The number of observed gravitational wave (GW) events is growing fast thanks to rapidly improving detector sensitivities. GWs from compact binary coalescences like Black Holes or Neutron Stars behave like standard sirens and can be used as cosmological probes. To this aim, generally, the observation of an electromagnetic counterpart and the measurement of the redshift are needed. However, even when those are not available, it is still possible to exploit these "dark sirens" via statistical methods. In this work, we explore a method that exploits the information contained in the cross-correlation of samples of GW events with matter over-density tracers like galaxy catalogues. Contrary to other currently employed dark-sirens methods, this approach does not suffer from systematic errors related to the incompleteness of the galaxy catalogue. To further enhance the technique, we implement tomography in redshift space for the galaxy catalogue and luminosity distance space for the GWs. We simulate future data collected by the array of currently existing detectors, namely LIGO, Virgo, and KAGRA, as well as planned third-generation ones such as the Einstein Telescope and Cosmic Explorers. We cross-correlate these data with those from upcoming photometric galaxy surveys such as Euclid. We perform a sensitivity forecast employing a full-likelihood approach and explore the parameter space with Monte Carlo Markov Chains. We find that with this method, third-generation detectors will be able to determine the Hubble constant H0 with an error of only 0.7%, which is enough to provide decisive information to shed light on the Hubble tension. Furthermore, for the other cosmological parameters, we find that the GWs and galaxy surveys information are highly complementary, and the use of both significantly improves the ability to constrain the underlying cosmology.

We present a complete analysis of Fermi Large Area Telescope (LAT) data of GRB 221009A, the brightest gamma-ray burst (GRB) ever detected. The burst emission above 30 MeV detected by the LAT preceded, by 1 s, the low-energy (<10 MeV) pulse that triggered the Fermi Gamma-Ray Burst Monitor (GBM), as has been observed in other GRBs. The prompt phase of GRB 221009A lasted a few hundred seconds. It was so bright that we identify a bad time interval of 64 s caused by the extremely high flux of hard X-rays and soft gamma rays, during which the event reconstruction efficiency was poor and the dead time fraction quite high. The late-time emission decayed as a power law, but the extrapolation of the late-time emission during the first 450 s suggests that the afterglow started during the prompt emission. We also found that high-energy events observed by the LAT are incompatible with synchrotron origin, and, during the prompt emission, are more likely related to an extra component identified as synchrotron self-Compton (SSC). A remarkable 400 GeV photon, detected by the LAT 33 ks after the GBM trigger and directionally consistent with the location of GRB 221009A, is hard to explain as a product of SSC or TeV electromagnetic cascades, and the process responsible for its origin is uncertain. Because of its proximity and energetic nature, GRB 221009A is an extremely rare event.

The Cherenkov Telescope Array Observatory (CTAO) will be a ground-based Cherenkov telescope performing wide-sky surveys, ideal for anisotropy studies such as cross-correlations with tracers of the cosmic large-scale structure. Cross-correlations can shed light on high-energy 7-ray sources and potentially reveal exotic signals from particle dark matter. In this work, we investigate CTAO sensitivity to crosscorrelation signals between 7-ray emission and galaxy distributions. We find that by using dense, lowredshift catalogs like 2 MASS, and for integration times around 50 hours, this technique achieves sensitivities to both annihilating and decaying dark matter signals that are competitive with those from dwarf galaxy and cluster analyses.

Our understanding of the γ -ray sky has improved dramatically in the past decade, however, the unresolved γ -ray background (UGRB) still has a potential wealth of information about the faintest γ -ray sources pervading the Universe. Statistical cross-correlations with tracers of cosmic structure can indirectly identify the populations that most characterize the γ -ray background. In this study, we analyze the angular correlation between the γ -ray background and the matter distribution in the Universe as traced by gravitational lensing, leveraging more than a decade of observations from the Fermi -Large Area Telescope (LAT) and 3 years of data from the Dark Energy Survey (DES). We detect a correlation at signal-to-noise ratio of 8.9. Most of the statistical significance comes from large scales, demonstrating, for the first time, that a substantial portion of the UGRB aligns with the mass clustering of the Universe as traced by weak lensing. Blazars provide a plausible explanation for this signal, especially if those contributing to the correlation reside in halos of large mass (∼ 10 14 M ⊙ ) and account for approximately 30–40% of the UGRB above 10 GeV. Additionally, we observe a preference for a curved γ -ray energy spectrum, with a log-parabolic shape being favored over a power-law. We also discuss the possibility of modifications to the blazar model and the inclusion of additional γ -ray sources, such as star-forming galaxies, misalinged active galactic nuclei, or particle dark matter.

