CAGIRE: a wide-field NIR imager for the COLIBRI 1.3 meter robotic telescope

The use of high energy transients such as Gamma Ray Bursts (GRBs) as probes of the distant universe relies on the close collaboration between space and ground facilities. In this context, the Sino-French mission SVOM has been designed to combine a space and a ground segment and to make the most of their synergy. On the ground, the 1.3 meter robotic telescope COLIBRI, jointly developed by France and Mexico, will quickly point the sources detected by the space hard X-ray imager ECLAIRs, in order to detect and localise their visible/NIR counterpart and alert large telescopes in minutes. COLIBRI is equipped with two visible cameras, called DDRAGO-blue and DDRAGO-red, and an infrared camera, called CAGIRE, designed for the study of high redshift GRBs candidates. Being a low-noise NIR camera mounted at the focus of an alt-azimutal robotic telescope imposes specific requirements on CAGIRE. We describe here the main characteristics of the camera: its optical, mechanical and electronics architecture, the ALFA detector, and the operation of the camera on the telescope. The instrument description is completed by three sections presenting the calibration strategy, an image simulator incorporating known detector effects, and the automatic reduction software for the ramps acquired by the detector. This paper aims at providing an overview of the instrument before its installation on the telescope.Comment: Accepted by Experimental Astronom

DFT2FEFFIT: a density-functional-theory-based structural toolkit to analyze EXAFS spectra

International audienceThis article presents a Python-based program, DFT2FEFFIT, to regress theoretical extended X-ray absorption fine structure (EXAFS) spectra calculated from density functional theory (DFT) structure models against experimental EXAFS spectra. To showcase its application, Ce-doped fluorapatite [Ca$_{10}$-(PO$_4$)$_6$F$_2$ ] is revisited as a representative of a material difficult to analyze by conventional multi-shell least-squares fitting of EXAFS spectra. The software is open source and publicly available

Channeltron Detector Readout ASIC in 0.35µm HV CMOS for Cold Solar Wind Analysis

International audienceLow-power analog front-end circuits for channeltron detectors (or Channel Electron Multiplier: CEMs) have been fabricated in 0.35-μm CMOS technology to characterize low energy solar wind particles. They have been designed to readout signals for incident charges ranging from 50 fC to 20 pC. Each front end circuit consists of a charge preamplifier, an amplifier, a discriminator, a monostable circuit and a LVDS. Requirement on the complete front end is to consume less than 6.5 mW/channel for a maximum event detecting rate of 40 MHz

Revealing the Incorporation of Cerium in Fluorapatite

International audienceFluorapatite (FAp, nominally Ca5(PO4)3F) is the most common phosphate mineral at the Earth’s surface and a main host for rare earth elements (REE) in magmatic and hydrothermal ore deposits and in marine sediments. Our understanding of the enrichment process of REE in FAp rests upon two foundations: (1) being able to elucidate the thermodynamic driving force for their partitioning between the Ca1 and Ca2 structural sites, and (2) being able to determine how the substitution of REE(III) for Ca(II) is charge compensated. A main unsolved question is the marked preference of the larger light REE (lanthanum → samarium) for the smaller Ca2 site. We used density functional theory (DFT) and high-energy resolution fluorescence-detected extended X-ray absorption fine structure (HERFD-EXAFS) spectroscopy to gain detailed insight into the bonding energy, electronic structure, and short-range order of cerium (Ce) in natural FAp. Results show that Ce(III) has a marked preference for a Ca2 site where the nearest five-valent phosphorous cation is replaced with a tetravalent silicon cation, thus balancing the charge excess of the Ce impurity locally. Atomic charge calculations show that the Ca2 site is more ionic than the Ca1 site and that the energetics of the site preference is linearly correlated to the ionization energy of the substituent. Cations with a low energy of ionization, like Ce, preferably occupy the Ca2 site. Novel combination of HERFD-EXAFS spectroscopy and DFT appears to be the most straightforward and reliable way to assess the crystal chemistry of trace elements in compositionally complex natural materials, and opens a previously unavailable avenue for mechanistic investigation of metal enrichment in ore deposits

