Corpuscular description of the speed of light in a homogeneous medium

We are used to describe the detection of light in terms of particles and its propagation from the source to the detection, by waves. For instance, the slowing down of light in a transparent medium is always explained within the electromagnetic wave framework. We propose to approach that phenomenon through a purely corpuscular description. We find expression for the refractive indices which differ slightly from the usual Maxwell wave approach. We thus compare these expressions against experimental refractive indices and we show that both reproduce well the data. We show also how this corpuscular framework gives a very natural interpretation to the self focusing Kerr effect. Finally an experimental expectation of fluctuation of the speed of light is presented.Comment: 16 pages, 2 figure

Slitless spectrophotometry with forward modelling: principles and application to atmospheric transmission measurement

In the next decade, many optical surveys will aim to tackle the question of dark energy nature, measuring its equation of state parameter at the permil level. This requires trusting the photometric calibration of the survey with a precision never reached so far, controlling many sources of systematic uncertainties. The measurement of the on-site atmospheric transmission for each exposure, or on average for each season or for the full survey, can help reach the permil precision for magnitudes. This work aims at proving the ability to use slitless spectroscopy for standard star spectrophotometry and its use to monitor on-site atmospheric transmission as needed, for example, by the Vera C. Rubin Observatory Legacy Survey of Space and Time supernova cosmology program. We fully deal with the case of a disperser in the filter wheel, which is the configuration chosen in the Rubin Auxiliary Telescope. The theoretical basis of slitless spectrophotometry is at the heart of our forward model approach to extract spectroscopic information from slitless data. We developed a publicly available software called Spectractor (https://github.com/LSSTDESC/Spectractor) that implements each ingredient of the model and finally performs a fit of a spectrogram model directly on image data to get the spectrum. We show on simulations that our model allows us to understand the structure of spectrophotometric exposures. We also demonstrate its use on real data, solving specific issues and illustrating how our procedure allows the improvement of the model describing the data. Finally, we discuss how this approach can be used to directly extract atmospheric transmission parameters from data and thus provide the base for on-site atmosphere monitoring. We show the efficiency of the procedure on simulations and test it on the limited data set available.Comment: 30 pages, 36 figures, submitted to Astronomy and Astrophysic

Determination of the sensitivity and the detection performances of the UV camera pixels of the EUSO-BALLOON instrument

International audienc

Development and design of a microelectronic circuit for space-borne JEM-EUSO cosmic rays detector

