The detection of ultrahigh-energy (UHE) neutrino sources would contribute significantly to solving the decades-old mystery of the origin of the highest-energy cosmic rays. We investigate the ability of a future UHE neutrino detector to identify the brightest neutrino point sources, by exploring the parameter space of the total number of observed events and the angular resolution of the detector. The favored parameter region can be translated to requirements for the effective area, sky coverage and angular resolution of future detectors, for a given source number density and evolution history. Moreover, by studying the typical distance to sources that are expected to emit more than one event for a given diffuse neutrino flux, we find that a significant fraction of the identifiable UHE neutrino sources may be located in the nearby Universe if the source number density is above $\sim10^{-6}\,\rm Mpc^{-3}$. If sources are powerful and rare enough, as predicted in blazar scenarios, they can first be detected at distant locations. Our result also suggests that if UHE cosmic-ray accelerators are neither beamed nor transients, it will be possible to associate the detected UHE neutrino sources with nearby UHE cosmic-ray and gamma-ray sources, and that they may also be observed using other messengers, including ones with limited horizons such as TeV gamma rays, UHE gamma rays and cosmic rays. We find that for a $\gtrsim5σ$ detection of UHE neutrino sources with a uniform density, $n_s\sim{10}^{-7}-{10}^{-5}~{\rm Mpc}^{-3}$, at least $\sim100-1000$ events and sub-degree angular resolution are needed, and the results depend on the source evolution model.
Sombrero Galaxy as an Accelerator of Ultrahigh Energy Cosmic Ray Nuclei
Lehman College, City University of New York（纽约市立大学莱曼学院）；Graduate Center, City University of New York（纽约市立大学研究生中心）；American Museum of Natural History（美国自然历史博物馆）
Ultrahigh energy neutrons and pions are likely to be produced in particle interactions inside cosmic ray sources and subsequently decay to neutrinos and other secondary particles ($π^\pm \rightarrow μ^\pmν_μ(\bar ν_μ),μ^\pm \rightarrow e^\pm \barν_μ(ν_μ) ν_e(\barν_e)$). In high magnetic fields of the cosmic acceleration sites, the ultrahigh energy charged particles may lose energy significantly due to synchrotron radiation before decay. We show that for gamma ray bursts in the internal shock model the flux of very high energy antineutrinos ($\bar ν_e$) produced from decaying ultrahigh energy n…
We explore inferences on ultrahigh energy cosmic ray (UHECR) source environments -- constrained by the spectrum and composition of UHECRs and non-observation of extremely high energy neutrinos -- and their implications for the observed high energy astrophysical neutrino spectrum. We find acceleration mechanisms producing power-law CR spectra~$\propto E^{-2}$ are compatible with UHECR data, if CRs at high rigidities are in the quasi-ballistic diffusion regime as they escape their source environment. Both gas-dominated and photon-dominated source environments are able to account for UHECR observ…
Ultrahigh-energy cosmic rays (UHECRs) arrive at Earth from the most energetic astrophysical accelerators in the universe. They collide with atoms in the upper atmosphere with energies about ten times higher than any man-made accelerator, and produce gigantic cascades of secondary particles, called extensive air showers (EAS). Extensive air showers can be detected spreading particle detectors over a large area to record the interactions of secondary particles. The Pierre Auger Observatory has been designed to investigate the origin and nature of UHECRs using the combination of information from …
The observation of neutrinos from cosmic accelerators will be revolutionary. High energy neutrinos are closely connected to ultrahigh energy cosmic rays and their sources. Cosmic ray sources are likely to produce neutrinos and the propagation of ultrahigh cosmic rays from distant sources can generate PeV to ZeV neutrinos. We briefly review recent progress on the observations of ultrahigh energy cosmic rays and their implications for the future detections of high energy neutrinos.
