Journal articles on the topic 'Radiative Emission of Neutrino Pair'
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Jentschura, Ulrich D., and István Nándori. "Neutrino Pair Cerenkov Radiation for Tachyonic Neutrinos." Advances in High Energy Physics 2017 (2017): 1–8. http://dx.doi.org/10.1155/2017/9850312.
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The emission of a charged light lepton pair by a superluminal neutrino has been identified as a major factor in the energy loss of highly energetic neutrinos. The observation of PeV neutrinos by IceCube implies their stability against lepton pair Cerenkov radiation. Under the assumption of a Lorentz-violating dispersion relation for highly energetic superluminal neutrinos, one may thus constrain the Lorentz-violating parameters. A kinematically different situation arises when one assumes a Lorentz-covariant, space-like dispersion relation for hypothetical tachyonic neutrinos, as an alternative to Lorentz-violating theories. We here discuss a hitherto neglected decay process, where a highly energetic tachyonic neutrino may emit other (space-like, tachyonic) neutrino pairs. We find that the space-like dispersion relation implies the absence of a q2 threshold for the production of a tachyonic neutrino-antineutrino pair, thus leading to the dominant additional energy loss mechanism for an oncoming tachyonic neutrino in the medium-energy domain. Surprisingly, the small absolute values of the decay rate and energy loss rate in the tachyonic model imply that these models, in contrast to the Lorentz-violating theories, are not pressured by the cosmic PeV neutrinos registered by the IceCube collaboration.
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Yoshimura, M., N. Sasao, and M. Tanaka. "Radiative emission of neutrino pair free of quantum electrodynamic backgrounds." Progress of Theoretical and Experimental Physics 2015, no. 5 (May 19, 2015): 53B06–0. http://dx.doi.org/10.1093/ptep/ptv064.
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Yoshimura, M., A. Fukumi, N. Sasao, and T. Yamaguchi. "Parity Violating Observables in Radiative Neutrino Pair Emission from Metastable Atoms." Progress of Theoretical Physics 123, no. 3 (March 1, 2010): 523–32. http://dx.doi.org/10.1143/ptp.123.523.
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Dinh, D. N., and S. T. Petcov. "Radiative emission of neutrino pairs in atoms and light sterile neutrinos." Physics Letters B 742 (March 2015): 107–16. http://dx.doi.org/10.1016/j.physletb.2015.01.020.
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Jentschura, U. D., I. Nándori, and G. Somogyi. "Lorentz breaking and SU(2)L × U(1)Y gauge invariance for neutrinos." International Journal of Modern Physics E 28, no. 09 (September 2019): 1950072. http://dx.doi.org/10.1142/s0218301319500721.
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Conceivable Lorentz-violating effects in the neutrino sector remain a research area of great general interest, as they touch upon the very foundations on which the Standard Model and our general understanding of fundamental interactions are laid. Here, we investigate the relation of Lorentz violation in the neutrino sector in light of the fact that neutrinos and the corresponding left-handed charged leptons form [Formula: see text] doublets under the electroweak gauge group. Lorentz-violating effects thus cannot be fully separated from questions related to gauge invariance. The model dependence of the effective interaction Lagrangians used in various recent investigations is explored with a special emphasis on neutrino splitting, otherwise known as the neutrino-pair Cerenkov radiation and vacuum-pair emission (electron–positron-pair Cerenkov radiation). We highlight two scenarios in which Lorentz-violating effects do not necessarily also break electroweak gauge invariance. The first of these involves a restricted set of gauge transformations, a subgroup of [Formula: see text], while in the second where differential Lorentz violation is exclusively introduced by the mixing of the neutrino flavor and mass eigenstates. Our study culminates in a model which fully preserves [Formula: see text] gauge invariance, involves flavor-dependent Lorentz-breaking parameters, and still allows for Cerenkov-type decays to proceed.
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Drewes, Marco, Jamie McDonald, Loïc Sablon, and Edoardo Vitagliano. "Neutrino Emissivities as a Probe of the Internal Magnetic Fields of White Dwarfs." Astrophysical Journal 934, no. 2 (July 28, 2022): 99. http://dx.doi.org/10.3847/1538-4357/ac7874.
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Abstract The evolution of white dwarfs (WDs) depends crucially on thermal processes. The plasma in their core can produce neutrinos that escape from the star, thus contributing to the energy loss. While in the absence of a magnetic field the main cooling mechanism is plasmon decay at high temperature and photon surface emission at low temperature, a large magnetic field in the core hiding beneath the surface even of ordinary WDs, and undetectable to spectropolarimetric measurements, could potentially leave an imprint in the cooling. In this paper, we revisit the contribution to WD cooling stemming from neutrino pair synchrotron radiation and the effects of the magnetic field on plasmon decay. Our key finding is that even if observations limit the magnetic field strength at the stellar surface, magnetic fields in the interior of WDs—with or without a surface magnetic field—can be strong enough to modify the cooling rate, with neutrino pair synchrotron emission being the most important contribution. This effect may not only be relevant for the quantification and interpretation of cooling anomalies, but suggests that the internal magnetic fields of WDs should be smaller than ∼ 6 × 1011 G, slightly improving bounds coming from a stability requirement. While our simplified treatment of the WD structure implies that further studies are needed to reduce the systematic uncertainties, the estimates based on comparing the emissivities illustrate the potential of neutrino emission as a diagnostic tool to study the interior of WDs.
