arXiv subjects

Michaël De Becker

Publications and source records attributed to Michaël De Becker.

16 recordsLinked to original sources

arXiv2026

Meerkat measurement of the radio emission from massive stars in the Galactic plane I. Wolf-Rayet stars

Massive stars, including Wolf-Rayet stars, are predominantly found in binary systems. These systems are known to emit both thermal emission from stellar winds and, occasionally, non-thermal emission produced by relativistic electrons accelerated in the wind-wind interaction region. We intend to provide the most complete census of radio emission from WR stars in the Galactic plane, using the SARAO MeerKAT Galactic Plane Survey (SMGPS) complemented by the MeerKAT Galactic Center Survey. Our main motivation is to identify hints of synchrotron radio emission indicative of particle-accelerating colliding-wind binaries (PACWBs). We compiled an input catalogue of 428 WR stars positionally covered by the SMGPS and the MGCS. Using the survey data, we measured the radio emission at 1.3 GHz for detected WR stars. We also measured the upper limits for objects located in sufficiently low radio background regions. For detected objects, we searched for a radio excess by comparing the measured fluxes to two different evaluators of the thermal emission from massive star winds. We detected 23 targets and determined the upper limits for 279 WR stars. Among the detected objects, 15 display a (significant or potential) radio excess that cannot be explained by unresolved circumstellar emission of any kind. After removing already known PACWBs, we report the identification of 12 potential new PACWB candidates. Our study has led to the compilation of the most extensive catalogue of Galactic WR radio emission to date, based on a homogeneous dataset covering the Galactic plane. The low detection rate indicates either a low occurrence rate of synchrotron emission or substantial attenuation by turnover processes that are clearly dominated by free-free absorption from the WR wind material. Our results open the door to dedicated follow-up observations aimed at ascertaining the nature of the identified radio excesses.

astro-ph.SR↗

arXiv2026

The influence of free-free absorption on the radio spectrum of Particle-Accelerating Colliding-Wind Binaries

The study of massive stars in binary and higher-multiplicity systems that participate in particle acceleration is a key topic at the crossroads of massive star physics, shock physics, and galactic cosmic ray astrophysics. From an observational perspective, radio measurements are our pri- mary tool for identifying these systems through their synchrotron radio emission. Out of the 54 such systems known to date, all but two have been discovered via their non-thermal radio emission. However, identifying these systems is not straightforward. The main challenge lies in free-free absorption, which can obscure the synchrotron signature and hinder detection. This paper summarizes recent developments in our understanding of these systems, with a particular focus on the strong observational bias introduced by free-free absorption. This bias significantly limits our ability to determine the true fraction of particle accelerators among colliding-wind binaries.

astro-ph.HE↗

arXiv2026

DESTINY: a new binding-energy-resolved astrochemical framework. Self-Consistent Competitiveness using Branched Absorbing Markov Chains

Under cryogenic interstellar conditions, the amorphous structure of interstellar ice results in binding-energy distributions (BEDs) per species. However, only few studies attempted their inclusion in astrochemical models. This paper introduces DESTINY, a deterministic astrochemical framework designed to incorporate BEDs while self-consistently accounting for the competition among activated surface processes. The framework is currently constrained to a monolayer. Surface processes initiated by surface species are reformulated using a trial-frequency-capped formalism represented through branched absorbing Markov chains. The ordinary differential equations (ODE) system is redefined based on normalized effective probabilities. Preliminary results based on a reduced surface network are discussed. To isolate the effects of the probabilistic reformulation from those induced by BED discretizations, DESTINY is benchmarked against Nautilus, a single-BE rate-equation based open source code. In the single-BE limit, DESTINY reproduces the behavior of Nautilus for most species. The largest deviations are obtained for CH$_{x = [2,4]}$ ; these are traced to a different treatment of the H$_2$ encounter effect, impacting both H$_2$ surface exploration and desorption efficiencies within the DESTINY framework. Introducing BEDs redistributes species among adsorption sites of different depths, altering the balance between diffusion, desorption, and reactions. Significant effects are found for H, H$_2$, NH$_x$, NO, CH$_x$, CO and H$_x$CO. Preliminary results showed that the self-consistent treatment of the H$_2$ encounter effect coupled with the explicit treatment of BEDs can substantially modify grain-surface chemistry. Further framework extensions are expected in the near future.

astro-ph.IM↗

arXiv2026

How to access astronomical observation facilities ?

