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At least 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Discovery of Cepheids in NGC 5253: Absolute peak brightness of SN Ia 1895B and SN Ia 1972E and the value of H(sub 0)

Observations of the Hubble Space Telescope (HST) between 1993 May 31 and 1993 July 19 in 20 epochs in the F555W passband and five epochs in the F785LP passband have led to the discovery of 14 Cepheids in the Amorphous galaxy NGC 5253. The apparent V distance modulus is (m-M)(sub AV) = 28.08 +/- 0.10 determined from the 12 Cepheids with normal amplitudes. The distance modulus using the F785LP data is consistent with the V value to within the errors. Five methods used to determine the internal reddening are consistent with zero differential reddening, accurate to a level of E(B-V) less than 0.05 mag, over the region occupied by Cepheids and the two supernovae (SNe) produced by NGC 5253. The apparent magnitudes at maximum for the two SNe in NGC 5253 are adopted as B(sub max) = 8.33 +/- 0.2 mag for SN 1895B, and B(sub max) = 8.56 +/- 0.1 and V(sub max) = 8.60 +/- 0.1 for SN 1972E which is a prototype SN of Type Ia. The apparent magnitude system used by Walker (1923) for SN 1859B has been corrected to the modern B scale and zero point to determine its adopted B(sub max) value.

Saha, A.↗
DOE OSTI2022

StaNdaRT: a repository of standardised test models and outputs for supernova radiative transfer

We present the first results of a comprehensive supernova (SN) radiative-transfer (RT) code-comparison initiative (StaNdaRT), where the emission from the same set of standardised test models is simulated by currently used RT codes. We ran a total of ten codes on a set of four benchmark ejecta models of Type Ia SNe. We consider two sub-Chandrasekhar-mass (M tot = 1.0 M ⊙ ) toy models with analytic density and composition profiles and two Chandrasekhar-mass delayed-detonation models that are outcomes of hydrodynamical simulations. We adopt spherical symmetry for all four models. The results of the different codes, including the light curves, spectra, and the evolution of several physical properties as a function of radius and time are provided in electronic form in a standard format via a public repository. We also include the detailed test model profiles and several Python scripts for accessing and presenting the input and output files. We also provide the code used to generate the toy models studied here. In this paper, we describe the test models, radiative-transfer codes, and output formats in detail, and provide access to the repository. We present example results of several key diagnostic features.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
NASA NTRS1991

Radioactivities and gamma-rays from supernovae

An account is given of the implications of several calculations relevant to the estimation of gamma-ray signals from various explosive astronomical phenomena. After discussing efforts to constrain the amounts of Ni-57 and Ti-44 produced in SN 1987A, attention is given to the production of Al-27 in massive stars and SNs. A 'delayed detonation' model of type Ia SNs is proposed, and the gamma-ray signal which may be expected when a bare white dwarf collapses directly into a neutron star is discussed.

Woosley, S. E.↗
DOE OSTI2025

An Integral-based Technique to Accelerate the Monte Carlo Radiative Transfer Computation for Supernovae

We present an integral-based technique (IBT) algorithm to accelerate supernova (SN) radiative transfer calculations. The algorithm utilizes “integral packets,” which are calculated by the path integral of the Monte Carlo (MC) energy packets, to synthesize the observed spectropolarimetric signal at a given viewing direction in a 3D time-dependent radiative transfer program. Compared to the event-based technique (EBT) proposed by M. Bulla et al., our algorithm significantly reduces the computation time and increases the MC signal-to-noise ratio (S/N). Using a 1D spherical symmetric Type Ia SN ejecta model DDC10 and its derived 3D model, the IBT algorithm has successfully passed the verification of spherical symmetry and cross comparison on a 3D SN model with the direct-counting technique and EBT. Notably, with our algorithm implemented in the 3D MC radiative transfer code SEDONA, the computation time is faster than EBT by a factor of 10−30, and the S/N is better by a factor of 1.5−3, with the same number of MC quanta.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Photometric Classification of Early-time Supernova Light Curves with SCONE