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Crinquand, B., B. Cerutti, and G. Dubus. "Kinetic modeling of the electromagnetic precursor from an axisymmetric binary pulsar coalescence." Astronomy & Astrophysics 622 (February 2019): A161. http://dx.doi.org/10.1051/0004-6361/201834610.
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Context. The recent detection of gravitational waves associated with a binary neutron star merger revives interest in interacting pulsar magnetospheres. Current models predict that a significant amount of magnetic energy should be released prior to the merger, leading to electromagnetic precursor emission. Aims. In this paper, we revisit this problem in the light of the recent progress in kinetic modeling of pulsar magnetospheres. We limit our work to the case of aligned magnetic moments and rotation axes, and thus neglect the orbital motion. Methods. We perform global two-dimensional axisymmetric particle-in-cell simulations of two pulsar magnetospheres merging at a rate consistent with the emission of gravitational waves. Both symmetric and asymmetric systems are investigated. Results. Simulations show a significant enhancement of magnetic dissipation within the magnetospheres as the two stars approach one another. Even though the magnetospheric configuration depends on the relative orientations of the pulsar spins and magnetic axes, all configurations present nearly the same radiative signature, indicating that a common dissipation mechanism is at work. The relative motion of both pulsars drives magnetic reconnection at the boundary between the two magnetospheres, leading to efficient particle acceleration and high-energy synchrotron emission. Polar-cap discharge is also strongly enhanced in asymmetric configurations, resulting in vigorous pair production and potentially additional high-energy radiation. Conclusions. We observe an increase in the pulsar radiative efficiency by two orders of magnitude over the last orbit before the merger, exceeding the spindown power of an isolated pulsar. The expected signal is too weak to be detected at high energies even in the nearby universe. However, if a small fraction of this energy is channeled into radio waves, it could be observed as a non-repeating fast radio burst.
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Florou, Ioulia, Maria Petropoulou, and Apostolos Mastichiadis. "A marginally fast-cooling proton–synchrotron model for prompt GRBs." Monthly Notices of the Royal Astronomical Society 505, no. 1 (May 7, 2021): 1367–81. http://dx.doi.org/10.1093/mnras/stab1285.
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ABSTRACT A small fraction of gamma-ray bursts (GRBs) with available data down to soft X-rays (∼0.5 keV) has been shown to feature a spectral break in the low-energy part (∼1–10 keV) of their prompt emission spectrum. The overall spectral shape is consistent with optically thin synchrotron emission from a population of particles that have cooled on a time-scale comparable to the dynamic time to energies that are still much higher than their rest-mass energy (marginally fast cooling regime). We consider a hadronic scenario and investigate if the prompt emission of these GRBs can originate from relativistic protons that radiate synchrotron in the marginally fast cooling regime. Using semi-analytical methods, we derive the source parameters, such as magnetic field strength and proton luminosity, and calculate the high-energy neutrino emission expected in this scenario. We also investigate how the emission of secondary pairs produced by photopion interactions and γγ pair production affect the broad-band photon spectrum. We support our findings with detailed numerical calculations. Strong modification of the photon spectrum below the break energy due to the synchrotron emission of secondary pairs is found, unless the bulk Lorentz factor is very large (Γ ≳ 103). Moreover, this scenario predicts unreasonably high Poynting luminosities because of the strong magnetic fields (106–107 G) that are necessary for the incomplete proton cooling. Our results strongly disfavour marginally fast cooling protons as an explanation of the low-energy spectral break in the prompt GRB spectra.
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Hirotani, K. "Gamma-ray Emission from Pulsar Outer Magnetospheres." Symposium - International Astronomical Union 195 (2000): 171–80. http://dx.doi.org/10.1017/s0074180900162904.
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We study the γ-ray emission from an outer-gap accelerator around a rotating neutron star. Assuming the existence of global currents in the magnetosphere, the charge depletion causes a large electric field along the magnetic field lines. This electric field accelerates migratory electrons and positrons which radiate gamma-rays via curvature radiation. These gamma-rays, in turn, produce yet more radiating particles by colliding with the X-rays, leading to a pair-production cascade. Imposing a gap-closure condition that a single pair produces one pair in the gap, on average, we explicitly solve the strength of the acceleration field and demonstrate how the peak energy and the luminosity of the curvature-radiated GeV photons and the cutoff energy and luminosity of Compton-scattered TeV photons depend on such parameters as the surface temperature, the rotational frequency, and the magnetic moment. It is demonstrated that both the GeV and TeV emissions of Geminga will be harder than those of B1055-52, B0656+14, and Vela, and that the TeV fluxes are too small to be observed by current ground-based telescopes.
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Itoh, Naoki. "Neutrino Emission Processes in the Weinberg-Salam Theory." International Astronomical Union Colloquium 108 (1988): 434–35. http://dx.doi.org/10.1017/s025292110009429x.