Ultrahigh energy protons and nuclei from extragalactic cosmic ray sources initiate intergalactic electromagnetic cascades, resulting in observable fluxes of $γ$-rays in the GeV-TeV energy domain. The total spectrum of such cascade $γ$-rays of hadronic nature is significantly harder than the one usually expected from blazars. The spectra of some sources known as "extreme TeV blazars" could be well-described by this "intergalactic hadronic cascade model" (IHCM). We calculate the shape of the observable point-like spectrum, as well as the observable angular distibution of $γ$-rays, for the first …
In this paper, we propose a hexagonal description for the flavor composition of ultrahigh-energy (UHE) neutrinos and antineutrinos, which will hopefully be determined at the future large neutrino telescopes. With such a geometrical description, we are able to clearly separate the individual flavor composition of neutrinos from that of antineutrinos in one single regular hexagon, which can be regarded as a natural generalization of the widely-used ternary plot. For illustration, we consider the $pp$ or $pγ$ collisions as the dominant production mechanism for UHE neutrinos and antineutrinos in t…
The IceCube experiment recently detected the first flux of high-energy neutrinos in excess of atmospheric backgrounds. We examine whether these neutrinos originate from within the same extragalactic sources as ultrahigh-energy cosmic rays. Starting from rather general assumptions about spectra and flavors, we find that producing a neutrino flux at the requisite level through pion photoproduction leads to a flux of protons well below the cosmic-ray data at ~10^18 eV, where the composition is light, unless pions/muons cool before decaying. This suggests a dominant class of accelerator that allow…
The origin of the highest energy cosmic rays is still unknown. The discovery of their sources will reveal the workings of the most energetic astrophysical accelerators in the universe. Current observations show a spectrum consistent with an origin in extragalactic astrophysical sources. Candidate sources range from the birth of compact objects to explosions related to gamma-ray bursts or to events in active galaxies. We discuss the main effects of propagation from cosmologically distant sources including interactions with cosmic background radiation and magnetic fields. We examine possible acc…
The sharp change in slope of the ultrahigh-energy cosmic ray spectrum around 10^{9.6} GeV (the ankle), combined with evidence of a light but extragalactic component near and below the ankle which evolves to intermediate/heavy composition above, has proved exceedingly challenging to understand theoretically. Recently, we introduced a very general model in which, for a range of source conditions, photo-disintegration of ultrahigh-energy nuclei in the region surrounding the accelerator naturally accounts for the observed spectrum and composition of the entire extragalactic component, which domina…
It is crucial to identify the ultrahigh-energy cosmic-ray (UHECR) sources and probe their unknown properties. Recent results from the Pierre Auger Observatory favor a heavy nuclear composition for the UHECRs. Under the requirement that heavy nuclei survive in these sources, using gamma-ray bursts as an example, we predict a diagnostic gamma-ray signal, unique to nuclei - the emission of de-excitation gamma rays following photodisintegration. These gamma rays, boosted from MeV to TeV-PeV energies, may be detectable by gamma-ray telescopes such as VERITAS, HESS, and MAGIC, and especially the nex…
Detecting neutrinos and photons is crucial to identifying the sources of ultrahigh-energy cosmic rays (UHECRs), especially for transient sources. We focus on ultrahigh-energy gamma-ray emission from transient sources such as gamma-ray bursts, since >EeV gamma rays can be more direct evidence of UHECRs than PeV neutrinos and GeV-TeV gamma rays. We demonstrate that coincident detections of about 1-100 events can be expected by current and future UHECR detectors such as Auger and JEM-EUSO, and the detection probability can be higher than that of neutrinos for nearby transient sources at <50-100 M…
Interactions of ultrahigh energy cosmic rays in the surroundings of their accelerators can naturally explain the observed spectrum and composition of UHECRs, including the abundance of protons below the ankle. We show that astrophysical properties of the UHECR source environment such as the temperature, size, and magnetic field can be constrained by UHECR and neutrino data. Applying this to candidate sources with a simple structure shows that starburst galaxies are consistent with these constraints, but galaxy clusters may be in tension with them. For multi-component systems like AGNs and GRBs…
In this paper, the connection between Pierre Auger Observatory measurements and photons is discussed. Three cases are presented: the search for photons in the ultrahigh-energy cosmic-ray radiation, the impact of the photon background in the cosmic ray propagation and the role of the ambient photon fields surrounding cosmic accelerators.
