35 research outputs found
Observational Evidence of the Accelerated Expansion of the Universe
The discovery of cosmic acceleration is one of the most important
developments in modern cosmology. The observation, thirteen years ago, that
type Ia supernovae appear dimmer that they would have been in a decelerating
universe followed by a series of independent observations involving galaxies
and cluster of galaxies as well as the cosmic microwave background, all point
in the same direction: we seem to be living in a flat universe whose expansion
is currently undergoing an acceleration phase. In this paper, we review the
various observational evidences, most of them gathered in the last decade, and
the improvements expected from projects currently collecting data or in
preparation.Comment: Accepted review article to appear in a special volume of the "Comptes
Rendus de l'Acad\'emie des Sciences" about Dark Energy and Dark Matte
Improved limits on photon velocity oscillations
The mixing of the photon with a hypothetical sterile paraphotonic state would
have consequences on the cosmological propagation of photons. The absence of
distortions in the optical spectrum of distant Type Ia supernov\ae allows to
extend by two orders of magnitude the previous limit on the Lorentz-violating
parameter associated to the photon-paraphoton transition, extracted
from the abscence of distortions in the spectrum of the cosmic microwave
background. The new limit is consistent with the interpretation of the dimming
of distant Type Ia supernov\ae as a consequence of a nonzero cosmological
constant. Observations of gamma-rays from active galactic nuclei allow to
further extend the limit on by ten orders of magnitude.Comment: 10 pages, 4 Postscript figures, use epsfig, amssym
The Type Ia supernovae rate with Subaru/XMM-Newton Deep Survey
We present measurements of the rates of high-redshift Type Ia supernovae
derived from the Subaru/XMM-Newton Deep Survey (SXDS). We carried out repeat
deep imaging observations with Suprime-Cam on the Subaru Telescope, and
detected 1040 variable objects over 0.918 deg in the Subaru/XMM-Newton Deep
Field. From the imaging observations, light curves in the observed -band
are constructed for all objects, and we fit the observed light curves with
template light curves. Out of the 1040 variable objects detected by the SXDS,
39 objects over the redshift range are classified as Type Ia
supernovae using the light curves. These are among the most distant SN Ia rate
measurements to date. We find that the Type Ia supernova rate increase up to and may then flatten at higher redshift. The rates can be fitted by a
simple power law, with
(stat.)(syst.), and
(stat.)(syst.).Comment: 21 pages, 16 figures, accepted to PAS
Towards a Cosmological Hubble Diagram for Type II-P Supernovae
We present the first high-redshift Hubble diagram for Type II-P supernovae
(SNe II-P) based upon five events at redshift up to z~0.3. This diagram was
constructed using photometry from the Canada-France-Hawaii Telescope Supernova
Legacy Survey and absorption line spectroscopy from the Keck observatory. The
method used to measure distances to these supernovae is based on recent work by
Hamuy & Pinto (2002) and exploits a correlation between the absolute brightness
of SNe II-P and the expansion velocities derived from the minimum of the Fe II
516.9 nm P-Cygni feature observed during the plateau phases. We present three
refinements to this method which significantly improve the practicality of
measuring the distances of SNe II-P at cosmologically interesting redshifts.
These are an extinction correction measurement based on the V-I colors at day
50, a cross-correlation measurement for the expansion velocity and the ability
to extrapolate such velocities accurately over almost the entire plateau phase.
We apply this revised method to our dataset of high-redshift SNe II-P and find
that the resulting Hubble diagram has a scatter of only 0.26 magnitudes, thus
demonstrating the feasibility of measuring the expansion history, with present
facilities, using a method independent of that based upon supernovae of Type
Ia.Comment: 36 pages, 16 figures, accepted for publication in Ap
The type Ia supernova SNLS-03D3bb from a super-Chandrasekhar-mass white dwarf star
The acceleration of the expansion of the universe, and the need for Dark
Energy, were inferred from the observations of Type Ia supernovae (SNe Ia).
There is consensus that SNe Ia are thermonuclear explosions that destroy
carbon-oxygen white dwarf stars that accrete matter from a companion star,
although the nature of this companion remains uncertain. SNe Ia are thought to
be reliable distance indicators because they have a standard amount of fuel and
a uniform trigger -- they are predicted to explode when the mass of the white
dwarf nears the Chandrasekhar mass -- 1.4 solar masses. Here we show that the
high redshift supernova SNLS-03D3bb has an exceptionally high luminosity and
low kinetic energy that both imply a super-Chandrasekhar mass progenitor.