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The neutrino emission processes play essential roles in stellar evolution as expemplified by the observations of the neutrinos from SN 1987a by the KAMIOKANDE-II and IMB experiments. Recently a very extensive study of the various neutrino emission processes based on the Weinberg-Salam theory has been completed by the present author and his collaborators. The neutrino emission processes calculated by the author’s group include pair, photo-, plasma, and bremsstrahlung neutrino processes. The neutrino energy loss rates due to pair, photo-, and plasma processes in the framework of the Weinberg-Salam theory are found to be substantially lower than the result obtained by Beaudet, Petrosian, and Salpeter. The reduction factor α is in the range 0.35 < α < 0.88 depending on the neutrino masses, density, and temperature. The ionic correlation effects play important roles in the bremsstrahlung neutrino process. The present author and his collaborators recently calculated the bremsstrahlung neutrino energy loss rate taking into account the ionic correlation effects in the crystalline lattice state as well as in the liquid metal state. They found that the ionic correlation effects suppress the bremsstrhlung neutrino energy loss typically by a factor 2-20. The present findings will bear great importance in neutrino astronomy.
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Yusof, N., H. Abu Kassim, L. G. Garba, and N. S. Ahmad. "The neutrino emission from thermal processes in very massive stars in the local universe." Monthly Notices of the Royal Astronomical Society 503, no. 4 (March 19, 2021): 5965–75. http://dx.doi.org/10.1093/mnras/stab762.
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ABSTRACT We present a new overview of the life of very massive stars (VMS) in terms of neutrino emission from thermal processes: pair annihilation, plasmon decay, photoneutrino process, bremsstrahlung, and recombination processes in burning stages of selected VMS models. We use the realistic conditions of temperature, density, electron fraction, and nuclear isotropic composition of the VMS. Results are presented for a set of progenitor stars with mass of 150, 200, and 300 M⊙Z = 0.002 and 500 M⊙Z = 0.006 rotating models which are expected to explode as a pair instability supernova at the end of their life except the 300 M⊙ would end up as a black hole. It is found that for VMS, thermal neutrino emission occurs as early as towards the end of hydrogen burning stage due to the high initial temperature and density of these VMS. We calculate the total neutrino emissivity, Qν and luminosity, Lν using the structure profile of each burning stages of the models and observed the contribution of photoneutrino at early burning stages (H and He) and pair annihilation at the advanced stages. Pair annihilation and photoneutrino processes are the most dominant neutrino energy loss mechanisms throughout the evolutionary track of the VMS. At the O-burning stage, the neutrino luminosity ∼1047−48 erg s−1 depending on their initial mass and metallicity are slightly higher than the neutrino luminosity from massive stars. This could shed light on the possibility of using detection of neutrinos to locate the candidates for pair instability supernova in our local universe.
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ESPOSITO, S., G. MANGANO, G. MIELE, I. PICARDI, and O. PISANTI. "RADIATIVE CORRECTIONS TO NEUTRINO ENERGY LOSS RATE IN STELLAR INTERIORS." Modern Physics Letters A 17, no. 08 (March 14, 2002): 491–502. http://dx.doi.org/10.1142/s0217732302006643.
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We consider radiative electromagnetic corrections, at order α, to the process [Formula: see text] at finite density and temperature. This process represents one of the main contributions to the cooling of stellar environments in the late stages of star evolution. We find that these corrections affect the energy loss rate by a factor (-4-1)% with respect to the tree level estimate, in the temperature and density ranges where the neutrino pair production via e+e- annihilation is the most efficient cooling mechanism.
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Jaikumar, Prashanth, and Madappa Prakash. "Neutrino pair emission from Cooper pair breaking and recombination in superfluid quark matter." Physics Letters B 516, no. 3-4 (September 2001): 345–52. http://dx.doi.org/10.1016/s0370-2693(01)00916-9.
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HATSUDA, T., C. S. LIM, and M. YOSHIMURA. "HARD X-RAY SPECTRUM FROM SN 1987A AND RADIATIVE NEUTRINO DECAY." Modern Physics Letters A 03, no. 12 (September 1988): 1133–36. http://dx.doi.org/10.1142/s0217732388001355.
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The radiative neutrino decay is shown to explain the hard X-ray energy spectrum (10 keV-200 keV) from SN 1987a, observed by Ginga and Kvant. After the outer expanding shell becomes transparent to the X-ray, the spectrum, in our picture, is nearly constant and directly reflects the dynamical mechanism of the neutrino emission and its subsequent decay.
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Rodríguez-Ramírez, J. C., Elisabete M. de Gouveia Dal Pino, and R. Alves Batista. "Neutrino and γ-ray Emission from the Core of NGC1275 by Magnetic Reconnection: GRMHD Simulations and Radiative Transfer/Particle Calculations." Proceedings of the International Astronomical Union 14, S342 (May 2018): 184–88. http://dx.doi.org/10.1017/s1743921318007950.
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AbstractVery high energy (VHE) emission has been detected from the radio galaxy NGC1275, establishing it as a potential cosmic-ray (CR) accelerator and a high energy neutrino source. We here study neutrino and γ-ray emission from the core of NGC1275 simulating the interactions of CRs assumed to be accelerated by magnetic reconnection, with the accreting plasma environment. To do this, we combine (i) numerical general relativistic (GR) magneto-hydrodynamics (MHD), (ii) Monte Carlo GR leptonic radiative transfer and, (iii) Monte Carlo interaction of CRs. A leptonic emission model that reproduces the SED in the [103-1010.5] eV energy range is used as the background target for photo-pion interactions+electromagnetic cascading. CRs injected with the power-law index κ=1.3 produce an emission profile that matches the VHE tail of NGC1275. The associated neutrino flux, below the IceCube limits, peaks at ∼PeV energies. However, coming from a single source, this neutrino flux may be an over-estimation.
