39 research outputs found
The Core Collapse Supernova Rate from the SDSS-II Supernova Survey
We use the Sloan Digital Sky Survey II Supernova Survey (SDSS-II SNS) data to
measure the volumetric core collapse supernova (CCSN) rate in the redshift
range (0.03<z<0.09). Using a sample of 89 CCSN we find a volume-averaged rate
of (1.06 +/- 0.19) x 10**(-4)/(yr Mpc**3) at a mean redshift of 0.072 +/-
0.009. We measure the CCSN luminosity function from the data and consider the
implications on the star formation history.Comment: Minor corrections to references and affiliations to conform with
published versio
Photometric Supernova Cosmology with BEAMS and SDSS-II
Supernova cosmology without spectroscopic confirmation is an exciting new
frontier which we address here with the Bayesian Estimation Applied to Multiple
Species (BEAMS) algorithm and the full three years of data from the Sloan
Digital Sky Survey II Supernova Survey (SDSS-II SN). BEAMS is a Bayesian
framework for using data from multiple species in statistical inference when
one has the probability that each data point belongs to a given species,
corresponding in this context to different types of supernovae with their
probabilities derived from their multi-band lightcurves. We run the BEAMS
algorithm on both Gaussian and more realistic SNANA simulations with of order
10^4 supernovae, testing the algorithm against various pitfalls one might
expect in the new and somewhat uncharted territory of photometric supernova
cosmology. We compare the performance of BEAMS to that of both mock
spectroscopic surveys and photometric samples which have been cut using typical
selection criteria. The latter typically are either biased due to contamination
or have significantly larger contours in the cosmological parameters due to
small data-sets. We then apply BEAMS to the 792 SDSS-II photometric supernovae
with host spectroscopic redshifts. In this case, BEAMS reduces the area of the
(\Omega_m,\Omega_\Lambda) contours by a factor of three relative to the case
where only spectroscopically confirmed data are used (297 supernovae). In the
case of flatness, the constraints obtained on the matter density applying BEAMS
to the photometric SDSS-II data are \Omega_m(BEAMS)=0.194\pm0.07. This
illustrates the potential power of BEAMS for future large photometric supernova
surveys such as LSST.Comment: 25 pages, 15 figures, submitted to Ap
PTF11kx: A Type-Ia Supernova with a Symbiotic Nova Progenitor
There is a consensus that Type-Ia supernovae (SNe Ia) arise from the
thermonuclear explosion of white dwarf stars that accrete matter from a binary
companion. However, direct observation of SN Ia progenitors is lacking, and the
precise nature of the binary companion remains uncertain. A temporal series of
high-resolution optical spectra of the SN Ia PTF 11kx reveals a complex
circumstellar environment that provides an unprecedentedly detailed view of the
progenitor system. Multiple shells of circumsteller are detected and the SN
ejecta are seen to interact with circumstellar material (CSM) starting 59 days
after the explosion. These features are best described by a symbiotic nova
progenitor, similar to RS Ophiuchi.Comment: 27 pages, 5 figures. In pres
The Sloan Digital Sky Survey-II Supernova Survey: Search Algorithm and Follow-up Observations
The Sloan Digital Sky Survey-II Supernova Survey has identified a large
number of new transient sources in a 300 sq. deg. region along the celestial
equator during its first two seasons of a three-season campaign. Multi-band
(ugriz) light curves were measured for most of the sources, which include solar
system objects, Galactic variable stars, active galactic nuclei, supernovae
(SNe), and other astronomical transients. The imaging survey is augmented by an
extensive spectroscopic follow-up program to identify SNe, measure their
redshifts, and study the physical conditions of the explosions and their
environment through spectroscopic diagnostics. During the survey, light curves
are rapidly evaluated to provide an initial photometric type of the SNe, and a
selected sample of sources are targeted for spectroscopic observations. In the
first two seasons, 476 sources were selected for spectroscopic observations, of
which 403 were identified as SNe. For the Type Ia SNe, the main driver for the
Survey, our photometric typing and targeting efficiency is 90%. Only 6% of the
photometric SN Ia candidates were spectroscopically classified as non-SN Ia
instead, and the remaining 4% resulted in low signal-to-noise, unclassified
spectra. This paper describes the search algorithm and the software, and the
real-time processing of the SDSS imaging data. We also present the details of
the supernova candidate selection procedures and strategies for follow-up
spectroscopic and imaging observations of the discovered sources.Comment: Accepted for publication in The Astronomical Journal (66 pages, 13
figures); typos correcte
The Peculiar SN 2005hk: Do Some Type Ia Supernovae Explode as Deflagrations?