We re-examine the possibility of ultrahigh energy cosmic rays being accelerated in nearby dormant quasars. We particularize our study to heavy nuclei to accommodate the spectrum and nuclear composition recently reported by the Pierre Auger Collaboration. Particle acceleration is driven by the Blandford-Znajek mechanism, which wires the dormant spinning black holes as Faraday unipolar dynamos. We demonstrate that energy losses are dominated by photonuclear interactions on the ambient photon fields. We argue that the local dark fossils of the past quasar activity can be classified on the basis o…
We study possible correlations between ultrahigh energy cosmic rays (UHECRs), observed by Auger, AGASA and Yakutsk, and nearby active galactic nuclei (AGNs) and $Fermi$ sources. We consider the deflection effects by a Galactic magnetic field (GMF) model constrained by the most updated measurements. We found that the average deflection angles of UHECRs by the Galactic magnetic fields are less than $4^\circ$. A correlation between the Auger cosmic-ray events and nearby AGNs with a significance level of $\sim 4σ$ was found for the Auger UHECR data sets with or without deflection correction. No co…
The sources of ultrahigh-energy cosmic rays (UHECRs) have been difficult to catch. It was recently pointed out that while sources of UHECR protons exhibit anisotropy patterns that become denser and compressed with rising energy, nucleus-emitting-sources give rise to a cepa stratis (onion-like) structure with layers that become more distant from the source position with rising energy. The peculiar shape of the hot spots from nucleus-accelerators is steered by the competition between energy loss during propagation and deflection on the Galactic magnetic field (GMF). Here, we run a full-blown sim…
Ultra-high energy photons (UHE, E > 10^19 eV) are inevitably produced during the propagation of 10^20 eV protons in extragalactic space. Their short interaction lengths (<20 Mpc) at these energies, combined with the impressive sensitivity of the Pierre Auger Observatory detector to these particles, makes them an ideal probe of nearby ultra-high-energy cosmic ray (UHECR) sources. We here discuss the particular case of photons from a single nearby (within 30 Mpc) source in light of the possibility that such an object might be responsible for several of the UHECR events published by the Auger col…
Variability is a general property of accretion discs and their associated jets. We introduce a semi-analytic model for particle acceleration and radio jet/lobe evolution and explore the effect of Myr timescale jet variability on the particles accelerated by an AGN jet. Our work is motivated by the need for local powerful ultrahigh energy cosmic ray (UHECR) sources and evidence for variability in AGN and radio galaxies. Our main results are: i) UHECR and nonthermal radiative luminosities track the jet power but with a response set by the escape and cooling times, respectively; ii) jet variabili…
The sharp change in slope of the ultrahigh energy cosmic ray (UHECR) spectrum around 10^18.6 eV (the ankle), combined with evidence of a light but extragalactic component near and below the ankle and intermediate composition above, has proved exceedingly challenging to understand theoretically, without fine-tuning. We propose a mechanism whereby photo-disintegration of ultrahigh energy nuclei in the region surrounding a UHECR accelerator accounts for the observed spectrum and inferred composition at Earth. For suitable source conditions, the model reproduces the spectrum and the composition ov…
A number of long-standing puzzles, such as the origin of ultrahigh-energy cosmic rays, could perhaps be solved if we found a mechanism for effectively transferring energy from black holes to particles and, correspondingly, accelerating the latter to (unboundedly, as long as we neglect the back reaction) large velocities. As of today the only such candidate mechanism in the case of the non-extreme Kerr black hole is colliding a particle that freely falls from infinity with a particle whose trajectory is subject to some special requirements to fulfil which it has to be suitably corrected by auxi…
The long-term accretion luminosity of V4641 Sgr through binary evolution simulations: implications for its ultrahigh-energy gamma-ray emission
