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Driving the nuclear fusion reaction p+11B -> 3 alpha + 8.7 MeV in laboratory conditions, by interaction between high-power laser pulses and matter, has become a popular field of research, due to numerous applications that it can potentially allow: an alternative to deuterium-tritium (DT) for fusion energy production, astrophysics studies and alpha-particle generation for medical treatments. A possible scheme for laser-driven p-11B reactions is to direct a beam of laser-accelerated protons onto a boron sample (the so-called 'pitcher-catcher' scheme). This technique was successfully implemented on large, energetic lasers, yielding hundreds of joules per shot at low repetition. We present here a complementary approach, exploiting the high-repetition rate of the VEGA III petawatt laser at CLPU (Spain), aiming at accumulating results from many interactions at much lower energy, for better controlling the parameters and the statistics of the measurements. Despite a moderate energy per pulse, our experiment allowed exploring the laser-driven fusion process with tens (up to hundreds) of laser shots. The experiment provided a clear signature of the produced reactions and of the fusion products, accumulated over many shots, leading to an improved optimization of the diagnostic for these experimental campaigns In this paper we discuss the effectiveness of the laser-driven p-11B fusion in the pitcher-catcher scheme, at high-repetition rate, addressing the challenges of this experimental scheme and highlighting its critical aspects. Our proposed methodologies allow evaluating the performance of this scheme for laser-driven alpha particle production and can be adapted to high-repetition rate laser facilities with higher energy and intensity.

This paper presents near-infrared spectropolarimetric and velocimetric observations of the young planet-hosting T Tauri star PDS 70, collected with SPIRou at the 3.6m Canada-France-Hawaii Telescope from 2020 to 2024. Clear Zeeman signatures from magnetic fields at the surface of PDS 70 are detected in our data set of 40 circularly polarized spectra. Longitudinal fields inferred from Zeeman signatures, ranging from -116 to 176 G, are modulated on a timescale of 3.008$\pm$0.006 d, confirming that this is the rotation period of PDS 70. Applying Zeeman-Doppler imaging to subsets of unpolarized and circularly polarised line profiles, we show that PDS 70 hosts low-contrast brightness spots and a large-scale magnetic field in its photosphere, featuring in particular a dipole component of strength 200-420 G that evolves on a timescale of months. From the broadening of spectral lines, we also infer that PDS 70 hosts a small-scale field of 2.51$\pm$0.12 kG. Radial velocities derived from unpolarized line profiles are rotationally modulated as well, and exhibit additional longer-term chromatic variability, most likely attributable to magnetic activity rather than to a close-in giant planet (with a 3sigma upper limit on its minimum mass of ~4 Mjup at a distance of ~0.2 au). We finally confirm that accretion occurs at the surface of PDS 70, generating modulated red-shifted absorption in the 1083.3-nm He i triplet, and show that the large-scale magnetic field, often strong enough to disrupt the inner accretion disc up to the corotation radius, weakens as the star gets fainter and redder (as in 2022), suggesting that dust from the disc more easily penetrates the stellar magnetosphere in such phases., Comment: MNRAS in press (20 pages, 12 figures, 5 tables)

Diffusive shock acceleration (DSA) is a prominent mechanism for energizing charged particles up to very large rigidities at astrophysical collisionless shocks. In addition to ions and electrons, it has been proposed that interstellar dust grains could also be accelerated through diffusive shock acceleration, for instance, at supernova remnants (SNRs). Considering interstellar dust grains of various size and composition, we investigate the possibility of grain acceleration at young SNR shocks (throughout the free expansion and Sedov-Taylor phases) and the maximum energies reached by the accelerated grains. We investigate the potential implications on the abundance of refractory species relative to volatile elements in the cosmic-ray composition. We rely on semi-analytical descriptions of particle acceleration at strong shocks, and on self-similar solutions for the dynamics of SNR shock waves. For simplicity, type Ia thermonuclear SNRs expanding in uniform interstellar medium are considered. We find that the acceleration of dust grains at relativistic speed is possible, up to Lorentz factor of $\sim 10^{2}$, kinetic energy $E_{\rm k}/\text{nuc}\sim 10^2$ GeV/nuc for the smaller grains of size $a\sim 5 \times 10^{-7}$ cm. We find that the subsequent sputtering of grains can produce nuclei with a rigidity sufficient to be injected in the process of diffusive shock acceleration. Such scenario can help naturally account for the overabundance of refractory elements in the Galactic cosmic-ray composition, provided that a fraction $\eta \sim 10^{-3}-10^{-2}$ of dust grains swept up by a SNR are energized through DSA., Comment: 7 Pages, 6 Figures. Accepted for publication in A&A

The detection of stellar variability often relies on the measurement of selected activity indicators such as coronal emission lines and non-thermal emissions. On the flip side, the effective stellar temperature is normally seen as one of the key fundamental parameters (with mass and radius) to understanding the basic physical nature of a star and its relation with its environment (e.g., planetary instellation). We present a novel approach for measuring disk-averaged temperature variations to sub-Kelvin accuracy inspired by algorithms developed for precision radial velocity. This framework uses the entire content of the spectrum, not just pre-identified lines, and can be applied to existing data obtained with high-resolution spectrographs. We demonstrate the framework by recovering the known rotation periods and temperature modulation of Barnard star and AU Mic in datasets obtained in the infrared with SPIRou at CHFT and at optical wavelengths on $\epsilon$ Eridani with HARPS at ESO 3.6-m telescope. We use observations of the transiting hot Jupiter HD189733\,b, obtained with SPIRou, to show that this method can unveil the minute temperature variation signature expected during the transit event, an effect analogous to the Rossiter-McLaughlin effect but in temperature space. This method is a powerful new tool for characterizing stellar activity, and in particular temperature and magnetic features at the surfaces of cool stars, affecting both precision radial velocity and transit spectroscopic observations. We demonstrate the method in the context of high-resolution spectroscopy but the method could be used at lower resolution., Comment: accepted for publication in AJ

For statistical modeling wherein the data regime is unfavorable in terms of dimensionality relative to the sample size, finding hidden sparsity in the ground truth can be critical in formulating an accurate statistical model. The so-called "l0 norm" which counts the number of non-zero components in a vector, is a strong reliable mechanism of enforcing sparsity when incorporated into an optimization problem. However, in big data settings wherein noisy estimates of the gradient must be evaluated out of computational necessity, the literature is scant on methods that reliably converge. In this paper we present an approach towards solving expectation objective optimization problems with cardinality constraints. We prove convergence of the underlying stochastic process, and demonstrate the performance on two Machine Learning problems.

A second-order block coordinate descent method is proposed for the unconstrained minimization of an objective function with Lipschitz continuous Hessian. At each iteration, a block of variables is selected by means of a greedy (Gauss-Southwell) rule which considers the amount of first-order stationarity violation, then an approximate minimizer of a cubic model is computed for the block update. In the proposed scheme, blocks are not required to have a prefixed structure and their size is allowed to change during the iterations. For non-convex objective functions, global convergence to stationary points is proved and a worst-case iteration complexity analysis is provided. In particular, given a tolerance $\epsilon$, we show that at most ${\cal O}(\epsilon^{-3/2})$ iterations are needed to drive the stationarity violation with respect to the selected block of variables below $\epsilon$, while at most ${\cal O}(\epsilon^{-2})$ iterations are needed to drive the stationarity violation with respect to all variables below $\epsilon$. Numerical results are finally provided.

