Search

Since the successful discovery of neutrinos, their origin is still a mystery until the association with TXS 0506+056. More messengers are achievable to study the intrinsic mechanism of extreme phenomena. Recently, Fermi-LAT Collaboration published the fourth catalogue of active galactic nuclei (4LAC), together with Data Release 2 later, including totally 3148 sources. The majority of these objects are blazars, which are classified into flat-spectrum radio quasars (FSRQs), BL Lac-type objects (BLLs), and blazars of uncertain type (BCUs) according to their optical observation feature. The BCUs take up to 38.2 per cent of total, whose classification is quite challenging and manpower consuming. However with the remarkable advances of technology, deep learning has been widely applied in astronomy. In this work, we take the advantage of 11 machine learning algorithms plus the convolutional neural network (CNN)-based deep learning algorithm to classify BCUs based on 10 parameters and the broad-band spectral energy distribution of each object obtained with vou-blazars. On average, this method has impressive performance, reaching above 95 per cent of balanced accuracy for the training sample, best among the studies so far. We correlate the IceCube neutrinos and blazars in 4LAC, found a few possible associations. With the machine learning prediction, we later elaborate the association of these BCUs with neutrinos samples and find out most of the BCUs associated with neutrinos are with low synchrotron peak frequency, which may be due to the energy distribution of high-energy particles. We propose neutrinos might be another feature for objects classification in the future. [ABSTRACT FROM AUTHOR]

The status of the Baikal-GVD neutrino telescope under construction and its main scientific results are presented. The detector consists of 2916 optical sensors located at 81 vertical strings deep below the surface of Lake Baikal. Its geometric configuration is optimized for detecting neutrinos with energies above 100 TeV. Events from muon neutrinos were identified, the flux of which is consistent with the expectation for the flux of atmospheric neutrinos. The data obtained during the alerts of the ANTARES and IceCube telescopes were analyzed. Candidate events for high-energy neutrinos of astrophysical origin have been obtained. [ABSTRACT FROM AUTHOR]

The wave instability acts in astrophysical plasmas to redistribute energy and momentum in the absence of frequent collisions. There are many different types of waves, and it is important to quantify the wave energy density and growth rate for understanding what types of wave instabilities are possible in different plasma regimes. There are many situations throughout our Universe where plasmas contain a significant fraction of relativistic particles. Theoretical estimates for the wave energy density and growth rate are constrained to either field-aligned propagation angles or non-relativistic considerations. Based on linear theory, we derive the analytic expressions for the energy density and growth rate of an arbitrary resonant wave with an arbitrary propagation angle in relativistic plasmas. For this derivation, we calculate the Hermitian and anti-Hermitian parts of the relativistic-plasma dielectric tensor. We demonstrate that our analytic expression for the wave energy density presents an explicit energy increase in resonant waves in the wavenumber range where the analytic expression for the growth rate is positive (i.e. where a wave instability is driven). For this demonstration, we numerically analyse the loss-cone driven instability, as a specific example, in which the whistler-mode waves scatter relativistic electrons into the loss cone in the radiation belt. Our analytic results further develop the basis for linear theory to better understand the wave instability, and have the potential to combine with quasi-linear theory, which allows to study the time evolution of not only the particle momentum distribution function but also resonant wave properties through an instability. [ABSTRACT FROM AUTHOR]

The Zwicky Transient Facility (ZTF) performs a systematic neutrino follow-up programme, searching for optical counterparts to high-energy neutrinos with dedicated Target-of-Opportunity (ToO) observations. Since first light in March 2018, ZTF has taken prompt observations for 24 high-quality neutrino alerts from the IceCube Neutrino Observatory, with a median latency of 12.2 h from initial neutrino detection. From two of these campaigns, we have already reported tidal disruption event (TDE) AT 2019dsg and likely TDE AT 2019fdr as probable counterparts, suggesting that TDEs contribute >7.8 per cent of the astrophysical neutrino flux. We here present the full results of our programme through to December 2021. No additional candidate neutrino sources were identified by our programme, allowing us to place the first constraints on the underlying optical luminosity function of astrophysical neutrino sources. Transients with optical absolutes magnitudes brighter that −21 can contribute no more than 87 per cent of the total, while transients brighter than −22 can contribute no more than 58 per cent of the total, neglecting the effect of extinction and assuming they follow the star formation rate. These are the first observational constraints on the neutrino emission of bright populations such as superluminous supernovae. None of the neutrinos were coincident with bright optical AGN flares comparable to that observed for TXS 0506+056/IC170922A, with such optical blazar flares producing no more than 26 per cent of the total neutrino flux. We highlight the outlook for electromagnetic neutrino follow-up programmes, including the expected potential for the Rubin Observatory. [ABSTRACT FROM AUTHOR]

Understanding the time-dependent relationship between the Sun's variability and cosmic rays (GCR) is essential for developing predictive models of energetic radiation in space. When traveling inside the heliosphere, GCRs are affected by magnetic turbulence and solar wind disturbances which result in the so-called solar modulation effect. To investigate this phenomenon, we have performed a data-driven analysis of the temporal dependence of the GCR flux over the solar cycle. With a global statistical inference of GCR data collected in space by AMS-02 and PAMELA on monthly basis, we have determined the rigidity and time dependence of the GCR diffusion mean free path. Here we present our results for GCR protons, we discuss their interpretation in terms of basic processes of particle transport and their relations with the dynamics of the heliospheric plasma. [ABSTRACT FROM AUTHOR]