We perform a comprehensive analysis of cosmic-ray propagation using the time-dependent AMS-02 flux measurements covering a full solar cycle, with particular emphasis on the role of solar modulation. We fit two representative Galactic propagation scenarios, convection- and re-acceleration-dominated models, in combination with three solar modulation prescriptions: the standard force-field approximation, an extended force-field model with a rigidity break, and the heliospheric propagation code . The inclusion of time-resolved antiproton data provides a unique probe of charge-sign-dependent modulation effects and low-energy systematics. We find that the force-field approximation can describe positively charged nuclei reasonably well outside the solar maximum in convection-dominated models, but fails during periods of high solar activity and for antiprotons at all times. In re-acceleration scenarios, strong degeneracies between solar modulation and low-energy propagation lead to unphysical results when simple modulation models are employed. Across all models, we identify systematic uncertainties of order 10-15

The recent detection of extended γ-ray emission around middle-aged pulsars is interpreted as inverse-Compton scattering of ambient photons by electron-positron pairs escaping the pulsar wind nebula, which are confined near the system by unclear mechanisms. This emerging population of γ-ray sources was first discovered at TeV energies and remains underexplored in the GeV range. To address this, we conducted a systematic search for extended sources along the Galactic plane using 14 years of Fermi-LAT data above 10 GeV, aiming to identify a number of pulsar halo candidates and extend our view to lower energies. The search covered the inner Galactic plane (| l|≤ 100^∘, | b|≤ 1^∘) and the positions of known TeV sources and bright pulsars, yielding broader astrophysical interest. We found 40 such sources, forming the Second Fermi Galactic Extended Sources Catalog (2FGES), most with 68 1.0^∘ and relatively hard spectra with photon indices below 2.5. We assessed detection robustness using field-specific alternative interstellar emission models and by inspecting significance maps. Noting 13 sources previously known as extended in the 4FGL-DR3 catalog and five dubious sources from complex regions, we report 22 newly detected extended sources above 10 GeV. Of these, 13 coincide with H.E.S.S., HAWC, or LHAASO sources; six coincide with bright pulsars (including four also coincident with TeV sources); six are associated with 4FGL point sources only; and one has no association in the scanned catalogs. Notably, six to eight sources may be related to pulsars as classical pulsar wind nebulae or pulsar halos.

We employ a data-driven approach to investigate the rigidity and spatial dependence of the diffusion of cosmic rays in the turbulent magnetic field of the Milky Way. Our analysis combines data sets from the experiments Voyager, AMS-02, CALET, and DAMPE for a range of cosmic ray nuclei from protons to oxygen. Our findings favor models with a smooth behavior in the diffusion coefficient, indicating a good qualitative agreement with the predictions of self-generated magnetic turbulence models. Instead, the current cosmic-ray data do not exhibit a clear preference for or against inhomogeneous diffusion, which is also a prediction of these models. Future progress might be possible by combining cosmic-ray data with gamma rays or radio observations, enabling a more comprehensive exploration.

We present 294 pulsars found in GeV data from the Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope. Another 33 millisecond pulsars (MSPs) discovered in deep radio searches of LAT sources will likely reveal pulsations once phase-connected rotation ephemerides are achieved. A further dozen optical and/or X-ray binary systems colocated with LAT sources also likely harbor gamma-ray MSPs. This catalog thus reports roughly 340 gamma-ray pulsars and candidates, 10% of all known pulsars, compared to ≤11 known before Fermi. Half of the gamma-ray pulsars are young. Of these, the half that are undetected in radio have a broader Galactic latitude distribution than the young radio-loud pulsars. The others are MSPs, with six undetected in radio. Overall, ≥236 are bright enough above 50 MeV to fit the pulse profile, the energy spectrum, or both. For the common two-peaked profiles, the gamma-ray peak closest to the magnetic pole crossing generally has a softer spectrum. The spectral energy distributions tend to narrow as the spindown power E ̇ decreases to its observed minimum near 10 33 erg s −1 , approaching the shape for synchrotron radiation from monoenergetic electrons. We calculate gamma-ray luminosities when distances are available. Our all-sky gamma-ray sensitivity map is useful for population syntheses. The electronic catalog version provides gamma-ray pulsar ephemerides, properties, and fit results to guide and be compared with modeling results.

