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Context. Low-energy (<300 keV) protons entering the field of view of XMM-Newton can scatter with the X-ray mirror surface and reach the focal plane. They are observed in the form of a sudden increase in the background level, the so-called soft proton flares, affecting up to 40% of the mission observing time. Soft protons can hardly be disentangled from true X-ray events and cannot be rejected on board. Aims. All future high throughput grazing incidence X-ray telescopes operating outside the radiation belts are potentially affected by soft proton-induced contamination that must be foreseen and limited since the design phase. In-flight XMM-Newton's observations of soft protons represent a unique laboratory to validate and improve our understanding of their interaction with the mirror, optical filters, and X-ray instruments. At the same time, such models would link the observed background flares to the primary proton population encountered by the telescope, converting XMM-Newton into a monitor for soft protons. Methods. We built a Geant4 simulation of XMM-Newton, including a verified mass model of the X-ray mirror, the focal plane assembly, and the EPIC MOS and pn-CCDs. Analytical computations and, when available, laboratory measurements collected from literature were used to verify the correct modelling of the proton scattering and transmission to the detection plane. Similarly to the instrument X-ray response, we encoded the energy redistribution and proton transmission efficiency into a redistribution matrix file (RMF), mapping the probability that a proton from 2 to 300 keV is detected in a certain detector channel, and an auxiliary response file (ARF), storing the grasp towards protons. Both files were formatted according to the standard NASA calibration database and any compliant X-ray data analysis tool can be used to simulate or analyse soft proton-induced background spectra. An overall systematic uncertainty of 30% was assumed on the basis of the estimated accuracy of the mirror geometry and transmission models. Results. For the validation, three averaged soft proton spectra, one for each filter configuration, were extracted from a collection of 13 years of MOS observations of the focused non X-ray background and analysed with Xspec. A similar power-law distribution is found for the three filter configurations, plus black-body-like emission below tens of keV used as a correction factor, based on the dedicated spectral analysis of 55 in-flight proton flares presented in Paper II. The best-fit model is in agreement with the power-law distribution predicted from independent measurements for the XMM-Newton orbit, spent mostly in the magnetosheath and nearby regions. For the first time we are able to link detected soft proton flares with the proton radiation environment in the Earth's magnetosphere, while proving the validity of the simulation chain in predicting the background of future missions. Benefiting from this work and contributions from the Athena instrument consortia, we also present the response files for the Athena mission and updated estimates for its focused charged background. [ABSTRACT FROM AUTHOR]

Context. To date, puzzlingly few bona fide RR Lyrae stars have been identified in binaries. Binarity in pulsating stars can be revealed through well-timed photometric data over sufficiently long time bases because of the light travel time effect (LTTE) on the pulsations, which manifests as variation in the timings of maximum light in the O−C (observed minus calculated) diagram. However, O−C variations can also have other causes, such as the Blazhko effect or a sudden or gradual change in the main pulsation period. Aims. We approach this challenge by disentangling the Blazhko effect and period changes from the potential LTTE on V1109 Cas, an RR Lyrae star suspected to be part of a binary system based on its O−C data in the GEOS database. In doing so, we aim to uncover the subtler signals indicative of a companion (LTTE). Methods. We analysed nine years of ground-based photometric data, using Fourier analysis to model the pulsation modulated by the Blazhko effect. From the fit to the observed light curves, we constructed a refined O−C diagram without the scatter caused by Blazhko modulation. Subsequently, we considered different possible scenarios, because distinguishing intrinsic period changes or breaks from the LTTE is challenging. Results. If the remaining O−C variation is due to a period break, refining the O−C diagram can almost entirely remove the trends. If we interpret the variation as an LTTE, we can consider possible configurations. While we currently favour a period break as the explanation for the residual O−C variations, more data on the star in the forthcoming years will help reveal whether the O−C variations are due to the LTTE or intrinsic period changes. Conclusions. Our study, based on a detailed light-curve fitting of V1109 Cas, offers insights into the discernment between Blazhko modulation, intrinsic period breaks, and the LTTE in binary systems. Our results highlight the complexity of determining binarity from O−C data traditionally used for detecting binary motion, calling for caution in this process. [ABSTRACT FROM AUTHOR]