Cosmic rays in star-forming galaxies are a dominant source of both diffuse γ-ray emission and ionization in gas too deeply shielded for photons to penetrate. Though the cosmic rays responsible for γ-rays and ionization are of different energies, they are produced by the same star formation-driven sources, and thus galaxies' star formation rates, γ-ray luminosities, and ionization rates should all be linked. In this paper, we use up-to-date cross-section data to determine this relationship, finding that cosmic rays in a galaxy of star formation rate |$\dot{M}_*$| and gas depletion time t dep produce a maximum primary ionization rate ζ ≈ 1 × 10−16(t dep/Gyr)−1 s−1 and a maximum γ-ray luminosity |$L_\gamma \approx 4\times 10^{39} (\dot{M}_*/\mathrm{M}_\odot \mbox{ yr}^{-1})$| erg s−1 in the 0.1–100 GeV band. These budgets imply either that the ionization rates measured in Milky Way molecular clouds include a significant contribution from local sources that elevate them above the Galactic mean, or that CR-driven ionization in the Milky Way is enhanced by sources not linked directly to star formation. Our results also imply that ionization rates in starburst systems are only moderately enhanced compared to those in the Milky Way. Finally, we point out that measurements of γ-ray luminosities can be used to place constraints on galactic ionization budgets in starburst galaxies that are nearly free of systematic uncertainties on the details of cosmic ray acceleration. [ABSTRACT FROM AUTHOR]

Neutrino emission from-ray bursts (GRBs) has been sought for a long time, and stringent limits on the most accredited GRB emission models have been obtained from IceCube. Multiwavelength GRB observations of the last decades have improved our knowledge of the GRB emission parameters, such as the Lorentz factor and the luminosity, which can vary from one GRB to another by several orders of magnitude. Empirical correlations among such parameters have been identified during the prompt phase, with direct implications on GRB models. In this work, we use the PSLab open-access code, developed for IceCube data analyses, to search for individual neutrino emission from the prompt and afterglow phases of selected GRBs, and for stacking emission from the ensemble of such GRBs. For the afterglow phase, we focus on GRBs with X-ray flares and plateaus in particular. While past stacking searches assumed the same GRB fluence at Earth, we present a stacking scheme based on physically motivated GRB weights. Moreover, we conceive a new methodology for the prompt phase that uses the empirical correlations to infer the GRB luminosity and Lorentz factor, when redshift measurements are not available. We do not observe any significant neutrino excess. Hence, we set constraints on the GRB neutrino fluxes and on relevant GRB parameters, including the magnetic field in the jet. Notably, the baryon loading is found to be less than ten for typical GRB jets. [ABSTRACT FROM AUTHOR]

Context. The source population(s) of ultra-high energy cosmic rays (UHECRs) with energies of -57 = 1018 eV (57 EeV) are still unknown and continue to be a subject of debate. The published arrival directions and energies of 303 UHECRs from the Pierre Auger Observatory and Telescope Array enable correlations with astronomical sources. However, deflections of UHECRs in the Galactic Magnetic Field (GMF) can be considerable, especially for heavy UHECR compositions. Aims. We aim to constrain the source(s) of UHECRs by focusing on the subset of UHECRs that experience minimal deflections by the Galactic magnetic field (GMF). Methods. We used Monte Carlo simulations of UHECR trajectories in a total of eight posited GMF models (and six UHECR compositions from H to Fe) to identify two subsamples of about 40 UHECRs. The H compositions of these subsamples suffer deflections of less than a few degrees in one (or most) of the GMFs. Both the total UHECR sample and the "least-deflected" (vs. the remaining "more-deflected") subsamples of UHECRs were cross-correlated with catalogs of astronomical sources (at D. 100 Mpc) and neutrino arrival directions. Results. For H compositions, the full sample of UHECRs is most closely correlated with Cen A, nearby (<75 Mpc) radiogalaxies, and optically selected active galactic nuclei (AGNs); the least-deflected sub sample shows a most consistent correlation with nearby (D. 25 Mpc) galaxies, although some GMF models show a preference for the IceCube muon-neutrino arrival detections. For oxygen compositions, the out-of-galaxy arrival directions of least-deflected UHECRs fall on the extragalactic plane (and thus close to nearby galaxies) in many GMFs. For Fe compositions, the out-of-galaxy UHECR arrival directions typically originate in a region 30 deg offset from Cen A, except in the case of the JF12 model; this offfset can be decreased by re-scaling (by 50%) the magnitudes of the dipole and disk fields of the relevant GMFs. [ABSTRACT FROM AUTHOR]

