Accurate reconstruction of the electromagnetic shower axis in the AMS-02 Electromagnetic Calorimeter (ECAL) is important for electron and gamma-ray analyses, including calorimeter-based tracking, track-to-cluster matching, and source-oriented studies that rely on precise shower pointing. We present an improved shower-axis reconstruction method based on a deep residual network adapted to the 18 × 72 imaging structure of the AMS-02 ECAL. Using the ECAL energy-deposition image together with the total deposited energy, the network reconstructs both the shower inclination angle and the incident position on the ECAL front surface. The model is trained with electron Monte Carlo samples from 2GeV to 4TeV and validated with independent positron Monte Carlo samples and high-purity cosmic-ray electron data collected by AMS-02 on the International Space Station. Compared with conventional AMS-02 ECAL reconstruction methods, the deep-residual-network approach improves the angular resolution significantly over a broad energy range. For example, relative to the three-dimensional fit method, the angular resolution improves by more than a factor of two at 10GeV, from 2.229° to 0.994°, and by about 31% at 100GeV, from 0.533° to 0.370°. A dedicated gamma-ray Monte Carlo study further shows comparable performance for neutral electromagnetic showers. These results demonstrate that deep residual networks can improve ECAL shower reconstruction and enhance the physics reach of AMS-02 gamma-ray and electron analyses.
The analysis traditionally employed by Imaging Atmospheric Cherenkov Telescopes involves optimizing quality cuts to select a sub-sample of high-quality events. These events are used for the scientific interpretation of the data, employing a single set of Instrument Response Functions (IRFs). All selected events are treated equally and assumed to be well represented by these IRFs, while the rest are discarded. An alternative approach, successfully applied in experiments such as Fermi-LAT, is an event-type-based analysis. This method divides datasets into subsamples, each containing events of a given expected reconstruction quality. IRFs are computed for each subsample independently, improving the accuracy with which IRFs represent the reconstruction quality of each event. The high-level analysis of these subsamples is performed treating them as independent observations, each with their own set of IRFs, and analyzed jointly.In this work we present a proof-of-concept implementation of an event-type-based analysis for the future Cherenkov Telescope Array Observatory (CTAO) using simulated data. A neural network (specifically a multi-layer perceptron) is trained to predict the direction reconstruction error of each event, and the simulated dataset is divided into event types based on this predicted variable. We compute IRFs for each event type and compare them with those from the standard analysis (without event types). Finally, we simulate observations using these event-type-wise IRFs and analyze them with high-level analysis tools to test the performance of both approaches. This implementation demonstrates notable improvements: 25% to 50% boost in spatial resolving power and ∼25% in sensitivity. This boost in performance will have strong implications in the scientific exploitation of the CTAO data, especially in crowded regions such as the Galactic Plane or searching for spectral signatures like Dark Matter annihilation lines.
Multimessenger observations suggest that Seyfert galaxies are promising sources of high-energy neutrinos, but their dense inner environments can strongly suppress the emerging very-high-energy gamma-ray emission. Active galactic nuclei (AGN) undergoing intense accretion episodes can enter a super-Eddington state, in which the accretion flow becomes geometrically and optically thick within a critical radius and develops strong magnetic fields in its innermost region. At the same time, large amounts of matter are expelled from the disk surface in the form of powerful, radiation-driven winds. In this work, we explore a scenario in which the cores of super-Eddington AGN provide suitable conditions for the acceleration of relativistic particles, including hadrons, via magnetic reconnection in a magnetically confined region close to the supermassive black hole. The accelerated hadronic component interacts with the intense photon field of the disk, leading to a copious neutrino flux peaking at 10–100 TeV that may be detectable with current observatories such as IceCube and KM3NeT, while the surrounding outflow efficiently absorbs the accompanying gamma-ray emission from the inner core. We also apply the model to the nearby super-Eddington Seyfert 1 NGC 7469 as a representative case with two reported neutrino events. In this framework, super-Eddington AGN, in particular Seyfert galaxies undergoing transient intense accretion episodes, emerge as plausible hidden neutrino sources, offering a natural explanation for the coexistence of efficient neutrino production and a strongly attenuated gamma-ray counterpart.
