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This paper explores the mechanics of high-velocity impact fragmentation in titanium alloys produced by Field-Assisted Sintering Technology. For that purpose, we have utilized the experimental setups recently developed by Nieto-Fuentes et al. (J Mech Phys Solids 174:105248, 2023a; Int J Impact Eng 180:104556, 2023b) for conducting dynamic expansion tests on rings and cylinders. The experiments involve firing a conical-nosed cylindrical projectile using a single-stage ight-gas gun against the stationary ring/cylinder at velocities ranging from$$\\approx 248~\\text {m}/\\text {s}$$≈ 248 m / s to$$\\approx 390~\\text {m}/\\text {s}$$≈ 390 m / s , corresponding to estimated strain rates in the specimen varying from$$\\approx 10050~\\text {s}^{-1}$$≈ 10050 s - 1 to$$\\approx 19125~\\text {s}^{-1}$$≈ 19125 s - 1 . The diameter of the cylindrical part of the projectile exceeds the inner diameter of the ring/cylinder, causing the latter to expand as the projectile moves forward, resulting in the formation of multiple necks and fragments. Two different alloys have been tested: Ti6Al4V and Ti5Al5V5Mo3Cr. These materials are widely utilized in aeronautical and aerospace industries for constructing structural elements such as compressor parts (discs and blades) and Whipple shields, which are frequently exposed to intense mechanical loading, including high-velocity impacts. However, despite the scientific and technological significance of Ti6Al4V and Ti5Al5V5Mo3Cr, and the extensive research on their mechanical and fracture behaviors, to the best of the authors’ knowledge, no systematic study has been conducted thus far on the dynamic fragmentation behavior of these alloys. Hence, this paper presents an ambitious fragmentation testing program, encompassing a total of 27 and 29 experiments on rings and cylinders, respectively. Monolithic and multimaterial samples—half specimen of Ti6Al4V and half specimen of Ti5Al5V5Mo3Cr—have been tested, taking advantage of the ability of Field-Assisted Sintering Technology to produce multimaterial parts. The fragments have been collected, weighed, sized, and analyzed using scanning electron microscopy. The experiments have shown that the number of necks, the number of fragments, and the proportion of necks developing into fragments generally increase with expansion velocity. The average distance between necks has been assessed against the predictions of a linear stability analysis (Zhou et al. in Int J Impact Eng 33:880–891 2006; Vaz-Romero et al. in Int J Solids Struct 125:232–243, 2017), revealing satisfactory agreement between theoretical predictions and experimental results. In addition, the experimental results have been compared with tests reported in the literature for various metals and alloys (Nieto-Fuentes et al. in J Mech Phys Solids 174:105248, 2023a; Zhang and Ravi-Chandar in Int J Fract 142:183–217, 2006, Zhang and Ravi-Chandar in Int J Fract 150:3–36, 2008) to examine the influence of material behavior on the statistics of fragments size and necks spacing.

The Cherenkov Telescope Array Observatory (CTAO) is a next-generation facility comprised of ground-based Imaging Atmospheric Cherenkov Telescopes (IACTs). The observatory, currently under construction, will include more than 70 telescopes at two locations: in the northern hemisphere, CTAO-North at the Observatorio del Roque de Los Muchachos (ORM), La Palma, Canary Islands, Spain, and in the southern hemisphere, CTAO-South at a site belonging to the European Southern Observatory (ESO), Cerro Paranal, Chile. IACTs indirectly detect high-energy cosmic photons in an energy range from tens of GeV to several hundreds of TeV by measuring Cherenkov light emitted by atmospheric showers of secondary particles, produced through interactions between incident photons and nuclei of atmospheric gasses in the upper layers. The size of the CTAO will improve the detection sensitivity in the designed energy range by about an order of magnitude with respect to present experiments and aim at improved energy and angular resolution, as well as greatly reduced systematic uncertainties. The key to achieving improvements in accuracy on the absolute energy and flux scales is the precise monitoring of the atmospheric properties for the Cherenkov light, which can be obtained with a specifically designed LIDAR. The Barcelona Raman LIDAR (BRL) prototype is the official CTAO-North Pathfinder and was deployed at ORM for extensive tests between February 2021 and May 2022. We report the BRL’s prospects for the CTAO-North, emphasizing the technical implementation and the preliminary data taken during its deployment period.