Super-Chandrasekhar mass SNe Ia should preferentially occur in a young stellar
population, so this may provide an explanation for the observed trend that
overluminous SNe Ia only occur in young environments. Since this supernova does
not obey the relations that allow them to be calibrated as standard candles,
and since no counterparts have been found at low redshift, future cosmology
studies will have to consider contamination from such events.Comment: 9 pages, 4 figures. To appear in Nature Sept. 21. Accompanying News &
Views in same issue. Supplementary information available at
www.nature.com/natur
LSST: from Science Drivers to Reference Design and Anticipated Data Products
(Abridged) We describe here the most ambitious survey currently planned in
the optical, the Large Synoptic Survey Telescope (LSST). A vast array of
science will be enabled by a single wide-deep-fast sky survey, and LSST will
have unique survey capability in the faint time domain. The LSST design is
driven by four main science themes: probing dark energy and dark matter, taking
an inventory of the Solar System, exploring the transient optical sky, and
mapping the Milky Way. LSST will be a wide-field ground-based system sited at
Cerro Pach\'{o}n in northern Chile. The telescope will have an 8.4 m (6.5 m
effective) primary mirror, a 9.6 deg field of view, and a 3.2 Gigapixel
camera. The standard observing sequence will consist of pairs of 15-second
exposures in a given field, with two such visits in each pointing in a given
night. With these repeats, the LSST system is capable of imaging about 10,000
square degrees of sky in a single filter in three nights. The typical 5
point-source depth in a single visit in will be (AB). The
project is in the construction phase and will begin regular survey operations
by 2022. The survey area will be contained within 30,000 deg with
, and will be imaged multiple times in six bands, ,
covering the wavelength range 320--1050 nm. About 90\% of the observing time
will be devoted to a deep-wide-fast survey mode which will uniformly observe a
18,000 deg region about 800 times (summed over all six bands) during the
anticipated 10 years of operations, and yield a coadded map to . The
remaining 10\% of the observing time will be allocated to projects such as a
Very Deep and Fast time domain survey. The goal is to make LSST data products,
including a relational database of about 32 trillion observations of 40 billion
objects, available to the public and scientists around the world.Comment: 57 pages, 32 color figures, version with high-resolution figures
available from https://www.lsst.org/overvie
The Discovery of a Gravitationally Lensed Supernova Ia at Redshift 2.22
We present the discovery and measurements of a gravitationally lensed supernova (SN) behind the galaxy cluster MOO J1014+0038. Based on multi-band Hubble Space Telescope and Very Large Telescope (VLT) photometry of the supernova, and VLT spectroscopy of the host galaxy, we find a 97.5% probability that this SN is a SN Ia, and a 2.5% chance of a CC SN. Our typing algorithm combines the shape and color of the light curve with the expected rates of each SN type in the host galaxy. With a redshift of 2.2216, this is the highest redshift SN Ia discovered with a spectroscopic host-galaxy redshift. A further distinguishing feature is that the lensing cluster, at redshift 1.23, is the most distant to date to have an amplified SN. The SN lies in the middle of the color and light-curve shape distributions found at lower redshift, disfavoring strong evolution to z = 2.22. We estimate an amplification due to gravitational lensing of 2.8+0.6-0.5 (1.10 +- 0.23 mag)---compatible with the value estimated from the weak-lensing-derived mass and the mass-concentration relation from LambdaCDM simulations---making it the most amplified SN Ia discovered behind a galaxy cluster
Rapidly Rising Transients in the Supernova - Superluminous Supernova Gap
The American Astronomical Society. All rights reserved..We present observations of four rapidly rising (trise ≈ 10 days) transients with peak luminosities between those of supernovae (SNe) and superluminous SNe (Mpeak ap; -20) - one discovered and followed by the Palomar Transient Factory (PTF) and three by the Supernova Legacy Survey. The light curves resemble those of SN 2011kl, recently shown to be associated with an ultra-long-duration gamma-ray burst (GRB), though no GRB was seen to accompany our SNe. The rapid rise to a luminous peak places these events in a unique part of SN phase space, challenging standard SN emission mechanisms. Spectra of the PTF event formally classify it as an SN II due to broad Hα emission, but an unusual absorption feature, which can be interpreted as either high velocity Hα (though deeper than in previously known cases) or Si ii (as seen in SNe Ia), is also observed. We find that existing models of white dwarf detonations, CSM interaction, shock breakout in a wind (or steeper CSM), and magnetar spin down cannot readily explain the observations. We consider the possibility that a "Type 1.5 SN" scenario could be the origin of our events. More detailed models for these kinds of transients and more constraining observations of future such events should help to better determine their nature. © 2016
Analyse des spectres VLT pour l'expérience SNLS (Qualification de transients cosmologiques)
PARIS7-Bibliothèque centrale (751132105) / SudocMEUDON-Observatoire (920482302) / SudocPARIS-Observatoire (751142302) / SudocAIX-MARSEILLE1.OAMP.Le Verrier (130552205) / SudocSudocFranceF