Context. Multi-conjugate adaptive optics (MCAO) is a crucial technology for achieving high-resolution imaging over a wide field of view with modern ground-based optical telescopes. The configuration of deformable mirrors (DMs) is a key component in the analysis and optimization of MCAO performance. Currently, the search for the optimal DM configuration often relies on iterative and time-consuming Monte Carlo simulations. This issue arises from the lack of an appropriate optimization method for DM configurations. Aims. The primary objective of this paper is to establish an optimization method for DM configurations in MCAO systems. We established a quantitative criterion for evaluating DM configurations by analyzing their correction capabilities for turbulence aberrations at different altitudes. Then, we optimized the DM configurations based on this criterion. This method provides a new theoretical foundation and practical tool for the design and performance optimization of MCAO systems. Methods. Based on the pupil phase structure function, we established a DM configuration evaluation criterion, namely the non-conjugate correction index (NCCI). Using NCCI as the optimal criterion, combined with the particle swarm optimization algorithm, we searched for the optimal solution across different DM configuration spaces. Results. We conducted simulations based on the turbulence profiles of typical telescope sites. We validated our proposed theoretical model against Monte Carlo simulation models and find that the NCCI error ranges from 0.05 to 0.1. For optimizing DM conjugate heights, the results of our optimization algorithm differ by less than 1 km from those obtained via Monte Carlo simulations. Regarding the performance of the DM optimization algorithm, the average convergence accuracy error is less than 0.1 km, and the average convergence speed is approximately ten iterations. Additionally, our optimization method runs in just a few minutes; Monte Carlo simulations, in comparison, require several dozen hours. [ABSTRACT FROM AUTHOR]

Context. Estimation of the number of cosmic-ray-induced background events is a challenging task for Imaging Atmospheric Cherenkov Telescopes (IACTs). Most approaches rely on a model of the background signal derived from archival observations, which is then normalised to the region of interest (ROI) and respective observation conditions using emission-free regions in the observation. However, this is disadvantageous for the analysis of large, extended γ-ray structures, where no sufficient source-free region can be found. Aims. We aim to address this issue by estimating the normalisation of a three-dimensional background model template from separate, matched observations of emission-free sky regions. As a result, the need for an emission-free region in the field of view of the observation becomes unnecessary. Methods. To this end, we implemented an algorithm to identify observation pairs with the most closely matching observation conditions. We used the open-source analysis package Gammapy to estimate the background rate, facilitating seamless adaptation of the framework to many γ-ray detection facilities. We employed public data from the High Energy Stereoscopic System (H.E.S.S.) to validate this methodology. Results. The analysis demonstrates that employing a background rate estimated through this run-matching approach yields results consistent with those obtained using the standard application of the background model template. Furthermore, we confirm the compatibility of the source parameters obtained through this approach with previous publications, and present an analysis employing the background model template approach, along with an estimation of the statistical and systematic uncertainties introduced by this method. [ABSTRACT FROM AUTHOR]

We present a comparative analysis of photometric observations of the cataclysmic variable TT Ari in its bright state obtained by the TESS orbital observatory in 2021 and 2023 and by ground-based amateur telescopes in 2022. The light curves from 2021 and 2022 are dominated by modulations with a period slightly shorter than the orbital one (negative superhumps), 0.13292 and 0.13273 d, respectively. From the data obtained in 2023, we see much stronger modulations appearing on a much longer timescale of a few days with an amplitude of up to 0.5 mag, compared to 0.2 mag in 2021. We also find the negative superhump variability with the period of 0.1338 d in the 2023 observations, but the significance of these negative superhumps is much lower than in the previous seasons. We detect less significant additional modulations with a period exceeding the orbital one (positive superhumps) in the observations from 2021 and 2022. Their periods are 0.15106 and 0.1523 d, respectively. We also find a previously unnoticed periodic signal corresponding to the orbital period of 0.13755 d in the TESS observations in 2021. Theoretical models of tidal precession of an elliptical disk predict a decrease in the precession period (and an increase in the period of the positive superhumps) with increasing disk radius, which is consistent with the observed photometric behavior of the system. This enables us to estimate the mass ratio q of the components in TT Ari to be in the range of 0.24–0.29. The tilted disk precession model predicts a period of nodal precession whose value is in general agreement with observations. [ABSTRACT FROM AUTHOR]