Access to astronomical data is a central component of astrophysical research. The allocation of telescope time is organized on an international scale through a highly competitive process. Over the past decades, this framework has evolved toward an increasingly professionalized system, particularly in the context of calls for telescope time proposals issued by major agencies or organizations, where hundreds of projects may compete for selection. Preparing a telescope time proposal is a demanding task for which junior researchers are not always adequately prepared. Astrophysicists typically acquire this expertise through first-hand experience, either by submitting their first proposal or by participating as members of a proposing team. At the same time, competition for telescope time is intense, and the significant effort invested in proposal preparation is accompanied by a non-negligible risk of rejection. This paper aims to present the general framework governing telescope time applications for both ground-based and space-borne observatories, with particular emphasis on the preparation of telescope time proposals. It discusses a set of key guidelines, some mandatory and others advisory, intended to help proposers navigate the application process more effectively, avoid common pitfalls and procedural missteps, and ultimately reduce the likelihood of preventable factors leading to a substantial decrease in the probability of selection.

astro-ph.IM↗

arXiv2026

Investigating particle acceleration in the Wolf-Rayet bubble NGC 2359

Massive stars have been proposed as candidates to be major factories of Galactic cosmic rays (GCRs). However, this claim lacks enough empirical evidence, especially for isolated stars. The powerful stellar winds from massive stars impact the ambient medium producing strong shocks suitable for accelerating relativistic particles. The detection of non-thermal emission-particularly synchrotron emission in low radio frequencies-serves as a key proof of particle acceleration sites. We aim to assess the potential of isolated massive stars as sources of GCRs. We observed the Wolf-Rayet bubble, NGC 2359, using the upgraded Giant Metrewave Radio Telescope at Band 3 (250-500 MHz) and Band 4 (550-950 MHz). Additionally, we used complementary archival radio datasets at different frequencies to derive the broad spectral energy distribution (SED) for several regions within the bubble. To further characterize the interaction between the stellar wind and the ambient medium, we introduced a composite SED model including synchrotron and free-free emission, and two low-frequency turnover processes, the Razin-Tsytovich (RT) effect and free-free absorption (FFA).We used a Bayesian inference approach to fit the SEDs and constrain the electron number density and magnetic field strength. The SEDs of several regions reveal spectral indices steeper than -0.5, indicative of synchrotron emission. and show a turnover below ~1 GHz. Our SED modelling suggests that the observed turnover is primarily caused by the RT effect, with a minor contribution from internal FFA. Our analysis confirms the presence of synchrotron radiation within NGC 2359. This is the second detection of non-thermal emission in a stellar bubble surrounding a WR star, reinforcing the idea that such environments are sites of relativistic particle acceleration and supporting the hypothesis that isolated massive stars are sources of GCRs of at least GeV energies.

astro-ph.HE↗

arXiv2025

Shock-type inference of L1157 B2 using methanol desorption

Shock types of low-velocity molecular outflows are not always well constrained. Astrochemical comparisons are often made between low-velocity and high-velocity outflows, but without considering the question of the shock type. We investigated molecular abundances of post-shock regions to determine whether strong differences between non-irradiated C-type and J-type shocks can be highlighted. One of the main application goals is to diagnose the shock type of the protostellar object L1157 B2 through the use of molecular tracers. We simulated grid sets of shock models with the Paris-Durham Shock code with velocities ranging from 5 to 19 km/s and low densities from $10^2$ to $10^5$ cm$^{-3}$. We computed the desorption percentage of methanol in these simulations and estimated it at higher velocities. We compared our results to observational measurements of L1157 B2 and with a benchmark of four already identified shocks. L1157 B2 has been diagnosed as a non-irradiated C-type shock, and the method showed a good applicability through the benchmark. Methanol formed in the icy mantle of grains can serve to trace the differences between shock types, at least in non-irradiated conditions. A requirement for the applicability of a species as a shock-type tracer is that it does not undergo significant enhancement or destruction, but is mainly impacted by desorption processes under shocked conditions. The desorption percentage of methanol is a good criterion in characterizing the shock type of L1157 B2 and should be investigated as a general method to diagnose the shock type in non-irradiated regions. We identify L1157 B2 as a non-irradiated C-type shock with velocities and densities fitting with previous studies.

