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Towards the Giant Radio Array for Neutrino Detection (GRAND): the GRANDProto300 and GRAND@Auger prototypes
No full textInternational audienceThe Giant Radio Array for Neutrino Detection (GRAND) is a proposed multi-messenger observatory of ultra-high-energy (UHE) particles of cosmic origin. Its main goal is to find the long-sought origin of UHE cosmic rays by detecting large numbers of them and the secondary particles created by their interaction -- gamma rays, and, especially, neutrinos. GRAND will do so using large arrays of radio antennas that look for the radio signals emitted by the air showers initiated by the interactions of the UHE particles in the atmosphere. Since 2023, three small-scale prototype GRAND arrays have been in operation: GRAND@Nançay in France, GRAND@Auger in Argentina, and GRANDProto300 in China. Together, their goal is to validate the detection principle of GRAND under prolonged field conditions, achieving efficient, autonomous radio-detection of air showers. We describe the hardware, software, layout, and operation of the GRAND prototypes and show the first radio spectra measured by them. Despite challenges, the successful operation of the prototypes confirms that the GRAND instrumentation is apt to address the goals of the experiment and lays the groundwork for its ensuing stages
Comparing PIC/MCC Simulations and Experimental Data for the PPS ® X00-ML Hall Thruster IEPC
No full textInternational audienceValidating simulation results against experimental measurements of Hall thruster (HT) performance has long been a major challenge. Few examples of successful comparison do exist in the literature. In this work, we compare the results of three codes: (1) fluid stationary, (2) fluid non-stationary, and (3) two dimensional Particle-in-Cell/Monte Carlo-Collisions (PIC/MCC), with experimental measurements on the Laboratory Model (ML) thruster PPS ® X00-ML HT by Safran Spacecraft Propulsion. The results show that fluid and PIC/MCC simulations can successfully reproduce some macroscopic measured quantities, such as discharge current, thrust, and specific impulse. Simulations also offer the possibility to inquire the state of the plasma inside the thruster, gaining a deeper insight on the plasma characteristics along the thruster axis.</div
Water and sulfur dioxide thermal mapping on Venus : Long-term monitoring and vertical distribution of SO2 within and above the clouds
No full textInternational audienceSulfur and water play a key role in the chemistry, dynamics, and radiative transfer taking place in the atmosphere of Venus. Temporal and local variations in SO2 and HDO, monitored within or above the clouds, can be indicators of photochemical/thermochemical processes or dynamical changes. Since 2012, ground-based monitoring of the SO2 ν2 and ν3 bands, centered at 7.4 mm and 18.9 mm respectively, has been performed with TEXES at the IRTF to probe different atmospheric levels atop and within the clouds ; according to the model, the cloud top, probed at 7.4 mm, is at z = 62 km; the lower level, probed at 19 mm, is at z = 57 km. HDO (used as a proxy of H2O) was simultaneously recorded at 7.4 mm. Since 2021, a third measurement has been systematically added at 8.6 mm to probe a higher atmospheric level (z = 67 km) in the n1 SO2 band. As reported in our previous analyses, the SO2 mixing ratio shows strong variations as a function of time but also over the disk, indicating the formation of SO2 plumes. These local maxima appear sporadically on the SO2 maps and stay visible over a few hours, but less than a day. In contrast, the H2O abundance is uniform over the disk and shows moderate variations as a function of time (Encrenaz et al. A&A 674, A199, 2023). Data recorded since 2021 have led to two main results: 1) The long-term variations of H2O and SO2 abundances at the cloud top were found to be anticorrelated between 2014 and 2019, but do not show this anticorrelation after 2021. While the disk-integrated H2O abundances are more or less constant around 750 ppbv, the disk-integrated SO2 abundances show variations with time by a factor up to 5 (from 100 to 500 ppbv) on a time scale of 2 months. 2) The n1 SO2 band observed at 8.6 mm, probing around z = 67 km, is now detected on all datasets for which SO2 is higher than 300 ppbv at the cloud top. From these data, we infer that the SO2 volume mixing ratio (vmr) at 67 km is about ten times lower than its value at the cloud top (z = 62 km in our model). The SO2 vmr gradient is also retrieved from the data at 7.4 mm (z = 62 km) and 18.9 mm. It is found to be close to 0 in most occasions (implying a constant vmr between 57 and 62 km), with a few exceptions where it can be either negative or positive ; the strongest negative values have been found at a period of high plume activity
OMEGA/Mars Express dust storm catalogue: a local dust storm survey