Extreme Universe Space Observatory on Japanese Experiment Module (JEM-EUSO) est conçu comme l expérience de rayons cosmiques de prochaine génération pour observer les particules hautement énergétiques au-dessus de 10 eV. Le projet est mené par RIKEN et soutenu par une collaboration de plus de 200 membres provenant de 13 pays. Cet observatoire, sous la forme d'un télescope fluorescent, sera arrimé à la Station Spatiale internationale (ISS) pour un lancement prévu en 2017. En observant les gerbes atmosphériques produites dans la troposphère, à une altitude de 400 km, cet observatoire de rayons cosmique offrira une grande surface de détection, qui est au moins 100 fois supérieur que le plus grand détecteur de rayons cosmiques jamais construit. La surface focale de JEM-EUSO sera équipée d'environ 5000 unités de photomultiplicateur multianode 8x8 pixels (MAPMT). Un circuit intégré (ASIC), connu sous le nom SPACIROC, a été proposé pour la lecture du MAPMT. Cet ASIC de 64 voies propose des fonctionnalités comme le comptage de photons, la mesure des charges et le transfert de données à haute vitesse. Par-dessus tout, cet ASIC doit peu consommé afin de respecter la contrainte de puissance de JEM-EUSO. Réalisé en utilisant la technologie AMS Silicium-Germanium (SiGe) 0,35 m, cet ASIC intègre 64 canaux de comptage de photons rapides (Photon Counting). La résolution de temps pour le comptage de photons est de 30 ns, ce qui permettra d atteindre la valeur maximale comptage qui est de l'ordre de 10 photons / s. Le système de mesure de charge est basé sur le Time-Over-Threshold qui offre 8 canaux de mesure. Chaque canal de mesure est une somme des 8 pixels du MAPMT et il est prévu que ce système est capable de mesurer jusqu'à 200 pC. La partie numérique fonctionne en continu et gère la conversion des données de chaque voie des blocs de Photon Counting et Time-Over-Threshold. Les données numériques sont transmises par l'intermédiaire de liaisons parallèles dédiées et ces opérations sont effectuées pendant une fenêtre de communication ou Gate Time Unit (GTU) de fréquence 400 kHz. Le taux de transfert des données d ASIC avoisine les 200 Mbps ou 576 bits / GTU. La dissipation de puissance est strictement inférieure à 1 mW par canal ou 64 mW pour l'ASIC. Le premier prototype de SPACIROC a été envoyé pour fabrication en Mars 2010 au Centre Multi Projet (CMP). Des puces nues et packagés ont été reçues en Octobre 2010, ce qui a débuté la phase de caractérisation de cet ASIC. Après une phase de test réussie, des puces SPACIROC ont été intégrés dans l'électronique frontale d'un instrument pour détecter les sursauts gamma - Ultra Fast Flash Observatoire (UFFO) qui va être lancé en 2013. Vers la fin de l'année 2012, des cartes électroniques frontales conçues autour des puces SPACIROC ont été fabriqués pour le projet EUSO-Balloon. Ce projet de vol en ballon stratosphérique à une altitude de 40 km servira comme le démonstrateur technologique et l'ingénierie d'un instrument miniaturisé JEM-EUSO. La deuxième génération de cet ASIC a été envoyée à la fonderie en Décembre 2011. Ce second prototype, SPACIROC2, a été testé à partir de mai 2012. Les principales améliorations sont les suivantes: la consommation d'énergie a été revue à la baisse, ainsi que l'amélioration de la résolution temporelle de Photon Counting et l'extension de la gamme dynamique pour le module Time-Over-Threshold. Les mesures en cours ont montré que SPACIROC2 présente un bon comportement général et apporte des améliorations par rapport à son prédécesseur.Extreme Universe Space Observatory on Japanese Experiment Module (JEM-EUSO) is conceived as the next generation cosmic rays experiment for observing the highly energetic particles above 5.10 eV. The project is lead by RIKEN and supported by an active collaboration of more than 200 members from 13 countries. This observatory, in the shape of a wide field-of-view UV telescope, will be attached to the International Space Station (ISS) for a planned launch in 2017. Observing the Air Showers generated in troposphere from an altitude of 400 km, this space based cosmic rays experiment will offer a very large instantaneous detection surface, which is at least 100 times bigger than the largest land based cosmic rays observatory. The detection surface of JEM-EUSO will be equipped with around 5000 units of 8x8 pixels Multianode Photomultiplier (MAPMT). A radiation hardened mixed signal application-specific integrated circuit (ASIC), known as SPACIROC, has been proposed for reading out the MAPMT. This ASIC features 64-channel analog inputs, fast photon counting capabilities, charge measurements and high-speed data transfer. Above all, the power dissipation of this ASIC is required to be very low in order to comply with the strict power budget of JEM-EUSO. By taking the advantages of high speed AMS 0.35 m Silicon-Germanium (SiGe) process, this ASIC integrates 64 fast Photon Counting channels. The photon counting time resolution is 30 ns, which allows the theoretical counting rate in the order of 10 photons/s. The charge measurement system is based on Time-Over-Threshold which offers 8 measurement channels. Each measurement channel is composed of 8 pixels of the MAPMT and it is expected that this system will measure up to 200 pC. The digital part is then required to operate continuously and handles data conversion of each Photon Counting and Time-Over-Threshold channel. For the first version of this ASIC, one channel measurement channel for the dynode is also available. The digital data are transmitted via dedicated parallel communication links and within the defined Gate Time Unit (GTU) of 400 kHz frequency. The ASIC data output rate is in the vicinity of 200 Mbps or 576 bits/GTU. The power dissipation is kept strictly below 1 mW per channel or 64 mW for the ASIC. The first prototype of SPACIROC was sent for tapeout in March 2010 through Centre Multi Projet (CMP) prototyping services. The packaged ASICs and bare dies have been received in October 2010 which marked the characterization phase of this chip. After successful testing phase, SPACIROC chips were integrated into the front-end electronics of an instrument pathfinder for detecting the gamma ray bursts Ultra Fast Flash Observatory (UFFO) which is foreseen to be launched in 2013. Towards the end of 2012, front-end board designed around SPACIROC chips have been fabricated for the EUSO-Balloon project. This balloon borne project will serve as a technical and engineering demonstrator of a fully miniaturized JEM-EUSO instrument which will be flown to the stratosphere at the altitude of 40 km. The second tapeout of this ASIC was done in December 2011. This second prototype, SPACIROC2, was tested from May 2012. The main improvements are as follows: lower power consumption due to better power management, enhancement in Photon Counting time resolution and extension the Time-Over-Threshold maximum input rate. The ongoing tests have shown that SPACIROC2 exhibits a good overall behavior and improvement compared to its predecessor.PARIS11-SCD-Bib. électronique (914719901) / SudocSudocFranceF

LPM eect and pair production in the geomagnetic ®eld: a signature of ultra-high energy photons in the Pierre Auger Observatory

Abstract The presence of photons in the cosmic rays of highest energy (above 10 20 eV) would be a strong indication of a``top± down'' production mechanism, e.g. the decay of topological defects. The Pierre Auger Observatory is aimed to detect cosmic rays in this energy range with a large statistics. The pair production in the magnetic ®eld of the Earth, followed by hard synchrotron radiation, generates early cascades containing mainly photons with energies below the LPM threshold (a few 10 19 eV) while unconverted photons above this energy produce in the atmosphere slowly developing showers. We describe some observables related to the¯uorescence pro®le and to the ground signals (lateral distribution and front curvature), which can provide a clear signature of abnormally delayed showers, even if they represent a small fraction of the¯ux. Moreover, the magnetic conversion exhibit a characteristic anisotropy with respect to the local direction of the ®eld, allowing an unambiguous con®rmation of photons, against the hypothesis of weakly interacting objects.

