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#### Detecting Strongly-Lensed Supernovae in Wide-field Space Telescope Imaging via Deep Learning
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-**Authors:** Fawad Kirmani, Arjun Karki, Steve Rodney, Kyle Lackey, Varsha P. Kulkarni, John R. Rose, Justin Pierel
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-**Subjects:** Subjects:
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Instrumentation and Methods for Astrophysics (astro-ph.IM)
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-**Arxiv link:**https://arxiv.org/abs/2512.19886
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-**Pdf link:**https://arxiv.org/pdf/2512.19886
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-**Abstract**
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Gravitationally lensed supernovae (SNe) are extremely rare and fade quickly; as a result, they are challenging to detect. To identify lensed SNe in large imaging datasets, current surveys primarily rely on the {\it magnification} effect of gravitational lensing -- searching for transients that appear brighter than expected \cite{c3}. In this work, we present a proof-of-concept study that uses a deep neural network to classify previously detected transients. Instead of relying on magnification, this network aims to identify doubly-imaged SNe with small separations ($<0.6$ arcsec) based on the {\it distorted shape} of the transient object. This proposed method is most applicable to space-based imaging surveys from wide-field imaging observatories such as the upcoming Roman Space Telescope. To train and test our network, we use archival Hubble Space Telescope (HST) imaging surveys. Due to the extreme rarity of lensed SNe, we cannot train a neural network on actual lensed SN data. Instead, we have used HST imaging data to generate simulated imaging datasets for both training and testing. Our simulations use astrophysical priors to define the separations, relative brightnesses, and colors of each multiply-imaged SN. We have also simulated false positives (image artifacts and unlensed supernovae), which are much more prevalent than true lensed SN. Our deep learning model is trained to identify lensed SNe from a single difference image (i.e., not using multiple epochs). This network achieves a recall score of 99\% on simulated gravitationally lensed SNe. The network successfully distinguishes between single supernovae (SNe) and those with gravitationally lensed SNe, as well as images with zero SNe, achieving recall scores of 90\% and 96\% for single-SNe and zero-SNe images, respectively.
#### The imprints of massive neutrinos on the 3-point correlation function of large-scale structures
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-**Authors:**Andrea Labate, Massimo Guidi, Michele Moresco, Alfonso Veropalumbo
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### Today: 1papers
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#### Detecting Strongly-Lensed Supernovae in Wide-field Space Telescope Imaging via Deep Learning
18
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-**Authors:**Fawad Kirmani, Arjun Karki, Steve Rodney, Kyle Lackey, Varsha P. Kulkarni, John R. Rose, Justin Pierel
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-**Subjects:** Subjects:
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Cosmology and Nongalactic Astrophysics (astro-ph.CO)
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-**Arxiv link:**https://arxiv.org/abs/2512.16992
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Instrumentation and Methods for Astrophysics (astro-ph.IM)
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-**Arxiv link:**https://arxiv.org/abs/2512.19886
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-**Pdf link:**https://arxiv.org/pdf/2512.16992
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-**Pdf link:**https://arxiv.org/pdf/2512.19886
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-**Abstract**
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Free-streaming of cosmic neutrinos impacts the distribution and growth of cosmic structures on small scales, allowing constraints on the sum of neutrino masses $M_\nu$ from clustering studies. In this work, we investigate for the first time the possibility of disentangling massive neutrino cosmologies with the 3-point correlation function (3PCF). We measure the isotropic connected 3PCF $\zeta$ and the reduced 3PCF $Q$ of halo catalogues from the Quijote suite of N-body simulations, considering $M_\nu =0.0, 0.1, 0.2,$ and $0.4 \, \mathrm{eV}$ in different redshift bins. We develop a framework to quantify the detectability of massive neutrinos for different triangle configurations and shapes, and apply it to a case compatible with a Stage-IV spectroscopic survey. We also compare our results with the analysis of simulations without neutrinos, but with different $\sigma_8$ values, to test whether the 3PCF can break the well-known degeneracy between the two parameters. We find that, as a result of free-streaming, the largest signal is found for quasi-isosceles and squeezed triangles; this signal is increasing for decreasing redshifts. Among these configurations, elongated triangles, tracing the filamentary structure of the cosmic web, are the most affected by the impact of massive neutrinos, with a 3PCF signal increasing with $M_\nu$. A complementary source of signal comes from right-angled triangles in $Q$. Importantly, we find that the signatures of a $\sigma_8$ variation appear significantly different on elongated triangles in $\zeta$ and right-angled triangles in $Q$, suggesting that the 3PCF can be used to effectively break the $M_\nu - \sigma_8$ degeneracy. These results open the possibility to use the 3PCF as a powerful complementary tool to constrain neutrino masses in current and future spectroscopic surveys like DESI, Euclid, 4MOST, and the Nancy Grace Roman Space Telescope.
