The rate of satellite glints in ZTF and LSST sky surveys

We assess the impact of satellite glints -- rapid flashes produced by reflections of a sunlight from flat surfaces of rotating satellites -- on current and future deep sky surveys such as the ones conducted by the Zwicky Transient Facility (ZTF) and the Vera C. Rubin Observatory upcoming Legacy Survey of Space and Time (LSST). In addition to producing a large number of streaks polluting the images, artificial satellites and space debris also generate great amount of false point-source alerts hindering the search for new rapid astrophysical transients. To investigate the extent of this problem, we perform an analysis of isolated single frame events detected by ZTF in more than three years of its operation, and, using three different methods, assess the fraction of them related to artificial satellites to be at least 20\%. The satellites causing them occupy all kinds of orbits around the Earth, and the duration of flashes produced by their rotation is from a fraction of a second down to milliseconds, with mean all-sky rate of up to 80,000 per hour.Comment: Proceedings of 17th INTEGRAL/BART Workshop (IBWS-2023). arXiv admin note: text overlap with arXiv:2202.0571

Full covariance of CMB and lensing reconstruction power spectra

CMB and lensing reconstruction power spectra are powerful probes of cosmology. However, they are correlated, since the CMB power spectra are lensed, and the lensing reconstruction is constructed using CMB multipoles. We perform a full analysis of the auto- and cross-covariances, including polarization power spectra and minimum-variance lensing estimators, and compare with simulations of idealized future CMBS4 observations. Covariances sourced by fluctuations in the unlensed CMB and instrumental noise can largely be removed by using a realization-dependent subtraction of lensing reconstruction noise, leaving a relatively simple covariance model that is dominated by lensing-induced terms and well described by a small number of principal components. The correlations between the CMB and lensing power spectra will be detectable at the level of ∼5σ for a CMB-S4 mission, and neglecting them could underestimate some parameter error bars by several tens of percent. However, we found that the inclusion of external priors or data sets to estimate parameter error bars can make the impact of the correlations almost negligible

Fink: early supernovae Ia classification using active learning

We describe how the Fink broker early supernova Ia classifier optimizes its ML classifications by employing an active learning (AL) strategy. We demonstrate the feasibility of implementation of such strategies in the current Zwicky Transient Facility (ZTF) public alert data stream. We compare the performance of two AL strategies: uncertainty sampling and random sampling. Our pipeline consists of 3 stages: feature extraction, classification and learning strategy. Starting from an initial sample of 10 alerts (5 SN Ia and 5 non-Ia), we let the algorithm identify which alert should be added to the training sample. The system is allowed to evolve through 300 iterations. Our data set consists of 23 840 alerts from the ZTF with confirmed classification via cross-match with SIMBAD database and the Transient name server (TNS), 1 600 of which were SNe Ia (1 021 unique objects). The data configuration, after the learning cycle was completed, consists of 310 alerts for training and 23 530 for testing. Averaging over 100 realizations, the classifier achieved 89% purity and 54% efficiency. From 01/November/2020 to 31/October/2021 Fink has applied its early supernova Ia module to the ZTF stream and communicated promising SN Ia candidates to the TNS. From the 535 spectroscopically classified Fink candidates, 459 (86%) were proven to be SNe Ia. Our results confirm the effectiveness of active learning strategies for guiding the construction of optimal training samples for astronomical classifiers. It demonstrates in real data that the performance of learning algorithms can be highly improved without the need of extra computational resources or overwhelmingly large training samples. This is, to our knowledge, the first application of AL to real alerts data.Comment: 8 pages, 7 figures - submitted to Astronomy and Astrophysics. Comments are welcom

Finding active galactic nuclei through Fink

We present the Active Galactic Nuclei (AGN) classifier as currently implemented within the Fink broker. Features were built upon summary statistics of available photometric points, as well as color estimation enabled by symbolic regression. The learning stage includes an active learning loop, used to build an optimized training sample from labels reported in astronomical catalogs. Using this method to classify real alerts from the Zwicky Transient Facility (ZTF), we achieved 98.0% accuracy, 93.8% precision and 88.5% recall. We also describe the modifications necessary to enable processing data from the upcoming Vera C. Rubin Observatory Large Survey of Space and Time (LSST), and apply them to the training sample of the Extended LSST Astronomical Time-series Classification Challenge (ELAsTiCC). Results show that our designed feature space enables high performances of traditional machine learning algorithms in this binary classification task.Comment: Accepted for the Machine learning and the Physical Sciences workshop of NeurIPS 202

