969 research outputs found

    Detection of a supernova signature associated with GRB 011121

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    Using observations from an extensive monitoring campaign with the Hubble Space Telescope we present the detection of an intermediate-time flux excess which is redder in color relative to the afterglow of GRB 011121, currently distinguished as the gamma-ray burst with the lowest known redshift. The red ``bump,'' which exhibits a spectral roll-over at ~7200 Angstrom, is well described by a redshifted Type Ic supernova that occurred approximately at the same time as the gamma-ray burst event. The inferred luminosity is about half that of the bright supernova 1998bw. These results serve as compelling evidence for a massive star origin of long-duration gamma-ray bursts. Models that posit a supernova explosion weeks to months preceding the gamma-ray burst event are excluded by these observations. Finally, we discuss the relationship between spherical core-collapse supernovae and gamma-ray bursts.Comment: Published in the Astrophysical Journal (Letters) on 20 May 2002. Seven LaTeX pages, three Postscript figures, one tabl

    500 Days of SN 2013dy: spectra and photometry from the ultraviolet to the infrared

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    SN 2013dy is a Type Ia supernova for which we have compiled an extraordinary dataset spanning from 0.1 to ~ 500 days after explosion. We present 10 epochs of ultraviolet (UV) through near-infrared (NIR) spectra with HST/STIS, 47 epochs of optical spectra (15 of them having high resolution), and more than 500 photometric observations in the BVrRiIZYJH bands. SN 2013dy has a broad and slowly declining light curve (delta m(B) = 0.92 mag), shallow Si II 6355 absorption, and a low velocity gradient. We detect strong C II in our earliest spectra, probing unburned progenitor material in the outermost layers of the SN ejecta, but this feature fades within a few days. The UV continuum of SN 2013dy, which is strongly affected by the metal abundance of the progenitor star, suggests that SN 2013dy had a relatively high-metallicity progenitor. Examining one of the largest single set of high-resolution spectra for a SN Ia, we find no evidence of variable absorption from circumstellar material. Combining our UV spectra, NIR photometry, and high-cadence optical photometry, we construct a bolometric light curve, showing that SN 2013dy had a maximum luminosity of 10.0^{+4.8}_{-3.8} * 10^{42} erg/s. We compare the synthetic light curves and spectra of several models to SN 2013dy, finding that SN 2013dy is in good agreement with a solar-metallicity W7 model.Comment: 22 pages, 18 figures, replaced with version accecpted for publication in MNRA

    SN2008am: A Super-Luminous Type IIn Supernova

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    We present observations and interpretation of the Type IIn supernova SN 2008am discovered by the ROTSE Supernova Verification Project (RSVP). SN 2008am peaked at approximately -22.3 mag at a redshift of z=0.2338, giving it a peak luminosity of 3 x 10^{44}erg/s and making it one of the most luminous supernovae ever observed. The total radiated energy is ~ 2 x 10^{51} erg. Photometric observations in the ultraviolet, optical and infrared bands (J,H,Ks) constrain the SED evolution. We obtained six optical spectra of the supernova, five on the early decline from maximum light and a sixth nearly a year later plus a very late-time spectrum (~2 yr) of the host galaxy. The spectra of SN 2008am show strong Balmer-line and He I lambda 5876A emission with intermediate widths (~25A) in the first ~40 days after optical maximum. We examine a variety of models for the line wings and conclude that multiple scattering is most likely, implying that our spectra contain no specific information on the bulk flow velocity. We examine a variety of models for the ROTSE light curve subject to the rise time and the nature of the spectra, including radioactive decay, shocks in optically-thick and optically-thin circumstellar media (CSM) and a magnetar. The most successful model is one for which the CSM is optically-thick and in which diffusion of forward shock-deposited luminosity gives rise to the observed light curve. Diffusion of the shock-deposited energy from the forward shock is found to be important to account for the rising part of the light curve. Although there are differences in detail, SN 2008am appears to be closely related to other super-luminous Type IIn supernovae, SN 2006gy, SN 2006tf and perhaps SN 2008iy, that may represent the deaths of very massive LBV-type progenitors and for which the luminosity is powered by the interaction of the ejecta with a dense circumstellar medium.Comment: 58 pages, 14 figure