We propose that early Super Massive Black Holes (SMBHs) grow at an enhanced Eddington rate facilitated by rotation. Recent theoretical work suggests that rotating Black Holes (BHs) can produce winds or jets carrying electric currents. These currents are driven by a pE-2 momentum spectrum of protons and anti-protons, which can reach EeV energies for near-maximal rotation - independent of the BHs mass. This electric current generated in the ergo-region leads to rapid collisions producing anti-particles and lots of pions. The associated electron population suffers extreme losses in the magnetic field observed, so that the protons, anti-protons, neutrons, anti-neutrons and pions altogether, carry a much larger mass/energy per electron than a single proton, while charge is conserved. This factor can be estimated, depends on the spin of the BH, and allows a significant enhancement of Eddington limited accretion. This effect is proposed to explain the rapid growth of early SMBHs observed by James Webb Space Telescope (JWST). The prediction is that these SMBHs rotate rapidly. When compared with cosmological simulations of structure evolution with SMBH formation and evolution without allowing for BH rotation, a second testable prediction is that the gravitational waves produced in ensuing SMBH mergers are enhanced due to high rotation, with ensuing increased total mass.
We suggest a model of Fermi Bubbles (FBs) in the Galactic halo of the altitude about 7-8 kpc, which is seen in non-thermal microwave and y-ray ranges. It was assumed that this emission is generated by relativistic electrons of cosmic rays whose origin is still under debate. It has been assumed that the FB shell is generated in the halo by the release of energy, generated by the routine capture of stars at the central black hole of the Galactic Centre (GC). In this case cosmic ray electrons (CR) in the shells of the FBs of sufficiently high energies are generated by the standard shock acceleration. However, one of the problems of this model is that the Mach number of the FB shock is not high enough to generate the observed non-thermal radiation from the halo. We propose an alternative model of stochastic CR acceleration by Rayleigh-Taylor (RT) instabilities in the shell of the FB at the late stages of the evolution of the shell in the halo. Unlike the shock model of CR acceleration, the RT model of in-situ acceleration in the FBs does not require strong shock fronts. In our model, we derived the spectrum of RT instabilities and estimate the spectra of kinetic equations for MHD-fluctuations needed for acceleration of CRs. We assessed the time of CR electron acceleration up to TeV energies that needed to interpret the observed data of y-ray and microwave emission from the envelope of FBs.
We study the influence of variations in the upper atmospheric temperature and interplanetary magnetic field on the cosmic ray induced atmospheric muon flux measured by the GRAPES-3 experiment over 22 years (2001-2022) of data; spanning three solar cycles: the declining phase of Solar Cycle 23, the full Cycle 24, and the rising and maximum phases of Cycle 25. Located in Ooty, India, the GRAPES-3 large area (560 m2) muon telescope detects similar to 4 billion muons daily above 1 GeV, with an angular resolution of similar to 4 degrees, enabling a statistical precision <0.01% on the hourly muon rate. After accounting for the effect of atmospheric pressure variations, we compare this data with the upper atmospheric temperature inferred from NASA's MERRA-2 dataset as well as magnetic field data from the ACE and WIND spacecraft at Lagrange point L1. A simultaneous iterative fitting method employing Fast Fourier Transforms and a narrow band-pass filter reveals the temperature and magnetic field coefficients to be alpha(T) = - 0.2241 +/- 0.04 (stat.) +/- 0.0220 (syst.) % K-1 and gamma(M) = - 0.574 +/- 0.027 (stat.) +/- 0.011 (syst.) % nT(-1), respectively, for an assumed hadronic attenuation length lambda=120 g cm(-2), underscoring the potential of the GRAPES-3 muon telescope to serve as a real time monitor of the upper atmospheric temperature or interplanetary magnetic field.
When high-energy cosmic ray primary particles interact in the upper atmosphere, they produce short-lived mesons which often decay and produce numerous muons in a broad energy range. Muons with high energies reaching deep underground are nearly collimated with small separation among them, forming a bundle of muons. Because the properties of muon bundles are closely related to cosmic ray primary particle energy, mass composition and zenith angle, the study of them is of great interest in cosmic ray and extensive air shower physics. As decay products of mesons produced in hadronic cascades, the characteristics of atmospheric muons also depend on the properties of the strong interaction over a wide range of energies. Should muons in a bundle be identified for decays of different parent particles in ultrahigh-energy hadronic cascades, they would shed light on heavy quark production in the forward region at energies beyond the reach of collider experiments. High-energy muons are also among the main causes of cosmogenic backgrounds in deep underground detectors. Proper characterization of their energy loss in deep detectors helps to understand the backgrounds in experiments searching for rare events such as astrophysical neutrinos, hypothetic dark matter particles, and neutrino-less double decays, etc. This work studied analytical expressions of muon bundle energy loss along its trajectory and the spatial distribution of the energy loss by taking into account the lateral distribution of high-energy muons at different slant depths. To justify the approximations in the calculation and explore expressions suitable for fitting muon bundle energy loss in deep underground (or ice, or water) detectors, the analytical expressions are compared with the energy loss by high-energy muons in Monte Carlo air showers generated by CORSIKA. Two semi-empirical expressions of differential energy loss by muon bundles are proposed, offering an option to construct likelihood functions for muon bundle energy loss reconstruction. Possible improvements and applications of the obtained results in the analysis of cosmic ray data are discussed by using IceCube as an example.