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#### Quantifying Systematic Age Discrepancies in Very Young Star Clusters
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-**Authors:** Joseph Guzman, Jeremiah Murphy, Emma Beasor, Julianne Dalcanton, Nathan Smith, Mojgan Aghakhanloo, Benjamin Williams, Andres Barrientos
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-**Subjects:** Subjects:
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Solar and Stellar Astrophysics (astro-ph.SR); Astrophysics of Galaxies (astro-ph.GA)
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-**Arxiv link:**https://arxiv.org/abs/2512.17033
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-**Pdf link:**https://arxiv.org/pdf/2512.17033
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-**Abstract**
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We infer the ages of three young stellar clusters, NGC 2004, NGC 7419, and NGC 2100, using Stellar Ages, a statistical algorithm designed to infer stellar population properties from color magnitude diagrams. Recent studies have revealed emerging inconsistencies in the inferred ages of very young stellar clusters with ages less than or equal to 50 Myr. Here, we identify and quantify two distinct discrepancies. First, we identify a systematic age offset of 0.55 plus minus 0.09 dex between red supergiant and bright blue star age estimates, equivalent to a factor of approximately 3.5 in linear age, with bright blue star ages appearing systematically younger than those inferred from red supergiants. Second, given the observed numbers of red supergiants and bright blue stars, we find a pronounced deficit of lower-mass main-sequence stars relative to expectations from a standard initial mass function. Although these discrepancies resemble those reported for intermediate-age clusters, their magnitude and character suggest that they are unique to the evolution of massive stars. Together, these results highlight population-level inconsistencies with single-star evolutionary models and underscore the need to consider multiple evolutionary tracers when age-dating young clusters. By combining individual stellar ages with population-wide constraints, our approach refines prior work on cluster age determinations and provides new insight into massive star evolution and the interpretation of cluster demographics.
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#### The mass distribution of clumpy accretion onto the nearby young star TW Hya
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-**Authors:** Tao Ji, Javier Serna, Gregory J. Herczeg, Shinsuke Takasao, Frederick M. Walter, Yuguang Chen, Antonio Armeni, Doug Johnstone, Jochen Eisloeffel, Min Fang, Sean P. Matt, Michal Siwak, Laura Venuti, Miguel Vioque, Lixin Dai
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-**Subjects:** Subjects:
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Solar and Stellar Astrophysics (astro-ph.SR); Earth and Planetary Astrophysics (astro-ph.EP)
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-**Arxiv link:**https://arxiv.org/abs/2512.17074
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-**Pdf link:**https://arxiv.org/pdf/2512.17074
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-**Abstract**
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The proliferation of high time-resolution and decades-long monitoring of classical T Tauri stars provides a vast opportunity to test the variability of the star-disk connections. However, most monitoring surveys use single broad-band filters, which makes the conversion of photometric variability into accretion rate difficult. In this study, we analyze accretion bursts onto the nearby young star TW Hya over short (hours, days) and long (months, years) timescales by calibrating TESS and ASAS-SN $g$-band photometry to accretion rates with simultaneous spectroscopy. The high cadence TESS light curve shows bursts of accretion in clumps with masses from a sensitivity limit of $\sim10^{-13}$~M$_\odot$ up to $3\times 10^{-11}$\,M$_\odot$. The average burst duration of 1.8 days is longer than a simple estimate of the thermal response timescale, supporting the interpretation that the photometric variability probes the instantaneous accretion rate. The reset timescale of 1.2--2 days derived from the structure function and previously reported quasi-periods of 3.5--4 days are consistent with bursts that may be related to the different rotation between the stellar magnetosphere and inner disk or with azimuthal asymmetries in the inner disk. The near-daily ASAS-SN light curve across 8 years reveals some seasonal changes in brightness with a standard deviation of $\sim 0.13$ mag, about half of the scatter seen on short timescales. This study demonstrates the importance of coordinating contemporaneous multi-epoch spectroscopy with time domain surveys to interpret light curves of young stars.
