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1703 Publications visible to you, out of a total of 1703
Modeling photometric reverberation mapping data for the next generation of big data surveys. Quasar accretion disks sizes with the LSST

Abstract (Expand)

Abstract Photometric reverberation mapping can detect the radial extent of the accretion disc (AD) in Active Galactic Nuclei by measuring the time delays between light curves observed in different …rves observed in different continuum bands. Quantifying the constraints on the efficiency and accuracy of the delay measurements is important for recovering the AD size-luminosity relation, and potentially using quasars as standard candles. We have explored the possibility of determining the AD size of quasars using next-generation Big Data surveys. We focus on the Legacy Survey of Space and Time (LSST) at the Vera C. Rubin Observatory, which will observe several thousand quasars with the Deep Drilling Fields and up to 10 million quasars for the main survey in six broadband filter during its 10-year operational lifetime. We have developed extensive simulations that take into account the characteristics of the LSST survey and the intrinsic properties of the quasars. The simulations are used to characterise the light curves from which AD sizes are determined using various algorithms. We find that the time delays can be recovered with an accuracy of 5 and 15% for light curves with a time sampling of 2 and 5 days, respectively. The results depend strongly on the redshift of the source and the relative contribution of the emission lines to the bandpasses. Assuming an optically thick and geometrically thin AD, the recovered time-delay spectrum is consistent with black hole masses derived with 30% uncertainty.

Authors: F Pozo Nuñez, C Bruckmann, S Desamutara, B Czerny, S Panda, A P Lobban, G Pietrzyński, K L Polsterer

Date Published: 6th Feb 2023

Publication Type: Journal

Stellar gravitational collapse, singularity formation and theory breakdown

Abstract (Expand)

We review three definitions (missing point(s) unsteadiness, infinite quadratic curvature invariant, and geodesic incompleteness) of what a gravitational singularity is, and argue that prediction of a …a gravitational singularity is problematic for General Relativity (GR), indicating breakdown of Lorentzian geometry, only insofar as it concerns the infinite curvature singularity characterization. In contrast, the geodesic incompleteness characterization is GR’s innovating hallmark, which is not meaningfully available in Newtonian gravity formulations (locally infinite density field, and locally infinite gravitational force) of what a gravitational singularity is. It is the continuous, non-quantized, nature of Lorentzian geometry which admits gravitational contraction be continued indefinitely. The Oppenheimer-Snyder 1939 analytical solution derives formation of a locally infinite curvature singularity and of incomplete geodesics, while Penrose’s 1965 theorem concerns formation of incomplete (null) geodesics only. We critically examine the main physical arguments against gravitational singularity formation in stellar collapse, with scope restriction to decades spanning in between Schwarzschild’s 1916 solution and Penrose’s 1965 singularity theorem. As the most robust curvature singularity formation counter-argument, we assess Markov’s derivation of an upper bound on the quadratic curvature invariant RμνλδRμνλδ≤1ℓP4 from a ratio of natural constants ħ, c and G, in connection with Wheeler’s grounding of the premise that the Planck scale ℓP is ultimate.

Author: Kiril Maltsev

Date Published: 1st Feb 2023

Publication Type: Journal

Modeling Type Ia supernovae with explosions in white dwarfs near and below the Chandrasekhar mass

Abstract (Expand)

The progenitor evolution and the explosion mechanism of Type Ia supernovae remain unexplained. Nonetheless, substantial progress has been made over the past years with three-dimensional hydrodynamic …c simulations of different scenarios. Here, we review some recent work pertaining to the leading paradigms of modeling: thermonuclear explosions of white dwarf stars near and below the Chandrasekhar mass limit. We discuss implications of the different explosion channels and their predictions of observables.

Authors: Friedrich K. Röpke, Florian Lach, Sabrina Gronow, Stuart A. Sim, Fionntan P. Callan, Christine E. Collins

Date Published: 1st Feb 2023

Publication Type: Journal

Family dispute: do Type IIP supernova siblings agree on their distance?

