E. S. Walker
A5077786023- Gamma-ray bursts and supernovae
- Astronomy and Astrophysical Research
- Astrophysics and Cosmic Phenomena
- Pulsars and Gravitational Waves Research
- Astrophysical Phenomena and Observations
- Stellar, planetary, and galactic studies
- Astro and Planetary Science
- Nuclear Physics and Applications
- Astronomical Observations and Instrumentation
- Galaxies: Formation, Evolution, Phenomena
- Solid-state spectroscopy and crystallography
- Crystal Structures and Properties
- Laser Design and Applications
- Spectroscopy and Laser Applications
- High-pressure geophysics and materials
- Methane Hydrates and Related Phenomena
- Geophysics and Gravity Measurements
- Advanced NMR Techniques and Applications
- Radiation Therapy and Dosimetry
- Medical Imaging Techniques and Applications
- Spectroscopy Techniques in Biomedical and Chemical Research
- Neutrino Physics Research
- Geological and Geophysical Studies
- Anatomy and Medical Technology
- Surgical Simulation and Training
École Polytechnique Fédérale de Lausanne
2023
Letterkenny University Hospital
2023
Virginia Tech
2023
Cardiff University
2023
Guyra Paraguay
2022
Yale University
2013-2018
Scuola Normale Superiore
2010-2014
University of Oxford
2008-2011
Trieste Astronomical Observatory
2010
Max Planck Institute for Astronomy
2008
We combine high redshift Type Ia supernovae from the first 3 years of Supernova Legacy Survey (SNLS) with other supernova (SN) samples, primarily at lower redshifts, to form a high-quality joint sample 472 SNe (123 low-$z$, 93 SDSS, 242 SNLS, and 14 {\it Hubble Space Telescope}). SN data alone require cosmic acceleration >99.9% confidence, including systematic effects. For dark energy equation state parameter (assumed constant out least $z=1.4$) in flat universe, we find $w =...
We present observational constraints on the nature of dark energy using Supernova Legacy Survey three-year sample (SNLS3) Guy et al. and Conley use 472 Type Ia supernovae (SNe Ia) in this sample, accounting for recently discovered correlations between SN luminosity host galaxy properties, include effects all identified systematic uncertainties directly cosmological fits. Combining SNLS3 data with full WMAP7 power spectrum, Sloan Digital Sky luminous red a prior Hubble constant H0 from SHOES,...
(Abridged) Precision cosmology with Type Ia supernovae (SNe Ia) makes use of the fact that SN luminosities depend on their light-curve shapes and colours. Using Supernova Legacy Survey (SNLS) other data, we show there is an additional dependence global characteristics host galaxies: events same shape colour are, average, 0.08mag (~4.0sigma) brighter in massive galaxies (presumably metal-rich) low specific star-formation rates (sSFR). SNe a sSFR also have smaller slope ("beta") between...
The Public European Southern Observatory Spectroscopic Survey of Transient Objects (PESSTO) began as a public spectroscopic survey in April 2012. We describe the data reduction strategy and products which are publicly available through ESO archive Data Release 1 (SSDR1). PESSTO uses New Technology Telescope with EFOSC2 SOFI to provide optical NIR spectroscopy imaging. target supernovae transients brighter than 20.5mag for classification. Science targets then selected follow-up based on...
The intermediate Palomar Transient Factory reports our discovery of a young supernova, iPTF13bvn, in the nearby galaxy, NGC 5806 (22.5 Mpc). Our spectral sequence optical and infrared suggests Type Ib classification. We identify blue progenitor candidate deep pre-explosion imaging within 2σ error circle 80 mas (8.7 pc). has an MB luminosity −5.52 ± 0.39 mag B − I color 0.25 mag. If confirmed by future observations, this would be first direct detection for Ib. Fitting power law to early light...
On May 31, 2011 UT a supernova (SN) exploded in the nearby galaxy M51 (the Whirlpool Galaxy). We discovered this event using small telescopes equipped with CCD cameras, as well by Palomar Transient Factory (PTF) survey, and rapidly confirmed it to be Type II supernova. Our early light curve spectroscopy indicates that PTF11eon resulted from explosion of relatively compact progenitor star evidenced rapid shock-breakout cooling seen curve, low temperature early-time spectra prompt appearance...