astro-ph.SR↗

arXiv2025

Robust Binding Energy Distribution Sampling on Amorphous Solid Water Models. Method testing and validation with NH3, CO and CH4

This work aims to develop a method based on a structurally reliable ice model and a statistically and physico-chemically robust approach for BE distribution inference, with the aim to be applicable to various relevant interstellar species. A multiscale computational approach is presented, with a Molecular Dynamics (MD) Heat & Quench protocol for the amorphous water ice model, and an ONIOM(B3LYP-D3(BJ)/6-311+G**:GFN2-xtb) scheme for the BE inference, with a prime emphasis onto the BE/real system size convergence. The sampling of the binding configurations is twofold, exploring both regularly spaced binding sites, as well as various adsorbate-to-substrate orientations on each locally distinct site. This second source of BE diversity accounts for the local roughness of the potential energy landscape of the substrate. Three different adsorbate test cases are considered, i.e. NH3, CO and CH4, owing to their significance in dust icy mantles, and their distinct binding behavior with water ices. The BE distributions for NH3, CO and CH4 have been inferred, with converged statistics. The distribution for NH3 is better represented by a double Gaussian component profile. Three starting adsorbate orientations per site are required to reach convergence for both Gaussian components of NH3, while 2 orientations are sufficient for CO, and one unique for CH4 (symmetric). Further geometrical and molecular surrounding insights have been provided. These results encompass previously reported results.

astro-ph.IM↗

arXiv2024

Investigation of the nature of the wind interaction in HD93205 based on multi-epoch X-ray observations

The study of the X-ray emission from massive binaries constitutes a relevant approach to investigate shock physics. The case of short period binaries may turn out to be quite challenging, especially in very asymmetric systems where the primary wind may overwhelm that of the secondary in the wind interaction. Our objective consists in providing an observational diagnostic of the X-ray behaviour of HD93205, that is a very good candidate to investigate these aspects. We analysed 31 epochs of XMM-Newton X-ray data spanning about two decades to investigate its spectral and timing behaviour. The X-ray spectrum is very soft along the full orbit, with a luminosity exclusively from the wind interaction region in the range of 2.3 -- 5.4\,$\times$10$^{32}$\,erg\,s$^{-1}$. The light curve peaks close to periastron, with a rather wide pre-periastron low-state coincident with the secondary's body hiding a part of the X-ray emitting region close to its surface. We determined a variability time scale of 6.0807\,$\pm$\,0.0013\,d, in full agreement with the orbital period. Making use of a one-dimensional approach to deal with mutual radiative effects, our results point to a very likely hybrid wind interaction, with a wind-photosphere occurring along most of the orbit, while a brief episode of wind-wind interaction may still develop close to apastron. Beside mutual radiative effects, the radiative nature of the shock that leads to some additional pre-shock obliquitity of the primary wind flow certainly explains the very soft emission. HD93205 constitutes a relevant target to investigate shock physics in short period, asymmetric massive binary systems, where various mutual radiative effects and radiative shocks concur to display an instructive soft X-ray behaviour. HD93205 should be considered as a valid, though challenging target for future three-dimensional modelling initiatives.