Context. The Crab Nebula emits exceptionally bright non-thermal radiation across the entire wavelength range from the radio to the most energetic photons. So far, the underlying physical model of a relativistic wind from the pulsar terminating in a hydrodynamic standing shock has remained fairly unchanged since the early 1970s when it was first introduced. One of the predictions of this model is an increase in the toroidal magnetic field downstream from the shock where the flow velocity drops quickly with increasing distance until it reaches its asymptotic value, matching the expansion velocity of the nebula. Aims. The magnetic field strength in the nebula is poorly known. Using the recent measurements of the spatial extension and improved spectroscopy of the gamma-ray nebula, it has become –for the first time – feasible to determine in a robust way both the strength as well as the radial dependence of the magnetic field in the downstream flow. Methods. In this work, we introduce a detailed radiative model which was used to calculate the emission from non-thermal electrons (synchrotron and inverse Compton) as well as from thermal dust present in the Crab Nebula in a self-consistent way to compare it quantitatively with observational data. Special care was given to the radial dependence of the electron and seed field density. Results. The radiative model was used to estimate the parameters related to the electron populations responsible for radio and optical/X-ray synchrotron emission. In this context, the mass of cold and warm dust was determined. A combined fit based upon a χ2 minimisation successfully reproduced the complete data set used. For the best-fitting model, the energy density of the magnetic field dominates over the particle energy density up to a distance of ≈1.3 rs (rs: distance of the termination shock from the pulsar). The very high energy (VHE: E > 100 GeV) and ultra-high energy (UHE: E > 100 TeV) gamma-ray spectra set the strongest constraints on the radial dependence of the magnetic field, favouring a model where B(r) = (264 ± 9) μG(r/rs)−0.51 ± 0.03. For a collection of VHE measurements during epochs of higher hard X-ray emission, a significantly different solution B(r) = (167 ± 5) μG(r/rs)−0.29(+0.03, −0.06) is found. Conclusions. The high energy (HE: E > 100 MeV) and VHE gamma-ray observations of the Crab Nebula lift the degeneracy of the synchrotron emission between particle and magnetic field energy density. The reconstructed magnetic field and its radial dependence indicates a ratio of Poynting to kinetic energy flux σ ≈ 0.1 at the termination shock, which is ≈30 times larger than estimated up to now. Consequently, the confinement of the nebula would require additional mechanisms to slow the flow down through, for example, excitation of small-scale turbulence with possible dissipation of the magnetic field. [ABSTRACT FROM AUTHOR]

Around one-third of the point-like sources in the Fermi-LAT catalogues remain as unidentified sources (unIDs) today. Indeed, these unIDs lack a clear, univocal association with a known astrophysical source. If dark matter (DM) is composed of weakly interacting massive particles (WIMPs), there is the exciting possibility that some of these unIDs may actually be DM sources, emitting gamma-rays from WIMPs annihilation. We propose a new approach to solve the standard, machine learning (ML) binary classification problem of disentangling prospective DM sources (simulated data) from astrophysical sources (observed data) among the unIDs of the 4FGL Fermi-LAT catalogue. We artificially build two systematic features for the DM data which are originally inherent to observed data: the detection significance and the uncertainty on the spectral curvature. We do it by sampling from the observed population of unIDs, assuming that the DM distributions would, if any, follow the latter. We consider different ML models: Logistic Regression, Neural Network (NN), Naive Bayes, and Gaussian Process, out of which the best, in terms of classification accuracy, is the NN, achieving around |$93.3{{\ \rm per\ cent}} \pm 0.7{{\ \rm per\ cent}}$| performance. Other ML evaluation parameters, such as the True Negative and True Positive rates, are discussed in our work. Applying the NN to the unIDs sample, we find that the degeneracy between some astrophysical and DM sources can be partially solved within this methodology. None the less, we conclude that there are no DM source candidates among the pool of 4FGL Fermi-LAT unIDs. [ABSTRACT FROM AUTHOR]

Summary: Igneous processes were quite widespread in the small bodies of the Solar System (SBSS) and were initially fueled by short-lived radioisotopes, the proto-Sun, impact heating, and differentiation heating. Once they finished, long-lived radioisotopes continued to warm the active bodies of the Earth, (possibly) Venus, and the cryovolcanism of Enceladus.The widespread presence of olivine and pyroxenes in planets and also in SBSS suggests that they were not necessarily the product of igneous processes and they might have been recycled from previous nebular processes or entrained in comets from interstellar space. The difference in temperature between the inner and the outer Solar System has clearly favored thermal annealing of the olivine close to the proto-Sun. Transport of olivine within the Solar System probably occurred also due to protostellar jets and winds but the entrainment in SBSS from interstellar space would overcome the requirement of initial turbulent regime in the protoplanetary nebula.

The alpha magnetic spectrometer (AMS) is a high-precision particle detector onboard the International Space Station containing six different subdetectors. The transition radiation detector and electromagnetic calorimeter (ECAL) are used to separate electrons/positrons from the abundant cosmic-ray proton background. The positron flux measured in space by AMS falls with a power law which unexpectedly softens above 25 GeV and then hardens above 280 GeV. Several theoretical models try to explain these phenomena, and a more accurate measurement of positrons at higher energies is needed to help test them. The currently used methods to reject the proton background at high energies involve extrapolating shower features from the ECAL to use as inputs for boosted decision tree and likelihood classifiers. We present a new approach for particle identification with the AMS ECAL using deep learning (DL). By taking the energy deposition within all the ECAL cells as an input and treating them as pixels in an image-like format, we train an MLP, a CNN, and multiple ResNets and convolutional vision transformers (CvTs) as shower classifiers. Proton rejection performance is evaluated using Monte Carlo (MC) events and ISS data separately. For MC, using events with a reconstructed energy between 0.2–2 TeV, at 90% electron accuracy, the proton rejection power of our CvT model is more than five times that of the other DL models. Similarly, for ISS data with a reconstructed energy between 50–70 GeV, the proton rejection power of our CvT model is more than 2.5 times that of the other DL models.