The Tarantula Nebula in the Large Magellanic Cloud is known for its high star formation activity. At its center lies the young massive star cluster R136, providing a significant amount of the energy that makes the nebula shine so brightly at many wavelengths. Recently, young massive star clusters have been suggested to also efficiently produce high-energy cosmic rays, potentially beyond PeV energies. Here, we report the detection of very-high-energy $\gamma$-ray emission from the direction of R136 with the High Energy Stereoscopic System, achieved through a multicomponent, likelihood-based modeling of the data. This supports the hypothesis that R136 is indeed a very powerful cosmic-ray accelerator. Moreover, from the same analysis, we provide an updated measurement of the $\gamma$-ray emission from 30 Dor C, the only superbubble detected at TeV energies presently. The $\gamma$-ray luminosity above $0.5\,\mathrm{TeV}$ of both sources is $(2-3)\times 10^{35}\,\mathrm{erg}\,\mathrm{s}^{-1}$. This exceeds by more than a factor of 2 the luminosity of HESS J1646$-$458, which is associated with the most massive young star cluster in the Milky Way, Westerlund 1. Furthermore, the $\gamma$-ray emission from each source is extended with a significance of $>3\sigma$ and a Gaussian width of about $30\,\mathrm{pc}$. For 30 Dor C, a connection between the $\gamma$-ray emission and the nonthermal X-ray emission appears likely. Different interpretations of the $\gamma$-ray signal from R136 are discussed., Comment: 10+11 pages, 4+6 figures. Corresponding authors: L. Mohrmann, N. Komin

We present in this paper an analysis of near-infrared observations of the 0.3-Msun protostar V347 Aur collected with the SPIRou high-resolution spectropolarimeter and velocimeter at the 3.6-m Canada-France-Hawaii Telescope from October 2019 to April 2023. From a set of 79 unpolarized and circularly polarized spectra of V347 Aur to which we applied Least-Squares Deconvolution (LSD), we derived radial velocities and longitudinal fields, along with their temporal variations over our monitoring campaign of 1258 d. Our data show that V347 Aur is an eccentric binary system with an orbital period 154.6$\pm$0.7 d, experiencing strong to extreme accretion events near periastron. The companion is a 29.0$\pm$1.6-Mjup brown dwarf, a rare member of the brown dwarf desert of close companions around M dwarfs. We detect weak longitudinal fields (<100 G) at the surface of V347 Aur, significantly weaker than those of more evolved prototypical T Tauri stars. These fields show small-amplitude rotational modulation, indicating a mainly axisymmetric parent large-scale magnetic topology, and larger fluctuations at half the orbital period, suggesting that what we dub a ``pulsed dynamo'' triggered by orbital motion and pulsed accretion operates in V347 Aur. Applying Zeeman-Doppler imaging to our circularly polarised LSD profiles, we find that the large-scale field of V347 Aur is mainly toroidal for most of our observations, with the toroidal component switching sign near periastron and apoastron. The weak large-scale dipole (~30 G) is not able to disrupt the disc beyond 1.3 Rstar even at the lowest accretion rates, implying longitudinally distributed (rather than localized) accretion at the surface of the protostar., Comment: MNRAS in press (18 pages, 12 figures, 5 tables)

We present an analysis of high-resolution optical spectra recorded for 30 stars of the split extended main-sequence turnoff (eMSTO) of the young ($\sim$ 40 Myr) Small Magellanic Cloud (SMC) globular cluster NGC 330. Spectra were obtained with the M2FS and MIKE spectrographs located on the Magellan-Clay 6.5m telescope. These spectra revealed the presence of Be stars, occupying primarily the cool side of the split main sequence (MS). Rotational velocity ($v\sin{i}$) measurements for most of the targets are consistent with the presence of two populations of stars in the cluster: one made up of rapidly rotating Be stars ($ \approx 200$ $\rm km\,s^{-1}$), and {the other} consisting of warmer stars with slower rotation ($<\!v\sin{i}\!>\approx50$ $\rm km\,s^{-1}$). Core emission in the H$\delta$ photospheric lines was observed for most of the H$\alpha$ emitters. The shell parameter computed for the targets in our sample indicate that most of the observed stars should have inclinations below 75$^{\circ}$. These results confirm the detection of Be stars obtained through photometry, but also reveal the presence of narrow H$\alpha$ and H$\delta$ features for some targets that cannot be detected with low-resolution spectroscopy or photometry. Asymmetry variability of H$\alpha$ line profiles on the timescales of a few years is also observed, and could provide information on the geometry of the decretion disks. Observations revealed the presence of nebular H$\alpha$ emission, strong enough in faint targets to compromise the extraction of spectra and to impact narrow band photometry used to assess the presence of H$\alpha$ emission., Comment: 15 pages, 13 figures, accepted for publication in The Astrophysical Journal

In this paper we report near-infrared observations of the classical T Tauri star TW Hya with the SPIRou high-resolution spectropolarimeter and velocimeter at the 3.6-m Canada-France-Hawaii Telescope in 2019, 2020, 2021 and 2022. By applying Least-Squares Deconvolution (LSD) to our circularly polarized spectra, we derived longitudinal fields that vary from year to year from -200 to +100 G, and exhibit low-level modulation on the 3.6 d rotation period of TW Hya, despite the star being viewed almost pole-on. We then used Zeeman-Doppler Imaging to invert our sets of unpolarized and circularly-polarized LSD profiles into brightness and magnetic maps of TW Hya in all 4 seasons, and obtain that the large-scale field of this T Tauri star mainly consists of a 1.0-1.2 kG dipole tilted at about 20{\deg} to the rotation axis, whereas the small-scale field reaches strengths of up to 3-4 kG. We find that the large-scale field is strong enough to allow TW Hya to accrete material from the disc on the polar regions at the stellar surface in a more or less geometrically stable accretion pattern, but not to succeed in spinning down the star. We also report the discovery of a radial velocity signal of semi-amplitude $11.1^{+3.3}_{-2.6}$ m/s (detected at 4.3$\sigma$ at a period of 8.3 d in the spectrum of TW Hya, whose origin may be attributed to either a non-axisymmetric density structure in the inner accretion disc, or to a $0.55^{+0.17}_{-0.13}$ Jupiter mass candidate close-in planet (if orbiting in the disc plane), at an orbital distance of $0.075\pm0.001$ au., Comment: MNRAS, in press (23 pages, 16 figures, 6 tables)

Supernova remnants (SNRs) are likely to be significant sources of cosmic rays up to the knee of the local cosmic-ray (CR) spectrum. They produce gamma-rays in the very-high-energy (VHE) ($E>0.1$ TeV) range via: hadronic interactions with the interstellar medium and leptonic interactions with soft photons. Current observations have lead to the detection of about a dozen of VHE SNRs and future instruments should increase this number. The details of particle acceleration at SNRs, and of the mechanisms producing VHE gamma-rays at SNRs are poorly understood. We aim to study the population of SNRs detected in the TeV range and its properties, and to address fundamental questions of particle acceleration at SNR shocks: What is the spectrum of accelerated particles? What is the efficiency of acceleration? Is the VHE emission dominated by hadronic or leptonic interactions? By means of Monte Carlo methods, we simulate the population of SNRs in the VHE domain and confront our simulations to H.E.S.S. Galactic Plane Survey (HGPS). We explore the parameter space: the slope of accelerated particles $\alpha$, the electron-to-proton ratio $K_{\rm ep}$, and the efficiency of particle acceleration $\xi $. We found sets of parameters for which $\gtrsim 90$\% of realisations are found in agreements with the HGPS data. These parameters are found $ 4.2 \gtrsim \alpha \gtrsim 4.1 $, $10^{-5} \lesssim K_{\rm ep} \lesssim 10^{-4.5}$, and $0.03 \lesssim \xi\lesssim 0.1 $ . We were able to strongly argue against some regions of the parameter space: $\alpha \lesssim 4.05$, $\alpha \gtrsim 4.35$, or $K_{\rm ep} \gtrsim 10^{-3}$. Our model is so far able to explain the SNR population of the HGPS. Our approach, confronted to the results of future systematic surveys, will help remove degeneracy in the solutions, and to better understand particle acceleration at SNR shocks., Comment: 15 pages, 12 figures. Accepted for publication in A&A