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#### A VLA search for compact radio sources in the explosive molecular outflows DR 21 and G5.89
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-**Authors:** Vanessa Yanza, Sergio A. Dzib, Aina Palau, William J. Henney, Luis F. Rodríguez, Luis A. Zapata
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-**Subjects:** Subjects:
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Solar and Stellar Astrophysics (astro-ph.SR); Astrophysics of Galaxies (astro-ph.GA)
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-**Arxiv link:**https://arxiv.org/abs/2512.17698
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-**Pdf link:**https://arxiv.org/pdf/2512.17698
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-**Abstract**
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We present high-angular-resolution ($\sim0\rlap{.}''1$) VLA Ku-band (12--18 GHz) observations of two explosive molecular outflows (EMOs), DR 21 and G5.89, in a search for runaway stars related to these explosive events. In DR 21, we identified 13 compact radio sources (CRS), 9 located in the DR 21 core and near the CO streamer ejection region. The radio properties of the CRSs show that three are nonthermal radio emitters, likely magnetically active stars, while the nature of the remaining CRSs cannot be conclusively identified. All detected CRSs are good candidates for follow-up proper motion studies to confirm whether they are runaway stars. We also identify multiple ionized arc-shaped structures that can be fitted with parabolas whose symmetry axes converge to a position coincident with CRSs #11, raising the possibility that this source is the main ionizing star. A re-analysis of the 18 molecular outflow streamers refines the center of the explosive event, which aligns closely with the position indicated by the arcs convergence point, supporting a common stellar origin for the EMOs and the HII-region. In G5.89, the observations reveal a shell with a square-like morphology. The strong extended emission from this HII region prevents the detection of weak compact radio sources inside the shell; only two were identified well beyond the shell, and a single parabolic arc was fitted within this region. Overall, arc structures in ionized regions seem to be good tracers of the origin of the ionizing sources.
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#### Pre-supernova O-C shell mergers could produce more $^{44}\mathrm{Ti}$ than the explosion
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-**Authors:** Joshua Issa, Falk Herwig
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-**Subjects:** Subjects:
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Solar and Stellar Astrophysics (astro-ph.SR); High Energy Astrophysical Phenomena (astro-ph.HE)
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-**Arxiv link:**https://arxiv.org/abs/2512.17705
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-**Pdf link:**https://arxiv.org/pdf/2512.17705
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-**Abstract**
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The formation of $^{44}\mathrm{Ti}$ in massive stars is thought to occur during explosive nucleosynthesis, however recent studies have shown it can be produced during O-C shell mergers prior to core collapse. We investigate how mixing according to 3D macro physics derived from hydrodynamic simulations impacts the pre-supernova O-C shell merger nucleosynthesis and if it can dominate the explosive supernova production of $^{44}\mathrm{Ti}$ and other radioactive isotopes. We compare a range of observations and models of explosive $^{44}\mathrm{Ti}$ yields to pre-explosive multi-zone mixing-burning nucleosynthesis simulations of an O-C shell merger in a $15~\mathrm{M}_\odot$ stellar model with mixing conditions corresponding to different 3D hydro mixing scenarios. Radioactive species produced in the O shell have a spread in their pre-explosive yields predictions across different 3D mixing scenarios of 2.14 dex on average. $^{44}\mathrm{Ti}$ has the largest spread of 4.78 dex. The pre-explosive production of $^{44}\mathrm{Ti}$ can be larger than the production of all massive star models in the NuGrid data set where $^{44}\mathrm{Ti}$ is dominated by the explosive nucleosynthesis contribution, as well all other massive star and supernova models. We conclude that quantitative predictions of $^{44}\mathrm{Ti}$ and other radioactive species more broadly require an understanding of the 3D hydrodynamic mixing conditions present during the O-C shell merger.