The Andromeda galaxy is the closest spiral galaxy to us and has been the subject of numerous studies. It harbors a massive dark matter halo, which may span up to ~600 kpc across and comprises ~90% of the galaxy's total mass. This halo size translates into a large diameter of 42° on the sky, for an M31-Milky Way (MW) distance of 785 kpc, but its presumably low surface brightness makes it challenging to detect with γ-ray telescopes. Using 7.6 yr of Fermi Large Area Telescope (Fermi-LAT) observations, we make a detailed study of the γ-ray emission between 1-100 GeV toward M31's outer halo, with a total field radius of 60° centered at M31, and perform an in-depth analysis of the systematic uncertainties related to the observations. We use the cosmic-ray propagation code GALPROP to construct specialized interstellar emission models to characterize the foreground γ-ray emission from the MW, including a self-consistent determination of the isotropic component. We find evidence for an extended excess that appears to be distinct from the conventional MW foreground, having a total radial extension upward of ~120-200 kpc from the center of M31. We discuss plausible interpretations of the excess emission, but emphasize that uncertainties in the MW foreground-and in particular, modeling of the H i-related components-have not been fully explored and may impact the results.

In order to identify the sources of the observed diffuse high-energy neutrino flux, it is crucial to discover their electromagnetic counterparts. To increase the sensitivity of detecting counterparts of transient or variable sources by telescopes with a limited field of view, IceCube began releasing alerts for single high-energy (Eνâ> â60 TeV) neutrino detections with sky localisation regions of order 1° radius in 2016. We used Pan-STARRS1 to follow-up five of these alerts during 2016-2017 to search for any optical transients that may be related to the neutrinos. Typically 10-20 faint (miP1âââ22.5 mag) extragalactic transients are found within the Pan-STARRS1 footprints and are generally consistent with being unrelated field supernovae (SNe) and AGN. We looked for unusual properties of the detected transients, such as temporal coincidence of explosion epoch with the IceCube timestamp, or other peculiar light curve and physical properties. We found only one transient that had properties worthy of a specific follow-up. In the Pan-STARRS1 imaging for IceCube-160427A (probability to be of astrophysical origin of ∼50%), we found a SN PS16cgx, located at 10.0′ from the nominal IceCube direction. Spectroscopic observations of PS16cgx showed that it was an H-poor SN at redshift zâ=â0.2895â ±â 0.0001. The spectra and light curve resemble some high-energy Type Ic SNe, raising the possibility of a jet driven SN with an explosion epoch temporally coincident with the neutrino detection. However, distinguishing Type Ia and Type Ic SNe at this redshift is notoriously difficult. Based on all available data we conclude that the transient is more likely to be a Type Ia with relatively weak Siâ» II absorption and a fairly normal rest-frame r-band light curve. If, as predicted, there is no high-energy neutrino emission from Type Ia SNe, then PS16cgx must be a random coincidence, and unrelated to the IceCube-160427A. We find no other plausible optical transient for any of the five IceCube events observed down to a 5σ limiting magnitude of miP1â≈â22 mag, between 1 day and 25 days after detection.

We present the first full-sky analysis of the cosmic ray arrival direction distribution with data collected by the High-Altitude Water Cherenkov and IceCube observatories in the northern and southern hemispheres at the same median primary particle energy of 10 TeV. The combined sky map and angular power spectrum largely eliminate biases that result from partial sky coverage and present a key to probe into the propagation properties of TeV cosmic rays through our local interstellar medium and the interaction between the interstellar and heliospheric magnetic fields. From the map, we determine the horizontal dipole components of the anisotropy δ 0h = 9.16 ×10-4 and δ 6h = 7.25 ×10-4 (±0.04 × 10-4). In addition, we infer the direction (229.°2 ± 3.°5 R.A., 11.°4 ± 3.°0 decl.) of the interstellar magnetic field from the boundary between large-scale excess and deficit regions from which we estimate the missing corresponding vertical dipole component of the large-scale anisotropy to be δN ∼ -3.97+1.0-2.0 × 10-4.

We present the first full-sky analysis of the cosmic ray arrival direction distribution with data collected by the High-Altitude Water Cherenkov and IceCube observatories in the northern and southern hemispheres at the same median primary particle energy of 10 TeV. The combined sky map and angular power spectrum largely eliminate biases that result from partial sky coverage and present a key to probe into the propagation properties of TeV cosmic rays through our local interstellar medium and the interaction between the interstellar and heliospheric magnetic fields. From the map, we determine the horizontal dipole components of the anisotropy δ 0h = 9.16 ×10 -4 and δ 6h = 7.25 ×10 -4 (±0.04 × 10 -4 ). In addition, we infer the direction (229.°2 ± 3.°5 R.A., 11.°4 ± 3.°0 decl.) of the interstellar magnetic field from the boundary between large-scale excess and deficit regions from which we estimate the missing corresponding vertical dipole component of the large-scale anisotropy to be δN ∼ -3.97 +1.0-2.0 × 10 -4 .

Extreme high-frequency peaked BL Lacs (EHBLs) are characterized by a synchrotron peak frequency exceeding 1017 Hz and a second peak that can be in the energy range of few GeVs to several TeVs. The Major Atmospheric Gamma Imaging Cherenkov Telescope (MAGIC) detected multi-TeV gamma-rays on 2018 April 19 for the first time from the EHBL PGC 2402248, which was simultaneously observed in multiwavelength by several other instruments. The broad-band spectral energy distribution of the source is conventionally modelled using the leptonic and the hadronic models. Due to the success of the photohadronic model in interpreting the enigmatic very high energy (VHE) flaring events from many high-energy blazars, we extend this model to explain the VHE events from PGC 2402248 observed by MAGIC telescopes and compare our results with other models. We conclude that the photohadronic fits are comparable and even fare better than most other models. Furthermore, we show that the spectrum is not hard and is in a low-emission state. The estimated bulk Lorentz factor for this flaring event is found to be ≲34. [ABSTRACT FROM AUTHOR]