The Crab Nebula is a unique laboratory for studying the acceleration of electrons and positrons through their non-thermal radiation. Observations of very-high-energy $\gamma$ rays from the Crab Nebula have provided important constraints for modelling its broadband emission. We present the first fully self-consistent analysis of the Crab Nebula's $\gamma$-ray emission between 1 GeV and $\sim$100 TeV, that is, over five orders of magnitude in energy. Using the open-source software package Gammapy, we combined 11.4 yr of data from the Fermi Large Area Telescope and 80 h of High Energy Stereoscopic System (H.E.S.S.) data at the event level and provide a measurement of the spatial extension of the nebula and its energy spectrum. We find evidence for a shrinking of the nebula with increasing $\gamma$-ray energy. Furthermore, we fitted several phenomenological models to the measured data, finding that none of them can fully describe the spatial extension and the spectral energy distribution at the same time. Especially the extension measured at TeV energies appears too large when compared to the X-ray emission. Our measurements probe the structure of the magnetic field between the pulsar wind termination shock and the dust torus, and we conclude that the magnetic field strength decreases with increasing distance from the pulsar. We complement our study with a careful assessment of systematic uncertainties., Comment: 18+6 pages, 15+2 figures. Accepted for publication in A&A. Corresponding authors: M. Meyer, L. Mohrmann, T. Unbehaun. v2: after A&A language editing

Monochromatic gamma-ray signals constitute a potential smoking gun signature for annihilating or decaying dark matter particles that could relatively easily be distinguished from astrophysical or instrumental backgrounds. We provide an updated assessment of the sensitivity of the Cherenkov Telescope Array (CTA) to such signals, based on observations of the Galactic centre region as well as of selected dwarf spheroidal galaxies. We find that current limits and detection prospects for dark matter masses above 300 GeV will be significantly improved, by up to an order of magnitude in the multi-TeV range. This demonstrates that CTA will set a new standard for gamma-ray astronomy also in this respect, as the world's largest and most sensitive high-energy gamma-ray observatory, in particular due to its exquisite energy resolution at TeV energies and the adopted observational strategy focussing on regions with large dark matter densities. Throughout our analysis, we use up-to-date instrument response functions, and we thoroughly model the effect of instrumental systematic uncertainties in our statistical treatment. We further present results for other potential signatures with sharp spectral features, e.g.~box-shaped spectra, that would likewise very clearly point to a particle dark matter origin., Comment: 44 pages JCAP style (excluding author list and references), 19 figures; minor changes to match published version

We report new observations of the classical T~Tauri star CI~Tau with the SPIRou near-infrared spectropolarimeter and velocimeter at the Canada-France-Hawaii Telescope (CFHT) in late 2019, 2020 and 2022, complemented with observations obtained with the ESPaDOnS optical spectropolarimeter at CFHT in late 2020. From our SPIRou and ESPaDOnS spectra, to which we applied Least-Squares Deconvolution, we infer longitudinal fields clearly modulated with the 9-d rotation period of CI~Tau. Using Zeeman-Doppler imaging, we reconstruct the large-scale magnetic topology, first from SPIRou data only in all three seasons, then from our 2020 SPIRou and ESPaDOnS data simultaneously. We find that CI~Tau hosts a mainly axisymmetric poloidal field, with a 1~kG dipole slightly tilted to the rotation axis and dark spots close to the pole that coincide with the footpoints of accretion funnels linking the star to the inner disc. Our results also suggest that CI~Tau accretes mass from the disc in a stable fashion. We further find that radial velocities (RV) derived from atomic and CO lines in SPIRou spectra are both rotationally modulated, but with a much lower amplitude than that expected from the putative candidate planet CI~Tau~b. We confirm the presence of a RV signal at a period of 23.86~d reported in a separate analysis, but detect it clearly in CO lines only and not in atomic lines, suggesting that it likely traces a non-axisymmetric structure in the inner disc of CI~Tau rather than a massive close-in planet., Comment: MNRAS, in press (22 pages, 11 figures, 6 tables)

In this paper, we analyze a derivative-free line search method designed for bound-constrained problems. Our analysis demonstrates that this method exhibits a worst-case complexity comparable to other derivative-free methods for unconstrained and linearly constrained problems. In particular, when minimizing a function with $n$ variables, we prove that at most ${\cal O}(n\epsilon^{-2})$ iterations are needed to drive a criticality measure below a predefined threshold $\epsilon$, requiring at most ${\cal O}(n^2\epsilon^{-2})$ function evaluations. We also show that the total number of iterations where the criticality measure is not below $\epsilon$ is upper bounded by ${\cal O}(n^2\epsilon^{-2})$. Moreover, we investigate the method capability to identify active constraints at the final solutions. We show that, after a finite number of iterations, all the active constraints satisfying the strict complementarity condition are correctly identified.

Cosmic rays are the only agent capable of ionizing the interior of dense molecular clouds and, thus, they are believed to play an essential role in determining the physical and chemical evolution of star-forming regions. In this work, we aim to study cosmic-ray induced ionization rates in starburst environments using non-thermal emissions of cosmic rays from starburst nuclei. To this end, we first revisit cosmic-ray models which could explain data of non-thermal emissions from radio to X-ray and gamma-ray from nuclei of three prototypical starburst galaxies NGC 253, M82, and Arp 220. These models are then applied to predict ionization rates in starburst environments which gives values around $10^{-14}$ s$^{-1}$. Such a high value of the ionization rate, which is 2 to 3 orders of magnitude higher than the typical values found in the Milky Way, is probably due to relatively high rates of supernova explosions occurring within the nuclei of these starburst galaxies. We also discuss in more details the case of NGC 253 where our predicted ionization rate is found to be, in most cases, a few times smaller than the values inferred from molecular line observations of clouds in the starburst nucleus. The general framework provided in this work illustrates how the use of non-thermal emission data could help to provide more insights into ionization rates or, more generally, cosmic-ray impact in starburst environments., Comment: 12 pages and 5 figures

Context. The galactic winds of starburst galaxies (SBGs) give rise to remarkable structures on kiloparsec scales. However, the evolution and shape of these giant wind bubbles, as well as the properties of the shocks they develop, are not yet fully understood. Aims. We aim to understand what shapes the galactic winds of SBGs, with a particular focus on the role of large-scale magnetic fields in the dynamical evolution of galactic wind-inflated bubbles. In addition, we aim to explore where the conditions for efficient particle acceleration are met in these systems. Methods. We performed magnetohydrodynamic simulations with the AMRVAC code (Adaptive Mesh Refinement Versatile Advection Code) with various configurations of the galactic medium density profile and magnetization. Results. We observe that the large-scale magnetic field, in which galactic winds expand, can impact the structure and evolution of inflated bubbles. However, the typical structures observed in starburst galaxies, such as M82, cannot be solely explained by the magnetic field structures that have been considered. This highlights the importance of other factors, such as the galactic disk, in shaping the galactic bubble. Furthermore, in all the magnetized cases we investigated, the forward wave resulting from the expanding bubbles only results in compression waves, whereas the wind termination shock features high Mach numbers, making it a promising site for diffusive shock acceleration up to $\sim 10^{2}$ PeV. The synthetic X-ray images generated from our models reveal an envelope surrounding the bubbles that extends up to 2 kpc, which could correspond to the polarized emission observed from planar geometry in M82, as well as a large structure inside the bubble corresponding to the shocked galactic wind., Comment: 17 pages