Instrumental systematics biases in CMB lensing reconstruction: a simulation-based assessment

Weak gravitational lensing of the cosmic microwave background (CMB) is an important cosmological tool that allows us to learn about the structure, composition and evolution of the Universe. Upcoming CMB experiments, such as the Simons Observatory (SO), will provide high-resolution and low-noise CMB measurements. We consider the impact of instrumental systematics on the corresponding high-precision lensing reconstruction power spectrum measurements. We simulate CMB temperature and polarization maps for an SO-like instrument and potential scanning strategy, and explore systematics relating to beam asymmetries and offsets, boresight pointing, polarization angle, gain drifts, gain calibration and electric crosstalk. Our analysis shows that the majority of the biases induced by the systematics we modeled are below a detection level of ∼0.6σ. We discuss potential mitigation techniques to further reduce the impact of the more significant systematics, and pave the way for future lensing-related systematics analyses

CMB-S4 Science Book, First Edition

This book lays out the scientific goals to be addressed by the next-generation ground-based cosmic microwave background experiment, CMB-S4, envisioned to consist of dedicated telescopes at the South Pole, the high Chilean Atacama plateau and possibly a northern hemisphere site, all equipped with new superconducting cameras. CMB-S4 will dramatically advance cosmological studies by crossing critical thresholds in the search for the B-mode polarization signature of primordial gravitational waves, in the determination of the number and masses of the neutrinos, in the search for evidence of new light relics, in constraining the nature of dark energy, and in testing general relativity on large scales

Making maps of cosmic microwave background polarization for B-mode studies: The POLARBEAR example

Analysis of cosmic microwave background (CMB) datasets typically requires some filtering of the raw time-ordered data. For instance, in the context of ground-based observations, filtering is frequently used to minimize the impact of low frequency noise, atmospheric contributions and/or scan synchronous signals on the resulting maps. In this work we have explicitly constructed a general filtering operator, which can unambiguously remove any set of unwanted modes in the data, and then amend the map-making procedure in order to incorporate and correct for it. We show that such an approach is mathematically equivalent to the solution of a problem in which the sky signal and unwanted modes are estimated simultaneously and the latter are marginalized over. We investigated the conditions under which this amended map-making procedure can render an unbiased estimate of the sky signal in realistic circumstances. We then discuss the potential implications of these observations on the choice of map-making and power spectrum estimation approaches in the context of B-mode polarization studies. Specifically, we have studied the effects of time-domain filtering on the noise correlation structure in the map domain, as well as impact it may haveon the performance of the popular pseudo-spectrum estimators. We conclude that although maps produced by the proposed estimators arguably provide the most faithful representation of the sky possible given the data, they may not straightforwardly lead to the best constraints on the power spectra of the underlying sky signal and special care may need to be taken to ensure this is the case. By contrast, simplified map-makers which do not explicitly correct for time-domain filtering, but leave it to subsequent steps in the data analysis, may perform equally well and be easier and faster to implement. We focused on polarization-sensitive measurements targeting the B-mode component of the CMB signal and apply the proposed methods to realistic simulations based on characteristics of an actual CMB polarization experiment, POLARBEAR. Our analysis and conclusions are however more generally applicable. \ua9 ESO, 2017

CMB-S4 Science Book, First Edition

This book lays out the scientific goals to be addressed by the next-generation ground-based cosmic microwave background experiment, CMB-S4, envisioned to consist of dedicated telescopes at the South Pole, the high Chilean Atacama plateau and possibly a northern hemisphere site, all equipped with new superconducting cameras. CMB-S4 will dramatically advance cosmological studies by crossing critical thresholds in the search for the B-mode polarization signature of primordial gravitational waves, in the determination of the number and masses of the neutrinos, in the search for evidence of new light relics, in constraining the nature of dark energy, and in testing general relativity on large scales

Analyse et exploitation scientifique des données de l'expérience d'observation des modes B du Fond Diffus Cosmologique, POLARBEAR