Hubble Space Telescope spectroscopic observations of the nearby type Ia supernova (SN Ia) SN2011fe, taken on 10 epochs from -13.1 to +40.8 days relative B-band maximum light, and spanning far-ultraviolet (UV) near-infrared (IR) are presented. This coverage makes SN2011fe best-studied local SN date. is a typical moderately-luminous with no evidence for dust extinction. Its near-UV spectral properties representative larger sample events (Maguire et al. 2012). The optical spectra modelled Monte...
We present optical spectra and light curves for three hydrogen-poor superluminous supernovae followed by the Public ESO Spectroscopic Survey of Transient Objects (PESSTO). Time series spectroscopy from a few days after maximum to 100 d later shows them be fairly typical this class, with dominated Ca ii, Mg Fe Si which evolve slowly over most post-peak photospheric phase. determine bolometric apply simple fitting tools, based on diffusion energy input magnetar spin-down, 56Ni decay, collision...
The nearby Type Ia supernova (SN Ia) SN 2011fe in M101 (cz = 241 km s−1) provides a unique opportunity to study the early evolution of "normal" Ia, its compositional structure, and elusive progenitor system. We present 18 high signal-to-noise spectra during first month beginning 1.2 days post-explosion with an average cadence 1.8 days. This gives clear picture how various line-forming species are distributed within outer layers ejecta, including that unburned material (C+O). follow C ii...
We present an analysis of the early, rising light curves 18 Type Ia supernovae (SNe Ia) discovered by Palomar Transient Factory and La Silla-QUEST variability survey. fit these early data flux using a simple power law (f(t) = α × tn) to determine time first (t0), hence rise (trise) from peak luminosity, exponent power-law (n). find mean uncorrected 18.98 ± 0.54 d, with individual supernova (SN) times ranging 15.98 24.7 d. The n shows significant departures 'fireball model' 2 (or f(t) ∝ t2)...
We present spectroscopic observations of the host galaxies 82 low-redshift Type Ia supernovae (SNe Ia) discovered by Palomar Transient Factory. determine star formation rates, gas-phase/stellar metallicities, and stellar masses ages these objects. As expected, strong correlations between SN light-curve width (stretch) age/mass/metallicity are found: fainter, faster declining events tend to be hosted older/massive/metal-rich galaxies. There is some evidence that redder SNe explode in higher...
A key tracer of the elusive progenitor systems Type Ia supernovae (SNe Ia) is detection narrow blueshifted time-varying Na i D absorption lines, interpreted as evidence circumstellar material surrounding system. The origin this controversial, but simplest explanation that it results from previous mass-loss in a system containing white dwarf and non-degenerate companion star. We present new single-epoch intermediate-resolution spectra 17 low-redshift SNe taken with XShooter on European...
We use three years of data from the Supernova Legacy Survey (SNLS) to study general properties core-collapse and type Ia supernovae. This is first such using "rolling search" technique which guarantees well-sampled SNLS light curves good efficiency for supernovae brighter than $i^\prime\sim24$. Using host photometric redshifts, we measure supernova absolute magnitude distribution down luminosities $4.5 {\rm mag}$ fainter normal SNIa. spectroscopy light-curve fitting discriminate against...
Massive stars undergo a violent death when the supply of nuclear fuel in their cores is exhausted, resulting catastrophic “core-collapse” supernova. Such events are usually only detected at least few days after star has exploded. Observations supernova SNLS-04D2dc with Galaxy Evolution Explorer space telescope reveal radiative precursor from shock before reached surface and show initial expansion beginning explosion. Theoretical models ultraviolet light curve confirm that progenitor was red...
Timmes, Brown & Truran found that metallicity variations could theoretically account for a 25% variation in the mass of 56Ni synthesized Type Ia supernovae (SNe Ia), and thus large fraction scatter observed SN luminosities. Higher-metallicity progenitors are more neutron-rich, producing stable burning products relative to radioactive 56Ni. We develop new method estimating bolometric luminosity yield SNe use it test theory with data from Supernova Legacy Survey. find average does drop high...
