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203706 research outputs found
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The MeerKLASS UHF On-the-Fly Continuum Survey -- Data Release I
No full textInternational audienceWe present the first public data release (DR1) from the interferometric component of the MeerKAT Large Area Synoptic Survey (MeerKLASS) UHF survey, a legacy program demonstrating a novel on-the-fly (OTF) mapping technique. This release is based on 12 hours of early science observations covering approximately 800 deg of the southern sky. We describe the data processing pipeline developed to calibrate and image these fast-scanning observations, producing high-fidelity continuum images at a central frequency of 816 MHz. The resulting mosaic reaches an RMS sensitivity of 35 Jy beam in its deepest regions, with a typical angular resolution of . In these images, we identify radio sources. We validate the catalogue through cross-matching with external surveys, confirming sub-arcsecond astrometric accuracy and a robust flux density scale. We compute the differential source counts, finding excellent agreement with existing measurements and validating our end-to-end processing. The success of this pilot study serves as a crucial proof of concept for the OTF observing strategy, and the public release of the images and source catalogue provides a valuable resource for a wide range of astrophysical studies. This work paves the way for the full MeerKLASS OTF survey and future large-area survey projects with the SKA
The Domain Adaptation problem in photometric redshift estimation: a solution applied to the HSC Survey
No full textInternational audienceThe multi-band HSC-CLAUDS survey comprises several sky regions with varying observing conditions, only one of which, the COSMOS Ultra Deep Field (UDF), offers extensive redshift coverage. We aim to exploit a complete sample of labeled galaxies from the COSMOS UDF at i<25 (z<~5) to train a convolutional neural network (CNN) and infer more accurate photometric redshifts in the other regions than those currently available from SED-fitting methods. To address the severe domain mismatch problem we observed when applying the trained CNN to regions other than the COSMOS UDF, we developed an unsupervised adversarial domain adaptation network that we grafted onto the CNN. The method is validated by three tests: the predicted redshifts are compared to the spectroscopic redshifts that are available for limited samples of mostly bright galaxies; the predicted redshift distributions of the entire galaxy population of a given field in several intervals of magnitude are compared to those of the COSMOS UDF, assumed to be representative; the redshifts predicted for a sample of galaxies selected by narrow-band filter observations sensitive to [OII] emitters at z~1.47 are compared to those of confirmed [OII] emission line galaxies. The results show successful domain adaptation: the network is able to transfer its redshift classification capability learnt from the COSMOS UDF to other regions of HSC-CLAUDS. Accuracy varies depending on magnitude and redshift, following that of the labels we used, but far exceeds that of currently available photometric redshifts. The catalogs of CNN redshifts we inferred for the XMM, DEEP2 and ELAIS fields and for the remaining COSMOS region (~4 million sources in total at i<25) are made public
Iron Metallurgy in Ancient Cambodia: Production Dynamics, Traditions and Chronologies in a Southeast Asian Context (9th–14th centuries CE)
No full textInternational audienceCollaborative studies in iron archaeometallurgy in Cambodia over the past decade, particularly through the IRANGKOR project, have advanced our understanding of iron production dynamics during the Angkorian period (9th–15th centuries CE). This research examines metallurgical remains and artifacts within a systemic framework, linking them to production sites, geological contexts, and usage settings, such as iron clamps in monumental constructions. Studied diachronically and across multiple spatial scales, these remains provide insights into production practices and “recipes,” production dynamics, and the circulation and supply of iron, particularly within the central production territory of Phnom Dek, historically recognized for its metallurgical tradition.The study explores the relationships between resources, production processes, metallurgical practices, and iron circulation. Central to the research is the use of provenance analyses, direct dating of the metal itself, and the examination of comparative patterns, providing precise chronological and spatial benchmarks. Combining historical and archaeological sources with material analysis of artifacts and smelting debris establishes a framework for interpreting these dynamics across the Angkorian territory.The resulting datasets reveal changes in metallurgical “recipes” as well as in supply strategies and demands over more than 1,400 years. This presentation synthesizes recent results, highlighting the contribution of compositional and chronological data to frameworks for understanding continuities and changes in ancient metallurgical practices. Situating these findings within a broader Asian context highlights similarities in practices and recipes and their implications for regional technical dynamics