Context. Stellar activity is comprised of various phenomena, mainly spots and faculae. It is one of the main sources of noise in exoplanetary observations because it affects both spectroscopic and photometric observations. In studying young active planetary systems, we need to model the activity of the host stars to remove astrophysical noise from our observational data. Aims. We model the contribution of stellar spots in photometric observations. Through the use of multi-band photometry, we aim to extract the geometric properties of the spots and constrain their temperatures. Methods. We analysed multi-band photometric observations acquired with the 80 cm Marcon telescope of the Osservatorio Polifunzionale del Chianti of V1298 Tau, assuming the photometric modulation observed in different bands is attributed to cold spots. Results We constrained the effective temperature of the active regions present on the surface of V1298 Tau, resulting from a combination of spots and faculae. We tested our hypothesis on solar data, verifying that we successfully measured the size of the dominant active region and its averaged effective temperature. [ABSTRACT FROM AUTHOR]

Context. Multiconjugate adaptive optics (MCAO) can overcome atmospheric anisoplanatism to achieve high-resolution imaging with a large field of view (FOV). Atmospheric tomography is the key technology for MCAO. The commonly used modal tomography approach reconstructs the three-dimensional atmospheric turbulence wavefront aberration based on the wavefront sensor (WFS) detection information from multiple guide star (GS) directions. However, the atmospheric tomography problem is severely ill-posed. The incomplete GS coverage in the FOV coupled with the WFS detection error significantly affects the reconstruction accuracy of the three-dimensional atmospheric turbulence wavefront aberration, leading to a nonuniform aberration detection precision over the whole FOV. Aims. We propose an efficient approach for achieving accurate atmospheric tomography to overcome the limitations of the traditional modal tomography approach. Methods. We employed a deep-learning-based approach to the tomographic reconstruction of the three-dimensional atmospheric turbulence wavefront aberration. We propose an atmospheric tomography residual network (AT-ResNet) that is specifically designed for this task, which can directly generate wavefronts of multiple turbulence layers based on the Shack-Hartmann (SH) WFS detection images from multiple GS directions. The AT-ResNet was trained under different turbulence intensity conditions to improve its generalization ability. We verified the performance of the proposed approach under different conditions and compared it with the traditional modal tomography approach. Results. The well-trained AT-ResNet demonstrates a superior performance compared to the traditional modal tomography approach under different atmospheric turbulence intensities, various turbulence layer distributions, higher-order turbulence aberrations, detection noise, and reduced GSs conditions. The proposed approach effectively addresses the limitations of the modal tomography approach, leading to a notable improvement in the accuracy of atmospheric tomography. It achieves a highly uniform and high-precision wavefront reconstruction over the whole FOV. This study holds great significance for the development and application of the MCAO technology. [ABSTRACT FROM AUTHOR]

Context. Dual-field interferometric observations with VLTI/GRAVITY sometimes require the use of a binary calibrator. This is a binary star whose individual components remain unresolved by the interferometer, with a separation between 400 and 2000 mas for observations with the Unit Telescopes (UTs), or 1200–3000 mas for the Auxiliary Telescopes (ATs). The separation vector also needs to be predictable to within 10 mas for a proper pointing of the instrument. Aims. No list of properly vetted calibrators was available so far for dual-field observations with VLTI/GRAVITY on the UTs. Our objective is to compile such a list and make it available to the community. Methods. We identified a list of candidates from the Washington Double Star (WDS) catalogue, all with appropriate separations and brightness, scattered over the southern sky. We observed them as part of a dedicated calibration programme, determined whether these objects were true binaries (excluding higher multiplicities resolved interferometrically, but unseen by imaging), and extracted measurements of the separation vectors. We combined these new measurements with those available in the WDS to determine updated orbital parameters for all our vetted calibrators. Results. We compiled a list of 13 vetted binary calibrators for observations with VLTI/GRAVITY on the UTs, and we provide orbital estimates and astrometric predictions for each of them. We show that our list guarantees that there are always two binary calibrators at least at an airmass < 2 in the sky over the Paranal observatory at any point in time. Conclusions. Any principal investigator wishing to use the dual-field mode of VLTI/GRAVITY with the UTs can now refer to this list to select an appropriate calibrator. We encourage the use of whereistheplanet to predict the astrometry of these calibrators, which seamlessly integrates with p2Gravity for VLTI/GRAVITY dual-field observing material preparation. [ABSTRACT FROM AUTHOR]