No full textInternational audienceMartian dust, composed of micrometer-sized mineral particles, is a key parameter of the Martian atmosphere because of its high mobility and capacity to form dust storms and alter the heat balance of the atmosphere. These dust storms are part of the Martian dust cycle and can occur over a wide range of spatial and time scales (from sub-km to planetary scale, and from the minute to months). The dust studies are mostly concentrated on regional storms (> 2000 km), which are detected using UV-VIS global imagers [1, 2] or thermal-IR spectrometers [3]. These observations provide information about the frequency and size of the storms. However, some characteristics of the dust cycle remain uncertain, such as the exact mechanisms of storm formation and growth processes, with implications for the predictability of dust storms and Global Dust Storms (GDS, storm at a planetary scale)
Euclid Quick Data Release (Q1): First visual morphology catalogue
No full textInternational audienceWe present a detailed visual morphology catalogue for Euclid's Quick Release 1 (Q1). Our catalogue includes galaxy features such as bars, spiral arms, and ongoing mergers, for the 378000 bright () or extended (area pixels) galaxies in Q1. The catalogue was created by finetuning the Zoobot galaxy foundation models on annotations from an intensive one month campaign by Galaxy Zoo volunteers. Our measurements are fully automated and hence fully scaleable. This catalogue is the first 0.4% of the approximately 100 million galaxies where Euclid will ultimately resolve detailed morphology
Détection par GPI+SPHERE d'une planète circumbinaire de 6,1 MJup autour de HD 143811
No full textInternational audienceContext. Owing to its sensitivity to wide-orbit giant exoplanets, direct imaging is uniquely positioned to shed light on the interplay between proto-planetary disks and stellar hosts. Besides constraining formation models, new detections are natural benchmarks for atmospheric characterization. Aims. The COBREX project performed an extensive reanalysis of archival observations from SPHERE and GPI using advanced post-processing techniques, enhancing detection sensitivity at close separation. Newly found companion candidates are being followed up to confirm new planets. Methods. Following the detection of a companion candidate around the young ( Myr) binary star HD 143811, we collected a new observation with SPHERE@VLT (m) to confirm the presence of the source and to assess its physical bond to the target. Results. We report the discovery of a new exoplanet orbiting HD 143811 at a projected separation of au. Thanks to a 9-yr-long baseline, we derive a mostly face-on and low eccentricity orbit with a period of years. The luminosity of the planet, constrained through H-band spectrum from GPI, H-band photometry from SPHERE/IRDIS and YJ upper limits from SPHERE/IFS, allows us to place strong constraints on the planet's intrinsic temperature (K), corresponding to a mass of MJup. Conclusions. HD 143811(AB)b is the second planet ever discovered by GPI; it joins the small cohort of circumbinary planets discovered through imaging, becoming a prime target for follow-up formation, dynamical, and characterization studies
Prospects for dark matter observations in dwarf spheroidal galaxies with the Cherenkov Telescope Array Observatory
No full textInternational audienceThe dSphs around the Milky Way are commonly considered as systems that are supported by velocity dispersion against self-gravitation. They have been long accounted among the best targets to search for indirect DM signatures in the GeV-to-TeV gamma-rays due to absence of astrophysical gamma-ray foreground or background emission. We present forecasts on the sensitivity of the future CTAO for the search for annihilating or decaying DM in such targets. We perform an original selection of candidates out of the current catalog of known objects, including both classical and ultra-faint targets. For each of them, we calculate the expected amount of DM using the most updated and complete available samples of photometric and spectroscopic data of member stars, adopting a common framework of data treatment for both classes of objects. In this way, we are able to generate novel astrophysical factor profiles for general indirect DM searches that we compare with the current literature. Out of a starting sample of 64 dSphs, we highlight the 8 most promising targets - DraI, CBe, UMaII, UMi and Wil1 in the Northern hemisphere; RetII, Scl and SgrII in the Southern hemisphere - for which different DM density models (either cored or cuspy) lead to similar expectations, at variance with what happens for other DM targets - thus resulting in more robust predictions. We find that CTAO will provide the strongest limits above ~10 TeV, down to values of velocity-averaged annihilation cross section of ~5 cm s and up to decay lifetimes of ~10 s for combined limits on the best targets. We argue that the largest source of inaccuracy is due to the still imprecise determination of the DM content, especially for ultra-faint dSphs. We propose possible strategies of observation for CTAO, either optimized on a deep focus on the best known candidates, or on the diversification of targets
Unprecedentedly bright X-ray flaring in Cygnus X-1 observed by INTEGRAL
