569 research outputs found
PHotometry Assisted Spectral Extraction (PHASE) and identification of SNLS supernovae
Aim: We present new extraction and identification techniques for supernova
(SN) spectra developed within the Supernova Legacy Survey (SNLS) collaboration.
Method: The new spectral extraction method takes full advantage of
photometric information from the Canada-France-Hawai telescope (CFHT) discovery
and reference images by tracing the exact position of the supernova and the
host signals on the spectrogram. When present, the host spatial profile is
measured on deep multi-band reference images and is used to model the host
contribution to the full (supernova + host) signal. The supernova is modelled
as a Gaussian function of width equal to the seeing. A chi-square minimisation
provides the flux of each component in each pixel of the 2D spectrogram. For a
host-supernova separation greater than <~ 1 pixel, the two components are
recovered separately and we do not use a spectral template in contrast to more
standard analyses. This new procedure permits a clean extraction of the
supernova separately from the host in about 70% of the 3rd year ESO/VLT spectra
of the SNLS. A new supernova identification method is also proposed. It uses
the SALT2 spectrophotometric template to combine the photometric and spectral
data. A galaxy template is allowed for spectra for which a separate extraction
of the supernova and the host was not possible.
Result: These new techniques have been tested against more standard
extraction and identification procedures. They permit a secure type and
redshift determination in about 80% of cases. The present paper illustrates
their performances on a few sample spectra.Comment: 27 pages, 18 Figures, 1 Table. Accepted for publication in A&
An Efficient Approach to Obtaining Large Numbers of Distant Supernova Host Galaxy Redshifts
We use the wide-field capabilities of the 2dF fibre positioner and the
AAOmega spectrograph on the Anglo-Australian Telescope (AAT) to obtain
redshifts of galaxies that hosted supernovae during the first three years of
the Supernova Legacy Survey (SNLS). With exposure times ranging from 10 to 60
ksec per galaxy, we were able to obtain redshifts for 400 host galaxies in two
SNLS fields, thereby substantially increasing the total number of SNLS
supernovae with host galaxy redshifts. The median redshift of the galaxies in
our sample that hosted photometrically classified Type Ia supernovae (SNe Ia)
is 0.77, which is 25% higher than the median redshift of spectroscopically
confirmed SNe Ia in the three-year sample of the SNLS. Our results demonstrate
that one can use wide-field fibre-fed multi-object spectrographs on 4m
telescopes to efficiently obtain redshifts for large numbers of supernova host
galaxies over the large areas of sky that will be covered by future
high-redshift supernova surveys, such as the Dark Energy Survey.Comment: 22 pages, 4 figures, accepted for publication in PAS
Two superluminous supernovae from the early universe discovered by the Supernova Legacy Survey
We present spectra and lightcurves of SNLS 06D4eu and SNLS 07D2bv, two
hydrogen-free superluminous supernovae discovered by the Supernova Legacy
Survey. At z = 1.588, SNLS 06D4eu is the highest redshift superluminous SN with
a spectrum, at M_U = -22.7 is one of the most luminous SNe ever observed, and
gives a rare glimpse into the restframe ultraviolet where these supernovae put
out their peak energy. SNLS 07D2bv does not have a host galaxy redshift, but
based on the supernova spectrum, we estimate it to be at z ~ 1.5. Both
supernovae have similar observer-frame griz lightcurves, which map to restframe
lightcurves in the U-band and UV, rising in ~ 20 restframe days or longer, and
declining over a similar timescale. The lightcurves peak in the shortest
wavelengths first, consistent with an expanding blackbody starting near 15,000
K and steadily declining in temperature. We compare the spectra to theoretical
models, and identify lines of C II, C III, Fe III, and Mg II in the spectrum of
SNLS 06D4eu and SCP 06F6, and find that they are consistent with an expanding
explosion of only a few solar masses of carbon, oxygen, and other trace metals.