The presence of live $^{60}$Fe nuclei (lifetime of 3.8~Myr) in cosmic rays detected by the ACE/CRIS instrument suggests a nearby nucleosynthesis source. $^{60}$Fe is primarily produced in core-collapse supernovae, and we aim to clarify whether the detected $^{60}$Fe nuclei can be associated with a particular local supernova. We consider 25 OB associations and sub-groups located within 1 kpc of the solar system based on recent $Gaia$ census. A model is developed that combines stellar population synthesis within these OB associations, cosmic-ray acceleration within associated superbubbles, and cosmic-ray transport to the solar system. The most critical model parameter impacting $^{60}$Fe cosmic-ray production is the explodability criterion, which determines if a massive star ends its life as a supernova. Our study points to the Sco-Cen OB association as the most probable origin of the observed $^{60}$Fe nuclei, particularly suggesting they were accelerated in the Sco-Cen superbubble by a young supernova aged $\leq500$ kyr with a progenitor mass of approximately $13-20~M_\odot$. A less likely source is the supernova at the origin of the Geminga pulsar 342 kyr ago, if the progenitor originated in the Orion OB1 association. The contribution of local OB associations to the cosmic-ray density of stable $^{56}$Fe is estimated to be around 20\%, with some sensitivity to cosmic ray acceleration efficiency and diffusion coefficient. These findings shed light on the origins of cosmic-ray nuclei, connecting them to nucleosynthesis events within our local cosmic neighborhood.

Laser technologies improved after the understanding of the Chirped Pulse Amplification (CPA) which allows energetic laser beams to be compressed to tens of femtosecond (fs) pulse durations and focused to few $\mu$m. Protons of tens of MeV can be accelerated using for instance the Target Normal Sheath Acceleration (TNSA) method and focused on secondary targets. In such conditions, nuclear reactions can occur and radioisotopes relevant for medical purposes be produced. High repetition lasers can be used to produce enough isotopes for medical applications. This route is competitive to conventional methods mostly based on accelerators. In this paper we study the production of $^{67}$Cu, $^{63}$Zn, $^{18}$F and $^{11}$C currently used in positron emission tomography (PET) and other applications. At the same time, we study the reaction $^{10}$B(p,$\alpha$)$^{7}$Be and $^{70}$Zn(p,4n)$^{67}$Ga to put further constraints to the proton distributions at different angles and to the reaction $^{11}$B(p,$\alpha$)$^{8}$Be relevant for energy production. The experiment was performed at the 1 petawatt (PW) laser facility at Vega III located in Salamanca-Spain. Angular distributions of radioisotopes in the forward (with respect to the laser direction) and backward directions were measured using a High Purity Germanium Detector (HPGE). Our results are reasonably reproduced by the numerical estimates following the approach of Kimura et al. (NIMA637(2011)167)

Determination of fundamental parameters of stars impacts all fields of astrophysics, from galaxy evolution to constraining the internal structure of exoplanets. This paper presents a detailed spectroscopic analysis of Barnard's star that compares an exceptionally high-quality (an average signal-to-noise ratio of $\sim$1000 in the entire domain), high-resolution NIR spectrum taken with CFHT/SPIRou to PHOENIX-ACES stellar atmosphere models. The observed spectrum shows thousands of lines not identified in the models with a similar large number of lines present in the model but not in the observed data. We also identify several other caveats such as continuum mismatch, unresolved contamination and spectral lines significantly shifted from their expected wavelengths, all of these can be a source of bias for abundance determination. Out of $>10^4$ observed lines in the NIR that could be used for chemical spectroscopy, we identify a short list of a few hundred lines that are reliable. We present a novel method for determining the effective temperature and overall metallicity of slowly-rotating M dwarfs that uses several groups of lines as opposed to bulk spectral fitting methods. With this method, we infer $T_{eff}$ = 3231 $\pm$ 21 K for Barnard's star, consistent with the value of 3238 $\pm$ 11 K inferred from the interferometric method. We also provide abundance measurements of 15 different elements for Barnard's star, including the abundances of four elements (K, O, Y, Th) never reported before for this star. This work emphasizes the need to improve current atmosphere models to fully exploit the NIR domain for chemical spectroscopy analysis., Comment: 29 pages, 23 figures, accepted for publication in ApJ

We present the results of an analysis aimed at probing the small-scale magnetic fields of M dwarfs observed with SPIRou, the nIR high-resolution spectro-polarimeter installed at the Canada-France-Hawaii Telescope, in the context of the SPIRou Legacy Survey. Our analysis relies on high-resolution median spectra built from several tens of spectra recorded between 2019 and 2022, and on synthetic spectra computed with the ZeeTurbo code for various combination of atmospheric parameters and magnetic field strengths. We pursue the efforts undertaken in a previous study and focus on 44 weakly to moderately active M dwarfs. We derive average magnetic field strengths (<$B$>) ranging from 0.05 to 1.15 kG, in good agreement with activity estimates and rotation periods. We found that including magnetic fields in our models has virtually no impact on our derived atmospheric parameters, and that a priori assumptions on the stellar surface gravity can affect our estimated <$B$>. Our results suggest that small-scale magnetic fields account for more than 70% of the overall average magnetic field for most targets whose large-scale fields were previously measured. We derived low magnetic fluxes for several targets in our sample, and found no clear evidence that <$B$> decreases with increasing Rossby number in the unsaturated dynamo regime. We even identified counterexamples (GJ 1289 and GJ 1286) where the small-scale field is unusually strong despite the long rotation period. Along with similar results on the large-scale fields, our findings further suggest that dynamo processes may operate in a non-conventional mode in these strongly magnetic, slowly-rotating stars., Comment: 27 pages, 25 figures, including appendix. Accepted for publication in MNRAS

The detection of gravitational waves from a binary neutron star merger by Advanced LIGO and Advanced Virgo (GW170817), along with the discovery of the electromagnetic counterparts of this gravitational wave event, ushered in a new era of multimessenger astronomy, providing the first direct evidence that BNS mergers are progenitors of short gamma-ray bursts (GRBs). Such events may also produce very-high-energy (VHE, > 100GeV) photons which have yet to be detected in coincidence with a gravitational wave signal. The Cherenkov Telescope Array (CTA) is a next-generation VHE observatory which aims to be indispensable in this search, with an unparalleled sensitivity and ability to slew anywhere on the sky within a few tens of seconds. New observing modes and follow-up strategies are being developed for CTA to rapidly cover localization areas of gravitational wave events that are typically larger than the CTA field of view. This work will evaluate and provide estimations on the expected number of of gravitational wave events that will be observable with CTA, considering both on- and off-axis emission. In addition, we will present and discuss the prospects of potential follow-up strategies with CTA., Comment: Presented at the 38th International Cosmic Ray Conference (ICRC 2023), 2023 (arXiv:2309.08219)

