arXiv subjects

S. Basa

Publications and source records attributed to S. Basa.

At least 19 recordsLinked to original sources

arXiv2026

PROVIDENCE: a ground station for space observation

PROVIDENCE is an ONERA-led project to install a new-generation optical ground station at the Haute-Provence Observatory (OHP) in South of France. Built around a 2.5-meter aperture, the station addresses five core science cases: space domain awareness, astronomy, laser activities and communications, atmospheric characterization, and instrumental prototyping. The project is organized into three parallel subprojects covering the telescope (Providence T), the building (Providence B), and the instruments (Providence I), the latter including the facility's first-light adaptive optics instrument, INTERSTELLAR. This paper presents the scientific motivation, the project architecture, the telescope technical specifications, the civil-engineering challenges associated with replacing the existing T152 equatorial telescope, and the station layout designed to host multiple co-active instrument teams. The project roadmap targets First Light in 2029, timed to track the close-approach flyby of asteroid Apophis.

astro-ph.IM↗

arXiv2026

First Gamma-Ray Burst Observations with SVOM

Following its launch on 22 June 2024, the Space-based multi-band astronomical Variable Objects Monitor (SVOM) successfully completed its flight acceptance, commissioning, and scientific validation phases in early 2025, during which several tens of gamma-ray bursts (GRBs) were detected onboard. Three quarters of these events have also been detected by other satellites, and a quarter are SVOM-only GRBs. In this article, we describe these early GRB observations, with a first description of the SVOM GRB sample that is emerging, and of the level of characterisation already achieved, and with a focus on a few events of particular interest. These early results are very encouraging regarding SVOM's ability to detect and fully characterise (including prompt emission, afterglow and distance) a wide range of GRBs (classical long GRBs, short GRBs, X-Ray Flashes, etc.) and to enable the use of these extreme high-energy transients as probes of the distant Universe.

astro-ph.HE↗

arXiv2026

Early results from the SVOM Observatory Science program

We present the organisation and early results from the Observatory Science program of the Space-based multi-band astronomical Variable Objects Monitor (SVOM), based on data collected between July 2024 and December 2025. Although primarily designed for gamma-ray burst studies, SVOM's wide-field, multi-wavelength instruments enable a broad range of high-energy astrophysical investigations. We summarize the execution and performance of the General Program and Target-of-Opportunity observations, and we describe the frameworks used for serendipitous source detection and monitoring with the ECLAIRs coded-mask instrument. Over this period, SVOM carried out more than a thousand pointed observations and detected several hundred non-GRB high-energy sources, mainly X-ray binaries, as well as blazars, stellar flares, magnetars, and unidentified events. We highlight some key results, including the monitoring of the microquasar Cygnus X-1, the detection of burst oscillations from the Low-Mass X-ray Binary 4U 0614+091, the spectral-state monitoring of Aql X-1, the first SVOM detection of an X-ray blazar flare from 1ES 1959+650, and observations of a stellar flare from HD 22468. These results demonstrate SVOM's strong capabilities for time-domain astrophysics beyond its core GRB program.

astro-ph.HE↗

arXiv2026

The SVOM mission, its profile and its system

The SVOM (Space-based Variable Objects Monitor) mission, launched into low Earth orbit on 22 June 2024, is a French-Chinese multi-wavelength observatory dedicated to the study of the transient sky. Inspired by the Neil Gehrels Swift Observatory, it consists of an autonomous rapid-slewing satellite, linked in real time to several ground-based telescopes. The space segment comprises two X-ray/gamma-ray wide-field instruments (ECLAIRs and GRM) with real-time triggering capabilities combined with two narrow-field telescopes in X-ray (MXT) and in visible (VT). In addition, the SVOM collaboration has also developed a unique visible and NIR ground-based follow-up system to promptly respond to the gamma-ray transients detected on board. The core program of SVOM will provide new insights into the Gamma-Ray Burst physics by providing a homogeneous dataset covering both the prompt and afterglow emissions, as well as better studying the low luminosity and soft Gamma-Ray Burst populations. As a versatile satellite platform with fast slewing capabilities, SVOM also comprises a Target of Opportunity program and a General Program consisting in pointed observations scheduled over the year that will both significantly contribute to the multi-messenger and time-domain astronomy.