The recent detections of binary stellar mass black hole mergers by the LIGO and Virgo Collaborations suggest that such mergers are common occurrences. Galaxy mergers further indicate that supermassive black holes in centres of galaxies also merge and are typically expected to have had at least one merger in their lifetime, possibly many. In the presence of a jet, these mergers are almost always accompanied by a change of the jet direction and a connected jet precession motion, leading to interactions of the jet with ambient matter and producing high-energy particles, and consequently high-energy gamma-rays and neutrinos. In this work, we investigate the possibility under which conditions such mergers could be the sources of the diffuse astrophysical neutrino flux measured by the IceCube Neutrino Observatory. The main free parameters in the calculation concern the frequency of the mergers and the fraction of energy that is transferred from the gravitationally released energy to neutrinos. We show that the merger rate for SMBBHs must lie between ∼10−7 and 10−5 Gpc−3 yr−1. The ratio of energy going to neutrinos during such mergers lies then between ∼10−6 and 3 × 10−4. For stellar mass BBH mergers, the rate needs to be ∼10–100 Gpc−3 yr−1 and the expected ratio of neutrino to GW energy lies in a comparable range as for SMBBHs, ∼2 × 10−5–10−3. These values lie in a reasonable parameter range, so that the production of neutrinos at the level of the detected neutrino flux is a realistic possibility. [ABSTRACT FROM AUTHOR]

ADA, short for Astroparticle Detectors Array, is an educational project aiming to detect cosmic radiation and possibly high-energy particles known as ultra-high-energy cosmic rays (UHECRs) or even to spot a supernova event. Its working process is the same as that used in professional cosmic ray observatories: it consists of simple detectors spread over the entire Italian territory and beyond. The detectors are hosted among high schools, associations, and private astronomical observatories. ADA has been operating since 2013 and was brought about with the intention of promoting astroparticle physics to any given level of outreach. Furthermore, ADA is becoming an interesting tool not only for teachers but also for independent and keen scientists. Over the years, we have discovered the importance of having a long series of data for studying the relation between and among cosmic rays, weather, and space weather and to investigate the main cause of oscillations in cosmic ray data. In this paper, we show what we find to be the most compelling results, such as the beautiful symmetry of the behavior between muons and the atmospheric temperature and, likewise, the evident anti-correlation between the intensity of the muons at ground level compared with solar activity. [ABSTRACT FROM AUTHOR]

Here, we present calculations on the energy delivered (and heating) by realistic cosmic rays (CRs) field at a typical molecular clump. The current model describes, with unprecedented spatial resolution, the energy delivery by a realistic CR field in molecular clumps. The calculations were performed employing the Geant4 code (considering full cascade physical processes and hadron physics) considering the cosmic ray field taken from the Voyager spacecraft measurements in the interstellar medium. The results showed that the total energy deposition rate, considering light particles (protons, electrons and alphas), medium-mass ions and heavy-ions, ranges from 400 MeV/g/s in the outer layer (at 105 AU) to roughly 100 MeV/g/s in the inner layer of the model (below 0.1 AU). The main energy deposition rate is due to the incoming protons. Incoming alphas represent 15–20 per cent of the energy deposition. In the deep core of the cloud, the fraction of energy delivered by medium-mass ions, electrons, and heavy ions are 5 per cent, 2.5 per cent, and 1 per cent, respectively. The heating induced by cosmic rays seems to affect mostly the regions above ∼500 AU. Considering a balanced heat model with warm dust grains (T∼16–18 K), we observe a small bump in temperature at 2000–5000 AU. We suggest this temperature enhancement by CRs might have some affect on the molecular formation or cometary formation in pristine Oort cloud region inside the Solar System. [ABSTRACT FROM AUTHOR]

Positron annihilation line at 511 keV is a known component of the gamma-ray diffuse emission. It is believed to be produced in the Galaxy, but there could be possible extragalactic contribution as well. E.g., positrons can be produced in jets of active galactic nuclei (AGN) and after that accumulate and gradually annihilate in hot gaseous halos around galaxies. In this work we test this hypothesis in application to an individual object—the Andromeda galaxy (M31) which is close and has a supermassive black hole in its center, which powered an AGN before. We compute the growth history of the supermassive black hole in M31, relate it to the evolution of jet luminosity and estimate the positron content in its halo. We calculate the 511 keV photon flux due to positron annihilation which should be observed at Earth and find the value of around photon cm s . It is very close to the observational limits ( photon cm s ) set by the INTEGRAL/SPI in the assumption of the point source, so further observations would be able to constrain leptonic models of the jets and propagation of cosmic rays in the circumgalactic medium of large spiral galaxies. [ABSTRACT FROM AUTHOR]

On its 10th edition, we provide some Concluding Remarks to the IWARA Workshop with highlights and comments meant to enrich and give a context to the oral scientific presentations. [ABSTRACT FROM AUTHOR]

We consider the synchrotron emission from electrons out in the Galactic halo bubble region where the Fermi bubble structures reside. Utilizing a simple analytical expression for the non-thermal electron distribution and a toy magnetic field model, we simulate polarized synchrotron emission maps at a frequency of 30 GHz. Comparing these maps with the observational data, we obtain constraints on the parameters of our toy Galactic halo bubble magnetic field model. Utilizing this parameter value range for the toy magnetic field model, we determine the corresponding range of arrival directions and suppression factors of ultra high energy cosmic rays (UHECRs) from potential local source locations. We find that high levels of flux suppression (down to 2 per cent) and large deflection angles (≥80°) are possible for source locations whose line of sight pass through the Galactic halo bubble region. We conclude that the magnetic field out in the Galactic halo bubble region can strongly dominate the level of deflection UHECRs experience whilst propagating from local sources to Earth. [ABSTRACT FROM AUTHOR]