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Barut, A. O., Z. Z. Aydin, and I. H. Duru. "Photoproduction of a neutrino pair from an electron and astrophysical implications of neutrino-emission processes." Physical Review D 32, no. 11 (December 1, 1985): 3051–54. http://dx.doi.org/10.1103/physrevd.32.3051.
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Leinson, Lev B. "Neutrino Emission from Cooper Pairs at Finite Temperatures." Advances in High Energy Physics 2018 (2018): 1–11. http://dx.doi.org/10.1155/2018/8963453.
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A brief review is given of the current state of the problem of neutrino pair emission through neutral weak currents caused by the Cooper pairs breaking and formation (PBF) in superfluid baryon matter at thermal equilibrium. The cases of singlet-state pairing with isotropic superfluid gap and spin-triplet pairing with an anisotropic gap are analyzed with allowance for the anomalous weak interactions caused by superfluidity. It is shown that taking into account the anomalous weak interactions in both the vector and axial channels is very important for a correct description of neutrino energy losses through the PBF processes. The anomalous contributions lead to an almost complete suppression of the PBF neutrino emission in spin-singlet superfluids and strong reduction of the PBF neutrino losses in the spin-triplet superfluid neutron matter, which considerably slows down the cooling rate of neutron stars with superfluid cores.
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Dzhioev, Alan A., and A. I. Vdovin. "Neutrino-antineutrino pair emission from thermally excited nuclei in stellar collapse." Physics of Atomic Nuclei 77, no. 9 (September 2014): 1166–72. http://dx.doi.org/10.1134/s1063778814080067.
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Leinson, L. B. "Neutrino pair emission from the inner crust of a neutron star." Space Science Reviews 74, no. 3-4 (November 1995): 481–84. http://dx.doi.org/10.1007/bf00751437.
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Maruyama, Tomoyuki, A. Baha Balantekin, Myung-Ki Cheoun, Toshitaka Kajino, and Grand J. Mathews. "Neutrino and Antineutrino pair-Emission in Strong Magnetic Field in Relativistic Quantum Approach." EPJ Web of Conferences 260 (2022): 11029. http://dx.doi.org/10.1051/epjconf/202226011029.
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We study the v\bar v\-pair emission from electrons and protons in a relativistic quantum approach. In this work we calculate the luminosity of the v\bar v\-pairs emitted from neutron-star-matter with a strong magnetic field, and find that this luminosity is much larger than that in the modified Urca process. The v\bar v\-pair emission processes in strong magnetic fields significantly contribute to the cooling of the magnetars.
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Smponias, Theodoros. "Synthetic Neutrino Imaging of a Microquasar." Galaxies 9, no. 4 (October 19, 2021): 80. http://dx.doi.org/10.3390/galaxies9040080.
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Microquasar binary stellar systems emit electromagnetic radiation and high-energy particles over a broad energy spectrum. However, they are so far away that it is hard to observe their details. A simulation offers the link between relatively scarce observational data and the rich theoretical background. In this work, high-energy particle emission from simulated twin microquasar jets is calculated in a unified manner. From the cascade of emission within an element of jet matter to the dynamic and radiative whole jet model, the series of physical processes involved are integrated together. A programme suite assembled around model data produces synthetic images and spectra directly comparable to potential observations by contemporary arrays. The model is capable of describing a multitude of system geometries, incorporating increasing levels of realism depending on need and available computational resources. As an application, the modelling process is applied to a typical microquasar, which is synthetically observed from different angles using various imaging geometries. Furthermore, the resulting intensities are comparable to the sensitivity of existing detectors. The combined background emission from a potential distribution of microquasars is also modelled.
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Chang, Yu-Ling, Bruno Arsioli, Wenlian Li, Donglian Xu, and Liang Chen. "Hunting for Neutrino Emission from Multifrequency Variable Sources." Astrophysical Journal 939, no. 2 (November 1, 2022): 123. http://dx.doi.org/10.3847/1538-4357/ac8c32.
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Abstract Pinpointing the neutrino sources is crucial to unveil the mystery of high-energy cosmic rays. The search for neutrino source candidates from coincident neutrino-photon signatures and objects with particular electromagnetic flaring behaviors can increase our chances of finding neutrino emitters. In this paper, we first study the temporal correlations of astrophysical flares with neutrinos, considering a few hundred multifrequency sources from the Atacama Large Millimeter/submillimeter Array, the Wide-field Infrared Survey Explorer (WISE), Swift, and Fermi in the containment regions of IceCube high-energy alerts. Furthermore, the spatial correlations between blazars and neutrinos are investigated using the subset of 10 yr IceCube track-like neutrinos with around 250,000 events. In a second test, we account for 2700 blazars with different types of flaring stages in addition to their position. No significant neutrino emissions were found from our analyses. Our results indicate an interesting trend showing that the infrared flaring phases of WISE blazars might be correlated with the arrival times of the neutrino alerts. A possible overflow of neutrinos associated with two of our selected blazar samples is discussed in detail. One is characterized by a significant flaring lag in infrared with respect to γ-rays, as seen for TXS 0506+056, and the other is characterized by highly simultaneous infrared and γ-ray flares. Our investigation suggests the need to improve current multifrequency light-curve catalogs to pair with the advent of more sensitive neutrino observatories.
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CH. ZHUKOVSKY, V., P. A. EMINOV, and A. E. GRIGORUK. "RADIATIVE DECAY OF A MASSIVE NEUTRINO IN THE WEINBERG–SALAM MODEL WITH MIXING IN A CONSTANT UNIFORM MAGNETIC FIELD." Modern Physics Letters A 11, no. 39n40 (December 28, 1996): 3119–26. http://dx.doi.org/10.1142/s0217732396003106.