astro-ph.HE↗

arXiv2026

COLIBRI (SVOM/FM-GFT): Instrumentation and Performances on the SVOM Alerts

COLIBRI, the French Mexican Ground Followup Telescope (FM GFT) for SVOM, is a 1.3 meter rapid response optical facility specifically developed for prompt, multiband observations of GRB afterglows and for delivering subarcsecond localisations of optical counterparts for detailed followup studies. The telescope operates through a fully automated system that manages the entire workflow, from alert reception to counterpart identification. Commissioning results confirm that the telescope meets design specifications, and this paper presents a comprehensive performance assessment of the capabilities.

astro-ph.IM↗

arXiv2026

GRB 241030A: a bright afterglow challenging forward shock emission

Gamma-Ray Burst GRB 241030A (z = 1.411) exhibited a bright afterglow (similar to GRB 221009A), detected across gamma-ray, X-ray, UV, and optical bands, providing a probe of GRB afterglow physics. We compiled multi-wavelength observations spanning from a minute to a week after the prompt emission, processing the data through a unified photometry pipeline. We analysed the observations both analytically and using Bayesian inference with two independent models. Our models assume that the afterglow emission arises from the strong forward shock of a laterally structured jet, with possible contributions from synchrotron self-Compton (SSC) scatterings. Our models reproduce X-ray to optical data, favouring a jet propagating into a constant-density interstellar medium, with a viewing angle within the jet core. However, both analyses require parameter values that are extreme compared to expectations from standard theory. In particular, our results imply extremely energetic jets despite regular prompt energy, leading to a very inefficient prompt emission. Furthermore, the jets are inefficient at accelerating particles, with low electron and magnetic energy fractions, leading to significant SSC emission. Our analyses indicate that the jets have large opening angles and propagate in high-density media. If the afterglow is indeed powered by radiation emitted behind a strong forward shock, our results place GRB 241030A within a sub-class of GRBs characterised by extreme kinetic energies, large jet opening angles, and very low prompt emission efficiencies, with strong SSC radiation. These predictions are difficult to reconcile with typical expectations from other GRBs. We therefore suggest that the afterglow of GRB 241030A is not solely powered by forward shock emission.

astro-ph.HE↗

arXiv2026

Multi-epoch afterglow rebrightenings in GRB 250129A: Evidence for successive shock interactions

Most long gamma-ray bursts (GRBs) exhibit afterglows broadly consistent with external forward-shock emission, typically described by smooth broken power-law decays in the multiband light curve. However, a minority of well-sampled GRBs deviate from this behavior, including GRB 250129A. This object shows multiple late-time rebrightenings at X-ray and optical wavelengths. Rebrightenings are often attributed to energy injection from prolonged central engine activity, refreshed shocks from delayed shell collisions, density jumps in the ambient medium, or angular jet structure and viewing-angle effects. After analysing the prompt emission observed in gamma-rays and the near-infrared, we investigate the origin of X-ray and optical flaring episodes in GRB 250129A. Physical processes in the afterglow light curves were investigated using methods ranging from empirical fitting to Bayesian inference. The well-sampled flares and the connection between the prompt and afterglow emission allow us to test the consistency of the fireball model and alternative scenarios. Conducting the prompt and time-resolved analyses, we obtained an isotropic-equivalent energy of E_iso,gamma = (1.35 +/- 0.12) x 10^53 erg. By modeling the afterglow using an agnostic Bayesian framework (NMMA), we rule out both a single external-shock evolution and a one-time energy-injection scenario. Numerical calculations show that the rebrightening episodes are consistent with refreshed shocks from delayed collisions between relativistic shells. Based on the consistency between our analyses of the prompt and afterglow GRB 250129A data, we find that two statistically significant rebrightening episodes occur within 1.1 days post trigger and can be explained by a sequence of refreshed shocks. Temporally and spectrally rich GRB datasets such as the one presented in this work, provide a powerful means to test current modeling frameworks.

astro-ph.HE↗

arXiv2025

Deep Learning Framework for Enhanced Neutrino Reconstruction of Single-line Events in the ANTARES Telescope

We present the $N$-fit algorithm designed to improve the reconstruction of neutrino events detected by a single line of the ANTARES underwater telescope, usually associated with low energy neutrino events ($\sim$ 100 GeV). $N$-Fit is a neural network model that relies on deep learning and combines several advanced techniques in machine learning --deep convolutional layers, mixture density output layers, and transfer learning. This framework divides the reconstruction process into two dedicated branches for each neutrino event topology --tracks and showers-- composed of sub-models for spatial estimation --direction and position-- and energy inference, which later on are combined for event classification. Regarding the direction of single-line events, the $N$-Fit algorithm significantly refines the estimation of the zenithal angle, and delivers reliable azimuthal angle predictions that were previously unattainable with traditional $\chi^2$-fit methods. Improving on energy estimation of single-line events is a tall order; $N$-Fit benefits from transfer learning to efficiently integrate key characteristics, such as the estimation of the closest distance from the event to the detector. $N$-Fit also takes advantage from transfer learning in event topology classification by freezing convolutional layers of the pretrained branches. Tests on Monte Carlo simulations and data demonstrate a significant reduction in mean and median absolute errors across all reconstructed parameters. The improvements achieved by $N$-Fit highlight its potential for advancing multimessenger astrophysics and enhancing our ability to probe fundamental physics beyond the Standard Model using single-line events from ANTARES data.