We reconstruct the extra-galactic gamma-ray source-count distribution, or dN/dS , of resolved and unresolved sources by adopting machine learning techniques. Specifically, we train a convolutional neural network on synthetic 2-dimensional sky-maps, which are built by varying parameters of underlying source-counts models and incorporate the Fermi -LAT instrumental response functions. The trained neural network is then applied to the Fermi -LAT data, from which we estimate the source count distribution down to flux levels a factor of 50 below the Fermi -LAT threshold. We perform our analysis using 14 years of data collected in the (1,10) GeV energy range. The results we obtain show a source count distribution which, in the resolved regime, is in excellent agreement with the one derived from cataloged sources, and then extends as dN/dS ∼ S -2 in the unresolved regime, down to fluxes of 5 · 10 -12 cm -2 s -1 . The neural network architecture and the devised methodology have the flexibility to enable future analyses to study the energy dependence of the source-count distribution.

We summarize the second radio synchrotron background workshop, which took place on 2022 June 15–17 in Barolo, Italy. This meeting was convened because available measurements of the diffuse radio zero level continue to suggest that it is several times higher than can be attributed to known Galactic and extragalactic sources and processes, rendering it the least well-understood electromagnetic background at present and a major outstanding question in astrophysics. The workshop agreed on the next priorities for investigations of this phenomenon, which include searching for evidence of the radio Sunyaev–Zel’dovich effect, carrying out cross-correlation analyses of radio emission with other tracers, and supporting the completion of the 310 MHz absolutely calibrated sky map project.

We report the discovery of GRB 221009A, the highest flux gamma-ray burst (GRB) ever observed by the Fermi Gamma-ray Burst Monitor (Fermi-GBM). This GRB has continuous prompt emission lasting more than 600 s, which smoothly transitions to afterglow emission visible in the Fermi-GBM energy range (8 keV–40 MeV), and total energetics higher than any other burst in the Fermi-GBM sample. By using a variety of new and existing analysis techniques we probe the spectral and temporal evolution of GRB 221009A. We find no emission prior to the Fermi-GBM trigger time ( t 0 ; 2022 October 9 at 13:16:59.99 UTC), indicating that this is the time of prompt emission onset. The triggering pulse exhibits distinct spectral and temporal properties suggestive of the thermal, photospheric emission of shock breakout, with significant emission up to ∼15 MeV. We characterize the onset of external shock at t 0 + 600 s and find evidence of a plateau region in the early-afterglow phase, which transitions to a slope consistent with Swift-XRT afterglow measurements. We place the total energetics of GRB 221009A in context with the rest of the Fermi-GBM sample and find that this GRB has the highest total isotropic-equivalent energy ( E γ ,iso = 1.0 × 10 55 erg) and second highest isotropic-equivalent luminosity ( L γ ,iso = 9.9 × 10 53 erg s –1 ) based on its redshift of z = 0.151. These extreme energetics are what allowed us to observe the continuously emitting central engine of Fermi-GBM from the beginning of the prompt emission phase through the onset of early afterglow.

We present 294 pulsars found in GeV data from the Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope. Another 33 millisecond pulsars (MSPs) discovered in deep radio searches of LAT sources will likely reveal pulsations once phase-connected rotation ephemerides are achieved. A further dozen optical and/or X-ray binary systems co-located with LAT sources also likely harbor gamma-ray MSPs. This catalog thus reports roughly 340 gamma-ray pulsars and candidates, 10% of all known pulsars, compared to $\leq 11$ known before Fermi. Half of the gamma-ray pulsars are young. Of these, the half that are undetected in radio have a broader Galactic latitude distribution than the young radio-loud pulsars. The others are MSPs, with 6 undetected in radio. Overall, >235 are bright enough above 50 MeV to fit the pulse profile, the energy spectrum, or both. For the common two-peaked profiles, the gamma-ray peak closest to the magnetic pole crossing generally has a softer spectrum. The spectral energy distributions tend to narrow as the spindown power $\dot E$ decreases to its observed minimum near $10^{33}$ erg s$^{-1}$, approaching the shape for synchrotron radiation from monoenergetic electrons. We calculate gamma-ray luminosities when distances are available. Our all-sky gamma-ray sensitivity map is useful for population syntheses. The electronic catalog version provides gamma-ray pulsar ephemerides, properties and fit results to guide and be compared with modeling results.