We report results of a spectropolarimetric monitoring of the young Sun-like star V1298~Tau based on data collected with the near-infrared spectropolarimeter SPIRou at the Canada-France-Hawaii Telescope between late 2019 and early 2023. Using Zeeman-Doppler Imaging and the Time-dependent Imaging of Magnetic Stars methods on circularly polarized spectra, we reconstructed the large-scale magnetic topology of the star (and its temporal evolution), found to be mainly poloidal and axisymmetric with an average strength varying from 90 to 170 G over the ~3.5 years of monitoring. The magnetic field features a dipole whose strength evolves from 85 to 245 G, and whose inclination with respect to the stellar rotation axis remains stable until 2023 where we observe a sudden change, suggesting that the field may undergo a polarity reversal, potentially similar to those periodically experienced by the Sun. Our data suggest that the differential rotation shearing the surface of V1298 Tau is about 1.5 times stronger than that of the Sun. When coupling our data with previous photometric results from K2 and TESS and assuming circular orbits for all four planets, we report a $3.9\sigma$ detection of the radial velocity signature of the outermost planet (e), associated with a most probable mass, density and orbital period of $M_e=0.95^{+0.33}_{-0.24} \ \rm M_{\rm jup}$, $\rho_e=1.66^{+0.61}_{-0.48}$ $\rm g\,cm^{-3}$ and $P_e=53.0039\pm0.0001 \ \rm d$, respectively. For the 3 inner planets, we only derive 99\% confidence upper limits on their mass of $0.44\ \rm M_{\rm jup}$, $0.22\ \rm M_{\rm jup}$ and $0.25\ \rm M_{\rm jup}$, for b, c and d, respectively., Comment: 45 pages, 28 figures, accepted for publication in MNRAS

A major endeavor of this decade is the direct characterization of young giant exoplanets at high spectral resolution to determine the composition of their atmosphere and infer their formation processes and evolution. Such a goal represents a major challenge owing to their small angular separation and luminosity contrast with respect to their parent stars. Instead of designing and implementing completely new facilities, it has been proposed to leverage the capabilities of existing instruments that offer either high contrast imaging or high dispersion spectroscopy, by coupling them using optical fibers. In this work we present the implementation and first on-sky results of the HiRISE instrument at the very large telescope (VLT), which combines the exoplanet imager SPHERE with the recently upgraded high resolution spectrograph CRIRES using single-mode fibers. The goal of HiRISE is to enable the characterization of known companions in the $H$ band, at a spectral resolution of the order of $R = \lambda/\Delta\lambda = 100\,000$, in a few hours of observing time. We present the main design choices and the technical implementation of the system, which is constituted of three major parts: the fiber injection module inside of SPHERE, the fiber bundle around the telescope, and the fiber extraction module at the entrance of CRIRES. We also detail the specific calibrations required for HiRISE and the operations of the instrument for science observations. Finally, we detail the performance of the system in terms of astrometry, temporal stability, optical aberrations, and transmission, for which we report a peak value of $\sim$3.9% based on sky measurements in median observing conditions. Finally, we report on the first astrophysical detection of HiRISE to illustrate its potential., Comment: 17 pages, 15 figures, 3 tables. Accepted in A&A on 24 October 2023

Galaxy clusters are expected to be dark matter (DM) reservoirs and storage rooms for the cosmic-ray protons (CRp) that accumulate along the cluster's formation history. Accordingly, they are excellent targets to search for signals of DM annihilation and decay at gamma-ray energies and are predicted to be sources of large-scale gamma-ray emission due to hadronic interactions in the intracluster medium. We estimate the sensitivity of the Cherenkov Telescope Array (CTA) to detect diffuse gamma-ray emission from the Perseus galaxy cluster. We perform a detailed spatial and spectral modelling of the expected signal for the DM and the CRp components. For each, we compute the expected CTA sensitivity. The observing strategy of Perseus is also discussed. In the absence of a diffuse signal (non-detection), CTA should constrain the CRp to thermal energy ratio within the radius $R_{500}$ down to about $X_{500}<3\times 10^{-3}$, for a spatial CRp distribution that follows the thermal gas and a CRp spectral index $\alpha_{\rm CRp}=2.3$. Under the optimistic assumption of a pure hadronic origin of the Perseus radio mini-halo and depending on the assumed magnetic field profile, CTA should measure $\alpha_{\rm CRp}$ down to about $\Delta\alpha_{\rm CRp}\simeq 0.1$ and the CRp spatial distribution with 10% precision. Regarding DM, CTA should improve the current ground-based gamma-ray DM limits from clusters observations on the velocity-averaged annihilation cross-section by a factor of up to $\sim 5$, depending on the modelling of DM halo substructure. In the case of decay of DM particles, CTA will explore a new region of the parameter space, reaching models with $\tau_{\chi}>10^{27}$s for DM masses above 1 TeV. These constraints will provide unprecedented sensitivity to the physics of both CRp acceleration and transport at cluster scale and to TeV DM particle models, especially in the decay scenario., Comment: 93 pages (including author list, appendix and references), 143 figures. Submitted to JCAP

SNRs are likely to be significant sources of Galactic cosmic rays up to the knee. They produce gamma rays in the very-high-energy (E>100 GeV) range mainly via two mechanisms: hadronic interactions of accelerated protons with the interstellar medium and leptonic interactions of accelerated electrons with soft photons. Observations with current instruments have lead to the detection of about a dozen SNRs in VHE gamma rays and future instruments will help significantly increase this number. Yet, the details of particle acceleration at SNRs, and of the mechanisms producing VHE gamma-ray at SNRs remain poorly understood: What is the spectrum of accelerated particles? What is the efficiency of particle acceleration? Is the gamma-ray emission dominated by hadronic or leptonic origin? To address these questions, we simulate the population of SNRs in the gamma-ray domain, and confront it to the current population of TeV SNRs. This method allows us to investigate several crucial aspects of particle acceleration at SNRs, such as the level of magnetic field around SNR shocks or scanning the parameter space of the accelerated particles (spectral index, electron to proton ratio and the acceleration efficiency of the shock) with the possibility to constrain some of the parameters., Comment: 8 pages, 5 figures, Proceedings for the 38th International Cosmic Ray Conference (ICRC2023)

We present near-infrared spectropolarimetric observations of a sample of 43 weakly- to moderately-active M dwarfs, carried with SPIRou at the Canada-France-Hawaii Telescope in the framework of the SPIRou Legacy Survey from early 2019 to mid 2022. We use the 6700 circularly polarised spectra collected for this sample to investigate the longitudinal magnetic field and its temporal variations for all sample stars, from which we diagnose, through quasi-periodic Gaussian process regression, the periodic modulation and longer-term fluctuations of the longitudinal field. We detect the large-scale field for 40 of our 43 sample stars, and infer a reliable or tentative rotation period for 38 of them, using a Bayesian framework to diagnose the confidence level at which each rotation period is detected. We find rotation periods ranging from 14 to over 60d for the early-M dwarfs, and from 70 to 200d for most mid- and late-M dwarfs (potentially up to 430d for one of them). We also find that the strength of the detected large-scale fields does not decrease with increasing period or Rossby number for the slowly rotating dwarfs of our sample as it does for higher-mass, more active stars, suggesting that these magnetic fields may be generated through a different dynamo regime than those of more rapidly rotating stars. We also show that the large-scale fields of most sample stars evolve on long timescales, with some of them globally switching sign as stars progress on their putative magnetic cycles., Comment: MNRAS, in press (25 pages, 15 figures, 3 tables)

Clustering (or community detection) on multilayer graphs poses several additional complications with respect to standard graphs as different layers may be characterized by different structures and types of information. One of the major challenges is to establish the extent to which each layer contributes to the cluster assignment in order to effectively take advantage of the multilayer structure and improve upon the classification obtained using the individual layers or their union. However, making an informed a-priori assessment about the clustering information content of the layers can be very complicated. In this work, we assume a semi-supervised learning setting, where the class of a small percentage of nodes is initially provided, and we propose a parameter-free Laplacian-regularized model that learns an optimal nonlinear combination of the different layers from the available input labels. The learning algorithm is based on a Frank-Wolfe optimization scheme with inexact gradient, combined with a modified Label Propagation iteration. We provide a detailed convergence analysis of the algorithm and extensive experiments on synthetic and real-world datasets, showing that the proposed method compares favourably with a variety of baselines and outperforms each individual layer when used in isolation.