Abstract In this work, we present classification results on early supernova light curves from SCONE, a photometric classifier that uses convolutional neural networks to categorize supernovae (SNe) by type using light-curve data. SCONE is able to identify SN types from light curves at any stage, from the night of initial alert to the end of their lifetimes. Simulated LSST SNe light curves were truncated at 0, 5, 15, 25, and 50 days after the trigger date and used to train Gaussian processes in wavelength and time space to produce wavelength–time heatmaps. SCONE uses these heatmaps to perform six-way classification between SN types Ia, II, Ibc, Ia-91bg, Iax, and SLSN-I. SCONE is able to perform classification with or without redshift, but we show that incorporating redshift information improves performance at each epoch. SCONE achieved 75% overall accuracy at the date of trigger (60% without redshift), and 89% accuracy 50 days after trigger (82% without redshift). SCONE was also tested on bright subsets of SNe ( r < 20 mag) and produced 91% accuracy at the date of trigger (83% without redshift) and 95% five days after trigger (94.7% without redshift). SCONE is the first application of convolutional neural networks to the early-time photometric transient classification problem. All of the data processing and model code developed for this paper can be found in the SCONE software package 1 1 github.com/helenqu/scone located at github.com/helenqu/scone (Qu 2021).

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2014

Slow-Speed Supernovae from the Palomar Transient Factory: Two Channels

Since the discovery of the unusual prototype SN 2002cx, the eponymous class of low-velocity, hydrogen-poor supernovae has grown to include at most another two dozen members identified from several heterogeneous surveys, in some cases ambiguously. Here we present the results of a systematic study of 1077 hydrogen-poor supernovae discovered by the Palomar Transient Factory, leading to nine new members of this peculiar class. Moreover we find there are two distinct subclasses based on their spectroscopic, photometric, and host galaxy properties: The "SN 2002cx-like" supernovae tend to be in later-type or more irregular hosts, have more varied and generally dimmer luminosities, have longer rise times, and lack a Ti II trough when compared to the \SN 2002es-like" supernovae. None of our objects show helium, and we counter a previous claim of two such events. We also find that these transients comprise 5.6+17 -3:7% (90% confidence) of all SNe Ia, lower compared to earlier estimates. Combining our objects with the literature sample, we propose that these subclasses have two distinct physical origins.

palomar↗
NASA NTRS1994

SN 1994I in M51 and the nature of type Ibc supernovae

Early spectra of SN 1994I in M51 (NGC 5194) are presented along with arguments that is a member of the class of helium-poor Type Ic supernovae. The issue of H and He in the spectra of Type Ib and Ic events is reexamined with the conclusion that Type Ib eject substantially less H than even transition events like SN 1993J and that Type Ic eject substantially less He than Type Ib and their optical spectra are consistent with no H or He. Type Ic show and absorption of the Si II lambda 6355 blend that characterizes Type Ia. This feature requires only a solar abundance of Si. Some Type Ic show an absorption that is probably C II lambda 6580. IR spectra are presented of SN 1990W which show the line of He I lambda 10830. The strength of this feature and the rather slow decay of the late time light curve suggest that this event could be better classified as a Type Ib. Even if trace abundances of H are present in Type Ib and of He in Type Ic the spectral differences still imply a distinctly different evolution for the progenitors of Type Ib from Type Ic and events like SN 1993J.

Wheeler, J. C.↗
DOE OSTI2023

Impact of Rubin Observatory Cadence Choices on Supernovae Photometric Classification

The Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST) will discover an unprecedented number of supernovae (SNe), making spectroscopic classification for all the events infeasible. LSST will thus rely on photometric classification, whose accuracy depends on the not-yet-finalized LSST observing strategy. In this work, we analyze the impact of cadence choices on classification performance using simulated multiband light curves. First, we simulate SNe with an LSST baseline cadence, a nonrolling cadence, and a presto-color cadence, which observes each sky location three times per night instead of twice. Each simulated data set includes a spectroscopically confirmed training set, which we augment to be representative of the test set as part of the classification pipeline. Then we use the photometric transient classification library snmachine to build classifiers. We find that the active region of the rolling cadence used in the baseline observing strategy yields a 25% improvement in classification performance relative to the background region. This improvement in performance in the actively rolling region is also associated with an increase of up to a factor of 2.7 in the number of cosmologically useful Type Ia SNe relative to the background region. However, adding a third visit per night as implemented in presto-color degrades classification performance due to more irregularly sampled light curves. Overall, our results establish desiderata on the observing cadence related to classification of full SNe light curves, which in turn impacts photometric SNe cosmology with LSST.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2016

