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![Diffuse gamma-ray emission from Galactic plane: The color map shows energy integrated neutrino flux from the KRAγ5\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\mathrm{KRA}_{\gamma }^{5}$\end{document} model (Gaggero et al. 2015b), illustrated as a function of direction in equatorial coordinates. Figure from (Albert et al. 2018)](publication/342456335/figure/fig3/AS:961324280475660@1606208977230/Diffuse-gamma-ray-emission-from-Galactic-plane-The-color-map-shows-energy-integrated.png)
Diffuse gamma-ray emission from Galactic plane: The color map shows energy integrated neutrino flux from the KRAγ5\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\mathrm{KRA}_{\gamma }^{5}$\end{document} model (Gaggero et al. 2015b), illustrated as a function of direction in equatorial coordinates. Figure from (Albert et al. 2018)
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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 h...
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... While photons from the Milky Way are easily observable-making the Galactic plane the brightest region in the sky-other particles like neutrinos are not so easily observable. Neutrinos can be produced via processes like stellar explosions or supernovae (see, e.g., Thompson et al. 2003), the interaction of cosmic rays with matter (Domokos et al. 1993), binary systems with a compact object and a massive star (Levinson & Waxman 2001;Kheirandish 2020), or other sources in our Galaxy. In this work, we study neutrinos in the TeV-PeV regime, which can be produced due to cosmicray interactions or sources like pulsars and supernova remnants in the Galaxy. ...
... Diffuse Galactic neutrino emission is generically expected from cosmic rays interacting with the interstellar medium to produce pions that decay to gamma rays and neutrinos. There are likely also individual astrophysical sources of neutrinos within the Galaxy (Kheirandish 2020 (Abbasi et al. 2022b), and LHASSO sources (Abbasi et al. 2023c). No significant emission has been found, and all these studies placed upper limits on the neutrino flux from Galactic sources. ...
Galactic and extragalactic objects in the Universe are sources of high-energy neutrinos that may contribute to the astrophysical neutrino signal seen by IceCube. Recently, a study done using cascade-like events seen by IceCube reported neutrino emission from the Galactic plane with >4 σ significance. In this work, we put a lower limit on the number of Galactic sources required to explain this emission. To achieve this, we use a simulation package created to simulate point sources in the Galaxy along with the neutrino and gamma-ray flux emissions originating from them. Along with using past IceCube discovery potential curves, we also account for Eddington bias effects due to Poisson fluctuations in the number of detected neutrino events. We present a toy Monte Carlo simulation to show that there must be at least eight sources, each with luminosity less than 1.6 × 10 ³⁵ erg s ⁻¹ , responsible for the Galactic neutrino emission. Our results constrain the number of individual point-like emission regions, which apply both to discrete astrophysical sources and to individual points of diffuse emission.
... On the other hand, neutrinos can be produced in various Galactic sources of high-energy radiation, see e.g. Kheirandish (2020); Troitsky (2021). ...
Baikal-GVD has recently published its first measurement of the diffuse astrophysical neutrino flux, performed using high-energy cascade-like events. We further explore the Baikal-GVD cascade dataset collected in 2018-2022, with the aim to identify possible associations between the Baikal-GVD neutrinos and known astrophysical sources. We leverage the relatively high angular resolution of the Baikal-GVD neutrino telescope (2-3 deg.), made possible by the use of liquid water as the detection medium, enabling the study of astrophysical point sources even with cascade events. We estimate the telescope's sensitivity in the cascade channel for high-energy astrophysical sources and refine our analysis prescriptions using Monte-Carlo simulations. We primarily focus on cascades with energies exceeding 100 TeV, which we employ to search for correlation with radio-bright blazars. Although the currently limited neutrino sample size provides no statistically significant effects, our analysis suggests a number of possible associations with both extragalactic and Galactic sources. Specifically, we present an analysis of an observed triplet of neutrino candidate events in the Galactic plane, focusing on its potential connection with certain Galactic sources, and discuss the coincidence of cascades with several bright and flaring blazars.
... Our strategy is similar to studies of the decay of TeV-PeV DM that use IceCube data (see, e.g., Ref. [51]), but has one important advantage. In the TeV-PeV range, it is possible that non-DM astrophysical processes produce an excess of neutrinos towards the GC that could obfuscate a signal of neutrinos from DM decay [76][77][78][79][80][81][82][83][84][85][86][87][88][89]. In contrast, in the UHE range, we expect no astrophysical process to produce neutrinos towards the GC, making the search for DM decay cleaner. ...
Next-generation ultra-high-energy (UHE) neutrino telescopes, presently under planning, will have the potential to probe the decay of heavy dark matter (DM) into UHE neutrinos, with energies in excess of $10^7$~GeV. Yet, this potential may be deteriorated by the presence of an unknown background of UHE neutrinos, cosmogenic or from astrophysical sources, not of DM origin and seemingly large enough to obscure the DM signature. We show that leveraging the angular and energy distributions of detected events safeguards future searches for DM decay against such backgrounds. We focus on the radio-detection of UHE neutrinos in the planned IceCube-Gen2 neutrino telescope, which we model in state-of-the-art detail. We report promising prospects for the discovery potential of DM decay into UHE neutrinos, the measurement of DM mass and lifetime, and limits on the DM lifetime, despite the presence of a large background, without prior knowledge of its size and shape.