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Influence of an external magnetic field on the neutrino decay process with emission of a linearly polarized photon is considered. The decay rate is shown to be enhanced as compared to the free case in the broad region where both the nonvanishing neutrino mass and the field make substantial contributions. In the limit of a negligible neutrino mass the emitted photons are totally linearly polarized, which may help in the identification of these photons.
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Shibata, S. "Modes of Energy Loss from Isolated Magnetized Neutron Star." Symposium - International Astronomical Union 125 (1987): 450. http://dx.doi.org/10.1017/s0074180900161121.
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Pulsar may be regarded as a discharge tube by electron-positron pair creation. On this viewpoint we carry out two numerical calculations. The obtained magnetic field is consistent with the flow. We find that pulsars emit their rotational energy through three modes simultaneously. The three modes are (1)relativistic acceleration and following gamma-ray emission in the closed current circuit in the magnetosphere, (2)wind of the electron-positron pair plasma, and (3)dipole radiation.
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Caputo, Andrea, Marco Regis, and Marco Taoso. "Searching for sterile neutrino with X-ray intensity mapping." Journal of Cosmology and Astroparticle Physics 2020, no. 03 (March 1, 2020): 001. http://dx.doi.org/10.1088/1475-7516/2020/03/001.
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The cosmological X-ray emission associated to the possible radiative decay of sterile neutrinos is composed by a collection of lines at different energies. For a given mass, each line corresponds to a given redshift. In this work, we cross correlate such line emission with catalogs of galaxies tracing the dark matter distribution at different redshifts. We derive observational prospects by correlating the X-ray sky that will be probed by the eROSITA and Athena missions with current and near future photometric and spectroscopic galaxy surveys. A relevant and unexplored fraction of the parameter space of sterile neutrinos can be probed by this technique.
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Rahman, N., H.-T. Janka, G. Stockinger, and S. E. Woosley. "Pulsational pair-instability supernovae: gravitational collapse, black hole formation, and beyond." Monthly Notices of the Royal Astronomical Society 512, no. 3 (March 23, 2022): 4503–40. http://dx.doi.org/10.1093/mnras/stac758.
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ABSTRACT We investigate the final collapse of rotating and non-rotating pulsational pair-instability supernova progenitors with zero-age-main-sequence masses of 60, 80, and 115 M⊙ and iron cores between 2.37 and 2.72 M⊙ by 2D hydrodynamics simulations. Using the general relativistic NADA-FLD code with energy-dependent three-flavour neutrino transport by flux-limited diffusion allows us to follow the evolution beyond the moment when the transiently forming neutron star (NS) collapses to a black hole (BH), which happens within 350–580 ms after bounce in all cases. Because of high neutrino luminosities and mean energies, neutrino heating leads to shock revival within ≲ 250 ms post bounce in all cases except the rapidly rotating 60 M⊙ model. In the latter case, centrifugal effects support a 10 per cent higher NS mass but reduce the radiated neutrino luminosities and mean energies by ∼20 per cent and ∼10 per cent, respectively, and the neutrino-heating rate by roughly a factor of two compared to the non-rotating counterpart. After BH formation, the neutrino luminosities drop steeply but continue on a 1–2 orders of magnitude lower level for several 100 ms because of aspherical accretion of neutrino and shock-heated matter, before the ultimately spherical collapse of the outer progenitor shells suppresses the neutrino emission to negligible values. In all shock-reviving models BH accretion swallows the entire neutrino-heated matter and the explosion energies decrease from maxima around 1.5 × 1051 erg to zero within a few seconds latest. Nevertheless, the shock or a sonic pulse moves outward and may trigger mass-loss, which we estimate by long-time simulations with the prometheus code. We also provide gravitational-wave signals.
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Asseo, E., G. Pelletier, and H. Sol. "A Non-Linear Emission Mechanism for Pulsar Radio Radiation." International Astronomical Union Colloquium 128 (1992): 322–25. http://dx.doi.org/10.1017/s0002731600155428.
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Among the various plasma instabilities which could be responsible for coherent pulsar radio emission, we investigate the two-stream instability, first introduced by Ruderman and Sutherland (1975) in order to account for the physical situation expected in the environment of neutron stars. They describe how, in a polar cap model, pair creation arises and leads to the formation of a very energetic beam of e+ (and/or e−) and of an e−e+ plasma, both with relativistic bulk motion along the bundle of dipolar magnetic field lines. The study of their interaction is limited to the cone of open B lines, a site which provides a natural geometry for the radio emission zone, observed as core and/or conal emission by Lyne and Manchester (1988) and Rankin (1983, 1986, 1990).
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Rowe, E. T. "Beams in Magnetised Pair Plasmas." International Astronomical Union Colloquium 177 (2000): 409–10. http://dx.doi.org/10.1017/s0252921100060152.
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AbstractThe radiative instability was considered in the context of pulsar radio emission by Goldreich & Keeley (1971) and rederived and extended by Asséo, Pellat, & Sol (1983) and by Asséo (1995). Their results can be generalised and reproduced by replacing the thin cylindrical ring of charged particles by an infinitesimally thin current carrying sheet in either planar or cylindrical geometry, suggesting that the local ring geometry may not be essential for the instability. It may be useful to further investigate the generalised dispersion equation given below.