In recent years, improvements in galaxy cluster observations have enabled a variety of tests of fundamental physics using these systems. In this work, we test the constancy of the speed of light, c, by combining X-ray gas mass fraction measurements from galaxy clusters with SNe Ia luminosity distance measurements from Pantheon+. We adopt the SH0ES prior on H0 and the Qb/Qm ratio from galaxy clustering observations, thereby minimizing the dependence of our analysis on any specific cosmological model. We explore different assumptions for the cluster mass calibration (mass bias), including CLASH, CCCP, and Planck-based estimates. We find no deviation from a constant c when adopting CLASH or CCCP priors, while Planck-based calibration yields a mild tension, with the hypothesis of constant c being only marginally consistent at the 2 sigma level, indicating a non-negligible sensitivity of the results to the adopted calibration scheme.
Electromagnetic cascades are initiated by TeV gamma rays propagating through the intergalactic medium (IGM), and they can be used to constrain the weak intergalactic magnetic field (IGMF) in cosmic voids. Primary TeV photons produce electrons and positrons through electromagnetic pair production, which can be deflected out of the line-of-sight to the observer by IGMF. In addition, electron-positron pairs can perturb the IGM, triggering plasma instabilities that can cool down the pairs before they upscatter cosmic background photons to GeV energies via inverse Compton (IC) scattering. In this work, we investigate the influence of plasma instabilities on the cascade spectrum by introducing a parameterized instability model within the publicly available Monte Carlo framework CRPropa 3.2 in the presence of IGMF. We first determine the instability parameters that best reproduce the Fermi-LAT observations in the absence of any IGMF. We then use extended-emission observations within the observer's field of view, including the effects of the IGMF, to constrain the IGMF strength in the presence of the corresponding best-fit instability-cooling parameters, based on the Fermi-LAT spectral observations of the blazar 1ES 0229+200. We find that plasma instabilities with a characteristic length scale of 120 kpc and a spectral index of a = -0.5 are consistent with the observed photon spectra. We also find that the fit of the observed data is improved by the presence of an IGMF: we obtain an IGMF lower limit of B >= 2.7 & times; 10-17 G for an observer field of view 1.0 degrees.
Ground-based neutron monitors (NM64) are the standard for tracking heliospheric modulation, yet their integral count rates are susceptible to bias from local environmental moderation (e.g., soil moisture, snow). To decouple these local effects from primary cosmic-ray variations, we present the deployment of the portable CEFNEN neutron spectrometer at Las Campanas Observatory (2320 m.a.s.l., Chile). The instrument, based an array of up to 16 moderated 3He detectors (11 utilized in this campaign), retrieves the cosmic-ray neutron spectrum with 15-minute temporal resolution. A key finding is that the spectral ratio R = ith/(iep + ifs) provides a model-independent proxy for near field hydrogen content. Because this ratio is dominated by multiply-scattered neutrons detected with moderate geometric anisotropy (K approximate to 1.3), angular effects largely cancel making R robust across isotropic, directional, mixed unfolding hypotheses. During a rapid snow precipitation event, R increased by +34% to +43%, tracking thermal flux enhancement (+20% to +24%) and epithermal suppression (-17% to-18%), all exceeding significance regardless of the angular treatment assumed. While the absolute high-energy flux shows a factor of-two sensitivity to these assumptions (affecting dosimetric estimates spanning H*(10) approximate to 31-64 nSv h-1), environmental signatures remain unambiguous. A dedicated geometric analysis reveals that the high-energy monitor exhibits an anisotropy ratio K = explaining the enhanced sensitivity to the downward cosmic-ray cascade. The barometric pressure correction uses beta LCO = 6.94 & times;10-3 mbar-1, estimated from the geomagnetic cutoff rigidity of the site (RC approximate to 10.5 GV) via empirical relation from literature. We conclude that R serves as a robust correction factor for environmental effects at neutron monitor stations, independent of assumptions about the angular distribution of the incident cosmic-ray field.
