| 1. |
- Bianco, Federica B., et al.
(author)
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Presto-Color : A Photometric Survey Cadence for Explosive Physics and Fast Transients
- 2019
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In: Publications of the Astronomical Society of the Pacific. - : IOP Publishing. - 0004-6280 .- 1538-3873. ; 131:1000
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Journal article (peer-reviewed)abstract
- We identify minimal observing cadence requirements that enable photometric astronomical surveys to detect and recognize fast and explosive transients and fast transient features. Observations in two different filters within a short time window (e.g., g-and-i, or r-and-z, within <0.5 hr) and a repeat of one of those filters with a longer time window (e.g., >1.5 hr) are desirable for this purpose. Such an observing strategy delivers both the color and light curve evolution of transients on the same night. This allows the identification and initial characterization of fast transient-or fast features of longer timescale transients-such as rapidly declining supernovae, kilonovae, and the signatures of SN ejecta interacting with binary companion stars or circumstellar material. Some of these extragalactic transients are intrinsically rare and generally all hard to find, thus upcoming surveys like the Large Synoptic Survey Telescope (LSST) could dramatically improve our understanding of their origin and properties. We colloquially refer to such a strategy implementation for the LSST as the Presto-Color strategy (rapid-color). This cadence's minimal requirements allow for overall optimization of a survey for other science goals.
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| 2. |
- Dhawan, Suhail, et al.
(author)
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A BayeSN distance ladder : H0 from a consistent modelling of Type Ia supernovae from the optical to the near-infrared
- 2023
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In: Monthly notices of the Royal Astronomical Society. - 0035-8711 .- 1365-2966. ; 524:1, s. 235-244
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Journal article (peer-reviewed)abstract
- The local distance ladder estimate of the Hubble constant (H-0) is important in cosmology, given the recent tension with the early universe inference. We estimate H-0 from the Type Ia supernova (SN Ia) distance ladder, inferring SN Ia distances with the hierarchical Bayesian SED model, BayeSN. This method has a notable advantage of being able to continuously model the optical and near-infrared (NIR) SN Ia light curves simultaneously. We use two independent distance indicators, Cepheids or the tip of the red giant branch (TRGB), to calibrate a Hubble-flow sample of 67 SNe Ia with optical and NIR data. We estimate H-0 = 74.82 +/- 0.97 (stat) +/- 0.84 (sys) km s(-1) Mpc(-1) when using the calibration with Cepheid distances to 37 host galaxies of 41 SNe Ia, and 70.92 +/- 1.14 (stat) +/- 1.49 (sys) km s(-1) Mpc(-1) when using the calibration with TRGB distances to 15 host galaxies of 18 SNe Ia. For both methods, we find a low intrinsic scatter sigma(int) less than or similar to 0.1 mag. We test various selection criteria and do not find significant shifts in the estimate of H-0. Simultaneous modelling of the optical and NIR yields up to similar to 15 per cent reduction in H-0 uncertainty compared to the equivalent optical-only cases. With improvements expected in other rungs of the distance ladder, leveraging joint optical-NIR SN Ia data can be critical to reducing the H-0 error budget.
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| 3. |
- Muthukrishna, Daniel, et al.
(author)
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RAPID : Early Classification of Explosive Transients Using Deep Learning
- 2019
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In: Publications of the Astronomical Society of the Pacific. - : IOP Publishing. - 0004-6280 .- 1538-3873. ; 131:1005
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Journal article (peer-reviewed)abstract
- We present Real-time Automated Photometric IDentification (RAPID), a novel time series classification tool capable of automatically identifying transients from within a day of the initial alert, to the full lifetime of a light curve. Using a deep recurrent neural network with gated recurrent units (GRUs), we present the first method specifically designed to provide early classifications of astronomical timeseries data, typing 12 different transient classes. Our classifier can process light curves with any phase coverage, and it does not rely on deriving computationally expensive features from the data, making RAPID well suited for processing the millions of alerts that ongoing and upcoming wide-field surveys such as the Zwicky Transient Facility (ZTF), and the Large Synoptic Survey Telescope (LSST) will produce. The classification accuracy improves over the lifetime of the transient as more photometric data becomes available, and across the 12 transient classes, we obtain an average area under the receiver operating characteristic curve of 0.95 and 0.98 at early and late epochs, respectively. We demonstrate RAPID's ability to effectively provide early classifications of observed transients from the ZTF data stream. We have made RAPID available as an open-source software package(8) for machine-learning-based alert brokers to use for the autonomous and quick classification of several thousand light curves within a few seconds.