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AKSENOV, A. G., R. RUFFINI, I. A. SIUTSOU, and G. V. VERESHCHAGIN. "DYNAMICS AND EMISSION OF MILDLY RELATIVISTIC PLASMA." International Journal of Modern Physics: Conference Series 12 (January 2012): 1–9. http://dx.doi.org/10.1142/s2010194512006204.
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Initially optically thick (with τ = 3⋅107) spherically symmetric outflow consisting of electron-positron pairs and photons is considered. We do not assume thermal equilibrium, and include the two-body processes that occur in such plasma: Möller and Bhabha scattering of pairs, Compton scattering, two-photon pair annihilation, two-photon pair production, together with their radiative three-body variants: bremsstrahlung, double Compton scattering, and three-photon pair annihilation, with their inverse processes. We solve numerically the relativistic Boltzmann equations in spherically symmetric case for distribution functions of pairs and photons. Three epochs are considered in details: a) the thermalization, which brings initially nonequilibrium plasma to thermal equilibrium; b) the self-accelerated expansion, which we find in agreement with previous hydrodynamic studies and c) decoupling of photons from the expanding electron-positron plasma. Photon spectra are computed, and appear to be non thermal near the peak of the luminosity. In particular, the low energy part of the spectrum contain more power with respect to the black body one.
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Li, Shao-Ze, Yun-Wei Yu, He Gao, Zi-Gao Dai, and Xiao-Ping Zheng. "A Powerful e ± Outflow Driven by a Proto-strange Quark Star." Astrophysical Journal 922, no. 2 (December 1, 2021): 214. http://dx.doi.org/10.3847/1538-4357/ac2d2f.
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Abstract An electron–positron layer can cover the surface of a bare strange star (SS), the electric field in which can excite the vacuum and drive a pair wind by taking away the heat of the star. In order to investigate the pair-emission ability of a proto-SS, we establish a toy model to describe its early thermal evolution, where the initial trapping of neutrinos is specially taken into account. It is found that the early cooling of the SS is dominated by the neutrino diffusion rather than the conventional Urca processes, which leads to the appearance of an initial temperature plateau. During this plateau phase, the surface e ± pair emission can maintain a constant luminosity of 1048 − 1050erg s−1 for about a few to a few tens of seconds, which is dependent on the value of the initial temperature. The total energy released through this e ± wind can reach as high as ∼1051 erg. In principle, this pair wind could be responsible for the prompt emission or extended emission of some gamma-ray bursts.
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Baring, Matthew G. "Synchrotron Radiation from Energetic Electrons Emitted by AGN: A Probe for Magnetic Fields in External Galaxies." Symposium - International Astronomical Union 140 (1990): 399. http://dx.doi.org/10.1017/s0074180900190631.
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Shock acceleration of protons in the central region of active galaxies can energize them to Lorentz factors as high as 108 (Sikora et al., 1987), and these can subsequently produce a host of other relativistic particles including pions, e+e– pairs and neutrons. The luminosities of each species are expected to be of the same order of magnitude. Rapid decay of the pions leads to the secondary production of photons and pairs with energies of around 109 − 1011 MeV. The electrons and positrons can escape the compact central region and interact with the microwave background forming a pair cascade, and can also emit synchrotron radiation in the magnetic field. The neutrons do not interact with the field, and a significant fraction of them can escape the central region of a galaxy (Kirk and Mastichiadis, 1989). They can travel until they decay, producing protons and electrons in outer regions of the galaxy. Their decay time of γnτn gives a typical length for decay of about 1 kpc for the most energetic neutrons. The synchrotron radiation of these decay product electrons is examined in Baring (1989, in preparation), and it produces definite signatures of galactic magnetic fields. Magnetic fields of 1μG imply synchrotron emission in the X-ray and soft gamma-ray range for maximum Lorentz factors of γe = 1010, with a continuum extending down to much lower energies. It is observed that cooler neutrons deposit electrons at smaller radii, and these electrons are cooler (in a decay γe ~ γn). Hence the radiation would be cooler at smaller radii. This provides a diagnostic for the magnetic field: estimates of the field strength are possible from cut-offs that are expected in spectra from galactic halos. The injection of energetic electrons via neutron decay is found to yield a sharp cut-off in the injection distribution at γm = γe ~ r/τnc at radius r. Below this, no electrons are injected since they are produced in decays at smaller radii. This implies a low energy cutoff of ωm = γ2mBmec2 in the spectrum at given radius. Typically for r = 10 pc and a field of 1μG, the cutoff is at 10−8mec2 in the far infra-red. At larger radii, this low energy cutoff rapidly increases to X-ray energies. This cut-off provides a good way to measure the magnetic field strength and obtain its spatial dependence. In practice the situation is complicated by the superposition of different regions within the galaxy along the line of sight. Ways in which the observations could be deconvolved are discussed in Baring (1989, in preparation). A real possibility exists for detecting these signatures of energetic neutron emission from central regions of nearby galaxies and using the electron synchrotron spectra to spatially map galactic fields.
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Leinson, L. B. "Collective neutrino-pair emission due to Cooper pairing of protons in superconducting neutron stars." Nuclear Physics A 687, no. 3-4 (May 2001): 489–511. http://dx.doi.org/10.1016/s0375-9474(00)00575-3.
