Giovanni Morlino

Context. Recently, the Large High-Altitude Air Shower Observatory (LHAASO) collaboration reported ultrahigh-energy (UHE; > 100 TeV) gamma rays from five microquasars. In all five sources, the emission extends beyond 100 TeV, making microquasars promising candidates for Galactic PeVatrons. Aims. We investigated whether gamma rays around 100 TeV originate from hadronic interactions of accelerated cosmic rays with the ambient medium, and we estimated the contribution of these sources to the measured cosmic-ray proton spectrum around the knee. We also derived upper limits on the contribution from the seven additional microquasars in the LHAASO field of view, from which no UHE emission was detected. Methods. We considered a cosmic-ray transport scenario in which particle propagation in the source vicinity is diffusion-dominated, with a diffusion coefficient largely suppressed with respect to the average Galactic value, while, at large distances from the source, the diffusion coefficient matches the Galactic value. In addition, we assumed continuous injection over timescales of t _age = 0.1 − 1 Myr. Results. Using available measurements of the gas density in the emission region, we find that hadronic interactions alone cannot fully account for the observed emission for any of the detected sources. However, in the case of GRS 1915+105 and MAXI J1820+070, the hadronic scenario may still be valid when considering acceleration efficiency higher than 10%. We subsequently derived upper limits on the hadronic contribution to the observed gamma-ray flux. We estimate that the detected sources contribute at most ∼4% of the Galactic cosmic-ray spectrum at 1 PeV for an injection timescale of 0.1 Myr and a cosmic-ray acceleration efficiency of 10%. When adopting the maximum acceleration efficiency allowed by the gamma-ray observations, instead, the contribution of these microquasars to the Galactic cosmic-ray spectrum at PeV energies rises to 37%. Longer injection timescales (∼1 Myr) lead to contributions exceeding the observational constraints. For sources not detected at UHE, we obtain a maximum contribution of ∼17%, achieved assuming continuous injection over 1 Myr.

Context. Gamma-ray emission has been detected from a variety of source classes in the Galaxy, including clusters of young massive stars. RCW 38, a very young embedded massive star cluster, is of particular interest: its gamma-ray emission detected up to hundreds of GeV, provides the first observational evidence of high-energy particle acceleration powered exclusively by stellar winds. Aims. In this work, we aim to characterize the emission mechanisms responsible for the gamma-ray flux in RCW 38 and to estimate the acceleration efficiency, as well as the fraction of accelerated electrons compared to protons, K _ep . Methods. We present the most comprehensive multiwavelength study of a single star cluster to date. Our analysis ranges from megahertz radio observations obtained with the GLEAM-X survey from the Murchison Widefield Array (MWA) to GeV gamma-ray data from Fermi -LAT, and includes gigahertz and terahertz measurements from Parkes, Planck , and IRAS. We modeled the thermal and nonthermal emission of RCW 38, including synchrotron, free-free, dust, bremsstrahlung, pion-decay, and inverse Compton processes, using an eight-parameter model constrained by the Markov chain Monte Carlo method. Results. Our results support an interpretation in which hadronic interactions with the host molecular cloud produce the gamma-ray emission from RCW 38. We derive robust constraints on the electron-to-proton ratio, with K _ep < 10 ⁻² , and on the acceleration efficiency, which we estimate to be ≳1%. These results are consistent with those required to explain the cosmic-ray composition, particularly its ²² Ne anomaly. Conclusions. These results strengthen the idea that stellar clusters significantly contribute to cosmic-ray protons in our Galaxy, at least up to energies of a few TeV. Future investigations with the next generation of ground-based detectors will determine whether stellar clusters also play a relevant role at higher energies, particularly in the context of the cosmic-ray knee.

Context. Growing observational evidence suggests that subrelativistic astrophysical jets may accelerate particles at slowly evolving standing shocks. Recollimation shocks are expected to develop when jets expand in dense environments; their formation may be mediated by the pressure of the cocoon surrounding the jet, while remaining compatible with a quasi-stationary behavior. Despite their high inclination relative to the jet axis, such shocks can be strong and can enable efficient particle acceleration. Aims. The aim of this work is to improve the general understanding of particle acceleration via diffusive shock acceleration at recollimation shocks by developing a versatile modeling framework applicable to different classes of astrophysical jets, including Seyfert galaxies, microquasars, and protostellar systems. Methods. We extended an analytic jet hydrodynamics model previously introduced in the literature to the subrelativistic regime and used it to identify the expected locations of the recollimation shock and the jet head. Within this framework, we formulated a semi-analytic acceleration and transport model for particles injected at the recollimation shock via diffusive shock acceleration. Results. By solving the space-dependent transport equation, we obtained particle distributions and spectra along the jet, as well as robust predictions for the maximum energies achievable as a function of the intrinsic properties of the system and the source class. Conclusions. Our results indicate that recollimation shocks may play a central role in particle acceleration in subrelativistic jets. In Seyfert galaxies such shocks may accelerate particles from PeV up to EeV energies, while in microquasars and protostellar jets maximum energies of respectively tens of PeV and up to TeV energies are expected. While leptonic emission may be associated with bright knots along the jet, accelerated protons are expected to escape the jet and interact with the surrounding cocoon. Depending on the properties of the system, proton interactions can give rise to extended hadronic emission morphologies.