The geographic South Pole provides unique opportunities to study cosmic particles in the Southern Hemisphere. It represents an optimal location to deploy large-scale neutrino telescopes in the deep Antarctic ice, such as AMANDA or IceCube. In both cases, the presence of an array, constructed to observe extensive air showers, enables hybrid measurements of cosmic rays. While additional neutron monitors can provide information on solar cosmic rays, large detector arrays, like SPASE or IceTop, allow for precise measurements of cosmic rays with energies above several 100 TeV. In coincidence with the signals recorded in the deep ice, which are mostly due to the high-energy muons produced in air showers, this hybrid detector setup provides important information about the nature of cosmic rays. In this review, we will discuss the historical motivation and developments towards measurements of cosmic rays at the geographic South Pole and highlight recent results reported by the IceCube Collaboration. We will emphasize the important contributions by Thomas K. Gaisser and his colleagues that ultimately led to the rich Antarctic research program which today provides crucial insights into cosmic-ray physics. [ABSTRACT FROM AUTHOR]

We present a search for coincidence between IceCube TeV neutrinos and fast radio bursts (FRBs). During the search period from 2010 May 31 to 2016 May 12, a total of 29 FRBs with 13 unique locations have been detected in the whole sky. An unbinned maximum likelihood method was used to search for spatial and temporal coincidence between neutrinos and FRBs in expanding time windows, in both the northern and southern hemispheres. No significant correlation was found in six years of IceCube data. Therefore, we set upper limits on neutrino fluence emitted by FRBs as a function of time window duration. We set the most stringent limit obtained to date on neutrino fluence from FRBs with an E -2 energy spectrum assumed, which is 0.0021 GeV cm-2 per burst for emission timescales up to ∼102 s from the northern hemisphere stacking search.

Abstract: We present shell model calculations of nuclear neutrino energy spectra for 70 sd-shell nuclei over the mass number range A = 21–35. Our calculations include nuclear excited states as appropriate for the hot and dense conditions characteristic of pre-collapse massive stars. We consider neutrinos produced by charged lepton captures and decays, and for the first time in tabular form, neutral current nuclear deexcitation, providing neutrino energy spectra on the Fuller–Fowler–Newman temperature–density grid for these interaction channels for each nucleus. We use the full sd-shell model space to compute initial nuclear states up to 20 MeV excitation with transitions to final states up to 35–40 MeV, employing a modification of the Brink-Axel hypothesis to handle high-temperature population factors and the nuclear partition functions.

High energy astrophysics has been actively developed since the last decades. The photons and neutrinos produced at astrophysical sources were detected up to energies of PeV, while the measured spectrum of cosmic rays lasts from GeV to ZeV energies. The challenges of modern detectors are not only pushing towards higher energies to reach the cosmic acceleration limit, but also increasing the resolution of the reconstruction of the energy, arrival direction and the type of the cosmic particle. Due to low flux of these particles, their detection is feasible only by measurement of air-showers, atmospheric cascades of secondary particles induced by the primary one. One of the promising methods of the air-shower detection is the sparse digital radio arrays, a young, but cost-effective technique aimed at the cosmic particles with energies beyond PeV. The future detectors aimed at detection of cosmic rays, photons and neutrinos of extreme energies are based on the antenna arrays located either in ice or on mountain slopes. The latter are sensitive both to downward-directional air-showers induced by cosmic rays, and upward-going ones produced by skimming neutrinos interacting with rock. The prototyping of such an array requires appropriate location (high-altitude mountains) with corresponding infrastructure and ideally additional cosmic-ray detector for the cross-calibration of antennas. The-Tien Shan High-altitude Scientific Station (TSHSS) located near Almaty, Kazakhstan, and equipped with air-shower instruments, is an ideal place for this prototype. In this work we discuss the prospects of the radio technique, its current challenges and report the recent advances of the prototype radio installations at TSHSS.

Dark matter (DM) with self-interactions is a promising solution for the small-scale problems of the standard cosmological model. Here we perform the first cosmological simulation of frequent DM self-interactions, corresponding to small-angle DM scatterings. The focus of our analysis lies in finding and understanding differences to the traditionally assumed rare DM (large-angle) self-scatterings. For this purpose, we compute the distribution of DM densities, the matter power spectrum, the two-point correlation function, and the halo and subhalo mass functions. Furthermore, we investigate the density profiles of the DM haloes and their shapes. We find that overall large-angle and small-angle scatterings behave fairly similarly with a few exceptions. In particular, the number of satellites is considerably suppressed for frequent compared to rare self-interactions with the same cross-section. Overall, we observe that while differences between the two cases may be difficult to establish using a single measure, the degeneracy may be broken through a combination of multiple ones. For instance, the combination of satellite counts with halo density or shape profiles could allow discriminating between rare and frequent self-interactions. As a by-product of our analysis, we provide – for the first time – upper limits on the cross-section for frequent self-interactions. [ABSTRACT FROM AUTHOR]