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Kurihara, Y., J. Fujimoto, T. Ishikawa, Y. Shimizu, and T. Munehisa. ": Event generator for the single- and double-photon emission associated with neutrino pair-production." Computer Physics Communications 136, no. 3 (May 2001): 250–68. http://dx.doi.org/10.1016/s0010-4655(00)00254-x.
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Schinder, Paul J., David N. Schramm, Paul J. Wiita, Steven H. Margolis, and David L. Tubbs. "Neutrino emission by the pair, plasma, and photo processes in the Weinberg-Salam model." Astrophysical Journal 313 (February 1987): 531. http://dx.doi.org/10.1086/164993.
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Gajiyeva, B. "General Formula for Impulse Losses in the Process of Emission of Neutrino Pairs by Electrons in a Magnetic Field." Bulletin of Science and Practice 7, no. 9 (September 15, 2021): 27–31. http://dx.doi.org/10.33619/2414-2948/70/02.
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Considered formula pulsed radiation losses pairs neutrinos electrons in a magnetic field. Gas consisting of polarized electrons in the direction of the magnetic field and spins composed of polarized electrons in the opposite direction of the magnetic field would receive a different impulse due to the asymmetric transmission of the impulse.
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Hakobyan, H., B. Ripperda, and A. A. Philippov. "Radiative Reconnection-powered TeV Flares from the Black Hole Magnetosphere in M87." Astrophysical Journal Letters 943, no. 2 (February 1, 2023): L29. http://dx.doi.org/10.3847/2041-8213/acb264.
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Abstract Active galactic nuclei in general, and the supermassive black hole in M87 in particular, show bright and rapid gamma-ray flares up to energies of 100 GeV and above. For M87, the flares show multiwavelength components, and the variability timescale is comparable to the dynamical time of the event horizon, suggesting that the emission may come from a compact region near the nucleus. However, the emission mechanism for these flares is not well understood. Recent high-resolution general-relativistic magnetohydrodynamic simulations show the occurrence of episodic magnetic reconnection events that can power flares near the black hole event horizon. In this work, we analyze the radiative properties of the reconnecting current layer under the extreme plasma conditions applicable to the black hole in M87 from first principles. We show that abundant pair production is expected in the vicinity of the reconnection layer, to the extent that the produced secondary pair plasma dominates the reconnection dynamics. Using analytic estimates backed by two-dimensional particle-in-cell simulations, we demonstrate that in the presence of strong synchrotron cooling, reconnection can produce a hard power-law distribution of pair plasma imprinted in the outgoing synchrotron (up to a few tens of MeV) and the inverse-Compton signal (up to TeV). We produce synthetic radiation spectra from our simulations, which can be directly compared with the results of future multiwavelength observations of M87* flares.
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Melatos, A. "Neutrinos from Pulsar Environments." Highlights of Astronomy 13 (2005): 18–23. http://dx.doi.org/10.1017/s1539299600014970.
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AbstractRecent calculations of the neutrino fluxes and spectra from pulsar magnetospheres and wind nebulae are reviewed. The neutrinos, produced in pp and pγ collisions via pion decays, are a signature of TeV ions accelerated electrostatically in the magnetosphere, in the wind termination shock (Fermi), or in the wind neutral sheet (wave surfing and/or reconnection). The fluxes and spectra are related to the energy and density of the accelerated ion beam and the densities of the target species, thereby constraining ion-loaded pulsar wind models originally developed to explain the variable wisps in pulsar-driven supernova remnants. The neutrino signal may be detectable by km2 telescopes (e.g. IceCube) and is correlated with TeV γ-ray emission. Related sources are also reviewed, such as early-phase post-supernova pulsar winds, pulsar-driven γ-ray-burst afterglows, and accreting neutron stars. The possibility of long baseline oscillation experiments, to search for fine splitting of neutrino mass eigenstates and non-radiative neutrino decays, is noted.
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LEVINSON, AMIR. "HIGH-ENERGY ASPECTS OF ASTROPHYSICAL JETS." International Journal of Modern Physics A 21, no. 30 (December 10, 2006): 6015–54. http://dx.doi.org/10.1142/s0217751x06035063.
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Various aspects of the high-energy emission from relativistic jets associated with compact astrophysical systems are reviewed. The main leptonic and hadronic processes responsible for the production of high-energy γ-rays, very-high-energy neutrinos and ultra-high energy cosmic rays are discussed. Relations between the γγ pair production and photomeson production opacities are derived, and their consequences for the relative emission of γ-rays and neutrinos are examined. The scaling of the size and location of the various emission zones and other quantities with black hole mass and dimensionless luminosity is elucidated. The results are applied to individual classes of objects, including blazars, microquasars and gamma-ray bursts. It is concluded that if baryons are present in the jet at sufficient quantities, then under optimal conditions most systems exhibiting relativistic jets may be detectable by upcoming neutrino telescopes. An exception is the class of TeV blazars, for which γ-ray observations imply neutrino yields well below detection limit.
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Astraatmadja, Tri L. "Detecting TeV γ-rays from GRBs with km3 neutrino telescopes." Proceedings of the International Astronomical Union 7, S279 (April 2011): 321–22. http://dx.doi.org/10.1017/s1743921312013154.