The measurement of the cosmic-ray electron+positron flux at high energy is a key tool to look for possible astrophysical sources of high-energy electrons/positrons and indirect signals of dark matter. The current measurement of the electron+positron flux is limited to an energy of about 7 TeV, and it is insufficient to reach a clear conclusion on these two possible contributions. The limitation in energy is mainly due to the geometric acceptance of the current in-orbit space experiments. Thanks to its innovative geometry, the future space experiment HERD will have a larger geometric factor and will extend the flux measurement up to tens of TeV. In this paper, using simulations, we study the performance of the calorimeter of the HERD experiment for the electron+positron flux measurement, demonstrating its capability to extend it up to 15 TeV and above.
Analyses of Imaging Atmospheric Cherenkov Telescope (IACT) data for extended γ-ray sources face the issue that the field of view does not offer sufficient regions for background estimations. In cases where the source angular size exceeds or occupies a significant part of the field of view, an independent background estimation method is necessary to carry out IACT analyses and to have a better understanding of the systematic uncertainties. The proposed new method utilizes Singular Value Decomposition to extract the low-dimension representations of the distribution of cosmic-ray events in OFF runs and uses cosmic-ray-like events in the ON runs to estimate the background of γ-like events. Using VERITAS archival data, we demonstrate that the new method is capable of providing reliable background modeling for observations across a wide range of observing conditions.
We report the first measurement of the underground cosmic muon flux at the Stawell Underground Physics Laboratory. The measurement uses eight EJ200 plastic scintillator panels, equipped with Hamamatsu R13089 PMT pairs at the ends, which are the primary components of the muon veto system for the upcoming SABRE South experiment. This study uses approximately 236 days of data collected between 2024 and 2025, with the muon veto system arranged in a telescopic configuration. SUPL, located 1025 metres below ground at the Stawell Gold Mine in Victoria, Australia, has a flat overburden of approximately 2.8 km of water equivalent, which significantly reduces the muon flux. The overburden is well characterised through data collected by the mining company, allowing tight constraints on systematic uncertainties. The measured muon flux is f = (6.33 +/- 0.04(stat) +/- 0.35(sys)) x 10-8 [s(-1) x cm(-2)]. This measurement is in excellent agreement with simulations, with a relative uncertainty an order of magnitude smaller than the modelling uncertainty.
We investigate whether stochastic acceleration associated with pressure-anisotropy-driven magnetogenesis can generate a dynamically significant population of cosmic rays (CRs) prior to nonlinear structure formation. As magnetic fields amplify in the early Universe, the associated increase in gyrofrequency enhances pitch-angle scattering, potentially shortening the stochastic acceleration time. We derive an analytic criterion for efficient cosmological acceleration by comparing the acceleration timescale with the Hubble time, which defines a critical magnetic field and a corresponding CR turn-on redshift zon. For representative parameters, we find zon 1.7. To quantify the resulting particle population, we solve a Fokker-Planck equation for the isotropic ion (proton) distribution in the redshift interval z = 10-zon, including Coulomb energy losses in a fully ionized intergalactic medium. Throughout most of this epoch, adiabatic expansion dominates over stochastic energization, and Coulomb cooling efficiently thermalizes low-energy particles, introducing an effective low-energy threshold at energies of order O(10) keV. As a result, the distribution remains close to a cooling Maxwellian, and the formation of a suprathermal tail is strongly suppressed even in the presence of a preexisting nonthermal component. Even under optimistic assumptions corresponding to the strong-scattering limit, the maximum attainable ion energy reaches at most O(102) GeV. These results indicate that efficient CR production in the intergalactic medium is intrinsically tied to the onset of structure-formation shocks, while earlier microinstability-driven stochastic processes can provide at most a modest pre-acceleration.