Context: Recent advances in the development of precise radial velocity (RV) instruments in the near-infrared (nIR) domain, such as SPIRou, have facilitated the study of M-type stars to more effectively characterize planetary systems. However, the nIR presents unique challenges in exoplanet detection due to various sources of planet-independent signals which can result in systematic errors in the RV data. Aims: In order to address the challenges posed by the detection of exoplanetary systems around M-type stars using nIR observations, we introduce a new data-driven approach for correcting systematic errors in RV data. The effectiveness of this method is demonstrated through its application to the star GJ 251. Methods: Our proposed method, referred to as $\texttt{Wapiti}$ (Weighted principAl comPonent analysIs reconsTructIon), uses a dataset of per-line RV time-series generated by the line-by-line (LBL) algorithm and employs a weighted principal component analysis (wPCA) to reconstruct the original RV time-series. A multi-step process is employed to determine the appropriate number of components, with the ultimate goal of subtracting the wPCA reconstruction of the per-line RV time-series from the original data in order to correct systematic errors. Results: The application of $\texttt{Wapiti}$ to GJ 251 successfully eliminates spurious signals from the RV time-series and enables the first detection in the nIR of GJ 251b, a known temperate super-Earth with an orbital period of 14.2 days. This demonstrates that, even when systematics in SPIRou data are unidentified, it is still possible to effectively address them and fully realize the instrument's capability for exoplanet detection. Additionally, in contrast to the use of optical RVs, this detection did not require to filter out stellar activity, highlighting a key advantage of nIR RV measurements., Comment: Submitted to A&A. For the publicly available Wapiti code, see https://github.com/HkmMerwan/wapiti

In this paper we present an analysis of near-infrared spectropolarimetric and velocimetric data of the young M dwarf AU Mic, collected with SPIRou at the Canada-France-Hawaii telescope from 2019 to 2022, mostly within the SPIRou Legacy Survey. With these data, we study the large- and small-scale magnetic field of AU Mic, detected through the unpolarized and circularly-polarized Zeeman signatures of spectral lines. We find that both are modulated with the stellar rotation period (4.86 d), and evolve on a timescale of months under differential rotation and intrinsic variability. The small-scale field, estimated from the broadening of spectral lines, reaches $2.61\pm0.05$ kG. The large-scale field, inferred with Zeeman-Doppler imaging from Least-Squares Deconvolved profiles of circularly-polarized and unpolarized spectral lines, is mostly poloidal and axisymmetric, with an average intensity of $550\pm30$ G. We also find that surface differential rotation, as derived from the large-scale field, is $\simeq$30% weaker than that of the Sun. We detect the radial velocity (RV) signatures of transiting planets b and c, although dwarfed by activity, and put an upper limit on that of candidate planet d, putatively causing the transit-timing variations of b and c. We also report the detection of the RV signature of a new candidate planet (e) orbiting further out with a period of $33.39\pm0.10$ d, i.e., near the 4:1 resonance with b. The RV signature of e is detected at 6.5$\sigma$ while those of b and c show up at $\simeq$4$\sigma$, yielding masses of $10.2^{+3.9}_{-2.7}$ and $14.2^{+4.8}_{-3.5}$ Earth masses for b and c, and a minimum mass of $35.2^{+6.7}_{-5.4}$ Earth masses for e., Comment: MNRAS, in press (20 pages and 12 figures + 9 pages of supplementary material)

The local Cosmic Ray (CR) energy spectrum exhibits a spectral softening at energies around 3~PeV. Sources which are capable of accelerating hadrons to such energies are called hadronic PeVatrons. However, hadronic PeVatrons have not yet been firmly identified within the Galaxy. Several source classes, including Galactic Supernova Remnants (SNRs), have been proposed as PeVatron candidates. The potential to search for hadronic PeVatrons with the Cherenkov Telescope Array (CTA) is assessed. The focus is on the usage of very high energy $\gamma$-ray spectral signatures for the identification of PeVatrons. Assuming that SNRs can accelerate CRs up to knee energies, the number of Galactic SNRs which can be identified as PeVatrons with CTA is estimated within a model for the evolution of SNRs. Additionally, the potential of a follow-up observation strategy under moonlight conditions for PeVatron searches is investigated. Statistical methods for the identification of PeVatrons are introduced, and realistic Monte--Carlo simulations of the response of the CTA observatory to the emission spectra from hadronic PeVatrons are performed. Based on simulations of a simplified model for the evolution for SNRs, the detection of a $\gamma$-ray signal from in average 9 Galactic PeVatron SNRs is expected to result from the scan of the Galactic plane with CTA after 10 hours of exposure. CTA is also shown to have excellent potential to confirm these sources as PeVatrons in deep observations with $\mathcal{O}(100)$ hours of exposure per source., Comment: 34 pages, 16 figures, Accepted for publication in Astroparticle Physics

We report first results on a method aimed at simultaneously characterising atmospheric parameters and magnetic properties of M dwarfs from high-resolution nIR spectra recorded with SPIRou in the framework of the SPIRou Legacy Survey. Our analysis relies on fitting synthetic spectra computed from MARCS model atmospheres to selected spectral lines, both sensitive and insensitive to magnetic fields. We introduce a new code, $\texttt{ZeeTurbo}$, obtained by including the Zeeman effect and polarised radiative transfer capabilities to $\texttt{Turbospectrum}$. We compute a grid of synthetic spectra with $\texttt{ZeeTurbo}$ for different magnetic field strengths and develop a process to simultaneously constrain $T_{\rm eff}$, $\log{g}$, [M/H], [$\alpha$/Fe] and the average surface magnetic flux. In this paper, we present our approach and assess its performance using simulations, before applying it to six targets observed in the context of the SPIRou Legacy Survey (SLS), namely AU Mic, EV Lac, AD Leo, CN Leo, PM J18482+0741, and DS Leo. Our method allows us to retrieve atmospheric parameters in good agreement with the literature, and simultaneously yields surface magnetic fluxes in the range 2-4 kG with a typical precision of 0.05 kG, in agreement with literature estimates, and consistent with the saturated dynamo regime in which most of these stars are., Comment: 17 pages plus supplementary material. Accepted for publication in MNRAS

Context. The rotation period of stars is an important parameter along with mass, radius, effective temperature. It is an essential parameter for any radial velocity monitoring, as stellar activity can mimic the presence of a planet at the stellar rotation period. Several methods exist to measure it, including long sequences of photometric measurements or temporal series of stellar activity indicators. Aims. Here, we use the circular polarization in near-infrared spectral lines for a sample of 43 quiet M dwarfs and compare the measured rotation periods to those obtained with other methods. Methods. From Stokes V spectropolarimetric sequences observed with SPIRou at CFHT and the data processed with the APERO pipeline, we compute the least squares deconvolution profiles using different masks of atomic stellar lines with known Land\'e factor appropriate to the effective temperature of the star. We derive the longitudinal magnetic field to examine its possible variation along the 50 to 200 observations of each star. For determining the stellar rotation period, we apply a Gaussian process regression enabling us to determine the rotation period of stars with evolving longitudinal field. Results. Among the 43 stars of our sample, we were able to measure a rotation period for 27 stars. For 8 stars, the rotation period was previously unknown. We find a good agreement of our rotation periods with periods found in the literature based on photometry and activity indicators and confirm that near-infrared spectropolarimetry is an important tool to measure rotation periods, even for magnetically quiet stars. Furthermore, we compute ages for 20 stars of our sample using gyrochronology.