School of Astronomy and Space Science, Nanjing University（南京大学天文与空间科学学院）；Key laboratory of Modern Astronomy and Astrophysics(Nanjing University),Ministry of Education（南京大学现代天文与天体物理教育部重点实验室）；Tianfu Cosmic Ray Research Center（天府宇宙线研究中心）
Identifying the accelerators that produce the Galactic and extragalactic cosmic rays has been a priority mission of several generations of high energy gamma ray and neutrino telescopes; success has been elusive so far. Detecting the gamma-ray and neutrino fluxes associated with cosmic rays reaches a new watershed with the completion of IceCube, the first neutrino detector with sensitivity to the anticipated fluxes, and the construction of CTA, a ground-based gamma ray detector that will map and study candidate sources with unprecedented precision. In this paper, we revisit the prospects for re…
Recent international efforts have brought us closer to unveiling the century old mystery of the origin of cosmic rays. Cosmic ray, gamma ray, and neutrino observatories are reaching the necessary sensitivity to study the highest energy cosmic accelerators and to begin the use of cosmic particles to study particle interactions above laboratory energies. The number of known gamma-ray sources has increased by orders of magnitude. Possible cosmic ray sources have narrowed down with the confirmation of an ankle and the GZK-like spectral feature at the highest energies. Anisotropies in the distribut…
High energy Astroparticles include Cosmic Ray, gamma ray and neutrinos, all of them coming from the universe. The origin and production, acceleration and propagation mechanisms of ultrahigh-energy CR (up to $10^{20}$ eV) are still unknown. Knowledge on particle interactions taking place at those energies, useful for studying current theories on particle physics, can be obtained only from measurements of high energy astroparticles. In the present document some techniques on data analysis of mass composition of UHECR with the Pierre Auger Observatory are described. The relevance of the muon comp…
We perform a realistic evaluation of the potential of IceCube, a kilometer-scale neutrino detector under construction at the South Pole, to detect neutrinos in the direction of the potential accelerators of the Galactic cosmic rays. We take fully account of the fact that the measurement of the energy of the secondary muons can be used to further discriminate between the signal and the background of atmospheric neutrinos. We conclude that IceCube could identify the sources in the Milagro sky map as the sources of the Galactic cosmic rays at the 3 sigma level in one year and at the 5 sigma level…
The NA61/SHINE experiment at the SPS accelerator at CERN is a unique facility for the study of hadronic interactions at fixed target energies. The data collected with NA61/SHINE is relevant for a broad range of topics in cosmic-ray physics including ultrahigh-energy air showers and the production of secondary nuclei and anti-particles in the Galaxy. Here we present an update of the measurement of the momentum spectra of anti-protons produced in $π^-$+C interactions at 158 and 350 GeV/c and discuss their relevance for the understanding of muons in air showers initiated by ultrahigh-energy cosmi…
High-energy neutrinos present the ultimate signature for a cosmic ray accelerator. Galactic sources responsible for acceleration of cosmic ray up to the knee in cosmic ray spectrum will provide a guaranteed, albeit subdominant, contribution to the high-energy cosmic neutrino flux. In this review, we discuss the the prospects for identification of high-energy neutrinos from sources of the very high energy gamma ray emission in the Milky Way. We present the status of the search for point-like and extended emission from these sources, and describe how the results of these studies indicate that ne…
The IceCube collaboration reports a detection of extra-terrestrial neutrinos. The isotropy and flavor content of the signal, and the coincidence, within current uncertainties, of the 50 TeV to 2 PeV flux and the spectrum with the Waxman-Bahcall bound, suggest a cosmological origin of the neutrinos, related to the sources of ultra-high energy, $>10^{10}$ GeV, cosmic-rays (UHECR). The most natural explanation of the UHECR and neutrino signals is that both are produced by the same population of cosmological sources, producing CRs (likely protons) at a similar rate, $E^2d\dot{n}/dE\propto E^{0}$, …
