4,044 research outputs found
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
The Subluminous and Peculiar Type Ia Supernova PTF09dav
PTF09dav is a peculiar subluminous type Ia supernova (SN) discovered by the
Palomar Transient Factory (PTF). Spectroscopically, it appears superficially
similar to the class of subluminous SN1991bg-like SNe, but it has several
unusual features which make it stand out from this population. Its peak
luminosity is fainter than any previously discovered SN1991bg-like SN Ia (M_B
-15.5), but without the unusually red optical colors expected if the faint
luminosity were due to extinction. The photospheric optical spectra have very
unusual strong lines of Sc II and Mg I, with possible Sr II, together with
stronger than average Ti II and low velocities of ~6000 km/s. The host galaxy
of PTF09dav is ambiguous. The SN lies either on the extreme outskirts (~41kpc)
of a spiral galaxy, or in an very faint (M_R>-12.8) dwarf galaxy, unlike other
1991bg-like SNe which are invariably associated with massive, old stellar
populations. PTF09dav is also an outlier on the light-curve-width--luminosity
and color--luminosity relations derived for other sub-luminous SNe Ia. The
inferred 56Ni mass is small (0.019+/-0.003Msun), as is the estimated ejecta
mass of 0.36Msun. Taken together, these properties make PTF09dav a remarkable
event. We discuss various physical models that could explain PTF09dav. Helium
shell detonation or deflagration on the surface of a CO white-dwarf can explain
some of the features of PTF09dav, including the presence of Sc and the low
photospheric velocities, but the observed Si and Mg are not predicted to be
very abundant in these models. We conclude that no single model is currently
capable of explaining all of the observed signatures of PTF09dav.Comment: Accepted for publication in Ap
Reyes, acreedores y conversos: el impacto de la política real y de la deuda corporativa en la identidad colectiva de los conversos de Mallorca después de 1391
Royal correspondence of the Kingdom of Majorca reveals that “external” economic factors and royal policies forced the first generations of 1391 conversos to remain a distinct social group. Not long after the anti-Jewish violence and mass conversions of 1391, the conversos of Majorca granted a percentage of their assets to King Joan I. At the same time, the conversos and surviving Jews had to repay the creditors of the former aljama, which had been dissolved following the attack against the Jewish quarter. These two collective financial obligations required the conversos to organize themselves as a group, following the precedent of the aljama, with elected leaders who organized an internal tax collection in order to pay these debts, and who lobbied on behalf of the conversos before the king and before their creditors. This administrative structure set the foundation for the converso confraternity of Sant Miquel, founded in 1404.Un examen detallado de la correspondencia real relativa a Mallorca muestra que factores económicos «externos» y directivas políticas reales obligaron a la primera generación de conversos de 1391 a permanecer como grupo social distintivo. Poco después de producirse la violencia anti-judía y las conversiones masivas de 1391, los conversos de Mallorca tuvieron que otorgar un porcentaje de sus propiedades al rey Juan I. Al mismo tiempo, conversos y judíos supervivientes debían seguir pagando los «censalers» de la aljama de judíos que había sido disuelta tras el ataque en 1391 contra la judería. Estas dos obligaciones financieras colectivas obligaron a los conversos a organizarse, siguiendo el precedente de la aljama, como grupo con líderes elegidos que administraron la colección fiscal interna a fin de pagar esas deudas, e interviniendo a favor de los conversos ante el rey y sus acreedores. Esta estructura administrativa puso los fundamentos de la cofradía conversa de Sant Miquel, establecida en 1404
The nebular spectrum of the type Ia supernova 2003hv: evidence for a non-standard event
The optical and near-infrared late-time spectrum of the under-luminous Type
Ia supernova 2003hv is analysed with a code that computes nebular emission from
a supernova nebula. Synthetic spectra based on the classical explosion model W7
are unable to reproduce the large \FeIII/\FeII\ ratio and the low infrared flux
at year after explosion, although the optical spectrum of SN\,2003hv
is reproduced reasonably well for a supernova of luminosity intermediate
between normal and subluminous (SN\,1991bg-like) ones. A possible solution is
that the inner layers of the supernova ejecta (v \lsim 8000\,\kms) contain
less mass than predicted by classical explosion models like W7. If this inner
region contains \sim 0.5 \Msun of material, as opposed to \sim 0.9 \Msun in
Chandrasekhar-mass models developed within the Single Degenerate scenario, the
low density inhibits recombination, favouring the large \FeIII/\FeII\ ratio
observed in the optical, and decreases the flux in the \FeII\ lines which
dominate the IR spectrum. The most likely scenario may be an explosion of a
sub-Chandrasekhar mass white dwarf. Alternatively, the violent/dynamical merger
of two white dwarfs with combined mass exceeding the Chandrasekhar limit also
shows a reduced inner density.Comment: MNRAS, in pres
Type Ia supernova diversity: white dwarf central density as a secondary parameter in three-dimensional delayed detonation models
Delayed detonations of Chandrasekhar-mass white dwarfs (WDs) have been very
successful in explaining the spectra, light curves, and the width-luminosity
relation of spectroscopically normal Type Ia supernovae (SNe Ia). The ignition
of the thermonuclear deflagration flame at the end of the convective carbon
"simmering" phase in the core of the WD is still not well understood and much
about the ignition kernel distribution remains unknown. Furthermore, the