Over the last two decades cosmology has been transformed from a data-starved to a data-driven, high precision science. This transformation happened thanks to improved observational techniques, allowing to collect progressively bigger and more powerful data sets. Studies of the Cosmic Microwave Background (CMB) anisotropies have played, and continue on doing so, a particularly important and impactful role in this process. The huge data sets produced by recent CMB experiments pose new challenges for the field due to their volumes and complexity. Its successful resolution requires combining mathematical, statistical and computational methods all of which form a keystone of the modern CMB data analysis.In this thesis, I describe data analysis of the first data set produced by one of the most advanced, current CMB experiments, POLARBEAR and the major results it produced. The POLARBEAR experiment is a leading CMB B-mode polarization experiment aiming at detection and characterization of the so-called B-mode signature of the CMB polarization. This is one of the most exciting topics in the current CMB research, which only just has started yielding new insights onto cosmology in part thanks to the results discussed hereafter.In this thesis I describe first the modern cosmological model, focusing on the physics of the CMB, and in particular its polarization properties, and providing an overview of the past experiments and results. Subsequently, I present the POLARBEAR instrument, data analysis of its first year data set and the scientific results drawn from it, emphasizing my major contributions to the overall effort. In the last chapter, and in the context of the next generation CMB B-mode experiments, I present a more systematic study of the impact of the presence of the so-called E-to-B leakage on the performance forecasts of CMB B-mode experiments, by comparing several methods including the pure pseudospectrum method and the minimum variance quadratic estimator. In particular, I detail how the minimum variance quadratic estimator in the case of azimuthally symmetric patches can be used to estimate efficiently parameters, and I present an efficient implementation based on existing parallel algorithms for computing Spherical Harmonic Transforms.L'évolution des techniques d'observation au cours des deux dernières décennies a rendu possible l'obtention de jeux de données de plus en plus précis, et a permis l'évolution de la cosmologie vers une science de haute précision.Les études menées sur les anisotropies du Fond Diffus Cosmologique n'ont jamais cessé de jouer un rôle prépondérant dans cette transformation, tant leurs impacts ont été importants. Néanmoins, les jeux de données extrêmement volumineux et complexes produits par les expériences de Fond Diffus en cours posent un nouveau défi pour le domaine, à tel point que la réussite de l'analyse moderne des données du Fond Diffus repose sur une forte interdisciplinarité combinant de la physique, des mathématiques, des méthodes statistiques ainsi que des méthodes de calcul numérique.Dans cette thèse, j'expose l'analyse du premier jeu de données produit par POLARBEAR, l'une des expériences actuelle de premier plan sur le Fond Diffus, ainsi que les résultats majeurs obtenus. L'expérience POLARBEAR est spécifiquement dédiée à la détection et à la caractérisation de la signature des modes B de la polarisation du Fond Diffus Cosmologique. La recherche des modes B est l'un des sujets actuel les plus passionnants pour le Fond Diffus, qui a commencé à ouvrir de nouvelles perspectives sur la cosmologie, en partie grâce aux résultats présentés et discutés dans ce travail.Dans cette thèse, je décris en premier lieu le modèle cosmologique actuel, en me concentrant sur la physique du Fond Diffus, et plus particulièrement ses propriétés de polarisation; ainsi qu'une vue d'ensemble des contributions et des résultats des expériences antérieures et en cours. Dans un deuxième temps, je présente l'instrument POLARBEAR, l'analyse des données prises lors de la première année d'observation, ainsi que les résultats scientifiques qui en ont été tirés, en soulignant principalement ma contribution au projet dans son ensemble. Dans le dernier chapitre, et dans le contexte des prochaines générations d'expérience sur les modes B, je détaille une étude plus systématique concernant l'impact de la présence des fuites des modes E dans les modes B sur les performances prévues par ces futures expériences, notamment en comparant plusieurs méthodes dont la méthodes des pseudospectres pures ainsi que l'estimateur quadratique à variance minimum.En particulier, dans le cas d'observation du ciel présentant une symétrie azimutale, je détaille comment l'estimateur quadratique à variance minimum peut être utilisé pour estimer de manière efficace les paramètres cosmologiques, et je présente une implémentation performante basée sur des algorithmes parallèles existants pour le calcul des transformations en harmoniques sphériques