Microlensing Black Hole Shadows-II: Constraining Primordial Black Hole Dark Matter using the photon rings of M87 and Sgr A
No full textInternational audienceThe resolution of photon rings of Sgr~A and M87 is the next milestone of upcoming EHT-like interferometries. We extend the formalism developed in our previous work~\cite{Verma:2023hes} to constrain primordial black hole (PBH) dark matter using microlensing-induced distortions of black hole shadows. Building upon the theoretical framework for microlensing of photon rings, we apply this methodology to both Sgr A* and M87, considering multiple PBH populations: (i) PBH dark matter spikes around central supermassive black holes, (ii) NFW halo contributions in the Milky Way and M87 galaxies, and (iii) foreground Milky Way PBH dark matter affecting M87* observations. The microlensing signal manifests as a time-dependent asymmetry and deformation of the photon ring, providing the most sensitive observable for lensing effects. We assess the detectability of these signatures with future EHT-like interferometers. Our analysis reveals that M87* provides the strongest constraints on PBH dark matter. We show that the absence of photon-ring asymmetries in observations with angular resolution of order can constrain PBHs in the mass range , with maximal sensitivity near , for PBH dark matter fractions as small as
Probing millisecond magnetar formation in binary neutron star mergers through X-ray follow-up of gravitational wave alerts
No full textInternational audienceThe nature of the remnant of a binary neutron star (BNS) merger is uncertain. Though certainly a black hole (BH) in the cases of the most massive BNSs, X-ray lightcurves from gamma-ray burst (GRB) afterglows suggest a neutron star (NS) as a viable candidate for both the merger remnant as well as the central engine of these transients. When jointly observed with gravitational waves (GWs), X-ray lightcurves from BNS merger events could provide critical constraints on the remnant's nature. We aim to assess the current and future capabilities to detect a NS remnant through X-ray observations following GW detections. To this end, we simulate GW signals from BNS mergers and the subsequent X-ray emission from newborn millisecond magnetars. The GW detectability is modeled for both current and next-generation interferometers, while the X-ray emission is reproduced using a dedicated numerical code that models magnetar spin-down and ejecta dynamics informed by numerical-relativity simulations. In our simulations, 2% - 16% of BNS mergers form millisecond magnetars. Among these, up to 70% could be detectable, amounting to up to 1 millisecond magnetar detection per year with SVOM/MXT-like instruments during the LIGO Virgo KAGRA LIGO India (LVKI) O5 run, with optimal detectability occurring about 2 hours post-merger. For next-generation GW interferometers, this rate could increase by up to three orders of magnitude, with peak detectability 3 to 4 hours post-merger. We also explore how the magnetar's magnetic field strength and observer viewing angle affect detectability and discuss optimized observational strategies. Although more likely with upcoming GW interferometers, detecting the spin-down emission of a millisecond magnetar may already be within reach, warranting sustained theoretical and observational efforts given the profound implications for mergers, GRBs, and NS physics of a single detection
Tara Polaris expeditions: Sustained decadal observations of the coupled Arctic system in rapid transition
No full textThe coupled Arctic system is in rapid transition and is set to undergo further dramatic changes over the coming decades. These changes will lead most likely to an ice-free ocean in summer, expected before mid-century. The Arctic will become more strongly influenced by atmospheric and oceanographic processes characteristic of mid-latitudes, increasing the prevalence of contaminants and new biological species. This ongoing transition of the Arctic to a new state necessitates systematic monitoring of all sentinels (variables that make an essential contribution to characterizing the Earth's state) to improve our understanding of the system, enhance forecasting and support knowledge-based decisions. Here, we describe a sustained multi-decadal observation program to be implemented on the Tara Polar Station between 2026 and 2046. The monitoring program is designed as a series of year-long drift expeditions, called Tara Polaris, in the central Arctic Ocean, covering all seasons. The multidisciplinary data will bridge ecological, geochemical, biological, and physical parameters and processes in the atmosphere, sea ice and ocean. In addition, data collected with consistent methodologies over a 20-year period will make it possible to distinguish long-term trends from seasonal and interannual variability. In this paper, we discuss specific measurement challenges in each compartment (i.e., atmosphere, sea ice and ocean) along key sentinels and the most pressing scientific questions to be addressed. The expected outcomes of the Tara Polaris program will enable us to understand and quantify the main feedbacks of the coupled Arctic system, with their seasonal and interannual trends and spatial variability.</div