We re-examine possible dependencies on redshift of the spectral parameters of blazars observed at very-high energies (VHEs) with Imaging Atmospheric Cherenkov telescopes. This is relevant to assess potential effects with the source distance of the photon to axion-like particle mixing that would deeply affect the propagation of VHE photons across the Universe. We focus our spectral analysis on 38 BL Lac objects (32 high-peaked and 6 intermediate-peaked) up to redshift z ≃ 0.5, and a small sample of 5 Flat Spectrum Radio Quasars up to z  = 1 treated independently to increase the redshift baseline. The 78 independent spectra of these sources are first of all carefully corrected for the gamma–gamma interaction with photons of the Extragalactic Background Light that are responsible for the major redshift-dependent opacity effect. Then, the corrected spectra are fitted with simple power laws to infer the intrinsic spectral indices Γem at VHE, to test the assumption that such spectral properties are set by the local rather than the global cosmological environment. We find some systematic anticorrelations with redshift of Γem that might indicate, although with low-significance, a spectral anomaly potentially requiring a revision of the photon propagation process. More conclusive tests with higher statistical significance will require the observational improvements offered by the forthcoming new generation of Cherenkov arrays (CTA, ASTRI, LHAASO). [ABSTRACT FROM AUTHOR]

The observed spectral lags of gamma-ray bursts (GRBs) have been widely used to explore possible violations of Lorentz invariance. However, these studies were generally performed by concentrating on the rough time lag of a single highest-energy photon and ignoring the intrinsic time lag at the source. A new way to test nonbirefringent Lorentz-violating effects has been proposed by analyzing the multi-photon spectral-lag behavior of a GRB that displays a positive-to-negative transition. This method gives both a plausible description of the intrinsic energy-dependent time lag and comparatively robust constraints on Lorentz-violating effects. In this work, we conduct a systematic search for Lorentz-violating photon dispersion from the spectral-lag transition features of 32 GRBs. By fitting the spectral-lag data of these 32 GRBs, we place constraints on a variety of isotropic and anisotropic Lorentz-violating coefficients with mass dimension d = 6 and 8. While our dispersion constraints are not competitive with existing bounds, they have the promise to complement the full coefficient space. [ABSTRACT FROM AUTHOR]

Since its discovery in 1995, the high-energy peaked blazar 1ES 2344+514 has undergone several episodes of GeV–TeV flaring and has been observed in the multiwavelength by several telescopes. The observed X-ray spectrum of 1996 and the flaring event of 2016 establish that 1ES 2344+514 has a temporary behaviour like that of an extremely high-energy peaked BL Lacertae object (EHBL). Such behaviour has also been observed in several nearby high-energy peaked blazars. We use the photohadronic model to account for the GeV–TeV flaring observed events of 1995 and 2007. Also, a recently proposed two-zone photohadronic model, which is successful in explaining the multi-TeV flaring events of many transient EHBL-like sources, is employed to explain the GeV–TeV flaring spectra of MJD 57611 and MJD 57612. We find that the zone-2 parameters of the two-zone photohadronic model play a central role in explaining these spectra. This is probably an indication of a new type of transient EHBL-like source. We find that our fits to the observed spectra are comparable or better than the other leptonic and hadronic models employed in the literature to address the same issue. [ABSTRACT FROM AUTHOR]

In this work, we revisit five different point sources within or behind galaxy clusters to constrain the coupling constant between axion-like particles (ALPs) and photons. We use three distinct machine learning (ML) techniques and compare our results with a standard χ2 analysis. For the first time, we apply approximate Bayesian computation to search for ALPs and find consistently good performance across ML classifiers. Further, we apply more realistic 3D magnetic field simulations of galaxy clusters and compare our results with previously used 1D simulations. We find constraints on the ALP-photon coupling at the level of state-of-the-art bounds with |$g_{a\gamma \gamma } \lesssim 0.6 \times 10^{-12} \, \rm{GeV}^{-1}$|⁠ , hence improving on previous constraints obtained from the same observations. [ABSTRACT FROM AUTHOR]

The presence of massive neutrinos in the early Universe is expected to have influenced the observed distribution of galaxies and their observed motions. In this work, we explore whether measurements of galaxy peculiar velocities could allow us to improve upon neutrino mass constraints from galaxy redshift surveys alone. Using Fisher matrix forecasts, we show that the galaxy peculiar motions do contain information on the sum of the masses of neutrinos ∑ m ν, and that this information can be used to improve upon constraints that may be obtained from low-redshift galaxy surveys (z < 0.5) combined with Planck measurements of the cosmic microwave background. Compared to the full constraining power offered by Planck and higher redshift DESI data, we find that the benefit of including peculiar velocities only marginally improves neutrino mass constraints. However, when one is limited to modelling only quasi-linear scales, adds additional degrees of freedom via a varying number of effective neutrino species (N eff), or does not include information from Planck , our results show that the inclusion of peculiar velocity measurements can still substantially improve upon the constraints. As such, we demonstrate that it may be possible to achieve upper bounds on ∑ m ν (⁠|$\sigma _{\sum m_{\nu }} = 0.051$| eV; 68 per cent confidence limit) comparable to those from Planck , from spectroscopic galaxy surveys alone, as long as the peculiar velocity data are available. This could allow for an independent comparison between constraints on ∑ m ν from the early- and late-time Universe probes that are particularly timely given current cosmological parameter tensions. [ABSTRACT FROM AUTHOR]