In the ultraviolet (UV), Type Ia supernovae (SNe Ia) show a much larger diversity in their properties than optical. Using stationary Monte Carlo radiative transfer code, grid of spectra at maximum light was created varying bolometric luminosity and amount metals outer layers SN ejecta. This model is then compared to sample high-redshift SNe order test whether observed diversities can be explained by metallicity changes alone. The dispersion broad-band UV flux colours approximately constant...
The Palomar Transient Factory (PTF) is an optical wide-field variability survey carried out using a camera with 7.8 square degree field of view mounted on the 48-in Oschin Schmidt telescope at Observatory. One key goals this to conduct high-cadence monitoring sky in order detect transient sources shortly after they occur. Here, we describe real-time capabilities PTF and our related rapid multiwavelength follow-up programs, extending from radio gamma-ray bands. We present as case study...
The La Silla-QUEST Low Redshift Supernova Survey is a part of the Southern Hemisphere Variability Survey. survey uses 10 deg2 QUEST camera installed at prime focus 1.0-m Schmidt Telescope European Observatory Silla, Chile, and utilizes essentially all observing time telescope. was on ESO telescope in 2009 after completing 5 year variability northern hemisphere using 1.2-m Oschin Palomar. started science operations September. low redshift supernova commenced 2011 December planned to continue...
We present an analysis of the maximum light, near ultraviolet (NUV; 2900-5500 A) spectra 32 low redshift (0.001<z<0.08) Type Ia supernovae (SNe Ia), obtained with Hubble Space Telescope (HST). combine this spectroscopic sample high-quality gri light curves robotic telescopes to measure photometric parameters, such as stretch, optical colour, and brightness. By comparing our data a comparable SNe at intermediate-z (0.4<z<0.9), we detect modest spectral evolution (3-sigma), in sense that mean...
We present an investigation of the optical spectra 264 low-redshift (z < 0.2) Type Ia supernovae (SNe Ia) discovered by Palomar Transient Factory, untargeted transient survey. focus on velocity and pseudo-equivalent width measurements Si II 4130, 5972, 6355 A lines, as well those Ca near-infrared (NIR) triplet, up to +5 days relative SN B-band maximum light. find that a high-velocity component NIR triplet is needed explain spectrum in ~95 per cent SNe observed before -5 days, decreasing ~80...
We present X-ray, UV/optical, and radio observations of the stripped-envelope, core-collapse supernova (SN) 2011ei, one least luminous SNe IIb or Ib observed to date. Our begin with a discovery within 1 day explosion span several months afterward. Early optical spectra exhibit broad, Type II-like hydrogen Balmer profiles that subside rapidly are replaced by Ib-like He-rich features on timescale week. High-cadence monitoring this transition suggests absorption attributable high velocity (>...
The Carnegie Supernova Project-II (CSP-II) was an NSF-funded, four-year program to obtain optical and near-infrared observations of a "Cosmology" sample ∼100 Type Ia supernovae located in the smooth Hubble flow (0.03 ≲ z 0.10). Light curves were also obtained "Physics" composed 90 nearby at ≤ 0.04 selected for spectroscopic timeseries observations. primary emphasis CSP-II is use combination photometry achieve distance precision better than 5%. In this paper, details supernova sample,...
Observations spanning a large wavelength range, from X-ray to radio, of the Type IIb supernova 2011hs are presented, covering its evolution during first year after explosion. The optical light curve presents narrower shape and fainter luminosity at peak than previously observed for SNe. High expansion velocities measured broad absorption H I He lines. From comparison bolometric time photospheric with hydrodynamical models, we found that SN is consistent explosion 3-4 Msun He-core progenitor...
We present photometric and spectroscopic observations of the interacting transient SN 2009ip taken during 2013 2014 observing seasons. characterize evolution as a steady smooth decline in all bands, with rate that is slower than expected for solely 56Co-powered supernova at late phases. No further outbursts or eruptions were seen over two year period from 2012 December until December. remains brighter its historic minimum pre-discovery images. Spectroscopically, continues to be dominated by...