Benefits from Exclusion Treatment of Unruptured Brain Arteriovenous Malformations on Epilepsy in Adults

International audienc

Intracellular amorphous Ca-carbonate and magnetite biomineralization by a magnetotactic bacterium affiliated to the Alphaproteobacteria

International audienceBacteria synthesize a wide range of intracellular submicrometer-sized inorganic precipitates of diverse chemical compositions and structures, called biominerals. Their occurrences, functions and ultrastructures are not yet fully described despite great advances in our knowledge of microbial diversity. Here, we report bacteria inhabiting the sediments and water column of the permanently stratified ferruginous Lake Pavin, that have the peculiarity to biomineralize both intracellular magnetic particles and calcium carbonate granules. Based on an ultrastructural characterization using transmission electron microscopy (TEM) and synchrotron-based scanning transmission X-ray microscopy (STXM), we showed that the calcium carbonate granules are amorphous and contained within membrane-delimited vesicles. Single-cell sorting, correlative fluorescent in situ hybridization (FISH), scanning electron microscopy (SEM) and molecular typing of populations inhabiting sediments affiliated these bacteria to a new genus of the Alphaproteobacteria. The partially assembled genome sequence of a representative isolate revealed an atypical structure of the magnetosome gene cluster while geochemical analyses indicate that calcium carbonate production is an active process that costs energy to the cell to maintain an environment suitable for their formation. This discovery further expands the diversity of organisms capable of intracellular Ca-carbonate biomineralization. If the role of such biomineralization is still unclear, cell behaviour suggests that it may participate to cell motility in aquatic habitats as magnetite biomineralization does

Design of the VenSpec-U instrument: a double UV imaging spectrometer to analyze sulfured gases in the Venus’ atmosphere

International audienceVenSpec-U, developed under LATMOS (Guyancourt, France) PI-ship, is part of the spectrometer suite named ”VenSpec” led by DLR (Berlin, Germany). This manuscript provides an overview of the current instrument design, at the time of the end of phase B1/early phase B2

End-to-end simulations for COLIBRI, ground follow-up telescope for the SVOM mission

International audienceWe present an overview of the development of the end-to-end simulations programs developed for COLIBRI (Catching OpticaL and Infrared BRIght), a 1.3m robotic follow-up telescope of the forthcoming SVOM (Space Variable Object Monitor) mission dedicated to the detection and study of gamma-ray bursts (GRBs). The overview contains a description of the Exposure Time Calculator, Image Simulator and photometric redshift code developed in order to assess the performance of COLIBRI. They are open source Python packages and were developed to be easily adaptable to any optical/ Near-Infrared imaging telescopes. We present the scientific performances of COLIBRI, which allows detecting about 95% of the current GRB dataset. Based on a sample of 500 simulated GRBs, a new Bayesian photometric redshift code predicts a relative photometric redshift accuracy of about 5% from redshift 3 to 7

COLIBRI, a wide-field 1.3 m robotic telescope dedicated to the transient sky

International audienceCosmic explosions have emerged as a major field of astrophysics over the last years with our increasing capability to monitor large parts of the sky in different wavelengths and with different messengers (photons, neutrinos, and gravitational waves). In this context, gamma-ray bursts (GRBs) play a very specific role, as they are the most energetic explosions in the Universe. The forthcoming Sino-French SVOM mission will make a major contribution to this scientific domain by improving our understanding of the GRB phenomenon and by allowing their use to understand the infancy of the Universe. In order to fulfill all of its scientific objectives, SVOM will be complemented by a fast robotic 1.3 m telescope, COLIBRI, with multiband photometric capabilities (from visible to infrared). This telescope is being jointly developed by France and Mexico. The telescope and one of its instruments are currently being extensively tested at OHP in France and will be installed in Mexico in spring 2023