Rapidly Rising Transients in the Supernova - Superluminous Supernova Gap

We present observations of four rapidly rising (t(sub rise) approximately equals 10 days) transients with peak luminosities between those of supernovae (SNe) and superluminous SNe (M(sub peak) approximately equals -20) - one discovered and followed by the PalomarTransient 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 H alpha emission, but an unusual absorption feature, which can be interpreted as either high velocity H alpha (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.

SNLS06D1hc↗
DOE OSTI2022

The Hubble Constant from Strongly Lensed Supernovae with Standardizable Magnifications

The dominant uncertainty in the current measurement of the Hubble constant (H 0 ) with strong gravitational lensing time delays is attributed to uncertainties in the mass profiles of the main deflector galaxies. Strongly lensed supernovae (glSNe) can provide, in addition to measurable time delays, lensing magnification constraints when knowledge about the unlensed apparent brightness of the explosion is imposed. We present a hierarchical Bayesian framework to combine a data set of SNe that are not strongly lensed and a data set of strongly lensed SNe with measured time delays. We jointly constrain (i) H 0 using the time delays as an absolute distance indicator, (ii) the lens model profiles using the magnification ratio of lensed and unlensed fluxes on the population level, and (iii) the unlensed apparent magnitude distribution of the SN population and the redshift–luminosity relation of the relative expansion history of the universe. We apply our joint inference framework on a future expected data set of glSNe and forecast that a sample of 144 glSNe of Type Ia with well-measured time series and imaging data will measure H 0 to 1.5%. We discuss strategies to mitigate systematics associated with using absolute flux measurements of glSNe to constrain the mass density profiles. Using the magnification of SN images is a promising and complementary alternative to using stellar kinematics. Future surveys, such as the Rubin and Roman observatories, will be able to discover the necessary number of glSNe, and with additional follow-up observations, this methodology will provide precise constraints on mass profiles and H 0 .

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2021

Spitzer’s Last Look at Extragalactic Explosions: Long-Term Evolution of Interacting Supernovae

Here we present new, yet final, mid-infrared (mid-IR) data for supernovae (SNe) based on measurements with the Spitzer Space Telescope. Comparing our recent 3.6 and 4.5 μm photometry with previously published mid-IR and further multiwavelength data sets, we were able to draw some conclusions about the origin and heating mechanism of the dust in these SNe or in their environments, as well as about possible connection with circumstellar matter (CSM) originating from pre-explosion mass-loss events in the progenitor stars. We also present new results regarding both certain SN classes and single objects. We highlight the mid-IR homogeneity of SNe Ia-CSM, which may be a hint of their common progenitor type and of their basically uniform circumstellar environments. Regarding single objects, it is worth highlighting the late-time interacting Type Ib SNe 2003gk and 2004dk, for which we present the first-ever mid-IR data, which seem to be consistent with clues of ongoing CSM interaction detected in other wavelength ranges. Our current study suggests that long-term mid-IR follow-up observations play a key role in a better understanding of both pre- and post-explosion processes in SNe and their environments. While Spitzer is not available anymore, the expected unique data from the James Webb Space Telescope, as well as long-term near-IR follow-up observations of dusty SNe, can bring us closer to the hidden details of this topic.