No full textInternational audienceWe study three extraordinarily bright X-ray flares originating from Cyg X-1 seen on 2023 July 10 detected with INTEGRAL. The flares had a duration on the order of only ten minutes each, and within seconds reached a 1-100 keV peak luminosity of erg/s. The associated INTEGRAL/IBIS count rate was about 10x higher than usual for the hard state. To our knowledge, this is the first time that such strong flaring has been seen in Cyg X-1, despite the more than 21 years of INTEGRAL monitoring, with almost 20 Ms of exposure, and the similarly deep monitoring with RXTE/PCA that lasted from 1997 to 2012. The flares were seen in all three X-ray and -ray instruments of INTEGRAL. Radio monitoring by the AMI Large Array with observations 6 h before and 40 h after the X-ray flares did not detect a corresponding increase in radio flux. The shape of the X-ray spectrum shows only marginal change during the flares, i.e., photon index and cut-off energy are largely preserved. The overall flaring behavior points toward a sudden and brief release of energy, either due to the ejection of material in an unstable jet or due to the interaction of the jet with the ambient clumpy stellar wind
Observations of carbon radio recombination lines with the NenuFAR telescope: I. Cassiopeia A and Cygnus A
No full textInternational audienceContext. Carbon radio recombination lines (CRRLs) at decametre wavelengths trace the diffuse phase of the interstellar medium (ISM) of the Galaxy. Observations of these lines allow for physical parameters of this phase to be measured.Aims. We observed CRRLs with the recently commissioned New Extension in Nançay Upgrading LOFAR (NenuFAR) telescope towards two of the brightest sources at low-frequency (10–85 MHz): Cassiopeia A and Cygnus A (hereafter, Cas A and Cyg A, respectively). We then measured the density, ne, and temperature, Te, of the electrons in line-of-sight clouds.Methods. We used NenuFAR’s beam-forming mode and integrated several tens of hours on each source. The nominal spectral resolution was 95.4 Hz. We developed a reduction pipeline primarily aimed at removing the radio frequency interference (RFI) contamination and correcting the baselines. We then performed a first fitting of the spectral lines observed in absorption associated with the line-of-sight clouds.Results. Cas A is the brightest source in the sky at low frequencies and represents an appropriate test bench for this new telescope. On this source, we detected 398 Cα lines between the principal quantum numbers n = 426 and n = 826. Cyg A is also a bright source, however, the Cα lines were observed to be fainter. We stacked the signal by groups of a few tens of lines to improve the quality of our fitting process. For both sources, we reached a significantly higher signal-to-noise ratio (S/N) and spectral resolution than the most recent detections by the LOw Frequency ARray (LOFAR). The variation of the spectral line widths with the electronic quantum number provides constraints on the physical properties of the clouds: Te, ne, and the temperature, T0, of the radiation field, the mean turbulent velocity, νt, and the typical size of the cloud.Conclusions. Our final constraints differ from those inferred from LOFAR results, with ∼50% lower Te, ∼35% lower ne, and from 10 to 80% higher νt, on average. The NenuFAR observations sample a larger space volume than LOFAR’s towards the same sources due to the differences in instrumental beam sizes. These discrepancies highlight the sensitivity of low-frequency CRRLs as probes of the diffuse ISM, paving the way towards large area surveys of CRRLs in our Galaxy
The EUSO-SPB2 Fluorescence Telescope for the Detection of Ultra-High Energy Cosmic Rays
No full textInternational audienceThe Extreme Universe Space Observatory on a Super Pressure Balloon 2 (EUSO-SPB2) flew on May 13 and 14 of 2023. Consisting of two novel optical telescopes, the payload utilized next-generation instrumentation for the observations of extensive air showers from near space. One instrument, the fluorescence telescope (FT) searched for Ultra-High Energy Cosmic Rays (UHECRs) by recording the atmosphere below the balloon in the near-UV with a 1~s time resolution using 108 multi-anode photomultiplier tubes with a total of 6,912 channels. Validated by pre-flight measurements during a field campaign, the energy threshold was estimated around 2~EeV with an expected event rate of approximately 1 event per 10 hours of observation. Based on the limited time afloat, the expected number of UHECR observations throughout the flight is between 0 and 2. Consistent with this expectation, no UHECR candidate events have been found. The majority of events appear to be detector artifacts that were not rejected properly due to a shortened commissioning phase. Despite the earlier-than-expected termination of the flight, data were recorded which provide insights into the detectors stability in the near-space environment as well as the diffuse ultraviolet emissivity of the atmosphere, both of which are impactful to future experiments