Context. BL Lacertae (BL Lac), the archetypal blazar of its subclass and one of the most studied blazars of recent decades, has undergone a series of major multi-wavelength outbursts since 2020, resulting in its highest recorded γ -ray flare to date between September and November 2022, together with those from August 2021 and October 2024. Aims. We characterised the γ -ray and multi-wavelength emission and spectral energy distribution (SED) of BL Lac, as well as their evolution during the major and extended γ -ray and multi-wavelength flare that occurred between September and November 2022. Methods. We evaluated the variability of the flare, focusing on the nights of October 20 and November 13, 2022 when clear intranight very-high-energy (VHE, E > 100 GeV) γ -ray variability was observed. We modelled the γ -ray and broadband SEDs during periods of stable emission identified with a Bayesian block analysis and interpreted the flare’s evolution in terms of the variability in the relativistic particles and the jet’s physical parameters. Results. During this flare, the VHE emission shows an average flux of 0.23 Crab units (C.U.) above 200 GeV and a variability amplitude of more than a factor of ten. We observe intranight flux-doubling variations as fast as ∼8 minutes during the nights of October 20 and November 13, 2022 with maximum fluxes of 4.4 C.U. above 100 GeV and 2.8 C.U. above 200 GeV. The spectral analysis reveals a transition of the X-ray emission from the high- to the low-energy SED peak and a shift in the γ -ray peak towards higher energies. We interpret the broadband emission within a leptonic two-zone model in which intranight variability is explained as magnetic reconnection in a compact region closely orientated with the line of sight, while variations in the relativistic electron distributions and the injection of freshly accelerated particles explain the weekly scale variations.

The Advanced Particle–astrophysics Telescope (APT) is a mission concept for a future space-based MeV-TeV observatory, designed to combine a Compton and $e^{+}{e}^{-}$ pair telescope, aiming to improve the sensitivity of the instruments to $\gamma$ rays in the MeV-GeV range by at least one order of magnitude. To validate and study the technologies that will be employed on the observatory, a small-scale prototype, the Antarctic Demonstrator for APT (ADAPT), is currently being developed to fly on a balloon in Antarctica during the local 2026–2027 flight season. Among its subdetectors there is an Imaging CsI calorimeter (ICC), consisting of 4 layers of CsI(Na) crystals with crossed WLS fibers, coupled to Silicon Photomultipliers (SiPMs). A key element of the design is the multichannel front-end electronics, based on the SMART (SiPM Multichannel ASIC for high-Resolution Cherenkov Telescopes) ASIC, which combines compactness, cost-effectiveness, and a high level of integration. This work reports the results of quality-control tests performed on the custom readout boards for the ICC, and provides an overview of the present status of the mission.

The High Energy cosmic-Radiation Detection (HERD) facility, that will be installed on board the Chinese Space Station, is expected to make significant advancements in cosmic-ray observations, dark matter searches, and gamma-ray astronomy, thanks to its innovative design. The HERD geometry is based on a 3-dimensional imaging calorimeter, which is surrounded on five sides by a fiber tracker, a plastic scintillator detector (PSD), and a silicon charge detector. This unique configuration enables HERD to address key questions in high-energy astrophysics with unprecedented sensitivity and resolution. The PSD will be used as an anti-coincidence system for precise gamma-ray detection (charged particle veto) and charged cosmic-ray nuclei identification. In order to achieve high performance in terms of detection efficiency and charge resolution, the PSD requires a highly segmented geometry, as well as the optimization of the light sensors and electronic read-out. The current design consists of long trapezoidal scintillator tiles coupled to Silicon Photomultipliers (SiPMs). Different prototypes have been built and tested at CERN, Switzerland, and at the CNAO (Centro Nazionale di Adroterapia Oncologica) facility in Italy to study and improve the performance of the PSD. In this contribution, we present the overall project design and the PSD preliminary performances achieved during the beam test campaign at CERN SPS, with a focus on the nuclei identification capability.

Context. The Galactic magnetar SGR 1935+2154 has exhibited prolific high-energy (HE) bursting activity in recent years. Aims. Investigating its potential tera-electronvolt counterpart could provide insights into the underlying mechanisms of magnetar emission and very high-energy (VHE) processes in extreme astrophysical environments. We aim to search for a possible tera-electronvolt counterpart to both its persistent and sub-second-scale burst emission. Methods. We analysed over 25 hour of observations from the Large-Sized Telescope prototype (LST−1) of the Cherenkov Telescope Array Observatory (CTAO) during periods of HE activity from SGR 1935+2154 in 2021 and 2022 to search for persistent emission. For bursting emission, we selected and analysed nine 0.1 s time windows centred around known short X-ray bursts, targeting potential sub-second-scale tera-electronvolt counterparts in a low-photon-statistics regime. Results. While no persistent or bursting emission was detected in our search, we establish upper limits for the tera-electronvolt emission of a short magnetar burst simultaneous to its soft gamma-ray flux. Specifically, for the brightest burst in our sample, the ratio between tera-electronvolt and X-ray flux is ≲10 ⁻³ . Conclusions. The non-detection of either persistent or bursting tera-electronvolt emission from SGR 1935+2154 suggests that if such components exist, they may occur under specific conditions not covered by our observations. This aligns with theoretical predictions of VHE components in magnetar-powered fast radio bursts and the detection of MeV–GeV emission in giant magnetar flares. These findings underscore the potential of magnetars, fast radio bursts, and other fast transients as promising candidates for future observations in the low-photon-statistics regime with Imaging Atmospheric Cherenkov Telescopes, particularly with the CTAO.

We have installed and operated a plastic scintillator detector counter to measure the flux of cosmic radiation during the 2023−2025 tour of the historical vessel Amerigo Vespucci. The Vespucci is the oldest ship of the Italian Navy and serves as a training vessel for Navy cadets. During its tour, some experiments were hosted onboard the vessel, providing unique opportunities for scientists working in different fields. We installed our detector upon the Vespucci’s departure from Darwin in early October 2024. The detector collected cosmic-ray data during the journey from Darwin to Trieste, where the worldwide tour ended in March 2025. After about one month of stop in Trieste, the ship continued its tour in the Mediterranean sea, and arrived in Genova on June 10, 2025. We performed measurements of the cosmic radiation reaching the sea level across a wide latitude range, from 15\(\phantom{0}^\circ\)S to about 45\(\phantom{0}^\circ\)N. The lowest rate (averaged over all azimuth angles) was measured at a geographic latitude of about 7\(\phantom{0}^\circ\)N, and was about 16% less than the highest value, which was measured at Trieste, the northernmost location of the journey. Latitude effects on the cosmic radiation flux at sea level are due to the quasi-dipole geomagnetic field configuration, tilted by an angle of about 11\(\phantom{0}^\circ\) with respect to Earth’s rotational axis.