astro-ph.SR↗

arXiv2024

Study of Wolf-Rayet stars using uGMRT

In recent years, systems involving massive stars with large wind kinetic power have been considered as promising sites for investigating relativistic particle acceleration in low radio frequencies. With this aim, we observed two Wolf-Rayet systems, WR 114 and WR 142, using upgraded Giant Meterwave Radio Telescope observations in Band 4 (550-950 MHz) and Band 5 (1050-1450 MHz). None of the targets was detected at these frequencies. Based on the non-detection, we report 3$σ$ upper limits to the radio flux densities at 735 and 1260 MHz (123 and 66 $μ$Jy for WR 114, and 111 and 96 $μ$Jy for WR 142, respectively). The plausible scenarios to interpret this non-detection are presented.

astro-ph.HE↗

arXiv2023

Search for particle acceleration in two massive Wolf-Rayet stars using uGMRT observations

Large wind kinetic power of Wolf-Rayet (WR) stars make them ideal targets in low radio frequencies to search for non-thermal emission due to relativistic particle acceleration. In this paper, we present observations of two WR stars, WR 114 and WR 142, in Band 4 (550-950 MHz) and Band 5 (1050-1450 MHz) using the upgraded Giant Meterwave Radio Telescope (uGMRT). Neither star is detected in the observed frequency bands, nor extended emission associated with them. The upper limit to the free-free radio emission from the stellar wind enables us to constrain the mass-loss rate of WR 114 to $\lesssim \rm 10^{-5}\,M_{ \odot}\,yr^{-1}$; this is a factor three smaller than previously estimated using spectroscopic modelling. If we further assume that the WR stars are binaries, the non-detection of synchrotron emission from the putative wind collision region implies that the stars are either in very wide binary systems away from periastron, or that the stars are in close binary systems with an orbital separation $<70$ AU for WR 114 and $<20$ AU for WR 142. The non-detection of low-frequency radio emission from these two systems thus provides evidence that narrows their nature, though it does not rule them out as bonafide particle-accelerating colliding-wind binaries.

astro-ph.HE↗

arXiv2023

A preliminary timing analysis of two intermediate polars: UU Col and Swift J0939.7-3224

We present the preliminary timing analysis of confirmed intermediate polar UU Col and possible intermediate polar Swift J0939.7-3224 in the optical band with the help of long-term, high-cadence continuous photometry from Transiting Exoplanet Survey Satellite (TESS). For UU Col, we revise previously reported orbital and spin periods as 3.464 $\pm$ 0.005 h and 863.74 $\pm$ 0.08 s, respectively. Using the second harmonic of the beat frequency, the beat period is estimated as $\sim$928 s. These findings indicate that UU Col is a disc-fed dominated disc-overflow accretor. For J0939, we establish the spin period as 2671.8 $\pm$ 0.8 s and refine the provisionally suggested orbital period as 8.49 $\pm$ 0.03 h. The absence of beat frequency in J0939 signifies that it might be a pure disc-fed accretor; however, an X-ray study of this source will help to understand its true nature.

astro-ph.SR↗

arXiv2023

Confirmation of two magnetic cataclysmic variables as polars: 1RXS J174320.1-042953 and YY Sex

We present our analysis of new and archived observations of two candidate magnetic cataclysmic variables, namely 1RXS J174320.1-042953 and YY Sex. 1RXS J174320.1-042953 was observed in two distinctive high and low states where a phase shift was seen, which could be due to the changes in the shape, size, and (or) location of the accretion region. We find that its orbital X-ray modulations only persist in the soft (0.3-2.0 keV) energy band, which could be attributed to the photoelectric absorption in the accretion flow. The X-ray spectra exhibit a multi-temperature post-shock region where the hard X-rays are absorbed through a thick absorber with an equivalent hydrogen column of $\sim$7.5 $\times$ 10$^{23}$ cm$^{-2}$, which partially covers $\sim$56 per cent of the emission. No soft X-ray excess was found to be present; however, a soft X-ray emission with a blackbody temperature of $\sim$97 eV describes the spectra. Extensive TESS observations of YY Sex allow us to refine its orbital period to 1.5746 $\pm$ 0.0011 h. We did not find any signature of previously reported spin or beat periods in this system. Furthermore, our new polarimetric observations show clear circular polarization modulated on the orbital period only. Finally, both systems show strong Balmer and He II 4686 A$^\circ$ emission lines in the optical spectra, further indicative of their magnetic nature.