Context. The measurement of pulsar pulse times-of-arrival (ToAs) is a crucial step in detecting low-frequency gravitational waves. To determine ToAs, we can use template-matching to compare each observed pulse profile with a standard template. However, using different combinations of templates and template-matching methods (TMMs) without careful consideration can lead to inconsistent results. Aims. In pulsar timing array (PTA) experiments, distinct ToAs from the same observations can be obtained due to the use of diverse templates and TMMs. In other words, employing diverse approaches can yield different timing results and would thus have a significant impact on subsequent gravitational wave searches. In this paper we examine several commonly used combinations to analyze their effect on pulse ToAs. Methods. We evaluated the potential impact of template and TMM selection on 13 typical millisecond pulsars within the European PTA. We employed pulsar timing methods, specifically the root mean square and reduced chi-square (χ2r) of the residuals of the best timing solution, to assess the outcomes. Additionally, we evaluated the system-limited noise floor (SLNF) for each pulsar at various telescopes operating around 1.4 GHz using frequency-resolved templates. Results. Our findings suggest that utilizing data-derived and smoothed templates in conjunction with the Fourier-domain with Markov chain Monte Carlo TMM is generally the most effective approach, though there may be exceptions that require further attention. Furthermore, we determine that pulse phase jitter noise does not significantly limit the current precision of the European PTA's timing, as jitter levels derived from other studies are much lower than the SLNF. [ABSTRACT FROM AUTHOR]

Context. Observations of meteors in the Earth's atmosphere offer a unique tool for determining the flux of meteoroids that are too small to be detected by direct telescopic observations. Although these objects are routinely observed from ground-based facilities, such as meteor and fireball networks, space-based instruments come with notable advantages and have the potential to achieve a broad and uniform exposure. Aims. In this paper, we describe the first observations of meteor events with Mini-EUSO, a very wide field-of-view telescope launched in August 2019 from the Baikonur cosmodrome and installed on board the Russian Zvezda module of the International Space Station. Mini-EUSO can map the night-time Earth in the near-UV range (290-130 nm) with a field of view equal to 44° × 44° and a spatial resolution of about 4.7 km at an altitude of 100 km from the ground. The detector saves triggered transient phenomena with a sampling frequency of 2.5 µs and 320 µs, as well as a continuous acquisition at 40.96 ms scale that is suitable for meteor observations. Methods. We designed two dedicated and complementary trigger methods, together with an analysis pipeline able to estimate the main physical parameters of the observed population of meteors, such as the duration, horizontal speed, azimuth, and absolute magnitude. To compute the absolute flux of meteors from Mini-EUSO observations, we implemented a simulation framework able to estimate the detection efficiency as a function of the meteor magnitude and the background illumination conditions. Results. The instrument detected 24 thousand meteors within the first 40 data-taking sessions from November 2019 to August 2021, for a total observation time of approximately 6 days with a limiting absolute magnitude of +6. Our estimation of the absolute flux density of meteoroids in the range of mass between 10−5 kg to 10−1 kg was found to be comparable to other results available in the literature. Conclusions. The results of this work prove the potential for space-based observations to increase the statistics of meteor observations achievable with instruments operating on the ground. The slope of the mass distribution of meteoroids sampled with Mini-EUSO suggests a mass index of either s = 2.09 ± 0.02 or s = 2.31 ± 0.03, according to two different methodologies for the computation of the pre-atmospheric mass starting from the luminosity of each event. [ABSTRACT FROM AUTHOR]