Abstract

Not specified

Authors: Géza Csörnyei, Christian Vogl, Stefan Taubenberger, Andreas Flörs, Stéphane Blondin, Maria Gabriela Cudmani, Alexander Holas, Sabrina Kressierer, Bruno Leibundgut, Wolfgang Hillebrandt

Date Published: 1st Feb 2023

Publication Type: Journal

Probabilistic Modelling of Time Series for explorative Big Data Analysis in Astronomy

Abstract

Not specified

Author: Fenja Schweder

Date Published: 1st Feb 2023

Publication Type: Master's Thesis

Accretion disks, quasars and cosmology: meandering towards understanding

Abstract (Expand)

Abstract As Setti and Woltjer noted back in 1973, one can use quasars to construct the Hubble diagram; however, the actual application of the idea was not that straightforward. It took years to implement …It took years to implement the proposition successfully. Most ways to employ quasars for cosmology now require an advanced understanding of their structure, step by step. We briefly review this progress, with unavoidable personal biases, and concentrate on bright unobscured sources. We will mention the problem of the gas flow character close to the innermost stable circular orbit near the black hole, as discussed five decades ago. This problem later led to the development of the slim disk scenario and is recently revived in the context of Magnetically Arrested Disks (MAD) and Standard and Normal Evolution (SANE) models. We also discuss the hot or warm corona issue, which is still under debate and complicates the analysis of X-ray reflection. We present the scenario of the formation of the low ionization part of the Broad Line Region as a failed wind powered by radiation pressure acting on dust (Failed Radiatively Driven Dusty Outflow – FRADO). Next, we examine the cosmological constraints currently achievable with quasars, primarily concentrating on light echo methods (continuum time delays and spectral-line time delays to the continuum) that are (or should be) incorporating the progress mentioned above. Finally, we briefly discuss prospects in this lively subject area.

Authors: Bożena Czerny, Shulei Cao, Vikram Kumar Jaiswal, Vladimír Karas, Narayan Khadka, Mary Loli Martínez-Aldama, Mohammad Hassan Naddaf, Swayamtrupta Panda, Francisco Pozo Nuñez, Raj Prince, Bharat Ratra, Marzena Sniegowska, Zhefu Yu, Michal Zajaček

Date Published: 1st Feb 2023

Publication Type: Journal

Machine Learning Methods Improve Specificity in Newborn Screening for Isovaleric Aciduria

Abstract (Expand)

Isovaleric aciduria (IVA) is a rare disorder of leucine metabolism and part of newborn screening (NBS) programs worldwide. However, NBS for IVA is hampered by, first, the increased birth prevalence due …prevalence due to the identification of individuals with an attenuated disease variant (so-called “mild” IVA) and, second, an increasing number of false positive screening results due to the use of pivmecillinam contained in the medication. Recently, machine learning (ML) methods have been analyzed, analogous to new biomarkers or second-tier methods, in the context of NBS. In this study, we investigated the application of machine learning classification methods to improve IVA classification using an NBS data set containing 2,106,090 newborns screened in Heidelberg, Germany. Therefore, we propose to combine two methods, linear discriminant analysis, and ridge logistic regression as an additional step, a digital-tier, to traditional NBS. Our results show that this reduces the false positive rate by 69.9% from 103 to 31 while maintaining 100% sensitivity in cross-validation. The ML methods were able to classify mild and classic IVA from normal newborns solely based on the NBS data and revealed that besides isovalerylcarnitine (C5), the metabolite concentration of tryptophan (Trp) is important for improved classification. Overall, applying ML methods to improve the specificity of IVA could have a major impact on newborns, as it could reduce the newborns’ and families’ burden of false positives or over-treatment.

Authors: Elaine Zaunseder, Ulrike Mütze, Sven F. Garbade, Saskia Haupt, Patrik Feyh, Georg F. Hoffmann, Vincent Heuveline, Stefan Kölker

Date Published: 1st Feb 2023

Publication Type: Journal

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