The AMS-02 experiment has provided high-precision measurements of several cosmic-ray (CR) species. The achieved percent-level accuracy gives access to small spectral differences among the different species and, in turn, this allows scrutinizing the universality of CR acceleration, which is expected in the standard scenario of CR shock acceleration. While pre-AMS-02 data already indicated a violation of the universality between protons and helium, it is still an open question if at least helium and heavier nuclei can be reconciled. To address this issue, we performed a joint analysis using the AMS-02 CR measurements of antiprotons, protons, helium, helium 3, boron, carbon, nitrogen, and oxygen. We explore two competing propagation scenarios, one with a break in the diffusion coefficient at a few GVs and no reacceleration, and another one with reacceleration and with a break in the injection spectra of primaries. Furthermore, we explicitly consider the impact of the uncertainties in the nuclear production cross sections of secondaries by including nuisance parameters in the fit. The resulting parameter space is explored with the help of Monte Carlo methods. We find that, contrary to the naive expectation, in the standard propagation scenarios CR universality is violated also for He, on the one hand, and C, N, and O, on the other hand, i.e., different injection slopes (at the level of Delta similar to 0.05) are required to explain the observed spectra. As an alternative, we explore further propagation scenarios, inspired by nonhomogeneous diffusion, which might save universality. Finally, we also investigate the universality of CR propagation, i.e., we compare the propagation properties inferred using only light nuclei ((p) over bar, p, He, He-3) with the ones inferred using only heavier nuclei (B, C, N, O).

Dark matter (DM) annihilation in our Galaxy may produce a linearly polarized synchrotron signal. We use, for the first time, synchrotron polarization to constrain the DM annihilation cross section by comparing theoretical predictions with the latest polarization maps obtained by the Planck satellite collaboration. We find that synchrotron polarization is typically more constraining than synchrotron intensity by about 1 order of magnitude, independently of uncertainties in the modeling of electron and positron propagation, or of the Galactic magnetic field. Our bounds compete with cosmic microwave background limits in the case of leptophilic DM.

In the last decade, the space-borne experiment AMS-02 has determined cosmic-ray spectra with unprecedented precision, potentially providing new insights into cosmic-ray propagation in our Galaxy. However, the analysis of this increasingly precise cosmic-ray data requires more careful modeling of systematic uncertainties. We analyze the recent AMS-02 comic-ray measurements of the secondaries Lithium, Beryllium, and Boron, and the primaries Carbon, Nitrogen and Oxygen. The data is used to study five different propagation frameworks, which for example differ by including or neglecting reacceleration or breaks in the diffusion coefficient. In this work, we particularly focus on systematic uncertainties related to the fragmentation cross section to produce secondary CRs. Furthermore, the impact of correlated systematic uncertainties in the AMS-02 data are studied. The cosmic-ray data from Li to O is well fitted in all the considered propagation frameworks. However, we find that the uncertainties on the nuclear production cross sections play a crucial role. Because of these uncertainties we cannot distinguish between different propagation frameworks. In this sense, cross section uncertainties currently prevent a deeper understanding of the properties of CR propagation. Nonetheless, we find some common and robust constraints. Above a few GV, the slope of the diffusion coefficient is determined to be in the range of X ' 0.4 − 0.5. Moreover, we find a lower bound on the half-height of the diffusion halo at Ih & 3 kpc.