Active galactic nuclei (AGN) can launch and sustain powerful winds featuring mildly relativistic velocity and wide opening angle. Such winds, known as ultra-fast outflows (UFOs), can develop a bubble structure characterized by a forward shock expanding in the host galaxy and a wind termination shock separating the fast cool wind from the hot shocked wind. In this work we explore whether diffusive shock acceleration can take place efficiently at the wind termination shock of UFOs. We calculate the spectrum of accelerated particles and find that protons can be energized up to the EeV range promoting UFOs to promising candidates for accelerating ultra-high energy cosmic rays (UHECRs). We also compute the associated gamma-ray and neutrino fluxes and compare them with available data in the literature. We observe that high-energy (HE) neutrinos are efficiently produced up to hundreds of PeV while the associated gamma rays could be efficiently absorbed beyond a few tens of GeV by the optical-ultraviolet AGN photon field. By assuming a typical source density of non-jetted AGN we expect that UFOs could play a dominant role as diffuse sources of UHECRs and HE neutrinos. We finally apply our model to the recently observed NGC1068 and we find out that under specific parametric conditions an obscured UFO could provide a sizeable contribution to the observed gamma-ray flux while only contributing up to ~10 per cent to the associated neutrino flux., Comment: 12 pages, 6 figures, 2 tables; submitted to MNRAS; matching version published in MNRAS

Graph Semi-Supervised learning is an important data analysis tool, where given a graph and a set of labeled nodes, the aim is to infer the labels to the remaining unlabeled nodes. In this paper, we start by considering an optimization-based formulation of the problem for an undirected graph, and then we extend this formulation to multilayer hypergraphs. We solve the problem using different coordinate descent approaches and compare the results with the ones obtained by the classic gradient descent method. Experiments on synthetic and real-world datasets show the potential of using coordinate descent methods with suitable selection rules., Comment: 24 pages, 10 figures

The stellar activity of M dwarfs is the main limitation for discovering and characterizing exoplanets orbiting them since it induces quasi-periodic RV variations. We aim to characterize the magnetic field and stellar activity of the early, moderately active, M dwarf Gl205 in the optical and nIR domains. We obtained high-precision quasi-simultaneous spectra in the optical and nIR with the SOPHIE spectrograph and SPIRou spectropolarimeter between 2019 and 2022. We computed the RVs from both instruments and the SPIRou Stokes V profiles. We used ZDI to map the large-scale magnetic field over the time span of the observations. We studied the temporal behavior of optical and nIR RVs and activity indicators with the Lomb-Scargle periodogram and a quasi-periodic GP regression. In the nIR, we studied the equivalent width of Al I, Ti I, K I, Fe I, and He I. We modeled the activity-induced RV jitter using a multi-dimensional GP regression with activity indicators as ancillary time series. The optical and nIR RVs have similar scatter but nIR shows a more complex temporal evolution. We observe an evolution of the magnetic field topology from a poloidal dipolar field in 2019 to a dominantly toroidal field in 2022. We measured a stellar rotation period of Prot=34.4$\pm$0.5 d in the longitudinal magnetic field. Using ZDI we measure the amount of latitudinal differential rotation (DR) shearing the stellar surface yielding rotation periods of Peq=32.0$\pm$1.8 d at the stellar equator and Ppol=45.5$\pm$0.3 d at the poles. We observed inconsistencies in the activity indicators' periodicities that could be explained by these DR values. The multi-dimensional GP modeling yields an RMS of the RV residuals down to the noise level of 3 m/s for both instruments, using as ancillary time series H$\alpha$ and the BIS in the optical, and the FWHM in the nIR., Comment: 41 pages, 24 figures. Accepted for publication in A&A. Improved quality of figures and reduced size of Appendix

TOI-1695 is a V-mag=13 M-dwarf star from the northern hemisphere at 45$\,$pc from the Sun, around which a 3.134-day periodic transit signal from a super-Earth candidate was identified in TESS photometry. With a transit depth of 1.3$\,$mmag, the radius of candidate TOI-1695.01 was estimated by the TESS pipeline to be 1.82$\,$R$_\oplus$ with an equilibrium temperature of $\sim 620\,$K. We successfully detect a reflex motion of the star and establish it is due to a planetary companion at an orbital period consistent with the photometric transit period thanks to a year-long radial-velocity monitoring of TOI-1695 by the SPIRou infrared spectropolarimeter. We use and compare different methods to reduce and analyse those data. We report a 5.5-$\sigma$ detection of the planetary signal, giving a mass of $5.5 \pm 1.0\,$M$_\oplus$ and a radius of $2.03 \pm 0.18\,$R$_\oplus$. We derive a mean equilibrium planet temperature of $590 \pm 90\,$K. The mean density of this small planet of $3.6 \pm 1.1\,$g$\,$cm$^{-3}$ is similar (1.7-$\sigma$ lower) than that of the Earth. It leads to a non-negligible fraction of volatiles in its atmosphere with $f_{H,He}=0.28^{+0.46}_{-0.23}$% or $f_\text{water}=23 \pm 12$%. TOI-1695$\,$b is a new sub-Neptune planet at the border of the M-dwarf radius valley that can help test formation scenarios for super-Earth/sub-Neptune-like planets., Comment: 15 pages (+9 appendix pages), 19 figures, 8 tables, accepted for publication in A&A

Striatal cholinergic interneurons (CINs) use acetylcholine (ACh) and glutamate (Glut) to regulate the striatal network since they express vesicular transporters for ACh (VAChT) and Glut (VGLUT3). However, whether ACh and Glut are released simultaneously and/or independently from cholinergic varicosities is an open question. The answer to that question requires the multichannel detection of vesicular transporters at the level of single synaptic vesicle (SV). Here, we used super-resolution STimulated Emission Depletion microscopy (STED) to characterize and quantify the distribution of VAChT and VGLUT3 in CINs SVs. Nearest-neighbor distances analysis between VAChT and VGLUT3-immunofluorescent spots revealed that 34% of CINs SVs contain both VAChT and VGLUT3. In addition, 40% of SVs expressed only VAChT while 26% of SVs contain only VGLUT3. These results suggest that SVs from CINs have the potential to store simultaneously or independently ACh and/or Glut. Overall, these morphological findings support the notion that CINs varicosities can signal with either ACh or Glut or both with an unexpected level of complexity.

MAXI J1820+070 is a low-mass X-ray binary with a black hole as a compact object. This binary underwent an exceptionally bright X-ray outburst from March to October 2018, showing evidence of a non-thermal particle population through its radio emission during this whole period. The combined results of 59.5 hours of observations of the MAXI J1820+070 outburst with the H.E.S.S., MAGIC and VERITAS experiments at energies above 200 GeV are presented, together with Fermi-LAT data between 0.1 and 500 GeV, and multiwavelength observations from radio to X-rays. Gamma-ray emission is not detected from MAXI J1820+070, but the obtained upper limits and the multiwavelength data allow us to put meaningful constraints on the source properties under reasonable assumptions regarding the non-thermal particle population and the jet synchrotron spectrum. In particular, it is possible to show that, if a high-energy gamma-ray emitting region is present during the hard state of the source, its predicted flux should be at most a factor of 20 below the obtained Fermi-LAT upper limits, and closer to them for magnetic fields significantly below equipartition. During the state transitions, under the plausible assumption that electrons are accelerated up to ~ 500 GeV, the multiwavelength data and the gamma-ray upper limits lead consistently to the conclusion that a potential high-energy and very-high-energy gamma-ray emitting region should be located at a distance from the black hole ranging between 10^11 and 10^13 cm. Similar outbursts from low-mass X-ray binaries might be detectable in the near future with upcoming instruments such as CTA., Comment: 15 pages, 5 figures. Accepted for publication in MNRAS