Context. The GRAVITY+ upgrade implies a complete renewal of its adaptive optics (AO) systems. Its complex design, featuring moving components between the deformable mirrors and the wavefront sensors, requires the monitoring and auto-calibrating of the lateral mis-registrations of the system while in operation. Aims. For preset and target acquisition, large lateral registration errors must be assessed in open loop to bring the system to a state where the AO loop closes. In closed loop, these errors must be monitored and corrected, without impacting the science. Methods. With respect to the first requirement, our method is perturbative, with two-dimensional modes intentionally applied to the system and correlated to a reference interaction matrix. For the second requirement, we applied a non-perturbative approach that searches for specific patterns in temporal correlations in the closed loop telemetry. This signal is produced by the noise propagation through the AO loop. Results. Our methods were validated through simulations and on the GRAVITY+ development bench. The first method robustly estimates the lateral mis-registrations, in a single fit and with a sub-subaperture resolution while in an open loop. The second method is not absolute, but it does successfully bring the system towards a negligible mis-registration error, with a limited turbulence bias. Both methods proved to robustly work on a system still under development and not fully characterised. Conclusions. Tested with Shack-Hartmann wavefront sensors, the proposed methods are versatile and easily adaptable to other AO instruments, such as the pyramid, which stands as a baseline for all future AO systems. The non-perturbative method, not relying on an interaction matrix model and being sparse in the Fourier domain, is particularly suitable to the next generation of AO systems for extremely large telescopes that will present an unprecedented level of complexity and numbers of actuators. [ABSTRACT FROM AUTHOR]

Context. Observations of blue-shifted X-ray absorption lines indicate the presence of wind from the accretion disc in X-ray binaries. Magnetohydrodynamic (MHD) driving is one possible wind-launching mechanism. Recent theoretical developments have made self-similar magnetic accretion-ejection solutions much more generalised, showing that wind can be launched at a much lower magnetisation than the equipartition value, which had previously been the only possibility. Aims. In this work, we model the transmitted spectra through MHD-driven photoionised wind models with different levels of magnetisation. We investigate the possibility of detecting absorption lines by upcoming instruments, such as XRISM and Athena. We investigate the robustness of the method of fitting asymmetric line profiles by multiple Gaussians. Methods. We used the photoionisation code XSTAR to simulate the transmitted model spectra. To cover the extensive range of velocity and density of the wind spanned over a large distance (∼105 gravitational radii), we divided the wind into slabs following a logarithmic radial grid. Fake observed spectra are finally produced by convolving model spectra with instrument responses. Since the line asymmetries are apparent in the convolved spectra as well, this can be used in future XRISM and Athena spectra as an observable diagnostic to fit for. We applied some amount of rigor in assessing the equivalent widths of the major absorption lines, including the Fe XXVI Lyα doublets, which will be clearly distinguishable thanks to the superior quality of future high-resolution spectra. Results. Disc magnetisation stands as another crucial MHD variable that can significantly alter the absorption line profiles. Pure MHD outflow models at low magnetisation are dense enough to be observed by the existing or upcoming instruments. Therefore, these models can serve as simpler alternatives to MHD-thermal models. Fitting with multiple Gaussians is a promising method for handling asymmetric line profiles, as well as the Fe XXVI Lyα doublets. [ABSTRACT FROM AUTHOR]

Space-based and ground-based telescopes have extensively documented the impact of satellites on astronomical observations. With the proliferation of satellite mega-constellation programmes, their influence on astronomical observations has become undeniable. Quantifying the impact of satellites on telescopes is crucial. To this end, we enhanced the circular orbit model for satellites and introduced a methodology based on two-line element orbit data. This involves constructing a satellite probability distribution model to evaluate the impact of satellites on telescopes. Using our method, we assessed the satellite impact on global grounded observatories. Our results indicate that the regions most severely affected by satellite interference at present are those near the equator, with latitudes of around ±50 and ±80 degrees experiencing the most significant impact from low-Earth-orbit satellites. Furthermore, we validated the reliability of our method using imaging data obtained from the focal surface acquisition camera of the LAMOST telescope. [ABSTRACT FROM AUTHOR]