M. Ackermann, M. Ajello, A. Albert, W. B. Atwood, L. Baldini, 3 G. Barbiellini, 7 D. Bastieri, 9 R. Bellazzini, E. Bissaldi, R. D. Blandford, R. Bonino, 13 E. Bottacini, J. Bregeon, P. Bruel, R. Buehler, G. A. Caliandro, 16 R. A. Cameron, M. Caragiulo, 11 P. A. Caraveo, E. Cavazzuti, C. Cecchi, 21 A. Chekhtman, J. Chiang, G. Chiaro, S. Ciprini, 20 R. Claus, J. Cohen-Tanugi, F. Costanza, A. Cuoco, 13 S. Cutini, 23, 20 F. D’Ammando, 25 A. de Angelis, F. de Palma, 27 R. Desiante, 12 S. W. Digel, L. Di Venere, 11 P. S. Drell, C. Favuzzi, 11 S. J. Fegan, W. B. Focke, A. Franckowiak, S. Funk, P. Fusco, 11 F. Gargano, D. Gasparrini, 20 N. Giglietto, 11 F. Giordano, 11 M. Giroletti, T. Glanzman, G. Godfrey, I. A. Grenier, J. E. Grove, S. Guiriec, 33 A. K. Harding, J.W. Hewitt, D. Horan, X. Hou, 36 G. Iafrate, 37 G. Jóhannesson, T. Kamae, M. Kuss, S. Larsson, 41 L. Latronico, J. Li, L. Li, 41 F. Longo, 7 F. Loparco, 11, ∗ M. N. Lovellette, P. Lubrano, 21 J. Magill, S. Maldera, A. Manfreda, M. Mayer, M. N. Mazziotta, † P. F. Michelson, W. Mitthumsiri, T. Mizuno, M. E. Monzani, A. Morselli, S. Murgia, E. Nuss, N. Omodei, E. Orlando, J. F. Ormes, D. Paneque, 3 J. S. Perkins, M. Pesce-Rollins, 3 V. Petrosian, F. Piron, G. Pivato, S. Rainò, 11 R. Rando, 9 M. Razzano, 50 A. Reimer, 3 O. Reimer, 3 T. Reposeur, C. Sgrò, E. J. Siskind, F. Spada, G. Spandre, P. Spinelli, 11 H. Takahashi, J. B. Thayer, D. J. Thompson, L. Tibaldo, D. F. Torres, 56 G. Tosti, 21 E. Troja, 43 G. Vianello, B. L. Winer, K. S. Wood, and M. Yassine

Michael Korsmeier 2, 3, 4, ∗ and Alessandro Cuoco 4, † Stockholm University and the Oskar Klein Centre for Cosmoparticle Physics, Alba Nova, 10691 Stockholm, Sweden Institute for Theoretical Particle Physics and Cosmology, RWTH Aachen University, Sommerfeldstr. 16, 52056 Aachen, Germany Dipartimento di Fisica, Università di Torino, Via P. Giuria 1, 10125 Torino, Italy Istituto Nazionale di Fisica Nucleare, Sezione di Torino, Via P. Giuria 1, 10125 Torino, Italy

We present here a quantitative estimate of the impact of uncertainties of astrophysical nature on the determination of the dark matter distribution within our Galaxy, the Milky Way. Based on an update of a previous analysis, this work is motivated by recent new determinations of astrophysical quantities of relevance – such as the Galactic parameters (R0, V0) – from the GRAVITY collaboration and the GAIA satellite, respectively. We find that even with these state-of-the-art determination and a range of uncertainties – both statistical and systematic – much narrowed with respect to previous literature, the uncertainties on the dark matter distribution and their impact on searches of physics beyond the standard model stays sizable.

Over its ten years of mission the Large Area Telescope onboard the Fermi Gamma-ray Space Telescope has collected the largest ever sample of high-energy cosmic-ray electron and positron events. Possible features in their energy spectrum could be a signature of the presence of nearby astrophysical sources or of more exotic sources, such as annihilating or decaying dark matter particles in the Galaxy. In addition, the capture and subsequent annihilation of dark matter particles in the Sun via long-lived dark mediators can yield high-energy electrons and positrons reaching the Earth, which are a probe for the dark matter-nucleon scattering cross section. We present the results of the search for possible features in the cosmic-ray electron and positron spectrum from our Galaxy and towards the Sun. We set constraints on the the velocity-averaged dark matter annihilation cross section and on the dark matter-nucleon scattering cross section up to dark matter masses of 1.7 TeV.

Dark matter particles from the galactic halo can be gravitationally trapped in the solar core or in external orbits. The enhanced density of dark matter particles either in the solar core or in external orbits can result in the annihilation of these particles producing gamma rays via long-lived intermediate states or directly outside the Sun, respectively. These processes would yield characteristic features in the energy spectrum of the subsequent gamma rays, i.e., a boxlike or linelike shaped feature, respectively. We have performed a dedicated analysis using a 10-year sample of gamma-ray events from the Sun collected by the Fermi Large Area Telescope searching for spectral features in the energy spectrum as a signature of dark matter annihilation. In the scenario of gamma-ray production via long-lived mediators, we have also evaluated the dark matter-nucleon spin-dependent and spin-independent scattering cross section constraints from the flux limits in a dark matter mass range from 3 GeV/c(2) up to about 1.8 TeV/c(2). In the mass range up to about 150 GeV/c(2), the limits are in the range 10(-46)-10(-45) cm(2) for the spin-dependent scattering and in the range 10(-48)-10(-47) cm(2) for the spin-independent case. The range of variation depends on the decay length of the mediator.