Young and massive stellar clusters are a potential source of galactic cosmic rays due to at least two acceleration mechanisms. Collective stellar winds from massive stars form a wind-blown bubble with a termination shock at which particle acceleration to PeV energies may be achieved. Furthermore, shock acceleration may occur at supernova remnants (SNRs) expanding inside the bubble. We apply a model of cosmic-ray acceleration at both the collective wind termination shock and SNR shocks to the catalog of known stellar clusters derived from the Gaia DR2. Predictions for the secondary fluxes of γ -ray and neutrino emission are derived based on hadro-nuclear interactions with the surrounding medium. We compare our modeling under baseline and optimistic scenarios to available data, finding consistent results. An anticipated flux range is provided for a shortlist of the most promising stellar clusters. Approximately 10 clusters may be detectable with future facilities, and one to three could be currently operating as PeVatrons. Among these, data from three γ -ray detected clusters can be consistently described by our model. Several further as-yet-undetected stellar clusters offer promising targets for future γ -ray observations, although the flux range allowed by our model can be broad (≳ factor 10). The large angular size of the wind-blown bubble may pose a challenge, leading to low surface brightness emission, thus exacerbating the problem of source confusion. Nevertheless, we discuss how further work will help to constrain stellar clusters as PeVatron candidates.

Background: Zoonotic spillover events with pandemic potential are increasingly associated with environmental change, ecosystem disruption, and intensified human–animal interactions. Although the specific origin and timing of future pandemics remain uncertain, there is a clear need to complement traditional preparedness strategies with approaches that support earlier anticipation and prevention. Objectives: This study aims to propose a conceptual approach to reframe pandemic preparedness toward proactive surveillance and spillover prevention. Methods: We introduce a tachyon-inspired conceptual approach, using a thought experiment based on hypothetical faster-than-light particles to illustrate anticipatory observation of pandemic emergence. The framework is informed by interdisciplinary literature on emerging infectious diseases, One Health surveillance, predictive epidemiology, and public-health preparedness. Results: The proposed approach highlights the importance of proactive, integrated surveillance systems that combine human, animal, and environmental data. Key elements include the use of advanced analytical tools such as neural networks, early characterization of population risk profiles, strengthened public-health infrastructure, coordinated governance, adaptable financial resources, and a resilient healthcare workforce. The integration of animal welfare considerations, translational research, and planetary health principles is emphasized as central to reducing spillover risk. Conclusions: Tachyon-inspired thinking offers a conceptual tool to support a shift from reactive pandemic response toward proactive anticipation and prevention. Embedding integrated surveillance and One Health principles into public-health systems may enhance early detection capacity and contribute to mitigating the impact of future pandemics.

Context. Young massive star clusters were long considered as potentially important sources of galactic cosmic rays (CRs). They have recently emerged as gamma-ray emitters up to very high energies. Aims. To quantify the contribution of these sources to Galactic CRs, we need to estimate their typical acceleration efficiency. Methods. We searched for emission in the GeV band because most of the energy is emitted in this band. We analyzed Fermi-LAT data collected toward the M16 region. This star-forming region is also known as the Eagle nebula and hosts the young massive star cluster NGC 6611. Based on the young age of the cluster, we assumed acceleration at the cluster wind-termination shock and modeled the propagation through the wind-blown bubble to derive the energetics of the process and interpret the GeV observations. Results. For the first time, we found significant GeV emission in correspondence of a molecular cloud associated with the young massive star cluster NGC 6611. We interpret this as hadronic emission associated with particles that are accelerated at the cluster wind-termination shock and propagated through the low-density wind-excavated bubble to the cloud. Our modeling allowed us to place firm constraints on the acceleration efficiency in NGC 6611. We assess that it lies between ∼1% and ∼4%.