Context. Since the discovery of the first exoplanet almost three decades ago, the number of known exoplanets has increased dramatically. By beginning of the 2000s it was clear that dedicated facilities to advance our studies in this field were needed. The CHaracterising ExOPlanet Satellite (CHEOPS) is a space telescope specifically designed to monitor transiting exoplanets orbiting bright stars. In September 2023, CHEOPS completed its nominal mission duration of 3.5 yr and remains in excellent operational conditions. As a testament to this, the mission has been extended until the end of 2026. Aims. Scientific and instrumental data have been collected throughout in-orbit commissioning and nominal operations, enabling a comprehensive analysis of the mission's performance. In this article, we present the results of this analysis with a twofold goal. First, we aim to inform the scientific community about the present status of the mission and what can be expected as the instrument ages. Secondly, we intend for this publication to serve as a legacy document for future missions, providing insights and lessons learned from the successful operation of CHEOPS. Methods. To evaluate the instrument performance in flight, we developed a comprehensive monitoring and characterisation (M&C) programme. It consists of dedicated observations that allow us to characterise the instrument's response and continuously monitor its behaviour. In addition to the standard collection of nominal science and housekeeping data, these observations provide valuable input for detecting, modelling, and correcting instrument systematics, discovering and addressing anomalies, and comparing the instrument's actual performance with expectations. Results. The precision of the CHEOPS measurements has enabled the mission objectives to be met and exceeded. The satellite's performance remains stable and reliable, ensuring accurate data collection throughout its operational life. Careful modelling of the instrumental systematics allows the data quality to be significantly improved during the light curve analysis phase, resulting in more precise scientific measurements. Conclusions. CHEOPS is compliant with the driving scientific requirements of the mission. Although visible, the ageing of the instrument has not affected the mission's performance. The satellite's capabilities remain robust, and we are confident that we will continue to acquire high-quality data during the mission extension. [ABSTRACT FROM AUTHOR]

Context. The spatial coherence wavefront outer scale (ℒ0) characterizes the size of the largest turbulence eddies in Earth's atmosphere, determining low spatial frequency perturbations in the wavefront of the light captured by ground-based telescopes. Advances in adaptive optics (AO) techniques designed to compensate for atmospheric turbulence emphasize the crucial role of this parameter for the next generation of large telescopes. Aims. The motivation of this work is to introduce a novel technique for estimating ℒ0 from seeing-limited integral field spectroscopic (IFS) data. This approach is based on the impact of a finite ℒ0 on the light collected by the pupil entrance of a ground-based telescope. Methods. We take advantage of the homogeneity of IFS observations to generate band filter images spanning a wide wavelength range, enabling the assessment of image quality (IQ) at the telescope's focal plane. Comparing the measured wavelength-dependent IQ variation with predictions derived from a first-order analytical approach based on turbulence statistics simplifications using the von Kármán model provides valuable insights into the prevailing ℒ0 parameter during the observations. We applied the proposed technique to observations from the Multi-Unit Spectroscopic Explorer (MUSE) in the wide-field mode obtained at the Paranal Observatory. Results. Our analysis successfully validates the first-order analytical expression, which combines the seeing (ε0) and the ℒ0 parameters, to predict the IQ variations with the wavelength in ground-based astronomical data. However, we observed some discrepancies between the measured and predictions of the IQ that are analyzed in terms of uncertainties in the estimated ε0 and dome-induced turbulence contributions. Conclusions. This work constitutes the empirical validation of the analytical expression for estimating IQ at the focal plane of ground-based telescopes under specific ε0 and finite ℒ0 conditions. Additionally, we provide a simple methodology to characterize the ℒ0 and dome-seeing (εdome) as by-products of IFS observations routinely conducted at major ground-based astronomical observatories. [ABSTRACT FROM AUTHOR]