A transmission hologram for slitless spectrophotometry on a convergent telescope beam. 1. Focus and resolution

International audienceWe report in this paper the test of a plane holographic optical element to be used as an aberration-corrected grating for a slitless spectrograph, inserted in a convergent telescope beam. Our long-term objective is the optimization of a specific hologram to switch the auxiliary telescope imager of the Vera Rubin Observatory into an accurate slitless spectrograph, dedicated to the atmospheric transmission measurement. We present and discuss here the promising results of tests performed with prototype holograms at the CTIO |$0.9\,$|m telescope during a run of 17 nights in 2017 May–June. After their on-sky geometrical characterization, the performances of the holograms as aberration-balanced dispersive optical elements have been established by analysing spectra obtained from spectrophotometric standard stars and narrow-band emitter planetary nebulae. Thanks to their additional optical function, our holographic disperser prototypes allow us to produce significantly better focused spectra within the full visible wavelength domain |$[370,1050]\,$|nm than a regular grating, which suffers from strong defocusing and aberrations when used in similar conditions. We show that the resolution of our slitless on-axis spectrograph equipped with the hologram approaches its theoretical performance. While estimating the benefits of a hologram for the spectrum resolution, the roadmap to produce a competitive holographic element for the Vera Rubin Observatory auxiliary telescope has been established

How in situ atmospheric transmission can affect cosmological constraints from type Ia supernovae ?

International audienceThe measurement of type Ia supernova colours in photometric surveys is the key to access to cosmological distances. But for future large surveys like the Large Survey of Space and Time undertaken by the Vera Rubin Observatory in Chile, the large statistical power of the promised catalogues will make the photometric calibration uncertainties dominant in the error budget and will limit our ability to use it for precision cosmology. The knowledge of the on-site atmospheric transmission on average for the full survey, or for season or each exposure can help reaching the sub-percent precision for magnitudes. We will show that measuring the local atmospheric transmission allows to correct the raw magnitudes to reduce the photometric systematic uncertainties. Then we will present how this strategy is implemented at the Rubin Observatory via the Auxiliary Telescope and its slitless spectrograph

Performance of the EUSO-Balloon UV Camera

International audienceJEM-EUSO [1] is intended to be a space-borne fruorescence te lescope onboard of JEM/EF (Japanese Experimental Modeul/Exposure Facility) on the International Space Station (ISS). The main goal of the JEM-EUSO project is to detect the Extensive A ir Showers (EAS) produced by the Extreme Energy Cosmic Rays (EECRs) with energies above 1 0 19 eV from the extragalactic objects. As a pathfinder, the JEM-EUSO collaboration is curr ently developing a balloon-borne fluorescence telescope experiment, called EUSO-Balloon, f unded by CNES, the French space agency. It will perform end-to-end tests of the JEM-EUSO sub systems and instrumental concept, and measure the UV background for space-based EECR detector s. It involves several French in- stitutes (LAL, APC and IRAP) as well as several key institute s of the JEM-EUSO collaboration. The EUSO-Balloon instrument consists of an UV telescope and an infrared camera. The UV telescope will be operated at an altitude of 40 km to observe t he background and possibly signal photons in the fluorescence UV range (290-430 nm), which are e mitted along shower tracks gen- erated by ultra high energy cosmic rays with energies above 1 0 18 eV interacting with the earth’s atmosphere. The balloon experiment will be equipped with el ectronics and acquisition systems, as close as possible to the ones designed for the UV telescope of main JEM-EUSO instrument. The past years have been devoted to the design, the fabricati on and the tests of the prototype boards of the PDM, of the digital processor, and the flight mod els of optics, electronics and the IR camera for EUSO-Balloon. Here we focus on the PDM, the core element of the JEM-EUSO foca l surface. We first describe all key items of the PDM, from the photodetectors to the FPGA b oard, the first stage of the data processing (DP). We then report on the tests carried out on th e integration to assess their func- tionality and their suitability for a balloon mission

SPACIROC: a Front-End Readout ASIC for the JEM-EUSO Observatory

OMEGA - JEM-EUSOInternational audienceThe SPACIROC ASIC is designed for the JEM-EUSO observatory onboard of the International Space Station (ISS). The main goal of JEM-EUSO is to observe Extensive Air Shower (EAS) produced in the atmosphere by the passage of the high energetic extraterrestrial particles above a few 10^19 eV. A low-power, rad-hard ASIC is proposed for reading out the 64-channel Multi-Anode Photomultipliers which are going to equip the detection surface of JEM-EUSO. Two main features of this ASIC are the photon counting mode for each input and the charge-to-time (Q-to-T) conversion for the multiplexed channels. In the photon counting mode, the 100% triggering efficiency is achieved for 50fC input charges. For the Q-to-T converter, the ASIC requires a minimum input of 2pC. In order to comply with the strict power budget available from the ISS, the ASIC is needed to dissipate less than 1mW/channel. The design of SPACIROC and the test results are presented in this paper. SPACIROC is a result of the collaboration between OMEGA/LAL-Orsay, France, RIKEN, ISAS/JAXA and Konan University, Japan on behalf of the JEM-EUSO consortium