... Neutrino emission would be a smoking gun. However, no sources have been found in more than a decade of searches [21][22][23][24][25] despite a series of optimistic predictions [26][27][28][29]. Figure 1 schematically illustrates the range of possibilities. ...
Observations of the Milky Way at TeV-PeV energies reveal a bright diffuse flux of hadronic cosmic rays and also bright point sources of gamma rays. If the gamma-ray sources are hadronic cosmic-ray accelerators, then they must also be neutrino sources. However, no neutrino sources have been detected. Where are they? We introduce a new population-based approach to probe Milky Way hadronic PeVatrons, demanding consistency between diffuse and point-source PeV-range data on cosmic rays, gamma rays, and neutrinos. For the PeVatrons, two extreme scenarios are allowed: (1) the hadronic cosmic-ray accelerators and the gamma-ray sources are the same objects, so that bright neutrino sources exist and improved telescopes can detect them, versus (2) the hadronic cosmic-ray accelerators and the gamma-ray sources are distinct, so that there are no detectable neutrino sources. The latter case is possible if hadronic accelerators have sufficiently thin column densities. We quantify present constraints and future prospects, showing how to reveal the nature of the hadronic PeVatrons.
... Some Galactic contribution helps to naturally explain (Palladino & Vissani 2016) the tension between different measurements of the neutrino spectrum, see, e.g., Abbasi et al. (2021). For a review of particular classes of Galactic sources, see Kheirandish (2020). Gamma-ray binaries were proposed as high-energy neutrino sources long ago (see, e.g., Levinson & Waxman 2001;Distefano et al. 2002;Bednarek 2005;Sahakyan et al. 2014). ...
The high-energy radiation from short period binaries containing a massive star with a compact relativistic companion was detected from radio to TeV γ- rays. We show here that PeV regime protons can be efficiently accelerated in the regions of collision of relativistic outflows of a compact object with stellar winds in these systems. The accelerated proton spectra in the presented Monte Carlo model have an upturn in the PeV regime and can provide very hard spectra of sub-PeV photons and neutrinos by photomeson processes in the stellar radiation field. The recent report of a possible sub-PeV γ -ray flare in coincidence with a high-energy neutrino can be understood in the frame of this model. The γ -ray binaries may contribute substantially to the Galactic component of the detected high-energy neutrino flux.
... Abbasi et al. (2021). For a review of particular classes of Galactic sources see Kheirandish (2020). Gamma-ray binaries were proposed as high-energy neutrino sources long ago (see e.g. ...
The high-energy radiation from short period binaries containing a massive star with a compact relativistic companion was detected from radio to TeV gamma rays. We show here that PeV regime protons can be efficiently accelerated in the regions of collision of relativistic outflows of a compact object with stellar winds in these systems. The accelerated proton spectra in the presented Monte Carlo model have an upturn in the PeV regime and can provide very hard spectra of sub-PeV photons and neutrinos by photo-meson processes in the stellar radiation field. Recent report of a possible sub-PeV gamma-ray flare in coincidence with a high-energy neutrino can be understood in the frame of this model. The gamma-ray binaries may contribute substantially to the Galactic component of the detected high-energy neutrino flux.
... Not surprisingly, many models of the Galactic origin of highenergy neutrinos have been developed, for a review see e.g. Kheirandish (2020). ...
Galactic sites of acceleration of cosmic rays to energies of order 10^15 eV and higher, dubbed PeVatrons, reveal themselves by recently discovered gamma radiation of energies above 100 TeV. However, joint gamma-ray and neutrino production, which marks unambiguously cosmic-ray interactions with ambient matter and radiation, was not observed until now. In November 2020, the IceCube neutrino observatory reported an ~150 TeV neutrino event from the direction of one of the most promising Galactic PeVatrons, the Cygnus Cocoon. Here we report on the observation of a 3.1-sigma (post trial) excess of atmospheric air showers from the same direction, observed by the Carpet-2 experiment and consistent with a few-months flare in photons above 300 TeV, in temporal coincidence with the neutrino event. The fluence of the gamma-ray flare is of the same order as that expected from the neutrino observation, assuming the standard mechanism of neutrino production. This is the first evidence for the joint production of high-energy neutrinos and gamma rays in a Galactic source.
Next-generation ultrahigh-energy (UHE) neutrino telescopes, presently under planning, will have the potential to probe the decay of heavy dark matter (DM) into UHE neutrinos, with energies in excess of 107 GeV. Yet, this potential may be deteriorated by the presence of an unknown background of UHE neutrinos, cosmogenic or from astrophysical sources, not of DM origin and seemingly large enough to obscure the DM signature. We show that leveraging the angular and energy distributions of detected events safeguards future searches for DM decay against such backgrounds. We focus on the radio detection of UHE neutrinos in the planned IceCube-Gen2 neutrino telescope, which we model in state-of-the-art detail. We report promising prospects for the discovery potential of DM decay into UHE neutrinos, the measurement of DM mass and lifetime, and limits on the DM lifetime, despite the presence of a large background, without prior knowledge of its size and shape.