Thus the progenitors appear to be related to those suspected for SNe Ic. A high
kinetic energy, 10^52 ergs, is also favored. Normal mechanisms of powering
core- collapse or thermonuclear supernovae do not seem to work for these
supernovae. We consider models powered by 56Ni decay and interaction with
circumstellar material, but find that the creation and spin-down of a magnetar
with a period of 2ms, magnetic field of 2 x 10^14 Gauss, and a 3 solar mass
progenitor provides the best fit to the data.Comment: ApJ, accepted, 43 pages, 15 figure
SiFTO: An Empirical Method for Fitting SNe Ia Light Curves
We present SiFTO, a new empirical method for modeling type Ia supernovae (SNe
Ia) light curves by manipulating a spectral template. We make use of
high-redshift SN observations when training the model, allowing us to extend it
bluer than rest frame U. This increases the utility of our high-redshift SN
observations by allowing us to use more of the available data. We find that
when the shape of the light curve is described using a stretch prescription,
applying the same stretch at all wavelengths is not an adequate description.
SiFTO therefore uses a generalization of stretch which applies different
stretch factors as a function of both the wavelength of the observed filter and
the stretch in the rest-frame B band. We compare SiFTO to other published
light-curve models by applying them to the same set of SN photometry, and
demonstrate that SiFTO and SALT2 perform better than the alternatives when
judged by the scatter around the best fit luminosity distance relationship. We
further demonstrate that when SiFTO and SALT2 are trained on the same data set
the cosmological results agree.Comment: Modified to better match published version in Ap
Constraint Logic Programming for Hedges: A Semantic Reconstruction
Abstract. We describe the semantics of CLP(H): constraint logic programming over hedges. Hedges are finite sequences of unranked terms, built over variadic function symbols and three kinds of variables: for terms, for hedges, and for function symbols. Constraints involve equations between unranked terms and atoms for regular hedge language membership. We give algebraic semantics of CLP(H) programs, define a sound, terminating, and incomplete constraint solver, and describe some fragments of constraints for which the solver returns a complete set of solutions.
Supernova search at intermediate z. III. Expansion velocities of the ejecta
We discuss the expansion velocities of different elements in the ejecta of
the intermediate-z SNe Ia discovered as a part of the International Time
Programme (ITP) project ``Omega and Lambda from Supernovae and the Physics of
Supernova Explosions'' at the European Northern Observatory (ENO). The
expansion velocities measured for each normal SNIa are found to be within the
typical velocity dispersion for their epoch. Meanwhile, the subluminous SN
2002lk SiII expansion velocity is significantly higher than that of SN 1991bg
shortly after maximum. The observed phase was younger in SN2002lk than in the
local subluminous SNIa SN1991bg.Comment: 2 pages, 1 figure, 1 table, to appear in ``1604-2004: Supernovae as
Cosmological Lighthouses'', (extended text upon request
Clustering of supernova Ia host galaxies
For the first time the cross-correlation between type Ia supernova host
galaxies and surrounding field galaxies is measured using the Supernova Legacy
Survey sample. Over the z=0.2 to 0.9 redshift range we find that supernova
hosts are correlated an average of 60% more strongly than similarly selected
field galaxies over the 3-100 arcsec range and about a factor of 3 more
strongly below 10 arcsec. The correlation errors are empirically established
with a jackknife analysis of the four SNLS fields. The hosts are more
correlated than the field at a significance of 99% in the fitted amplitude and
slope, with the point-by-point difference of the two correlation functions
having a reduced for 8 degrees of freedom of 4.3, which has a
probability of random occurrence of less than 3x10^{-5}. The correlation angle
is 1.5+/-0.5 arcsec, which deprojects to a fixed co-moving correlation length
of approximately 6.5+/- 2/h mpc. Weighting the field galaxies with the mass and
star formation rate supernova frequencies of the simple A+B model produces good
agreement with the observed clustering. We conclude that these supernova
clustering differences are primarily the expected outcome of the dependence of
supernova rates on galaxy masses and stellar populations with their clustering
environment.Comment: ApJ (Letts) accepte
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