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1.
LensWatch. II. improved photometry and time-delay constraints on the strongly lensed type Ia supernova 2022qmx ("SN Zwicky") with Hubble Space Telescope template observations
C. Larison, Justin Pierel, M. J. B. Newman, S. W. Jha, D. Gilman, E. E. Hayes, A. Agrawal, N. Arendse, Mateusz Bronikowski, Tanja Petrushevska, 2025, original scientific article

Abstract: Abstract Strongly lensed supernovae (SNe) are a rare class of transient that can offer tight cosmological constraints that are complementary to methods from other astronomical events. We present a follow-up study of one recently discovered strongly lensed SN, the quadruply imaged type Ia SN 2022qmx (aka “SN Zwicky”), at z = 0.3544. We measure updated, template-subtracted photometry for SN Zwicky and derive improved time delays and magnifications. This is possible because SNe are transient, fading away after reaching their peak brightness. Specifically, we measure point-spread-function photometry for all four images of SN Zwicky in three Hubble Space Telescope WFC3/UVIS passbands (F475W, F625W, and F814W) and one WFC3/IR passband (F160W), with template images taken ∼11 months after the epoch in which the SN images appear. We find consistency to within 2σ between lens-model-predicted time delays (≲1 day) and measured time delays with HST colors (≲2 days), including the uncertainty from chromatic microlensing that may arise from stars in the lensing galaxy. The standardizable nature of SNe Ia allows us to estimate absolute magnifications for the four images, with images A and C being elevated in magnification compared to lens model predictions by about 6σ and 3σ, respectively, confirming previous work. We show that millilensing or differential dust extinction is unable to explain these discrepancies, and we find evidence for the existence of microlensing in images A, C, and potentially D that may contribute to the anomalous magnification.
Keywords: supernova, strong lensing, astronomy
Published in RUNG: 10.03.2025; Views: 233; Downloads: 0
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2.
Spectroscopic analysis of the strongly lensed SN Encore : constraints on cosmic evolution of Type Ia supernovae
S. Dhawan, Justin Pierel, M. Gu, A. B. Newman, C. Larison, M. Siebert, Tanja Petrushevska, F. Poidevin, S. W. Jha, W. Chen, 2024, original scientific article

Abstract: Abstract Strong gravitational lensing magnifies the light from a background source, allowing us to study these sources in detail. Here, we study the spectra of a z = 1.95 lensed Type Ia supernova SN Encore for its brightest Image A, taken 39 days apart. We infer the spectral age with template matching using the supernova identification (SNID) software and find the spectra to be at 29.0 ±5.0 and 37.4 ±2.8 rest-frame days post maximum respectively, consistent with separation in the observer frame after accounting for time-dilation. Since SNe Ia measure dark energy properties by providing relative distances between low- and high-z SNe, it is important to test for evolution of spectroscopic properties. Comparing the spectra to composite low-z SN Ia spectra, we find strong evidence for similarity between the local sample and SN Encore. The line velocities of common SN Ia spectral lines, Si II 6355 and Ca II NIR triplet are consistent with the distribution for the low-z sample as well as other lensed SNe Ia, e.g. iPTF16geu (z = 0.409)and SN H0pe (z = 1.78). The consistency between the low-z sample and lensed SNe at high-z suggests no obvious cosmic evolution demonstrating their using as high-z distance indicators, though this needs to be confirmed/refuted via a larger sample. We also find that the spectra of SN Encore match the predictions for explosion models very well. With future large samples of lensed SNe Ia e.g. with the Vera C. Rubin Observatory, spectra at such late phases will be important to distinguish between different explosion scenarios.
Keywords: Encore
Published in RUNG: 29.10.2024; Views: 750; Downloads: 3
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Cluster-lensed supernovae with the Roman Space Telescope and Vera Rubin observatory
Mateusz Bronikowski, Tanja Petrushevska, Justin Pierel, 2022, published scientific conference contribution abstract

Abstract: I will present our current efforts to enable the use of strongly lensed supernovae behind galaxy clusters as powerful tools to tackle several open questions in astrophysics and cosmology. As a preparatory task, we are collecting all available gravitational telescopes into a database, and estimating the properties of all reported multiply-imaged galaxies behind clusters. We are building a tool that will enable accurate estimates of cluster-lensed supernova yields for a given survey. In addition, we are developing the methods to extract the cosmological parameters from cluster-lensed supernovae in the Rubin and Roman data.
Keywords: supernova, gravitational lensing, Vera Rubin Observatory, Roman Space telescope, LSST, Hubble constant
Published in RUNG: 09.11.2022; Views: 2306; Downloads: 8
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