astro-ph.HE↗

arXiv2019

All-sky Medium Energy Gamma-ray Observatory: Exploring the Extreme Multimessenger Universe

The All-sky Medium Energy Gamma-ray Observatory (AMEGO) is a probe class mission concept that will provide essential contributions to multimessenger astrophysics in the late 2020s and beyond. AMEGO combines high sensitivity in the 200 keV to 10 GeV energy range with a wide field of view, good spectral resolution, and polarization sensitivity. Therefore, AMEGO is key in the study of multimessenger astrophysical objects that have unique signatures in the gamma-ray regime, such as neutron star mergers, supernovae, and flaring active galactic nuclei. The order-of-magnitude improvement compared to previous MeV missions also enables discoveries of a wide range of phenomena whose energy output peaks in the relatively unexplored medium-energy gamma-ray band.

astro-ph.IM↗

arXiv2019

Energetic Particles of Cosmic Accelerators I: Galactic Accelerators

The high-energy universe has revealed that energetic particles are ubiquitous in the cosmos and play a vital role in the cultivation of cosmic environments on all scales. Energetic particles in our own galaxy, galactic cosmic rays (GCRs), engage in a complex interplay with the interstellar medium and magnetic fields in the galaxy, giving rise to many of its key characteristics. This White Paper is the first of a two-part series highlighting the most well-known high-energy cosmic accelerators and contributions that MeV gamma-ray astronomy will bring to understanding their energetic particle phenomena. The focus of this white paper is galactic cosmic rays, supernova remnants, protostellar jets and superbubbles, and colliding wind binaries.

astro-ph.HE↗

arXiv2013

The Hot and Energetic Universe: A White Paper presenting the science theme motivating the Athena+ mission

This White Paper, submitted to the recent ESA call for science themes to define its future large missions, advocates the need for a transformational leap in our understanding of two key questions in astrophysics: 1) How does ordinary matter assemble into the large scale structures that we see today? 2) How do black holes grow and shape the Universe? Hot gas in clusters, groups and the intergalactic medium dominates the baryonic content of the local Universe. To understand the astrophysical processes responsible for the formation and assembly of these large structures, it is necessary to measure their physical properties and evolution. This requires spatially resolved X-ray spectroscopy with a factor 10 increase in both telescope throughput and spatial resolving power compared to currently planned facilities. Feedback from supermassive black holes is an essential ingredient in this process and in most galaxy evolution models, but it is not well understood. X-ray observations can uniquely reveal the mechanisms launching winds close to black holes and determine the coupling of the energy and matter flows on larger scales. Due to the effects of feedback, a complete understanding of galaxy evolution requires knowledge of the obscured growth of supermassive black holes through cosmic time, out to the redshifts where the first galaxies form. X-ray emission is the most reliable way to reveal accreting black holes, but deep survey speed must improve by a factor ~100 over current facilities to perform a full census into the early Universe. The Advanced Telescope for High Energy Astrophysics (Athena+) mission provides the necessary performance (e.g. angular resolution, spectral resolution, survey grasp) to address these questions and revolutionize our understanding of the Hot and Energetic Universe. These capabilities will also provide a powerful observatory to be used in all areas of astrophysics.

astro-ph.HE↗

arXiv2008

The Multiwavelength Picture of Star Formation in the Very Young Open Cluster NGC6383

We review the properties of the very young (2 Myr) open cluster NGC6383. The cluster is dominated by the massive binary HD159176 (O7V + O7V). The distance to NGC6383 is consistently found to be 1.3 +- 0.1 kpc and the average reddening is determined to be E(B-V) = 0.32 +- 0.02. Several pre-main sequence candidates have been identified using different criteria relying on the detection of emission lines, infrared excesses, photometric variability and X-ray emission.

astro-ph↗