physics.comp-ph↗

arXiv2025

Search for steady and flaring neutrino emission from cosmic sources using the complete ANTARES dataset

ANTARES, a neutrino detector located in the depths of the Mediterranean Sea, operated successfully for over 15 years before being decommissioned in 2022. The telescope offered an ideal vantage view of the Southern Sky and benefited from optimal water properties for enhanced angular resolution. This study makes use of data collected over the entire operational period of ANTARES to search for sources of high-energy cosmic neutrinos, considering both steady and flaring emission scenarios. First, a time-integrated search for high-energy neutrino clustering across the celestial sphere is conducted. The most significant accumulation is found at coordinates $(\alpha, \delta) =(200.5^\circ\, 17.7^\circ)$ with a post-trial p-value equal to 0.38. A dedicated search in the Galactic Plane is also performed for extended sources, yielding no significant excess. Additionally, a list of potential neutrino sources are investigated. The blazar MG3 J225517+2409 is identified as the most significant object, yet the excess remains compatible with background fluctuations. A mild local excess of 2.4$\sigma$ is found for the blazar TXS 0506+056. The full sky is also examined for the presence of flaring neutrino emissions. The most significant excess in this case corresponds to a $\sim$4-day flare from the direction $(\alpha, \delta) = (141.3^\circ\, 9.8^\circ)$, with a post-trial p-value of 0.30. Finally, the directions of sources highlighted in IceCube's time-dependent searches are investigated. Temporal overlaps between ANTARES and IceCube flares are identified for PKS 1502+106 and TXS 0506+056, with an estimated chance probability of about 0.02%, making this observation particularly noteworthy.

astro-ph.HE↗

arXiv2025

SVOM GRB 250314A at z $\simeq$ 7.3: an exploding star in the era of reionization

Most long Gamma-ray bursts originate from a rare type of massive stellar explosion. Their afterglows, while rapidly fading, can be initially extremely luminous at optical/near-infrared wavelengths, making them detectable at large cosmological distances. Here we report the detection and observations of GRB 250314A by the SVOM satellite and the subsequent follow-up campaign with the near-infrared afterglow discovery and the spectroscopic measurements of its redshift z $\simeq$ 7.3 . This burst happened when the Universe was only $\sim$ 5% of its current age. We discuss the signature of these rare events within the context of the SVOM operating model, and the ways to optimize their identification with adapted ground follow-up observation strategies.

astro-ph.HE↗

arXiv2025

Search for Magnetic Monopoles with the Complete ANTARES Dataset

This study presents a novel search for magnetic monopoles using data collected over a 14 year period (2008-2022) by the ANTARES neutrino telescope. The interaction of magnetic monopoles with matter was modeled according to Kazama, Yang, and Goldhaber cross-section. Upper limits on the flux of magnetic monopoles are obtained for velocities both above and below the Cherenkov threshold. No events consistent with the passage of magnetic monopoles were detected, enabling the setting of an upper flux limit for relativistic magnetic monopoles of the order of $10^{-18} \mathrm{cm}^{-2} \mathrm{s}^{-1} \mathrm{sr}^{-1}$.

hep-ex↗

arXiv2025

The ANTARES detector: two decades of neutrino searches in the Mediterranean Sea

Interest for studying cosmic neutrinos using deep-sea detectors has increase after the discovery of a diffuse flux of cosmic neutrinos by the IceCube collaboration and the possibility of wider multi-messenger studies with the observations of gravitational waves. The ANTARES detector was the first neutrino telescope in seawater, operating successfully in the Mediterranean Sea for more than a decade and a half. All challenges related to the operation in the deep sea were accurately addressed by the collaboration. Deployment and connection operations became smoother over time; data taking and constant re-calibration of the detector due to the variable environmental conditions were fully automated. A wealth of results on the subject of astroparticle physics, particle physics and multi-messenger astronomy have been obtained, despite the relative modest size of the detector, paving the way to a new generation of larger undersea detectors. This review summarizes the efforts by the ANTARES collaboration that made the possibility to operate neutrino telescopes in seawater a reality and the results obtained in this endeavor.