Context. Out-of-focus (OOF) holography can be used to determine the aperture deformations of radio telescopes that lead to errors in the phase of the complex aperture distribution. In contrast to traditional methods, OOF holography can be performed without a reference antenna, which has a number of practical advantages. Aims. The aim of this work is to develop a standard procedure for OOF holography at the Effelsberg telescope. This includes performing OOF holography observations and the development of dedicated software, the pyoof package, to compute aberrations of the telescope's optical system. Methods. Based on the OOF holography method developed at the Green Bank telescope, we adapted the approach to the Effelsberg 100 m telescope in order to determine the aberrations of the aperture phase distribution (phase-error maps). Results. The developed OOF holography software is presented as well as the results from observations at Effelsberg. Early results reveal gravitation-related residual deformation not contained in the previously existing aperture and pointing model, and hence we propose changes to the model to counteract aberrations in the telescope's surface. Conclusions. The OOF holography method (observations and pyoof package) works as expected at the Effelsberg 100 m telescope and is able to validate the good performance of the existing finite element model. Test measurements show that slight improvements of the aperture efficiency and gain elevation dependence are possible but limited in the current configuration. [ABSTRACT FROM AUTHOR]

Context. The presence of clouds during observations with Imaging Atmospheric Cherenkov Telescopes can strongly affect the performance of the instrument due to additional absorption of light and scattering of light beyond the field of view of the instrument. If not corrected for, the presence of clouds leads to increased systematic errors in the results. Aims. One approach to correct for the effects of clouds is to include clouds in Monte Carlo simulations to produce models for primary particle classification, and energy and direction estimation. However, this method is challenging due to the dynamic nature of cloudy conditions and requires extensive computational resources. The second approach focuses on correcting the data themselves for cloud effects, which allows the use of standard simulations. However, existing corrections often prioritise the limitation of systematic errors without optimising overall performance. By correcting the data already at the image level, it is possible to improve event reconstruction without the need for specialised simulations. Methods. We introduce a novel analysis method based on a geometrical model that can correct the data already at the image level given a vertical transmission profile of a cloud. Using Monte Carlo simulations of an array of four of the Large-Sized Telescopes of the Cherenkov Telescope Array, we investigated the effect of the correction on the image parameters and the performance of the system. We compared the data correction at the camera level with the use of dedicated simulations for clouds with different transmissions and heights. Results. The proposed method efficiently corrects the extinction of light in clouds, eliminating the need for dedicated simulations. Evaluation using Monte Carlo simulations demonstrates improved gamma-ray event reconstruction and overall system performance. [ABSTRACT FROM AUTHOR]

Context. Spacecraft formation flying serves as a method of astronomical instrumentation that enables the construction of large virtual structures in space. The formation-flying interferometry generally requires very high control accuracy, and extraterrestrial orbits are typically selected. To pave the way for comprehensive missions, proposals have been made for preliminary space missions, involving nano- or small satellites, to demonstrate formation-flying interferometry technologies, especially in low Earth orbits. From a theoretical perspective, however, it is unknown where and to what extent feasible regions for formation-flying interferometry should exist in geocentric orbits. Aims. This study aims to demonstrate the feasibility of formation-flying interferometry in geocentric orbits in which various perturbation sources exist. Geocentric orbits offer the advantage of economic accessibility and the availability of proven formation-flying technologies tailored for Earth orbits. Its feasibility depends on the existence of specific orbits that satisfy a small-disturbance environment with good observation conditions. Methods. Spacecraft motions in Earth orbits subjected to perturbations are analytically modeled based on celestial mechanics. The magnitudes of the accelerations required to counteract these perturbations are characterized by parameters such as the semimajor axis and the size of the formation. Results. Small-perturbation regions tend to appear in higher-altitude and shorter-separation regions in geocentric orbits. Candidate orbits are identified in high Earth orbits for the triangular laser-interferometric gravitational-wave telescope, which is 100 km in size, and in medium Earth orbits for the linear astronomical interferometer, which is 0.5 km in size. A low Earth orbit with a separation of approximately 0.1 km may be suitable for experimental purposes. Conclusions. Geocentric orbits are potentially applicable for various types of formation-flying interferometry. [ABSTRACT FROM AUTHOR]