    Extensive Spectroscopy and Photometry of the Type IIP Supernova 2013ej

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    We present extensive optical (UBVRIUBVRI, grizg'r'i'z', and open CCD) and near-infrared (ZYJHZYJH) photometry for the very nearby Type IIP SN ~2013ej extending from +1 to +461 days after shock breakout, estimated to be MJD 56496.9±0.356496.9\pm0.3. Substantial time series ultraviolet and optical spectroscopy obtained from +8 to +135 days are also presented. Considering well-observed SNe IIP from the literature, we derive UBVRIJHKUBVRIJHK bolometric calibrations from UBVRIUBVRI and unfiltered measurements that potentially reach 2\% precision with a BVB-V color-dependent correction. We observe moderately strong Si II λ6355\lambda6355 as early as +8 days. The photospheric velocity (vphv_{\rm ph}) is determined by modeling the spectra in the vicinity of Fe II λ5169\lambda5169 whenever observed, and interpolating at photometric epochs based on a semianalytic method. This gives vph=4500±500v_{\rm ph} = 4500\pm500 km s1^{-1} at +50 days. We also observe spectral homogeneity of ultraviolet spectra at +10--12 days for SNe IIP, while variations are evident a week after explosion. Using the expanding photosphere method, from combined analysis of SN 2013ej and SN 2002ap, we estimate the distance to the host galaxy to be 9.00.6+0.49.0_{-0.6}^{+0.4} Mpc, consistent with distance estimates from other methods. Photometric and spectroscopic analysis during the plateau phase, which we estimated to be 94±794\pm7 days long, yields an explosion energy of 0.9±0.3×10510.9\pm0.3\times10^{51} ergs, a final pre-explosion progenitor mass of 15.2±4.215.2\pm4.2~M_\odot and a radius of 250±70250\pm70~R_\odot. We observe a broken exponential profile beyond +120 days, with a break point at +183±16183\pm16 days. Measurements beyond this break time yield a 56^{56}Ni mass of 0.013±0.0010.013\pm0.001~M_\odot.Comment: 29 pages, 23 figures, 15 tables, Published in The Astrophisical Journa

    New interpretation of variational principles for gauge theories. I. Cyclic coordinate alternative to ADM split

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    I show how there is an ambiguity in how one treats auxiliary variables in gauge theories including general relativity cast as 3 + 1 geometrodynamics. Auxiliary variables may be treated pre-variationally as multiplier coordinates or as the velocities corresponding to cyclic coordinates. The latter treatment works through the physical meaninglessness of auxiliary variables' values applying also to the end points (or end spatial hypersurfaces) of the variation, so that these are free rather than fixed. [This is also known as variation with natural boundary conditions.] Further principles of dynamics workings such as Routhian reduction and the Dirac procedure are shown to have parallel counterparts for this new formalism. One advantage of the new scheme is that the corresponding actions are more manifestly relational. While the electric potential is usually regarded as a multiplier coordinate and Arnowitt, Deser and Misner have regarded the lapse and shift likewise, this paper's scheme considers new {\it flux}, {\it instant} and {\it grid} variables whose corresponding velocities are, respectively, the abovementioned previously used variables. This paper's way of thinking about gauge theory furthermore admits interesting generalizations, which shall be provided in a second paper.Comment: 11 page

    Measuring brain atrophy with a generalized formulation of the boundary shift integral.

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    Brain atrophy measured using structural magnetic resonance imaging (MRI) has been widely used as an imaging biomarker for disease diagnosis and tracking of pathologic progression in neurodegenerative diseases. In this work, we present a generalized and extended formulation of the boundary shift integral (gBSI) using probabilistic segmentations to estimate anatomic changes between 2 time points. This method adaptively estimates a non-binary exclusive OR region of interest from probabilistic brain segmentations of the baseline and repeat scans to better localize and capture the brain atrophy. We evaluate the proposed method by comparing the sample size requirements for a hypothetical clinical trial of Alzheimer's disease to that needed for the current implementation of BSI as well as a fuzzy implementation of BSI. The gBSI method results in a modest but reduced sample size, providing increased sensitivity to disease changes through the use of the probabilistic exclusive OR region
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