The origin of high-energy cosmic neutrinos is one of the biggest mysteries in astroparticle physics. The fact that diffuse intensities of high-energy neutrinos, ultrahigh-energy cosmic rays, and GeV-TeV gamma rays are all comparable suggests that these messengers are physically connected. The IceCube data above 100 TeV energies can be naturally explained by cosmic-ray reservoir models. In particular, starburst galaxies and galaxy clusters/groups serve as natural storage rooms of cosmic rays, and it has been theoretically predicted that these sources are promising sites of high-energy neutrinos…
This conference proceedings is a write-up of the Gamma-ray Indirect rapporteur talk given at the 37th International Cosmic Ray Conference (ICRC 2021). In contrast to previous ICRCs, this years edition was held in a fully virtual format, with dedicated discussion sessions organised around specific scientific themes. Many of these topics span the two categories of Gamma-ray Indirect (GAI) and Gamma-ray Direct (GAD), observations of gamma-rays by ground-based and space-based facilities respectively. To cover this organisation by topic in a coherent manner, this GAI rapporteur contribution focuses…
Direct dark matter detection experiments will soon be sensitive to neutrinos from astrophysical sources, including the Sun, the atmosphere, and supernova. This sets an important benchmark for these experiments, and opens up a new window in neutrino physics and astrophysics. The detection of these neutrinos will be complementary to accelerator and reactor-based experiments which study neutrinos over the same energy range. Here we review the physics and astrophysics that can be extracted from the detection of these neutrinos, highlighting the potential for identifying new physics in the form of …
We aim to explain in a unified way the experimental data on ultrahigh energy cosmic rays (UHECR) and neutrinos, using a single source class and obeying limits on the extragalactic diffuse gamma-ray background (EGRB). If UHECRs only interact hadronically with gas around their sources, the resulting diffuse CR flux can be matched well to the observed one, providing at the same time large neutrino fluxes. However, air showers in the Earth's atmosphere induced by UHECRs with energies $E>3\times 10^{18}$ eV would reach in such a case their maxima too high. Therefore additional photo-hadronic intera…
The Pierre Auger Observatory is the world's largest detector for observation of ultra-high-energy cosmic rays (UHECRs) (above the energy of $10^{17}$ eV). It consists of a Fluorescence Detector (FD) and an array of particle detectors known as the Surface Detector (SD). Observations of extensive air showers by the Observatory can be used to probe hadronic interactions at high energy, in a kinematic and energy region inaccessible to experiments at man-made accelerators and to measure the muon component of the shower. Air showers induced by different primaries have different muon contents. With i…
Microquasar remnants as reservoirs of PeV cosmic rays
Instituto Argentino de Radioastronomía (CCT La Plata, CONICET（阿根廷射电天文研究所）；CICPBA（拉普拉塔国立大学天文学与地球物理学学院）；UNLP)（巴塞罗那大学量子物理与天体物理系、宇宙科学研究所）；Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata；Departament de Física Quàntica i Astrofísica, Institut de Ciències del Cosmos (ICC), Universitat de Barcelona (IEEC-UB)
The flux, spectrum and angular distribution of the excess neutrino signal detected by IceCube between 50TeV and 2PeV are inconsistent with those expected for Galactic sources. The coincidence of the excess, $E_ν^2Φ_ν=3.6\pm1.2\times10^{-8}(GeV/ cm^2 sr s)$, with the Waxman-Bahcall (WB) bound, $E_ν^2Φ_{WB}=3.4\times10^{-8}(GeV/cm^2 sr s)$, is probably a clue to the origin of IceCube's neutrinos. The most natural explanation of this coincidence is that both the neutrino excess and the ultra-high energy, $>10^{19}$ eV, cosmic-ray (UHECR) flux are produced by the same population of cosmologically …
Ultrahigh energy cosmic ray air showers probe particle physics at energies beyond the reach of accelerators. Here we introduce a new method to test hadronic interaction models without relying on the absolute energy calibration, and apply it to events with primary energy 6-16 EeV (E_CM = 110-170 TeV), whose longitudinal development and lateral distribution were simultaneously measured by the Pierre Auger Observatory. The average hadronic shower is 1.33 +- 0.16 (1.61 +- 0.21) times larger than predicted using the leading LHC-tuned models EPOS-LHC (QGSJetII-04), with a corresponding excess of muo…