We present extensive u'g'r'i'BVRIYJHKs photometry and optical spectroscopy of
SN 2005hk. These data reveal that SN 2005hk was nearly identical in its
observed properties to SN 2002cx, which has been called ``the most peculiar
known type Ia supernova.'' Both supernovae exhibited high ionization SN
1991T-like pre-maximum spectra, yet low peak luminosities like SN 1991bg. The
spectra reveal that SN 2005hk, like SN 2002cx, exhibited expansion velocities
that were roughly half those of typical type Ia supernovae. The R and I light
curves of both supernovae were also peculiar in not displaying the secondary
maximum observed for normal type Ia supernovae. Our YJH photometry of SN 2005hk
reveals the same peculiarity in the near-infrared. By combining our optical and
near-infrared photometry of SN 2005hk with published ultraviolet light curves
obtained with the Swift satellite, we are able to construct a bolometric light
curve from ~10 days before to ~60 days after B maximum. The shape and unusually
low peak luminosity of this light curve, plus the low expansion velocities and
absence of a secondary maximum at red and near-infrared wavelengths, are all in
reasonable agreement with model calculations of a 3D deflagration which
produces ~0.25 M_sun of 56Ni.Comment: Accepted by PASP, to appear in April 2007 issue, 63 pages, 16
figures, 11 table
Hubble Space Telescope studies of low-redshift Type Ia supernovae: Evolution with redshift and ultraviolet spectral trends
We present an analysis of the maximum light, near ultraviolet (NUV; 2900-5500
A) spectra of 32 low redshift (0.001<z<0.08) Type Ia supernovae (SNe Ia),
obtained with the Hubble Space Telescope (HST). We combine this spectroscopic
sample with high-quality gri light curves obtained with robotic telescopes to
measure photometric parameters, such as stretch, optical colour, and
brightness. By comparing our data to a comparable sample of SNe Ia at
intermediate-z (0.4<z<0.9), we detect modest spectral evolution (3-sigma), in
the sense that our mean low-z NUV spectrum has a depressed flux compared to its
intermediate-z counterpart. We also see a strongly increased dispersion about
the mean with decreasing wavelength, confirming the results of earlier surveys.
These trends are consistent with changes in metallicity as predicted by
contemporary SN Ia spectral models. We also examine the properties of various
NUV spectral diagnostics in the individual spectra. We find a general
correlation between stretch and the velocity (or position) of many NUV spectral
features. In particular, we observe that higher stretch SNe have larger Ca II
H&K velocities, that also correlate with host galaxy stellar mass. This latter
trend is probably driven by the well-established correlation between stretch
and stellar mass. We find no trends between UV spectral features and optical
colour. Mean spectra constructed according to whether the SN has a positive or
negative Hubble residual show very little difference at NUV wavelengths,
indicating that the NUV evolution and variation we identify do not directly
correlate with Hubble residuals. Our work confirms and strengthens earlier
conclusions regarding the complex behaviour of SNe Ia in the NUV spectral
region, but suggests the correlations we find are more useful in constraining
progenitor models than improving the use of SNe Ia as cosmological probes.Comment: 22 pages, 14 figures, accepted in MNRAS with minor changes - Spectra
are available on WISeREP, http://www.weizmann.ac.il/astrophysics/wiserep
First-Year Spectroscopy for the SDSS-II Supernova Survey
This paper presents spectroscopy of supernovae discovered in the first season
of the Sloan Digital Sky Survey-II Supernova Survey. This program searches for
and measures multi-band light curves of supernovae in the redshift range z =
0.05 - 0.4, complementing existing surveys at lower and higher redshifts. Our
goal is to better characterize the supernova population, with a particular
focus on SNe Ia, improving their utility as cosmological distance indicators
and as probes of dark energy. Our supernova spectroscopy program features
rapid-response observations using telescopes of a range of apertures, and
provides confirmation of the supernova and host-galaxy types as well as precise
redshifts. We describe here the target identification and prioritization, data
reduction, redshift measurement, and classification of 129 SNe Ia, 16
spectroscopically probable SNe Ia, 7 SNe Ib/c, and 11 SNe II from the first
season. We also describe our efforts to measure and remove the substantial host
galaxy contamination existing in the majority of our SN spectra.Comment: Accepted for publication in The Astronomical Journal(47pages, 9
figures
Observational and Physical Classification of Supernovae
This chapter describes the current classification scheme of supernovae (SNe).
This scheme has evolved over many decades and now includes numerous SN Types
and sub-types. Many of these are universally recognized, while there are
controversies regarding the definitions, membership and even the names of some
sub-classes; we will try to review here the commonly-used nomenclature, noting
the main variants when possible. SN Types are defined according to
observational properties; mostly visible-light spectra near maximum light, as
well as according to their photometric properties. However, a long-term goal of
SN classification is to associate observationally-defined classes with specific
physical explosive phenomena. We show here that this aspiration is now finally
coming to fruition, and we establish the SN classification scheme upon direct
observational evidence connecting SN groups with specific progenitor stars.
Observationally, the broad class of Type II SNe contains objects showing strong
spectroscopic signatures of hydrogen, while objects lacking such signatures are
of Type I, which is further divided to numerous subclasses. Recently a class of
super-luminous SNe (SLSNe, typically 10 times more luminous than standard
events) has been identified, and it is discussed. We end this chapter by
briefly describing a proposed alternative classification scheme that is
inspired by the stellar classification system. This system presents our
emerging physical understanding of SN explosions, while clearly separating
robust observational properties from physical inferences that can be debated.
This new system is quantitative, and naturally deals with events distributed
along a continuum, rather than being strictly divided into discrete classes.
Thus, it may be more suitable to the coming era where SN numbers will quickly
expand from a few thousands to millions of events.Comment: Extended final draft of a chapter in the "SN Handbook". Comments most
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