The Cherenkov Telescope Array Observatory (CTAO), currently under construction, is the next-generation very-high-energy gamma-ray observatory, providing the coverage for photons in the energy range 20GeV to 300TeV. CTAO will increase detection sensitivity in the 100 GeV to 10TeV range by a factor of 5 — 10 with respect to present experiments. CTAO retrieves the properties of very-high-energy gamma-rays by measuring Cherenkov light emitted by atmospheric showers of secondary particles that incident gamma rays produce in upper layers of the atmosphere. The key for reaching the required energy measurement accuracy is a precise knowledge of the atmospheric transmittance for Cherenkov light, which can be obtained using a dedicated Raman LIDAR. The device should operate at 355nm (near the maximum of Cherenkov light spectrum) and have the capability of taking data at specific azimuth and zenith angles up to distances of 30 km, so that atmospheric transmission along all possible air-shower directions can be determined. The Barcelona Raman LIDAR (BRL) is the official CTAO Pathfinder prototype, developed for atmospheric characterization of the Northern CTAO Site at the Observatorio del Roque de los Muchachos (ORM) on the Canary island of La Palma. BRL was deployed at ORM for extensive on-field tests between February 2021 and May 2022. We report on the commissioning results, including the remote operation capabilities of the system and its contribution to the understanding of atmospheric phenomena during its deployment period. In particular, we report on the properties of the volcanic plume from the eruption of the Cumbre Vieja volcano on 22 September 2021.

The Cherenkov Telescope Array (CTA) is the next-generation ground-based very-high-energy gamma-ray observatory. By using three types of telescopes CTA can cover a wide energy range (20 GeV–300 TeV) with an order of magnitude higher sensitivity than the current telescopes. The Large-Sized Telescope (LST) is designed to detect 20 GeV–1 TeV gamma rays thanks to the large light collection area, sensitive photosensors, a fast trigger system, and readout electronics. The camera readout system must have a high signal-to-noise ratio and a linear signal sampling with a large dynamic range in order to efficiently detect dim and low-energy atmospheric showers. To meet this requirement we use the Domino Ring Sampler version 4 (DRS4), which also enables ultra-fast sampling with low power consumption. Some of the intrinsic characteristics of DRS4 chips require software corrections. These procedures lower the effect of non-Gaussian noise contribution and improve the timing resolution of the system. In this contribution we discuss the calibration algorithms and the resulting performance.

Supermassive black holes with masses of millions to billions of solar masses are commonly found in the centers of galaxies. Astronomers seek to image jet formation using radio interferometry but still suffer from insufficient angular resolution. An alternative method to resolve small structures is to measure the time variability of their emission. Here we report on gamma-ray observations of the radio galaxy IC 310 obtained with the MAGIC (Major Atmospheric Gamma-ray Imaging Cherenkov) telescopes, revealing variability with doubling time scales faster than 4.8 min. Causality constrains the size of the emission region to be smaller than 20% of the gravitational radius of its central black hole. We suggest that the emission is associated with pulsar-like particle acceleration by the electric field across a magnetospheric gap at the base of the radio jet.

Long-duration [gamma]-ray bursts (GRBs) originate from ultra-relativistic jets launched from the collapsing cores of dying massive stars. They are characterized by an initial phase of bright and highly variable radiation in the kiloelectronvolt-to-megaelectronvolt band, which is probably produced within the jet and lasts from milliseconds to minutes, known as the prompt emission.sup.1,2. Subsequently, the interaction of the jet with the surrounding medium generates shock waves that are responsible for the afterglow emission, which lasts from days to months and occurs over a broad energy range from the radio to the gigaelectronvolt bands.sup.1-6. The afterglow emission is generally well explained as synchrotron radiation emitted by electrons accelerated by the external shock.sup.7-9. Recently, intense long-lasting emission between 0.2 and 1 teraelectronvolts was observed from GRB 190114C.sup.10,11. Here we report multi-frequency observations of GRB 190114C, and study the evolution in time of the GRB emission across 17 orders of magnitude in energy, from 5 × 10.sup.-6 to 10.sup.12 electronvolts. We find that the broadband spectral energy distribution is double-peaked, with the teraelectronvolt emission constituting a distinct spectral component with power comparable to the synchrotron component. This component is associated with the afterglow and is satisfactorily explained by inverse Compton up-scattering of synchrotron photons by high-energy electrons. We find that the conditions required to account for the observed teraelectronvolt component are typical for GRBs, supporting the possibility that inverse Compton emission is commonly produced in GRBs.