Recently, the Large High-Altitude Air Shower Observatory (LHAASO) collaboration has obtained a measurement of the gamma-ray diffuse emission in the ultra-high energy range, 10–10^3 TeV after masking the contribution of known sources. The measurement is provided in two Galactic regions and appears to be 2–3 times higher than the gamma-ray signal expected from the hadronic interactions of diffuse cosmic rays with the interstellar medium, potentially implying that either additional emission sources exist or cosmic ray intensities have spatial variations. In this work, we calculate the hadronic gamma-ray diffuse emission outside the masks, considering a realistic gas distribution. We present a comprehensive calculation of the emission, which includes systematic uncertainties in the gas content of the Galactic disk, in the energy and spatial distribution of cosmic rays, as well as in the hadronic interaction cross-sections. Our results show that these factors mitigate the tension between data and predictions. The LHAASO data appear compatible with our baseline model in the outer Galactic region. In the inner region, the data show an excess with respect to the predictions below ∼ 50 TeV, while at higher energies they are well described by our model. We argue that two plausible explanations for enhanced gamma-ray emission — unresolved sources and CR spectral hardening in the inner Galaxy — are likely suppressed by the LHAASO masking strategy, which excludes regions where both effects are expected to be most prominent.

Context. Young massive stellar clusters (YMSCs) have emerged as potential γ-ray sources after the recent association of a dozen YMSCs with extended γ-ray emission. The large size of the detected halos, comparable to that of the wind-blown bubble expected around YMSCs, makes the γ-ray detection of individual YMSCs rather challenging. As a result, the emission from most of the Galactic YMSCs could be unresolved, thus contributing to the diffuse γ-ray radiation observed along the Galactic Plane. Aims. In this study, we estimate the possible contribution to the Galactic diffuse γ-ray emission from a synthetic population of YMSCs, and we compare it with observations obtained with different experiments, from 1 GeV to hundreds of teraelectronvolt, in three regions of the Galactic Plane. Methods. As the population of galactic YMSCs is only known locally, we evaluated the contribution of γ-ray emission relying on the simulation of synthetic populations of YMSCs based on the observed properties of local clusters. We computed the γ-ray emission from each cluster assuming that the radiation is purely hadronic in nature and produced by cosmic rays that are accelerated at the cluster’s collective wind termination shock. Results. We find that the γ-ray emission from unresolved YMSCs can significantly contribute to the observed Galactic diffuse flux, especially in the inner part of the Galaxy, and that an important role is played by kinetic power injected by the Wolf-Rayet stellar winds. The predicted γ-ray flux should be considered as a lower limit, given that our calculation does not include the contribution of supernovae exploding in YMSCs.

Context. The supernova remnant (SNR) W44 and its surroundings are a prime target for studying the acceleration of cosmic rays (CRs). Several previous studies established an extended gamma-ray emission that is set apart from the radio shell of W44. This emission is thought to originate from escaped high-energy CRs that interact with a surrounding dense molecular cloud complex. Aims. We present a detailed analysis of Fermi-LAT data with an emphasis on the spatial and spectral properties of W44 and its surroundings. We also report the results of the observations performed with the MAGIC telescopes of the northwestern region of W44. Finally, we present an interpretation model to explain the gamma-ray emission of the SNR and its surroundings. Methods. We first performed a detailed spatial analysis of 12 years of Fermi-LAT data at energies above 1 GeV, in order to exploit the better angular resolution, while we set a threshold of 100 MeV for the spectral analysis. We performed a likelihood analysis of 174 hours of MAGIC data above 130 GeV using the spatial information obtained with Fermi-LAT. Results. The combined spectra of Fermi-LAT and MAGIC, extending from 100 MeV to several TeV, were used to derive constraints on the escape of CRs. Using a time-dependent model to describe the particle acceleration and escape from the SNR, we show that the maximum energy of the accelerated particles has to be ≃40 GeV. However, our gamma-ray data suggest that a small number of lower-energy particles also needs to escape. We propose a novel model, the broken-shock scenario, to account for this effect and explain the gamma-ray emission.

We present observations of the supernova remnant Tycho obtained with OSIRIS at the Gran Telescopio Canaria. With its large field-of-view (4t×4t), spatial sampling of 0.25tt and spectral resolution of 650 kms−1, we covered a large portion of the remnant and resolved the broad Hα component (∼ 1000 km s−1). Previously, we observed the narrow (∼ 10 km s−1) and intermediate (∼ 100 km s−1) component in the same region using GHαFaS on the William Herschel Telescope. Observing all three line components at exactly the samelocations along the filaments and applying shock models give more precise information on the overall conditions in the shock, and enable us to quantify cosmic-ray properties.