Aims. We present a campaign designed to train the Global Rapid Advanced Network Devoted to the Multi-messenger Addicts (GRANDMA) network and its infrastructure to follow up on transient alerts and detect their early afterglows. In preparation for O4 II campaign, we focused on gamma-ray burst (GRB) alerts since they are expected to serve as the electromagnetic counterpart of gravitational-wave events. Our goal was to improve our response to the alerts and to start prompt observations as soon as possible, so that we may better prepare the GRANDMA network for the fourth observational run of LIGO-Virgo-Kagra (launched at the end of May 2023) and future missions such as SM. Methods. We set up a dedicated infrastructure and organized a rota of follow-up advocates (FAs) to guarantee round-the-clock assistance to our telescope teams, with an aim to receive, manage, and send out observational plans to our partner telescopes. To ensure a large number of observations, we focused on Swift GRBs whose localization errors were generally smaller than the GRANDMA telescopes' field of view. This allowed us to bypass the transient identification process and focus on the reaction time and efficiency of the network. Results. During the 'Ready for O4 II' phase, 11 Swift/INTEGRAL GRB triggers were selected. Of these, nine fields had been observed and three afterglows had been detected (GRB 220403B, GRB 220427A, GRB 220514A) with 17 GRANDMA telescopes and 17 amateur astronomers from the citizen science project Kilonova-Catcher. Here, we highlight the GRB 220427A analysis, where our long-term follow-up of the host galaxy allowed us to obtain a photometric redshift of z = 0.82 ± 0.09 and its lightcurve evolution, as well as to fit the decay slope of the afterglows and study the properties of the host galaxy. Conclusions. During this eight-week-long GRB follow-up campaign, we successfully fulfilled our goal of training telescope teams for O4 and improving the associated technical toolkits. For seven of the GRB alerts, our network was able to start the first observations less than one hour after the GRB trigger time. We also characterized the network efficiency to observe GRB afterglow given the resulting time delay and limiting magnitude, and to its light curve evolution based on the observation of GRB 220427A. [ABSTRACT FROM AUTHOR]

Context. With the Extremely Large Telescope (ELT) generation of telescopes come new challenges. The complexity of these telescopes' pupils creates new problems for adaptive optics (AO) that prevent the telescopes from reaching the theoretical resolutions that their size allows. In particular, the large spiders necessary to support the massive optics of these telescopes create discontinuities in the wavefront measurement. These discontinuities appear as a new phase error dubbed the "petal mode." This error is described as a differential piston between the fragment of the pupil separated by the spiders and is responsible for a strong degradation in the imaging quality, reducing the European ELT's resolution to that of a 15m telescope. Aims. The aim of this paper is to study the measurement of the petal mode by AO sensors. In particular, we want to understand why the pyramid wavefront sensor (PyWFS), the first-light wavefront sensor of any ELT-generation telescope, cannot measure this petal mode under normal conditions, and how to enable this measurement by adapting the AO control scheme and the PyWFS. Methods. To facilitate our study, we considered a simplified version of the petal mode, featuring a simpler pupil than the ELT. This allowed us to quickly simulate the properties of the petal mode and its measurement by the PyWFS. We studied specifically how a system that separates the atmospheric turbulence from the petal measurement would behave. Studying the petal mode's power spectral density, we proposed using a spatial filter to reduce the contribution of AO residuals to the benefit of petal mode contribution, eventually enabling it to be measured. Finally, we demonstrated our proposed system with end-to-end simulations. Results. A solution proposed to measure the petal mode is to use an unmodulated PyWFS (uPyWFS), but the uPyWFS does not make accurate measurements in the presence of atmospheric residuals. A spatial filtering step, consisting of a pinhole around the pyramid tip, reduces the first path residuals seen by the uPyWFS and restores its accuracy. This system was able to measure and control the petal mode during the end-to-end simulation. Conclusions. To address the petal problem, a two-path AO with a sensor dedicated to the measurement of the petal mode seems necessary. The question remains as to what could be used as the second path petalometer. Through this paper, we demonstrate that an uPyWFS can confuse the petal mode with the residuals from the first path. However, adding a spatial filter on top of said uPyWFS makes it a good petalometer candidate. This spatial filtering step makes the uPyWFS less sensitive to the first path residuals while retaining its ability to measure the petal mode. [ABSTRACT FROM AUTHOR]