arXiv subjects

Gilles Koziol

Publications and source records attributed to Gilles Koziol.

4 recordsLinked to original sources

arXiv2026

Probing Stellar Kinematics with the Time-Asymmetric Hanbury Brown and Twiss Effect

Intensity interferometry (II) offers a powerful means to observe stellar objects with a high resolution. In this work, we demonstrate that II can also probe internal stellar kinematics by revealing a time-asymmetric Hanbury Brown and Twiss (HBT) effect, causing a measurable shift in the temporal correlation peak away from zero delay. We develop numerical models to simulate this effect for two distinct astrophysical scenarios: an emission-line circumstellar disk and an absorption-line binary system. Our simulations reveal a clear sensitivity of this temporal asymmetry to the system's inclination angle, velocity symmetry, and internal dynamics. This suggests that, with sufficiently high time resolution, II can be used to extract quantitative information about internal kinematics, offering a new observational window on stellar dynamics.

astro-ph.IM↗

arXiv2025

Exploiting light coherence in astrophysics

The Hanbury Brown-Twiss (HBT) effect, discovered in the 1950s and further developed in the 1960s, was originally used to estimate stellar angular diameters through intensity correlations measured by spatially separated detectors. Further developments started from HBT experiments to exploit quantum bunching of photons in incoherent light sources played foundational role in the development of quantum optics. When the two detectors in an HBT experiment are co-located, typically implemented using a beam splitter, a zero-baseline intensity correlation is obtained, which after deconvolution of the detector response function, yields the temporal component of the second-order coherence function. Unlike spatial correlations, this function is independent of the source brightness distribution, or its size, giving direct insight into the properties of the source's emission process itself - photon statistics. Along with photometric and spectral information, the second order coherence function can be used to constrain the emission mechanisms and discriminate between thermal, synchrotron, bremsstrahlung and stimulated emission processes. Evolution of the emission processes would likewise drive changes in the second order coherence. Light coherence information along with multi-wavelength observations, can become a complementary "messenger", carrying internal information about the astronomical source.

astro-ph.GA↗

arXiv2024

Response of the first POLAR-2 Prototype to Polarized Beams

POLAR-2 is a dedicated gamma-ray polarimeter currently foreseen to be launched towards the China Space Station around 2027. The design of the detector is based on the legacy of its predecessor mission POLAR which was launched in 2016. POLAR-2 aims to measure the polarization of the Gamma-ray Burst prompt emission within the 30-800 keV energy range. Thanks to its high sensitivity to gamma-ray polarization, as well as its large effective area, POLAR-2 will provide the most precise measurements of this type to date. Such measurements are key to improve our understanding of the astrophysical processes responsible for Gamma-Ray Bursts. The detector consists of a segmented array of plastic scintillator bars, each one of which is read out by a Silicon PhotoMultiplier channel. The flight model of POLAR-2 will contain a total of 6400 scintillators. These are divided into 100 groups of 64 bars each, in so-called polarimeter modules. In recent years, the collaboration has designed and produced the first prototypes of these polarimeter modules and subjected these to space qualification tests. In addition, in April 2023, the first of these modules were calibrated using fully polarized gamma-ray beams at the European Synchrotron Radiation Facility (ESRF) in France. In this work, we will present the results of this calibration campaign and compare these to the simulated performance of the POLAR-2 modules. Potential improvements to the design are also discussed. Finally, the measurements are used, in combination with the verified simulation framework, to estimate the scientific performance of the full POLAR-2 detector and compare it to its predecessor.

astro-ph.IM↗

arXiv2023

HAGRID -- High Accuracy GRB Rapid Inference with Deep learning

Since their discoveries in 1967, Gamma-Ray Bursts (GRBs) continue to be one of the most researched objects in astrophysics. Multi-messenger observations are key to gaining a deeper understanding of these events. In order to facilitate such measurements, fast and accurate localization of the gamma-ray prompt emission is required. As traditional localization techniques are often time consuming or prone to significant systematic errors, here we present a novel method which can be applied on the POLAR-2 observatory. POLAR-2 is a dedicated GRB polarimeter, which will be launched towards the China Space Station (CSS) in 2025. The CSS provides POLAR-2 access to a GPU, which makes it possible and advantageous to run a Deep Learning model on it. In this work, we explore the possibility to identify GRBs in real time and to infer their location and spectra with deep learning models. Using POLAR simulations and data, a feasibility experiment was performed to implement this method on POLAR-2. Our results indicate that using this method, in combination with real time data downlinking capabilities, POLAR-2 will be able to provide accurate localization alerts within 2 minutes of the GRB onset.

astro-ph.IM↗