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| 4. |
- Sagués Carracedo, Ana, 1993-
(author)
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Chasing Cosmic Rarities : Kilonovae and Gravitationally Lensed Supernovae in Optical Surveys
- 2024
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Doctoral thesis (other academic/artistic)abstract
- This thesis focuses on two important topics in astrophysics: the detection of kilonovae (KNe) and gravitationally lensed supernovae (glSNe) in optical surveys. In the first part, the study quantifies the impact of survey depth and choice of filters on the detection probability of KNe. The results highlight the importance of accounting for asymmetries expected for KNe, and despite several search campaigns, no KNe were detected by the Zwicky Transient Facility (ZTF). Nonetheless, non-detection studies provided meaningful constraints on the luminosity function and on the rates of KNe. The findings contribute to advancing our understanding of these rare, fast, and faint transients. I also discuss the improvements in measuring the Hubble constant with follow-up data of KNe, including broadband photometry and spectrophotometric data from the upcoming IFU instrument MAAT. The second part of the thesis focuses on gravitationally lensed supernovae. The ZTF survey was expected to detect more than one strongly lensed supernova per year, but only one was identified in the first five years. The study presents simulations of lightcurves for lensed supernovae and new rates based on realistic survey simulations for ZTF. Optimal cuts to distinguish lensed supernovae from normal unlensed supernovae are also provided. The thesis discusses time delay and lightcurve modeling for the one event found during ZTF, SN Zwicky, and the lessons learned from it.The techniques developed in this thesis can be applied to future surveys to increase the detection rate of KNe and glSNe. These events and their underlying physics provide valuable insights in cosmology.
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| 5. |
- Ward, Sam M., et al.
(author)
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Relative Intrinsic Scatter in Hierarchical Type Ia Supernova Sibling Analyses : Application to SNe 2021hpr, 1997bq, and 2008fv in NGC 3147
- 2023
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In: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 956:2
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Journal article (peer-reviewed)abstract
- We present Young Supernova Experiment grizy photometry of SN 2021hpr, the third Type Ia supernova sibling to explode in the Cepheid calibrator galaxy, NGC 3147. Siblings are useful for improving SN-host distance estimates and investigating their contributions toward the SN Ia intrinsic scatter (post-standardization residual scatter in distance estimates). We thus develop a principled Bayesian framework for analyzing SN Ia siblings. At its core is the cosmology-independent relative intrinsic scatter parameter, σRel: the dispersion of siblings distance estimates relative to one another within a galaxy. It quantifies the contribution toward the total intrinsic scatter, σ0, from within-galaxy variations about the siblings' common properties. It also affects the combined distance uncertainty. We present analytic formulae for computing a σRel posterior from individual siblings distances (estimated using any SN model). Applying a newly trained BAYESN model, we fit the light curves of each sibling in NGC 3147 individually, to yield consistent distance estimates. However, the wide σRel posterior means σRel ≈ σ0 is not ruled out. We thus combine the distances by marginalizing over σRel with an informative prior: σRel ∼ U(0, σ0). Simultaneously fitting the trio's light curves improves constraints on distance and each sibling's individual dust parameters, compared to individual fits. Higher correlation also tightens dust parameter constraints. Therefore, σRel marginalization yields robust estimates of siblings distances for cosmology, as well as dust parameters for sibling–host correlation studies. Incorporating NGC 3147's Cepheid distance yields H0 = 78.4 ± 6.5 km s−1 Mpc−1. Our work motivates analyses of homogeneous siblings samples, to constrain σRel and its SN-model dependence.
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