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#### Asymptotic behaviour of galactic small-scale dynamos at modest magnetic Prandtl number
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-**Authors:** Frederick A. Gent, Mordecai-Mark Mac Low, Maarit J. Korpi-Lagg, Touko Puro, Matthias Reinhardt
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-**Subjects:** Subjects:
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Astrophysics of Galaxies (astro-ph.GA); Distributed, Parallel, and Cluster Computing (cs.DC)
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-**Arxiv link:**https://arxiv.org/abs/2512.17885
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-**Pdf link:**https://arxiv.org/pdf/2512.17885
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-**Abstract**
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Magnetic fields are critical at many scales to galactic dynamics and structure, including multiphase pressure balance, dust processing, and star formation. Dynamo action determines their dynamical structure and strength. Simulations of combined large- and small-scale dynamos have successfully developed mean fields with strength and topology consistent with observations but with turbulent fields much weaker than observed, while simulations of small-scale dynamos with parameters relevant to the interstellar medium yield turbulent fields an order of magnitude below the values observed or expected theoretically. We use the Pencil Code accelerated on GPUs with Astaroth to perform high-resolution simulations of a supernova-driven galactic dynamo including heating and cooling in a periodic domain. Our models show that the strength of the turbulent field produced by the small-scale dynamo approaches an asymptote at only modest magnetic Prandtl numbers. This allows us to use these models to suggest the essential characteristics of this constituent of the magnetic field for inclusion in global galactic models. The asymptotic limit occurs already at magnetic Prandtl number of only a few hundred, many orders of magnitude below physical values in the the interstellar medium and consistent with previous findings for isothermal compressible flows.
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Gravitationally lensed supernovae (SNe) are extremely rare and fade quickly; as a result, they are challenging to detect. To identify lensed SNe in large imaging datasets, current surveys primarily rely on the {\it magnification} effect of gravitational lensing -- searching for transients that appear brighter than expected \cite{c3}. In this work, we present a proof-of-concept study that uses a deep neural network to classify previously detected transients. Instead of relying on magnification, this network aims to identify doubly-imaged SNe with small separations ($<0.6$ arcsec) based on the {\it distorted shape} of the transient object. This proposed method is most applicable to space-based imaging surveys from wide-field imaging observatories such as the upcoming Roman Space Telescope. To train and test our network, we use archival Hubble Space Telescope (HST) imaging surveys. Due to the extreme rarity of lensed SNe, we cannot train a neural network on actual lensed SN data. Instead, we have used HST imaging data to generate simulated imaging datasets for both training and testing. Our simulations use astrophysical priors to define the separations, relative brightnesses, and colors of each multiply-imaged SN. We have also simulated false positives (image artifacts and unlensed supernovae), which are much more prevalent than true lensed SN. Our deep learning model is trained to identify lensed SNe from a single difference image (i.e., not using multiple epochs). This network achieves a recall score of 99\% on simulated gravitationally lensed SNe. The network successfully distinguishes between single supernovae (SNe) and those with gravitationally lensed SNe, as well as images with zero SNe, achieving recall scores of 90\% and 96\% for single-SNe and zero-SNe images, respectively.
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