4,988 research outputs found
Diversity of Decline-Rate-Corrected Type Ia Supernova Rise Times: One Mode or Two?
B-band light-curve rise times for eight unusually well-observed nearby Type
Ia supernovae (SNe) are fitted by a newly developed template-building
algorithm, using light-curve functions that are smooth, flexible, and free of
potential bias from externally derived templates and other prior assumptions.
From the available literature, photometric BVRI data collected over many
months, including the earliest points, are reconciled, combined, and fitted to
a unique time of explosion for each SN. On average, after they are corrected
for light-curve decline rate, three SNe rise in 18.81 +- 0.36 days, while five
SNe rise in 16.64 +- 0.21 days. If all eight SNe are sampled from a single
parent population (a hypothesis not favored by statistical tests), the rms
intrinsic scatter of the decline-rate-corrected SN rise time is 0.96 +0.52
-0.25 days -- a first measurement of this dispersion. The corresponding global
mean rise time is 17.44 +- 0.39 days, where the uncertainty is dominated by
intrinsic variance. This value is ~2 days shorter than two published averages
that nominally are twice as precise, though also based on small samples. When
comparing high-z to low-z SN luminosities for determining cosmological
parameters, bias can be introduced by use of a light-curve template with an
unrealistic rise time. If the period over which light curves are sampled
depends on z in a manner typical of current search and measurement strategies,
a two-day discrepancy in template rise time can bias the luminosity comparison
by ~0.03 magnitudes.Comment: As accepted by The Astrophysical Journal; 15 pages, 6 figures, 2
tables. Explanatory material rearranged and enhanced; Fig. 4 reformatte
First Impressions: Early-Time Classification of Supernovae using Host Galaxy Information and Shallow Learning
Substantial effort has been devoted to the characterization of transient
phenomena from photometric information. Automated approaches to this problem
have taken advantage of complete phase-coverage of an event, limiting their use
for triggering rapid follow-up of ongoing phenomena. In this work, we introduce
a neural network with a single recurrent layer designed explicitly for early
photometric classification of supernovae. Our algorithm leverages transfer
learning to account for model misspecification, host galaxy photometry to solve
the data scarcity problem soon after discovery, and a custom weighted loss to
prioritize accurate early classification. We first train our algorithm using
state-of-the-art transient and host galaxy simulations, then adapt its weights
and validate it on the spectroscopically-confirmed SNe Ia, SNe II, and SNe Ib/c
from the Zwicky Transient Facility Bright Transient Survey. On observed data,
our method achieves an overall accuracy of % within 3 days of an
event's discovery, and an accuracy of % within 30 days of discovery.
At both early and late phases, our method achieves comparable or superior
results to the leading classification algorithms with a simpler network
architecture. These results help pave the way for rapid photometric and
spectroscopic follow-up of scientifically-valuable transients discovered in
massive synoptic surveys.Comment: 24 pages, 8 figures. Accepted to Ap
The Rise Time of Type Ia Supernovae from the Supernova Legacy Survey
We compare the rise times of nearby and distant Type Ia supernovae (SNe Ia)
as a test for evolution using 73 high-redshift spectroscopically-confirmed SNe
Ia from the first two years of the five year Supernova Legacy Survey (SNLS) and
published observations of nearby SN. Because of the ``rolling'' search nature
of the SNLS, our measurement is approximately 6 times more precise than
previous studies, allowing for a more sensitive test of evolution between
nearby and distant supernovae. Adopting a simple early-time model (as in
previous studies), we find that the rest-frame rise times for a fiducial SN
Ia at high and low redshift are consistent, with values
and
days, respectively; the statistical significance of this difference is only 1.4
\sg . The errors represent the uncertainty in the mean rather than any
variation between individual SN. We also compare subsets of our high-redshift
data set based on decline rate, host galaxy star formation rate, and redshift,
finding no substantive evidence for any subsample dependence.Comment: Accepted for publication in AJ; minor changes (spelling and
grammatical) to conform with published versio
Abundance stratification in Type Ia Supernovae - II: The rapidly declining, spectroscopically normal SN 2004eo
The variation of properties of Type Ia supernovae, the thermonuclear
explosions of Chandrasekhar-mass carbon-oxygen white dwarfs, is caused by
different nucleosynthetic outcomes of these explosions, which can be traced
from the distribution of abundances in the ejecta. The composition
stratification of the spectroscopically normal but rapidly declining SN2004eo
is studied performing spectrum synthesis of a time-series of spectra obtained
before and after maximum, and of one nebular spectrum obtained about eight
months later. Early-time spectra indicate that the outer ejecta are dominated
by oxygen and silicon, and contain other intermediate-mass elements (IME),
implying that the outer part of the star was subject only to partial burning.