Efeitos do suavizamento do lençol freático controlado pela resolução da grade topográfica no fluxo regional simulado de água subterrânea
No full textInternational audienceThe assessment and management of groundwater often depend on large regional numerical models that predict hydrological stresses, such as those caused by climate change and resource exploitation. While regional and continental-scale models have been developed to evaluate these impacts, they typically use coarse grid cells that smooth land surface topography. This study investigates the impact of topography-controlled water table smoothing on simulated groundwater discharge to streams (baseflow) and associated groundwater age. A simplified 2D cross-sectional model of a topographically driven regional aquifer system was developed, under the assumption that the water table is a replica of the land surface topography. Scenarios with varying topography, derived from resampling digital elevation model (DEM) resolutions ranging from 30 to 10,000 m, were analyzed using a consistent, high-resolution numerical hydrogeological model mesh. Results show that baseflow rates decrease significantly as resolution declines, primarily due to reduced hydraulic gradients, with a flux dif- ference of an order of magnitude simulated between resolutions of 30 and 1000 m. Although shallow groundwater flows in more permeable aquifer layers are significantly affected, deeper regional flow remains stable across all scenarios. Regional groundwater flow paths and associated residence times are less sensitive to changes in resolution, particularly at depths greater than 50 m in the model used. The study thus demonstrates that low-resolution models need to overestimate hydraulic conductivity during calibration to accurately match fluxes to streams. This study highlights the critical importance of care- fully considering topographic resolution in regional models to ensure representative predictions of streamflow driven by subsurface–surface interactions
Shapiro Delay Measurements from Fifteen Years of PSR J12311411 Radio Observations
No full textInternational audienceWe present 15 years of Nançay and Green Bank radio telescope timing observations for PSR J12311411. This millisecond pulsar is a primary science target for the Neutron Star Interior Composition Explorer telescope (NICER, which discovered its X-ray pulsations), has accumulated near-continuous -ray data since the Fermi-Large Area Telescope's launch, and has been studied extensively with the Green Bank and Nançay radio telescopes. We have undertaken a campaign with the Green Bank Telescope targeting specific orbital phases designed to improve our constraint on the pulsar's mass through the detection of a relativistic Shapiro delay. Both frequentist and Bayesian techniques -- the latter incorporating priors from white dwarf binary evolution models -- are applied to fifteen years of radio observations, yielding relatively weak constraints on the companion and pulsar masses of M and M, respectively (68.3% CI from Bayesian fits); however, the orbital inclination is measured to better relative precision ( degrees). Restricting the maximum allowed pulsar mass to 3 M while simultaneously sampling the noise and timing models improves the constraint and lowers the measured mass to M. While our radio-derived inclination result has informed recent NICER X-ray studies of PSR J12311411, the lessons learned from this troublesome pulsar will also bolster future high-precision mass measurement campaigns and resulting constraints on the neutron star interior equation of state
Magnetically supramassive and hypermassive compact stars
No full textInternational audienceIt is known that the mass of magnetized relativistic compact star is larger than that of non-magnetized one for the same equation of state and central density, albeit the excess of mass is sizable only if the magnetic fields are strong enough B~10^17-10^18G. Using our recently developed numerical code COCAL, we systematically compute such compact star solutions in equilibrium associated with mixed poloidal and toroidal magnetic fields, and show the magnetically supramassive solutions whose masses exceed by more than 10% of the maximum mass of the static and spherically symmetric solutions. For some extremely strong magnetic field configurations, we also obtain solutions more massive than the maximum mass of the uniformly rotating solutions at the Kepler (mass-shedding) limit, namely magnetically hypermassive solutions