We describe advances on a method designed to derive accurate parameters of M dwarfs. Our analysis consists in comparing high-resolution infrared spectra acquired with the near-infrared spectro-polarimeter SPIRou to synthetic spectra computed from MARCS model atmospheres, in order to derive the effective temperature ($T_{\rm eff}$), surface gravity ($\rm \log{g}$), metallicity ([M/H]) and alpha-enhancement ($\rm [\alpha/Fe]$) of 44 M dwarfs monitored within the SPIRou Legacy Survey (SLS). Relying on 12 of these stars, we calibrated our method by refining our selection of well modelled stellar lines, and adjusted the line list parameters to improve the fit when necessary. Our retrieved $T_{\rm eff}$, $\rm \log{g}$ and [M/H] are in good agreement with literature values, with dispersions of the order of 50 K in $T_{\rm eff}$ and 0.1 dex in $\rm \log{g}$ and [M/H]. We report that fitting $\rm [\alpha/Fe]$ has an impact on the derivation of the other stellar parameters, motivating us to extend our fitting procedure to this additional parameter. We find that our retrieved $\rm [\alpha/Fe]$ are compatible with those expected from empirical relations derived in other studies., Comment: 13 pages, 9 figures + appendix and supplementary material; accepted for publication in MNRAS

Young massive stellar clusters are extreme environments and potentially provide the means for efficient particle acceleration. Indeed, they are increasingly considered as being responsible for a significant fraction of cosmic rays (CRs) accelerated within the Milky Way. Westerlund 1, the most massive known young stellar cluster in our Galaxy is a prime candidate for studying this hypothesis. While the very-high-energy $\gamma$-ray source HESS J1646-458 has been detected in the vicinity of Westerlund 1 in the past, its association could not be firmly identified. We aim to identify the physical processes responsible for the $\gamma$-ray emission around Westerlund 1 and thus to better understand the role of massive stellar clusters in the acceleration of Galactic CRs. Using 164 hours of data recorded with the High Energy Stereoscopic System (H.E.S.S.), we carried out a deep spectromorphological study of the $\gamma$-ray emission of HESS J1646-458. We furthermore employed H I and CO observations of the region to infer the presence of gas that could serve as target material for interactions of accelerated CRs. We detected large-scale ($\sim 2^\circ$ diameter) $\gamma$-ray emission with a complex morphology, exhibiting a shell-like structure and showing no significant variation with $\gamma$-ray energy. The combined energy spectrum of the emission extends to several tens of TeV, and is uniform across the entire source region. We did not find a clear correlation of the $\gamma$-ray emission with gas clouds as identified through H I and CO observations. We conclude that, of the known objects within the region, only Westerlund 1 can explain the bulk of the $\gamma$-ray emission. Several CR acceleration sites and mechanisms are conceivable, and discussed in detail. (abridged), Comment: 15 pages, 9 figures. Corresponding authors: L. Mohrmann, S. Ohm, R. Rauth, A. Specovius. v2: corrected affiliation of M. Vecchi (still incorrect in journal version)

In this paper, we consider lasso problems with zero-sum constraint, commonly required for the analysis of compositional data in high-dimensional spaces. A novel algorithm is proposed to solve these problems, combining a tailored active-set technique, to identify the zero variables in the optimal solution, with a 2-coordinate descent scheme. At every iteration, the algorithm chooses between two different strategies: the first one requires to compute the whole gradient of the smooth term of the objective function and is more accurate in the active-set estimate, while the second one only uses partial derivatives and is computationally more efficient. Global convergence to optimal solutions is proved and numerical results are provided on synthetic and real datasets, showing the effectiveness of the proposed method. The software is publicly available.

Diffusive shock acceleration at collisionless shocks remains the most likely process for accelerating particles in a variety of astrophysical sources. While the standard prediction for strong shocks is that the spectrum of accelerated particles is universal, $f(p)\propto p^{-4}$, numerous phenomena affect this simple conclusion. In general, the non-linear dynamical reaction of accelerated particles leads to a concave spectrum, steeper than $p^{-4}$ at momenta below a few tens of GeV/c and harder than the standard prediction at high energies. However, the non-linear effects become important in the presence of magnetic field amplification, which in turn leads to higher values of the maximum momentum $p_{max}$. It was recently discovered that the self-generated perturbations that enhance particle scattering, when advected downstream, move in the same direction as the background plasma, so that the effective compression factor at the shock decreases and the spectrum becomes steeper. We investigate the implications of the excitation of the non-resonant streaming instability on these spectral deformations, the dependence of the spectral steepening on the shock velocity and the role played by the injection momentum., Comment: 11 pages, 6 figures, accepted for publication in ApJ

We report the detection and characterization of the transiting sub-Neptune TOI-1759 b, using photometric time-series from TESS and near infrared spectropolarimetric data from SPIRou on the CFHT. TOI-1759 b orbits a moderately active M0V star with an orbital period of $18.849975\pm0.000006$ d, and we measure a planetary radius and mass of $3.06\pm0.22$ R$_\oplus$ and $6.8\pm2.0$ M$_\oplus$. Radial velocities were extracted from the SPIRou spectra using both the CCF and the LBL methods, optimizing the velocity measurements in the near infrared domain. We analyzed the broadband SED of the star and the high-resolution SPIRou spectra to constrain the stellar parameters and thus improve the accuracy of the derived planet parameters. A LSD analysis of the SPIRou Stokes $V$ polarized spectra detects Zeeman signatures in TOI-1759. We model the rotational modulation of the magnetic stellar activity using a GP regression with a quasi-periodic covariance function, and find a rotation period of $35.65^{+0.17}_{-0.15}$ d. We reconstruct the large-scale surface magnetic field of the star using ZDI, which gives a predominantly poloidal field with a mean strength of $18\pm4$ G. Finally, we perform a joint Bayesian MCMC analysis of the TESS photometry and SPIRou RVs to optimally constrain the system parameters. At $0.1176\pm0.0013$ au from the star, the planet receives $6.4$ times the bolometric flux incident on Earth, and its equilibrium temperature is estimated at $433\pm14$ K. TOI-1759 b is a likely gas-dominated sub-Neptune with an expected high rate of photoevaporation. Therefore, it is an interesting target to search for neutral hydrogen escape, which may provide important constraints on the planetary formation mechanisms responsible for the observed sub-Neptune radius desert., Comment: Accepted for publication in the 10. Planets and planetary systems section of Astronomy & Astrophysics

Type II-P supernov\ae~(SNe), the most common core-collapse SNe type, result from the explosions of red supergiant stars. Their detection in the radio domain testifies of the presence of relativistic electrons, and shows that they are potentially efficient energetic particle accelerators. If hadrons can also be accelerated, these energetic particles are expected to interact with the surrounding medium to produce a gamma-ray signal even in the multi--TeV range. The intensity of this signal depends on various factors, but an essential one is the density of the circumstellar medium. Such a signal should however be limited by electron-positron pair production arising from the interaction of the gamma-ray photons with optical photons emitted by the supernova photosphere, which can potentially degrade the gamma-ray signal by over ten orders of magnitude in the first days/weeks following the explosion. We calculate the gamma-gamma opacity from a detailed modelling of the time evolution of the forward shock and supernova photosphere, taking a full account of the non-isotropy of the photon interactions. We discuss the time-dependent gamma-ray TeV emission from type II-P SNe as a function of the stellar progenitor radius and mass-loss rate, as well as the explosion energy and mass of the ejected material. We evaluate the detectability of the SNe with the next generation of Cherenkov telescopes. We find that, while most extragalactic events may be undetectable, type II-P SNe exploding in our Galaxy or in the Magellanic Clouds should be detected by gamma-ray observatories such as the upcoming Cherenkov Telescope Array., Comment: 9 pages, 8 figures, Accepted for publication in MNRAS