The radio detection of extensive air showers provides a powerful method for studying the origin of high-energy cosmic rays. The Low-Frequency Array (LOFAR) offers unprecedentedly detailed measurements of the radio emission footprint. However, fully exploiting this information requires advanced reconstruction techniques. In this paper, we introduce a novel framework for air shower reconstruction based on Bayesian inference and Information Field Theory (IFT). Our method is built on a fully differentiable forward model of the radio signal, which incorporates a physical emission parameterization and a precise wavefront model. Additionally, we augment this physical model with Gaussian processes to account for systematic uncertainties in both the signal fluence and arrival timing. By leveraging gradient information, our approach enables efficient (three orders of magnitude acceleration w.r.t. the legacy method) and robust inference of the underlying physical shower parameters, such as primary energy and the depth of shower maximum, X_max. This work provides not only point estimates but also a rigorous quantification of uncertainties. We achieve a resolution in X_max of 25 g/cm^2 and a radiation energy resolution of 12% on simulations for LOFAR.
The mass composition of ultra-high-energy cosmic rays (UHECRs) is commonly inferred from the first two moments of the depth of shower maximum, X-max, measured by fluorescence and hybrid detectors. Such analyses require fast and accurate mappings between the moments of X-max and those of the logarithmic mass, ln A, based on realistic air-shower simulations. In this work we provide updated parametrizations of the X-max moments and distributions for air showers initiated by nuclei from proton to iron, simulated with CONEX for three state-of-the-art hadronic interaction models: E-pos-LHC, S-IBYLL,2.3(E), and QGSJ(ET)-III-01. We parametrize the mean depth (X-max) and the variance sigma(2)(X-max) as functions of energy and mass. For the variance we compare a second-order polynomial model with an exponential model. In addition, we model the full Xmax distributions with a three-parameter generalized Gumbel function. The Gumbel parameters are fitted using an unbinned likelihood and are validated by comparing the implied mean and variance with the raw CONEX samples and with the moment parametrizations. Across the full energy range considered, residuals between the parametrizations (or the Gumbel representation) and the simulations are at the level of a few g cm(-2) for the mean and a few (g cm(-2))(2) for the variance, making these parametrizations suitable for precision UHECR composition studies and forward-folding analyses of X-max distributions.
The Milky Way hosts astrophysical accelerators capable of producing high-energy cosmic rays. These cosmic rays can interact with the interstellar medium (ISM) across the Galaxy to produce neutrinos and gamma rays (propagation component), while their interactions with ambient material at their acceleration sites, such as supernova remnants, can give rise to the source component of the gamma-ray and neutrino flux. In this paper, we estimate the source component of the Galactic neutrino flux using simulated populations of Galactic gamma-ray sources. We compare our results with observations from neutrino experiments in the energy range of 1-30 TeV. Using simulated populations of Galactic TeV gamma-ray sources, we exploit the correlation between gamma rays and neutrinos and introduce a bracketing approach to constrain the range for the source contribution of the Galactic neutrino flux. For the upper limit, we used a simulation describing the entity of Galactic gamma-ray sources, whereas the lower limit was estimated using the hadronic component of the Galactic supernova remnant population. Our results show that the difference between this maximum and minimum is less than an order of magnitude and the flux range is comparable to the Galactic neutrino flux from the cosmic-ray interaction with the ISM. The results agree with the observed signals from IceCube and ANTARES and suggest that the propagation component, combined with the minimum source contribution predicted by the supernova-remnant model, approaches the observed neutrino flux, leaving little room for significant enhancements of the emission originating from propagating cosmic rays.
The IceCube neutrino telescope has provided upper limits on neutrino emission from gamma-ray bursts. These constraints provided by the IceCube detector have been instrumental in investigating the properties of the GRB jet and its emission models. During the prompt phase of gamma-ray burst emission, intense radiation components are generated that interact with the shock-accelerated particles within the jet. We study various GRB emission models, such as the internal shock model, the photospheric models, and also include a model-independent case. Based on these models, we calculate the neutrino fluence using the photo-hadronic interaction process. We estimate the bulk Lorentz factor using the well-known correlations between prompt phase observables, which is then used to calculate the emission site for the model-dependent scenarios. For GRB 221009A, we find that a low baryon loading scenario is consistent with the IceCube upper limits; however, for GRB 240825A, a higher value of baryon loading is preferred. Also, the values of the microphysical parameters epsilon(e) and epsilon(B) for GRB 240825A are lower by factors of approximately 10 and 100, respectively, compared to those of GRB 221009A. Further, using neutrino upper limits for these two sources, we estimate the lower limits on the dissipation radius for our models. The current TeV-PeV upper limits for GRB 221009A are already useful for constraining parameter space for the BPH and MPH models.