central density at the time of ignition depends on the still uncertain screened
carbon fusion reaction rates, the accretion history and cooling time of the
progenitor, and the composition. We present the results of twelve
high-resolution three-dimensional delayed detonation SN Ia explosion
simulations that employ a new criterion to trigger the deflagration to
detonation transition (DDT). All simulations trigger our DDT criterion and the
resulting delayed detonations unbind the star. We find a trend of increasing
iron group element (IGE) production with increasing central density for bright,
faint, and intermediate SNe. The total 56Ni yield, however, remains more or
less constant, even though increased electron captures at high density result
in a decreasing 56Ni mass fraction of the IGE material. We attribute this to an
approximate balance of 56Ni producing and destroying effects. The deflagrations
that were ignited at higher density initially have a faster growth rate of
subgrid-scale turbulence. Hence, the effective flame speed increases faster,
which triggers the DDT criterion earlier, at a time when the central density of
the expanded star is higher. This leads to an overall increase of IGE
production, which off-sets the percental reduction of 56Ni due to
neutronization.Comment: 8 pages, 6 figures, 2 tables, accepted for publication in MNRAS. v2
now includes correct Fig. 6, which was missing from v
The ESSENCE Supernova Survey: Survey Optimization, Observations, and Supernova Photometry
We describe the implementation and optimization of the ESSENCE supernova
survey, which we have undertaken to measure the equation of state parameter of
the dark energy. We present a method for optimizing the survey exposure times
and cadence to maximize our sensitivity to the dark energy equation of state
parameter w=P/rho c^2 for a given fixed amount of telescope time. For our
survey on the CTIO 4m telescope, measuring the luminosity distances and
redshifts for supernovae at modest redshifts (z~0.5 +- 0.2) is optimal for
determining w. We describe the data analysis pipeline based on using reliable
and robust image subtraction to find supernovae automatically and in near
real-time. Since making cosmological inferences with supernovae relies
crucially on accurate measurement of their brightnesses, we describe our
efforts to establish a thorough calibration of the CTIO 4m natural photometric
system. In its first four years, ESSENCE has discovered and spectroscopically
confirmed 102 type Ia SNe, at redshifts from 0.10 to 0.78, identified through
an impartial, effective methodology for spectroscopic classification and
redshift determination. We present the resulting light curves for the all type
Ia supernovae found by ESSENCE and used in our measurement of w, presented in
Wood-Vasey et al, 2007.Comment: Submitted to ApJ. Companion paper to Wood-Vasey et al (2007).
Electronic tables available at http://www.ctio.noao.edu/essence/wresult
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
The effect of progenitor age and metallicity on luminosity and 56Ni yield in Type Ia supernovae
Timmes, Brown & Truran found that metallicity variations could theoretically
account for a 25% variation in the mass of 56Ni synthesized in Type Ia
supernovae (SNe Ia), and thus account for a large fraction of the scatter in
observed SN Ia luminosities. Higher-metallicity progenitors are more
neutron-rich, producing more stable burning products relative to radioactive
56Ni. We develop a new method for estimating bolometric luminosity and 56Ni
yield in SNe Ia and use it to test the theory with data from the Supernova
Legacy Survey. We find that the average 56Ni yield does drop in SNe Ia from
high metallicity environments, but the theory can only account for 7%--10% of
the dispersion in SN Ia 56Ni mass, and thus luminosity. This is because the
effect is dominant at metallicities significantly above solar, whereas we find
that SN hosts have predominantly subsolar or only moderately above-solar
metallicities. We also show that allowing for changes in O/Fe with the
metallicity [Fe/H] does not have a major effect on the theoretical prediction
of Timmes, Brown & Truran, so long as one is using the O/H as the independent
variable. Age may have a greater effect than metallicity -- we find that the
luminosity weighted age of the host galaxy is correlated with 56Ni yield, and
thus more massive progenitors give rise to more luminous explosions. This is
hard to understand if most SNe Ia explode when the primaries reach the
Chandrasekhar mass. Finally, we test the findings of Gallagher et al., that the
residuals of SNe Ia from the Hubble diagram are correlated with host galaxy
metallicity, and we find no such correlation.Comment: ApJ, accepted, 34 pages, 11 figures, apologies for one column format
-- necessary for the equation
Quasi-Elastic Scattering in the Inclusive (He, t) Reaction
The triton energy spectra of the charge-exchange C(He,t) reaction
at 2 GeV beam energy are analyzed in the quasi-elastic nucleon knock-out
region. Considering that this region is mainly populated by the charge-exchange
of a proton in He with a neutron in the target nucleus and the final proton
going in the continuum, the cross-sections are written in the distorted-wave
impulse approximation. The t-matrix for the elementary exchange process is
constructed in the DWBA, using one pion- plus rho-exchange potential for the
spin-isospin nucleon- nucleon potential. This t-matrix reproduces the
experimental data on the elementary pn np process. The calculated
cross-sections for the C(He,t) reaction at to triton
emission angle are compared with the corresponding experimental data, and are
found in reasonable overall accord.Comment: 19 pages, latex, 11 postscript figures available at
[email protected], submitted to Phy.Rev.
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