Supernovae↗
DOE OSTI2020

Spatially resolved molecular gas properties of host galaxy of Type I superluminous supernova SN 2017egm

Abstract We present the results of CO(1–0) observations of the host galaxy of a Type I superluminous supernova (SLSN-I), SN 2017egm, one of the closest SLSNe-I at z = 0.03063, by using the Atacama Large Millimeter/submillimeter Array. The molecular gas mass of the host galaxy is Mgas = (4.8 ± 0.3) × 109 M⊙, placing it on the sequence of normal star-forming galaxies in an Mgas–star-formation rate (SFR) plane. The molecular hydrogen column density at the location of SN 2017egm is higher than that of the Type II SN PTF10bgl, which is also located in the same host galaxy, and those of other Type II and Ia SNe located in different galaxies, suggesting that SLSNe-I have a preference for a dense molecular gas environment. On the other hand, the column density at the location of SN 2017egm is comparable to those of Type Ibc SNe. The surface densities of molecular gas and the SFR at the location of SN 2017egm are consistent with those of spatially resolved local star-forming galaxies and follow the Schmidt–Kennicutt relation. These facts suggest that SLSNe-I can occur in environments with the same star-formation mechanism as in normal star-forming galaxies.

Hatsukade, Bunyo (ORCID:0000000164698725)↗
NASA NTRS1991

Hot gas metallicity and the history of supernova activity in elliptical galaxies

Calculations of the dynamical evolution of the hot interstellar medium (ISM) in a massive elliptical galaxy are described, with a variety of past variations of the SN rate being assumed. The investigation focuses on iron enrichment in the ISM. The equivalent widths of the 6.7-keV iron line are calculated as a function of redshift and of galactic projected radius. The present-day interstellar gas in elliptical galaxies contains a fossil record of past SN activity that can be determined from measurements of iron line equivalent widths at several projected radii in the galaxy. It is proposed that the ISM iron abundance is likely to be quite inhomogeneous. The hydrogen-free ejecta of type Ia SN also result in pronounced ISM abundance inhomogeneities that probably eventually cool and move in pressure equilibrium with the local ISM flow velocity. The 6.7-keV iron line emission is greater if the iron is confined to ionized regions of pure iron.

Loewenstein, Michael↗
DOE OSTI2020

Supernova host galaxies in the dark energy survey: I. Deep coadds, photometry, and stellar masses

ABSTRACT The 5-yr Dark Energy Survey Supernova Programme (DES-SN) is one of the largest and deepest transient surveys to date in terms of volume and number of supernovae. Identifying and characterizing the host galaxies of transients plays a key role in their classification, the study of their formation mechanisms, and the cosmological analyses. To derive accurate host galaxy properties, we create depth-optimized coadds using single-epoch DES-SN images that are selected based on sky and atmospheric conditions. For each of the five DES-SN seasons, a separate coadd is made from the other four seasons such that each SN has a corresponding deep coadd with no contaminating SN emission. The coadds reach limiting magnitudes of order ∼27 in g band, and have a much smaller magnitude uncertainty than the previous DES-SN host templates, particularly for faint objects. We present the resulting multiband photometry of host galaxies for samples of spectroscopically confirmed type Ia (SNe Ia), core-collapse (CCSNe), and superluminous (SLSNe) as well as rapidly evolving transients (RETs) discovered by DES-SN. We derive host galaxy stellar masses and probabilistically compare stellar-mass distributions to samples from other surveys. We find that the DES spectroscopically confirmed sample of SNe Ia selects preferentially fewer high-mass hosts at high-redshift compared to other surveys, while at low redshift the distributions are consistent. DES CCSNe and SLSNe hosts are similar to other samples, while RET hosts are unlike the hosts of any other transients, although these differences have not been disentangled from selection effects.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Photometric classification of Hyper Suprime-Cam transients using machine learning

Abstract The advancement of technology has resulted in a rapid increase in supernova (SN) discoveries. The Subaru/Hyper Suprime-Cam (HSC) transient survey, conducted from fall 2016 through spring 2017, yielded 1824 SN candidates. This gave rise to the need for fast type classification for spectroscopic follow-up and prompted us to develop a machine learning algorithm using a deep neural network with highway layers. This algorithm is trained by actual observed cadence and filter combinations such that we can directly input the observed data array without any interpretation. We tested our model with a dataset from the LSST classification challenge (Deep Drilling Field). Our classifier scores an area under the curve (AUC) of 0.996 for binary classification (SN Ia or non-SN Ia) and 95.3% accuracy for three-class classification (SN Ia, SN Ibc, or SN II). Application of our binary classification to HSC transient data yields an AUC score of 0.925. With two weeks of HSC data since the first detection, this classifier achieves 78.1% accuracy for binary classification, and the accuracy increases to 84.2% with the full dataset. This paper discusses the potential use of machine learning for SN type classification purposes.

