn and to fully explain their high UV luminosities. © 2014. The American Astronomical Society. All rights reserved.


Brown P.J.,Mitchell Institute | Breeveld A.A.,University College London | Holland S.,Space Telescope Science Center | Kuin P.,University College London | Pritchard T.,Pennsylvania State University
Astrophysics and Space Science | Year: 2014

The Ultra-Violet Optical Telescope on the Swift spacecraft has observed hundreds of supernovae, covering all major types and most subtypes. Here we introduce the Swift Optical/Ultraviolet Supernova Archive (SOUSA), which will contain all of the supernova images and photometry. We describe the observation and reduction procedures and how they impact the final data. We show photometry from well-observed examples of most supernova classes, whose absolute magnitudes and colors may be used to infer supernova types in the absence of a spectrum. A full understanding of the variety within classes and a robust photometric separation of the groups requires a larger sample, which will be provided by the final archive. The data from the existing Swift supernovae are also useful for planning future observations with Swift as well as future UV observatories. © 2014, Springer Science+Business Media Dordrecht.


Page M.J.,University College London | Kuin N.P.M.,University College London | Breeveld A.A.,University College London | Hancock B.,University College London | And 12 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2013

The dynamic range of photon counting micro-channel-plate (MCP) intensified chargedcoupled device (CCD) instruments such as the Swift Ultraviolet/Optical Telescope (UVOT) and the XMM-Newton Optical Monitor (XMM-OM) is limited at the bright end by coincidence loss, the superposition of multiple photons in the individual frames recorded by the CCD. Photons which arrive during the brief period in which the image frame is transferred for read out of the CCD are displaced in the transfer direction in the recorded images. For sufficiently bright sources, these displaced counts form read-out streaks. Using UVOT observations of Tycho-2 stars, we investigate the use of these read-out streaks to obtain photometry for sources which are too bright (and hence have too much coincidence loss) for normal aperture photometry to be reliable. For read-out-streak photometry, the bright-source limiting factor is coincidence loss within the MCPs rather than the CCD. We find that photometric measurements can be obtained for stars up to 2.4 mag brighter than the usual full-frame coincidence-loss limit by using the read-out streaks. The resulting bright-limit Vega magnitudes in the UVOT passbands are UVW2 = 8.80, UVM2 = 8.27, UVW1 = 8.86, u = 9.76, b = 10.53, v = 9.31 and White = 11.71; these limits are independent of the windowing mode of the camera. We find that a photometric precision of 0.1 mag can be achieved through read-out streak measurements. A suitable method for the measurement of read-out streaks is described and all necessary calibration factors are given. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

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