On February 17, 2016, the IceCube real-time neutrino search identified, for the first time, three muon neutrino candidates arriving within 100 s of one another, consistent with coming from the same point in the sky. Such a triplet is expected once every 13.7 years as a random coincidence of background events. However, considering the lifetime of the follow-up program the probability of detecting at least one triplet from atmospheric background is 32%. Follow-up observatories were notified in order to search for an electromagnetic counterpart. Observations were obtained by Swift's X-ray telescope, by ASAS-SN, LCO and MASTER at optical wavelengths, and by VERITAS in the very-high-energy gamma-ray regime. Moreover, the Swift BAT serendipitously observed the location 100 s after the first neutrino was detected, and data from the Fermi LAT and HAWC observatory were analyzed. We present details of the neutrino triplet and the follow-up observations. No likely electromagnetic counterpart was detected, and we discuss the implications of these constraints on candidate neutrino sources such as gamma-ray bursts, core-collapse supernovae and active galactic nucleus flares. This study illustrates the potential of and challenges for future follow-up campaigns.

The IceCube neutrino observatory has established the existence of a flux of high-energy astrophysical neutrinos, which is inconsistent with the expectation from atmospheric backgrounds at a significance greater than 5σ. This flux has been observed in analyses of both track events from muon neutrino interactions and cascade events from interactions of all neutrino flavors. Searches for astrophysical neutrino sources have focused on track events due to the significantly better angular resolution of track reconstructions. To date, no such sources have been confirmed. Here we present the first search for astrophysical neutrino sources using cascades interacting in IceCube with deposited energies as small as 1 TeV. No significant clustering was observed in a selection of 263 cascades collected from 2010 May to 2012 May. We show that compared to the classic approach using tracks, this statistically independent search offers improved sensitivity to sources in the southern sky, especially if the emission is spatially extended or follows a soft energy spectrum. This enhancement is due to the low background from atmospheric neutrinos forming cascade events and the additional veto of atmospheric neutrinos at declinations ≲-30.

We present an all-sky search for muon neutrinos produced during the prompt γ-ray emission of 1172 gamma-ray bursts (GRBs) with the IceCube Neutrino Observatory. The detection of these neutrinos would constitute evidence for ultra-high-energy cosmic-ray (UHECR) production in GRBs, as interactions between accelerated protons and the prompt γ-ray field would yield charged pions, which decay to neutrinos. A previously reported search for muon neutrino tracks from northern hemisphere GRBs has been extended to include three additional years of IceCube data. A search for such tracks from southern hemisphere GRBs in five years of IceCube data has been introduced to enhance our sensitivity to the highest energy neutrinos. No significant correlation between neutrino events and observed GRBs is seen in the new data. Combining this result with previous muon neutrino track searches and a search for cascade signature events from all neutrino flavors, we obtain new constraints for single-zone fireball models of GRB neutrino and UHECR production.

We present an all-sky search for muon neutrinos produced during the prompt γ-ray emission of 1172 gamma-ray bursts (GRBs) with the IceCube Neutrino Observatory. The detection of these neutrinos would constitute evidence for ultra-high-energy cosmic-ray (UHECR) production in GRBs, as interactions between accelerated protons and the prompt γ-ray field would yield charged pions, which decay to neutrinos. A previously reported search for muon neutrino tracks from northern hemisphere GRBs has been extended to include three additional years of IceCube data. A search for such tracks from southern hemisphere GRBs in five years of IceCube data has been introduced to enhance our sensitivity to the highest energy neutrinos. No significant correlation between neutrino events and observed GRBs is seen in the new data. Combining this result with previous muon neutrino track searches and a search for cascade signature events from all neutrino flavors, we obtain new constraints for single-zone fireball models of GRB neutrino and UHECR production.

We present a search for very high-energy gamma-ray emission from the Northern Fermi Bubble region using data collected with the High Altitude Water Cherenkov gamma-ray observatory. The size of the data set is 290 days. No significant excess is observed in the Northern Fermi Bubble region, so upper limits above 1 TeV are calculated. The upper limits are between and . The upper limits disfavor a proton injection spectrum that extends beyond 100 TeV without being suppressed. They also disfavor a hadronic injection spectrum derived from neutrino measurements.

Simultaneous measurements of air showers with the fluorescence and surface detectors of the Pierre Auger Observatory allow a sensitive search for EeV photon point sources. Several Galactic and extragalactic candidate objects are grouped in classes to reduce the statistical penalty of many trials from that of a blind search and are analyzed for a significant excess above the background expectation. The presented search does not find any evidence for photon emission at candidate sources, and combined p-values for every class are reported. Particle and energy flux upper limits are given for selected candidate sources. These limits significantly constrain predictions of EeV proton emission models from non-transient Galactic and nearby extragalactic sources, as illustrated for the particular case of the Galactic center region.

Since the recent detection of an astrophysical flux of high-energy neutrinos, the question of its origin has not yet fully been answered. Much of what is known about this flux comes from a small event sample of high neutrino purity, good energy resolution, but large angular uncertainties. In searches for point-like sources, on the other hand, the best performance is given by using large statistics and good angular reconstructions. Track-like muon events produced in neutrino interactions satisfy these requirements. We present here the results of searches for point-like sources with neutrinos using data acquired by the IceCube detector over 7 yr from 2008 to 2015. The discovery potential of the analysis in the northern sky is now significantly below E2v doφ/dEv = 10-12 TeV cm-2 s-1, on average 38% lower than the sensitivity of the previously published analysis of 4 yr exposure. No significant clustering of neutrinos above background expectation was observed, and implications for prominent neutrino source candidates are discussed.