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In this article, we present a study of high-energy neutrino emission in gravitational collapse. A compact star is treated as a complete degenerate Fermi gas of neutrons, protons and electrons. In gravitational collapse, its density reaches the thresholds for muon and pion productions, leading to high-energy neutrinos production. By using adiabatic approximation that macroscopic collapsing processes are much slower than microscopic processes of particle interactions, we adopt equilibrium equations of microscopic processes to obtain the number of neutrino productions. Assuming 10% of variation in gravitational binding energy converted to the energy of produced neutrinos, we obtain fluxes of 10MeV electron-neutrinos and GeV electron and muon neutrinos. In addition, we compute the ratio (< 1) of total muon neutrino number to the total electron neutrino number at the source and at the Earth considering neutrino oscillations. We approximately obtain the number of GeV antineutrino events (gtrsim 1) in an ordinary detector such as Kamiokande and total energy of neutrino flux (gtrsim 10^{53} erg), as a function of collapsing star mass.
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Supermassive black hole (SMBH) coalescences are ubiquitous in the history of the Universe and often exhibit strong accretion activities and powerful jets. These SMBH mergers are also promising candidates for future gravitational wave detectors such as Laser Space Inteferometric Antenna (LISA). In this work, we consider neutrino counterpart emission originating from the jet-induced shocks. The physical picture is that relativistic jets launched after the merger will push forward inside the premerger disk wind material, and then they subsequently get collimated, leading to the formation of internal shocks, collimation shocks, forward shocks and reverse shocks. Cosmic rays can be accelerated in these sites and neutrinos are expected via the photomeson production process. We formulate the jet structures and relevant interactions therein, and then evaluate neutrino emission from each shock site. We find that month-to-year high-energy neutrino emission from the postmerger jet after the gravitational wave event is detectable by IceCube-Gen2 within approximately five to ten years of operation in optimistic cases where the cosmic-ray loading is sufficiently high and a mildly super-Eddington accretion is achieved. We also estimate the contribution of SMBH mergers to the diffuse neutrino intensity, and find that a significant fraction of the observed very high-energy ($E_ ugtrsim1$ PeV) IceCube neutrinos could originate from them in the optimistic cases. In the future, such neutrino counterparts together with gravitational wave observations can be used in a multimessenger approach to elucidate in greater detail the evolution and the physical mechanism of SMBH mergers.
SN 2008D, a core collapse supernova at a distance of 27 Mpc, was serendipitously discovered by the Swift satellite through an associated X-ray flash. Core collapse supernovae have been observed in association with long gamma-ray bursts and X-ray flashes and a physical connection is widely assumed. This connection could imply that some core collapse supernovae possess mildly relativistic jets in which high-energy neutrinos are produced through proton-proton collisions. The predicted neutrino spectra would be detectable by Cherenkov neutrino detectors like IceCube. A search for a neutrino signal in temporal and spatial correlation with the observed X-ray flash of SN 2008D was conducted using data taken in 2007-2008 with 22 strings of the IceCube detector. Events were selected based on a boosted decision tree classifier trained with simulated signal and experimental background data. The classifier was optimized to the position and a soft jet neutrino spectrum assumed for SN 2008D. Using three search windows placed around the X-ray peak, emission time scales from 100 - 10000 s were probed. No events passing the cuts were observed in agreement with the signal expectation of 0.13 events. Upper limits on the muon neutrino flux from core collapse supernovae were derived for different emission time scales and the principal model parameters were constrained.
ANTARES is the largest high-energy neutrino telescope in the Northern Hemisphere. A search for neutrinos in coincidence with gamma-ray bursts using ANTARES data from late 2007 to 2011 is presented here. An extended maximum likelihood ratio search was employed to optimise the discovery potential for a neutrino signal as predicted by the numerical NeuCosmA model. No significant excess was found, so 90% confidence upper limits on the fluxes as expected from analytically approximated neutrino-emission models as well as on up-to-date numerical predictions were placed.
We investigate the possibility that radio-bright active galactic nuclei (AGN) are responsible for the TeV--PeV neutrinos detected by IceCube. We use an unbinned maximum-likelihood-ratio method, 10 years of IceCube muon-track data, and 3388 radio-bright AGN selected from the Radio Fundamental Catalog. None of the AGN in the catalog have a large global significance. The two most significant sources have global significance of $simeq$ 1.5$sigma$ and 0.8$sigma$, though 4.1$sigma$ and 3.8$sigma$ local significance. Our stacking analyses show no significant correlation between the whole catalog and IceCube neutrinos. We infer from the null search that this catalog can account for at most 30% (95% CL) of the diffuse astrophysical neutrino flux measured by IceCube. Moreover, our results disagree with recent work that claimed a 4.1$sigma$ detection of neutrinos from the sources in this catalog, and we discuss the reasons of the difference.
Pulsar wind nebulae (PWNe) are main gamma-ray emitters in the Galactic plane. Although the leptonic scenario is able to explain most PWNe emission well, a hadronic contribution cannot be excluded. High-energy emission raises the possibility that gamma-rays are hadronically produced which inevitably leads to the production of neutrinos. We report a stacking analysis to search for neutrino emission from 35 PWNe that are very-high-energy gamma-ray emitters and the results using 9.5 years of all-sky IceCube data. In the absence of any significant correlation, we set upper limits on the total neutrino emission from those PWNe and constraints on the hadronic component.
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