hep-ex↗

arXiv2024

A simple model of dust extinction in gamma-ray burst host galaxies

Gamma-ray burst (GRB) afterglows are powerful probes for studying the different properties of their host galaxies (e.g., the interstellar dust) at all redshifts. By fitting their spectral energy distribution (SED) over a large range of wavelengths, we can gain direct insights into the properties of the interstellar dust by studying the extinction curves. Unlike the dust extinction templates, such as the average Milky Way (MW) or the Small and Large Magellanic Cloud (SMC and LMC), the extinction curves of galaxies outside the Local Group exhibit deviation from these laws. Altogether, X-ray and gamma-ray satellites as well as ground-based telescopes, such as Neil Gehrels Swift Observatory (Swift) and Gamma-Ray Optical and Near-Infrared Detector (GROND), provide measurements of the afterglows from the X-ray to the NIR, which can be used to extract information on dust extinction curves along their lines of sight. The study presented in this paper undertakes such a photometric study, comprising a preparatory work for the SVOM mission and its ground-based follow-up telescope COLIBRI. We propose a simple parameterization of the dust extinction curve of GRB host galaxies. Our model is based on a power law form with the addition of a Loretzian-like Drude profile with two parameters: the extinction slope, $\gamma$, and the 2175 $\AA$ bump amplitude, $E_\rm{b}$. Using the seven GROND filter bands, we tested our dust extinction model and explored the parameter space in extinction and redshift by fitting SEDs of simplified simulations of GRB afterglow spectra based on different extinction curve templates. From a final sample of 10 real Swift/GROND extinguished GRBs, we determined the quantities of the dust extinction in their host and measured their extinction curves. The measured average extinction curve is equivalent to a quasi-featureless in-between SMC-LMC template.

astro-ph.HE↗

arXiv2024

Constraints on the energy spectrum of the diffuse cosmic neutrino flux from the ANTARES neutrino telescope

High-significance evidences of the existence of a high-energy diffuse flux of cosmic neutrinos have emerged in the last decade from several observations by the IceCube Collaboration. The ANTARES neutrino telescope took data for 15 years in the Mediterranean Sea, from 2007 to 2022, and collected a high-purity all-flavour neutrino sample. The search for a diffuse cosmic neutrino signal using this dataset is presented in this article. This final analysis did not provide a statistically significant observation of the cosmic diffuse flux. However, this is converted into limits on the properties of the cosmic neutrino spectrum. In particular, given the sensitivity of the ANTARES neutrino telescope between 1 and 50 TeV, constraints on single-power-law hypotheses are derived for the cosmic diffuse flux below 20 TeV, especially for power-law fits of the IceCube data with spectral index softer than 2.8.

astro-ph.HE↗

arXiv2024

Acoustic Positioning for Deep Sea Neutrino Telescopes with a System of Piezo Sensors Integrated into Glass Spheres

Position calibration in the deep sea is typically done by means of acoustic multilateration using three or more acoustic emitters installed at known positions. Rather than using hydrophones as receivers that are exposed to the ambient pressure, the sound signals can be coupled to piezo ceramics glued to the inside of existing containers for electronics or measuring instruments of a deep sea infrastructure. The ANTARES neutrino telescope operated from 2006 until 2022 in the Mediterranean Sea at a depth exceeding 2000m. It comprised nearly 900 glass spheres with 432mm diameter and 15mm thickness, equipped with photomultiplier tubes to detect Cherenkov light from tracks of charged elementary particles. In an experimental setup within ANTARES, piezo sensors have been glued to the inside of such - otherwise empty - glass spheres. These sensors recorded signals from acoustic emitters with frequencies from 46545 to 60235Hz. Two waves propagating through the glass sphere are found as a result of the excitation by the waves in the water. These can be qualitatively associated with symmetric and asymmetric Lamb-like waves of zeroth order: a fast (early) one with $v_e \approx 5$mm/$\mu$s and a slow (late) one with $v_\ell \approx 2$mm/$\mu$s. Taking these findings into account improves the accuracy of the position calibration. The results can be transferred to the KM3NeT neutrino telescope, currently under construction at multiple sites in the Mediterranean Sea, for which the concept of piezo sensors glued to the inside of glass spheres has been adapted for monitoring the positions of the photomultiplier tubes.