Long-duration [gamma]-ray bursts (GRBs) are the most luminous sources of electromagnetic radiation known in the Universe. They arise from outflows of plasma with velocities near the speed of light that are ejected by newly formed neutron stars or black holes (of stellar mass) at cosmological distances.sup.1,2. Prompt flashes of megaelectronvolt-energy [gamma]-rays are followed by a longer-lasting afterglow emission in a wide range of energies (from radio waves to gigaelectronvolt [gamma]-rays), which originates from synchrotron radiation generated by energetic electrons in the accompanying shock waves.sup.3,4. Although emission of [gamma]-rays at even higher (teraelectronvolt) energies by other radiation mechanisms has been theoretically predicted.sup.5-8, it has not been previously detected.sup.7,8. Here we report observations of teraelectronvolt emission from the [gamma]-ray burst GRB 190114C. [gamma]-rays were observed in the energy range 0.2-1 teraelectronvolt from about one minute after the burst (at more than 50 standard deviations in the first 20 minutes), revealing a distinct emission component of the afterglow with power comparable to that of the synchrotron component. The observed similarity in the radiated power and temporal behaviour of the teraelectronvolt and X-ray bands points to processes such as inverse Compton upscattering as the mechanism of the teraelectronvolt emission.sup.9-11. By contrast, processes such as synchrotron emission by ultrahigh-energy protons.sup.10,12,13 are not favoured because of their low radiative efficiency. These results are anticipated to be a step towards a deeper understanding of the physics of GRBs and relativistic shock waves.

The detection of Earth-skimming tau neutrinos has turned into a very promising strategy for the observation of UHE cosmic neutrinos. The sensitivity of this channel crucially depends on the parameters of the propagation of the tau neutrino (and the tau lepton) through the terrestrial crust, which governs the flux of emerging tau leptons that can be detected. This propagation problem is usually treated in a simplified framework where several effects are neglected, e.g. the possibility of multiple regenerations of the tau neutrino, the weak interactions of the tau lepton, as well as the stochastic nature of its energy losses. We discuss here the validity of such approximations by studying the propagation in standard rock of tau leptons and neutrinos with both mono-energetic and power-law spectra. We also investigate the impact of such simplifications in non-standard scenarios for the neutrino-nucleon interactions as well as for the tau energy losses.

A novel instrumented baffle surrounding the suspended end mirror in the input mode cleaner cavity of the Virgo interferometer was installed in spring 2021. Since then, the device has been regularly operated in the experiment and the obtained results indicate a good agreement with simulations of the stray light inside the optical cavity. The baffle will operate in the upcoming O4 observation run, serving as a demonstrator of the technology designed to instrument the baffles in front of the main mirrors in time for O5. In this paper we present a detailed description of the baffle design, including mechanics, front-end electronics, data acquisition, as well as optical and vacuum tests, calibration and installation procedures, and performance results.

We present very high-energy optical photometry and spectroscopic observations of SN 2024bch in the nearby galaxy NGC 3206 (\\sim 20 Mpc). We used gamma-ray observations performed with the first Large-Sized Telescope (LST-1) of the Cherenkov Telescope Array Observatory (CTAO) and optical observations with the Liverpool Telescope (LT) combined with data from public repositories to evaluate the general properties of the event and the progenitor star. No significant emission above the LST-1 energy threshold for this observation (\\sim 100 GeV) was detected in the direction of SN 2024bch, and we computed an integral upper limit on the photon flux of F_\\gamma(>100 GeV) \\le 3.61 \\times 10^{-12} cm^{-2} s^{-1} based on six nonconsecutive nights of observations with the LST-1, between 16 and 38 days after the explosion. Employing a general model for the gamma-ray flux emission, we found an upper limit on the mass-loss-rate to wind-velocity ratio of \\dot M/u_{w} \\le 10^{-4} \\frac{M_\\odot}{yr}\\frac{s}{km}, although gamma-gamma absorption could potentially have skewed this estimation, effectively weakening our constraint. From spectro-photometric observations we found progenitor parameters of M_{pr} = 11 - 20 M_\\odot and R_{pr} = 531 \\pm 125 R_\\odot. Finally, using archival images from the Hubble Space Telescope, we constrained the luminosity of the progenitor star to log(L_{pr}/L_\\odot) \\le 4.82 and its effective temperature to T_{pr} \\le 4000 K. Our results suggest that SN 2024bch is a type IIn-L supernova that originated from a progenitor star consistent with a red supergiant. We show how the correct estimation of the mass-loss history of a supernova will play a major role in future multiwavelength observations.