Takahashi, Ichiro↗
NASA NTRS2014

Uncovering the Putative B-Star Binary Companion of the SN 1993J Progenitor

The Type IIb supernova (SN) 1993J is one of only a few stripped-envelope SNe with a progenitor star identified in pre-explosion images. SN IIb models typically invoke H envelope stripping by mass transfer in a binary system. For the case of SN 1993J, the models suggest that the companion grew to 22 solar mass and became a source of ultraviolet (UV) excess. Located in M81, at a distance of only 3.6 Mpc, SN 1993J offers one of the best opportunities to detect the putative companion and test the progenitor model. Previously published near-UV spectra in 2004 showed evidence for absorption lines consistent with a hot (B2 Ia) star, but the field was crowded and dominated by flux from the SN. Here we present Hubble Space Telescope Cosmic Origins Spectrograph and Wide-Field Camera 3 observations of SN 1993J from 2012, at which point the flux from the SN had faded sufficiently to potentially measure the UV continuum properties from the putative companion. The resulting UV spectrum is consistent with contributions from both a hot B star and the SN, although we cannot rule out line-of-sight coincidences.

Hubble Space Telescope Cosmic Origins Spectrograph↗
NASA NTRS1990

Observations of Sk-69 deg 203 and the interstellar extinction towards SN 1987A

Optical and UV spectroscopic observations of the Large Magellanic Cloud (LMC) star Sk-69 deg 203 are discussed. The optical data reveal Sk-69 deg 203 to be a BO.7 Ia supergiant with a moderate nitrogen enhancement, and its UV spectrum is consistent with this classification. UV interstellar extinction curves were constructed for the star using, as flux standards, two lightly reddened LMS supergiants, which bracket Sk-69 deg 203's spectral type. The resultant extinction curves are consistent with the extinction law derived previously for the 30 Doradus region, and the results for Sk-69 deg 203 suggest that the general 30 Doradus extinction law is appropriate for dereddening the observed fluxes of SN 1987A. Published H I 21 observations place SN 1987A in a region with a strong E-W gradient in the total hydrogen content. Comparison with the H I column density implied by the reddening indicates that the supernova is imbedded approximately in the middle of the main H I complex.

Fitzpatrick, Edward L.↗
DOE OSTI2024

The Dark Energy Survey Supernova Program: Light Curves and 5 Yr Data Release

We present griz photometric light curves for the full 5 yr of the Dark Energy Survey Supernova (DES-SN) program, obtained with both forced point-spread function photometry on difference images (DiffImg) performed during survey operations, and scene modelling photometry (SMP) on search images processed after the survey. This release contains 31,636 DiffImg and 19,706 high-quality SMP light curves, the latter of which contain 1635 photometrically classified SNe that pass cosmology quality cuts. This sample spans the largest redshift (z) range ever covered by a single SN survey (0.1 < z < 1.13) and is the largest single sample from a single instrument of SNe ever used for cosmological constraints. We describe in detail the improvements made to obtain the final DES-SN photometry and provide a comparison to what was used in the 3 yr DES-SN spectroscopically confirmed Type Ia SN sample. We also include a comparative analysis of the performance of the SMP photometry with respect to the real-time DiffImg forced photometry and find that SMP photometry is more precise, more accurate, and less sensitive to the host-galaxy surface brightness anomaly. The public release of the light curves and ancillary data can be found at github.com/des-science/DES-SN5YR and doi:10.5281/zenodo.12720777.

79 ASTRONOMY AND ASTROPHYSICS↗