astro-ph.IM↗

arXiv2024

Multi-purpose InSTRument for Astronomy at Low-resolution: MISTRAL@OHP

MISTRAL is the new Faint Object Spectroscopic Camera mounted at the folded Cassegrain focus of the 1.93m telescope of Haute-Provence Observatory. We describe the design and components of the instrument and give some details about its operation. We emphasise in particular the various observing modes and the performances of the detector. A short description is also given about the working environment. Various types of objects, including stars, nebulae, comets, novae, galaxies have been observed during various test phases to evaluate the performances of the instrument. The instrument covers the range of 4000 to 8000A with the blue setting, or from 6000 to 10000A with the red setting, at an average spectral resolution of 700. Its peak efficiency is about 22% at 6000A. In spectroscopy, a limiting magnitude of 19.5 can be achieved for a point source in one hour with a signal to noise of 3 in the continuum (and better if emission lines are present). In imaging mode, limiting magnitudes of 20-21 can be obtained in 10-20mn (with average seing conditions of 2.5 arcsec at OHP). The instrument is very users-friendly and can be put into operations in less than 15mn (rapid change-over from the other instrument in use) if required by the science (like for Gamma-Rays Bursts). Some first scientific results are described for various types of objects, and in particular for the follow-up of GRBs. While some further improvements are still under way, in particular to ease the switch from blue to red setting and add more grisms or filters, MISTRAL is ready for the follow-up of transients and other variable objects, in the soon-to-come era of e.g. the SVOM satellite and of the Rubin telescope.

astro-ph.IM↗

arXiv2024

Results of the follow-up of ANTARES neutrino alerts

High-energy neutrinos could be produced in the interaction of charged cosmic rays with matter or radiation surrounding astrophysical sources. To look for transient sources associated with neutrino emission, a follow-up program of neutrino alerts has been operating within the ANTARES Collaboration since 2009. This program, named TAToO, has triggered robotic optical telescopes (MASTER, TAROT, ROTSE and the SVOM ground based telescopes) immediately after the detection of any relevant neutrino candidate and scheduled several observations in the weeks following the detection. A subset of ANTARES events with highest probabilities of being of cosmic origin has also been followed by the Swift and the INTEGRAL satellites, the Murchison Widefield Array radio telescope and the H.E.S.S. high-energy gamma-ray telescope. The results of twelve years of observations are reported. No optical counterpart has been significantly associated with an ANTARES candidate neutrino signal during image analysis. Constraints on transient neutrino emission have been set. In September 2015, ANTARES issued a neutrino alert and during the follow-up, a potential transient counterpart was identified by Swift and MASTER. A multi-wavelength follow-up campaign has allowed to identify the nature of this source and has proven its fortuitous association with the neutrino. The return of experience is particularly important for the design of the alert system of KM3NeT, the next generation neutrino telescope in the Mediterranean Sea.

astro-ph.HE↗

arXiv2023

Multi-band analyses of the bright GRB 230812B and the associated SN2023pel

GRB~230812B is a bright and relatively nearby ($z =0.36$) long gamma-ray burst (GRB) that has generated significant interest in the community and has thus been observed over the entire electromagnetic spectrum. We report over 80 observations in X-ray, ultraviolet, optical, infrared, and sub-millimeter bands from the GRANDMA (Global Rapid Advanced Network for Multi-messenger Addicts) network of observatories and from observational partners. Adding complementary data from the literature, we then derive essential physical parameters associated with the ejecta and external properties (i.e. the geometry and environment) of the GRB and compare with other analyses of this event. We spectroscopically confirm the presence of an associated supernova, SN2023pel, and we derive a photospheric expansion velocity of v $\sim$ 17$\times10^3$ km s$^{-1}$. We analyze the photometric data first using empirical fits of the flux and then with full Bayesian Inference. We again strongly establish the presence of a supernova in the data, with a maximum (pseudo-)bolometric luminosity of $5.75 \times 10^{42}$ erg/s, at $15.76^{+0.81}_{-1.21}$ days (in the observer frame) after the trigger, with a half-max time width of 22.0 days. We compare these values with those of SN1998bw, SN2006aj, and SN2013dx. Our best-fit model favours a very low density environment ($\log_{10}({n_{\rm ISM}/{\rm cm}^{-3}}) = -2.38^{+1.45}_{-1.60}$) and small values for the jet's core angle $\theta_{\rm core} = 1.54^{+1.02}_{-0.81} \ \rm{deg}$ and viewing angle $\theta_{\rm obs} = 0.76^{+1.29}_{-0.76} \ \rm{deg}$. GRB 230812B is thus one of the best observed afterglows with a distinctive supernova bump.

astro-ph.HE↗