In the inner part, nuclear statistical equilibrium (NSE) material dominates,
but the production of 56Ni was limited to ~0.43 \pm 0.05 Msun. An innermost
zone containing ~0.25 Msun of stable Fe-group material is also present. The
relatively small amount of NSE material synthesised by SN2004eo explains both
the dimness and the rapidly evolving light curve of this SN.Comment: 12 pages, 7 figures. Accepted for publication in MNRA
Type Ia supernova SN 2003du: optical observations
UBVRI photometry and optical spectra of type Ia supernova SN 2003du obtained
at the Indian Astronomical Observatory for nearly a year since discovery are
presented.
The apparent magnitude at maximum was B=13.53 +/- 0.02 mag, and the colour
(B-V) = -0.08 +/- 0.03 mag. The luminosity decline rate, Delta(m_{15}(B)) =
1.04 +/- 0.04 mag indicates an absolute B magnitude at maximum of M_B = -19.34
+/- 0.3 mag and the distance modulus to the parent galaxy as mu=32.89 +/-
0.4.The light curve shapes are similar, though not identical, to those of SNe
1998bu and 1990N, both of which had luminosity decline rates similar to that of
SN 2003du and occurred in spiral galaxies. The peak bolometric luminosity
indicates that 0.9 Msun mass of 56Ni was ejected by the supernova. The spectral
evolution and the evolution of the Si II and Ca II absorption velocities
closely follows that of SN 1998bu, and in general, is within the scatter of the
velocities observed in normal type Ia supernovae.
The spectroscopic and photometric behaviour of SN 2003du is quite typical for
SNe Ia in spirals.
A high velocity absorption component in the Ca II (H & K) and IR-triplet
features, with absorption velocities of ~20,000 km/s and ~22,000 km/s
respectively, is detected in the pre-maximum spectra of days -11 and -7.Comment: 10 pages, 10 figures; Accepted for publication in A&
Optical and Infrared Photometry of the Unusual Type Ia Supernova 2000cx
We present optical and infrared photometry of the unusual Type Ia supernova
2000cx. With the data of Li et al. (2001) and Jha (2002), this comprises the
largest dataset ever assembled for a Type Ia SN, more than 600 points in
UBVRIJHK. We confirm the finding of Li et al. regarding the unusually blue B-V
colors as SN 2000cx entered the nebular phase. Its I-band secondary hump was
extremely weak given its B-band decline rate. The V minus near infrared colors
likewise do not match loci based on other slowly declining Type Ia SNe, though
V-K is the least ``abnormal''. In several ways SN 2000cx resembles other slow
decliners, given its B-band decline rate (Delta m_15(B) = 0.93), the appearance
of Fe III lines and weakness of Si II in its pre-maximum spectrum, the V-K
colors and post-maximum V-H colors. If the distance modulus derived from
Surface Brightness Fluctuations of the host galaxy is correct, we find that the
rate of light increase prior to maximum, the characteristics of the bolometric
light curve, and the implied absolute magnitude at maximum are all consistent
with a sub-luminous object with Delta m_15(B) ~ 1.6-1.7 having a higher than
normal kinetic energy.Comment: 46 pages, 17 figures, to be published in Publications of the
Astronomical Society of the Pacifi
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