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AbstractObserving TeV photons from GRBs can greatly enhance our understanding of their emission mechanisms. Under-sea/ice neutrino telescopes—such as ANTARES in the Mediterranean Sea or IceCube at the South Pole—can also operate as a γ-ray observatory by detecting downgoing muons from the electromagnetic cascade induced by the interaction of the photons with the Earth's atmosphere. Theoretical calculations of the number of detectable muons from single GRB events, located at different redshifts and zenith distances, have been performed. The attenuation by pair production of TeV photons with cosmic infrared background photons has also been included.
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Leinson, L. B. "Neutrino-pair emission due to electron-phonon scattering in a neutron star crust: a reappraisal." Physics Letters B 469, no. 1-4 (December 1999): 166–70. http://dx.doi.org/10.1016/s0370-2693(99)01278-2.
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Pétri, Jérôme. "Electrodynamics and Radiation from Rotating Neutron Star Magnetospheres." Universe 6, no. 1 (January 15, 2020): 15. http://dx.doi.org/10.3390/universe6010015.
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Neutron stars are compact objects rotating at high speed, up to a substantial fraction of the speed of light (up to 20% for millisecond pulsars) and possessing ultra-strong electromagnetic fields (close to and sometimes above the quantum critical field of 4.4 × 10 9 T ). Moreover, due to copious e ± pair creation within the magnetosphere, the relativistic plasma surrounding the star is forced into corotation up to the light cylinder where the corotation speed reaches the speed of light. The neutron star electromagnetic activity is powered by its rotation which becomes relativistic in the neighborhood of this light cylinder. These objects naturally induce relativistic rotation on macroscopic scales about several thousands of kilometers, a crucial ingredient to trigger the central engine as observed on Earth. In this paper, we elucidate some of the salient features of this corotating plasma subject to efficient particle acceleration and radiation, emphasizing several problems and limitations concerning current theories of neutron star magnetospheres. Relativistic rotation in these systems is indirectly probed by the radiation produced within the magnetosphere. Depending on the underlying assumptions about particle motion and radiation mechanisms, different signatures on their light curves, spectra, pulse profiles and polarization angles are expected in their broadband electromagnetic emission. We show that these measurements put stringent constraints on the way to describe particle electrodynamics in a rotating neutron star magnetosphere.
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Ito, Hirotaka, Amir Levinson, and Shigehiro Nagataki. "Monte Carlo simulations of relativistic radiation-mediated shocks: II. photon-starved regime." Monthly Notices of the Royal Astronomical Society 492, no. 2 (December 23, 2019): 1902–13. http://dx.doi.org/10.1093/mnras/stz3591.
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ABSTRACT Radiation-mediated shocks (RMS) play a key role in shaping the early emission observed in many transients. In most cases, e.g. shock breakout in supernovae, llGRBs, and neutron star mergers, the upstream plasma is devoid of radiation, and the photons that ultimately reach the observer are generated predominantly inside and downstream of the shock. Predicting the observed spectrum requires detailed calculations of the shock structure and thermodynamic state that account properly for the shock microphysics. We present results of self-consistent Monte Carlo simulations of photon-starved RMS, which yield the shock structure and emission for a broad range of shock velocities, from subrelativistic (βsh = 0.1) to highly relativistic (Γsh = 20). Our simulations confirm that in relativistic RMS the immediate downstream temperature is regulated by exponential pair creation, ranging from 50 keV at βsh = 0.5–200 keV at Γsh = 20. At lower velocities, the temperature becomes sensitive to the shock velocity, with kT ∼ 0.5 keV at βsh = 0.1. We also confirm that in relativistic shocks the opacity is completely dominated by newly created pairs, which has important implications for the breakout physics. We find the transition to pair dominance to occur at βsh = 0.5 roughly. In all cases examined, the spectrum below the νFν peak has been found to be substantially softer than the Planck distribution. This has important implications for the optical emission in fast and relativistic breakouts, and their detection. The applications to GRB 060218 and GRB 170817A are discussed.
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Buchal, Ch, and M. Löken. "Silicon-Based Metal-Semiconductor-Metal Detectors." MRS Bulletin 23, no. 4 (April 1998): 55–59. http://dx.doi.org/10.1557/s088376940003027x.
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Photodetectors must provide fast and efficient conversion of photons to charge carriers. When considering semiconductor light sources, the indirect bandgap of silicon and germanium represents a serious obstacle to radiative electron-hole recombinations. Momentum conservation demands the simultaneous interaction of the electron-hole pair with a momentum-matching phonon. As a consequence, radiative recombinations are five orders of magnitude less probable in Si if compared to a direct semiconductor such as GaAs.Although the absorption of a photon and the generation of an electron-hole pair may be considered as the inverse process to emission, photon absorption within indirect semiconductors is a highly probable process if the photon energy is sufficient to bridge the energy gap in a direct process. The resulting electronhole pair is created in an excited state and relaxes sequentially. The ubiquitous-silicon solar cells operate this way. In the visible spectral range, Si photodetectors have demonstrated fast and efficient performance, being readily adapted for opto electronic applications and being fully compatible to standard-silicon processing schemes.
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Wang, Ze-Rui, and Rui Xue. "Hadronuclear interpretation of the possible neutrino emission from PKS B1424-418, GB6 J1040+0617 and PKS 1502+106." Research in Astronomy and Astrophysics 21, no. 12 (December 1, 2021): 305. http://dx.doi.org/10.1088/1674-4527/21/12/305.
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Abstract In addition to neutrino event IceCube-170922A which is observed to be associated with a γ-ray flare from blazar TXS 0506+056, there are also several neutrino events that may be associated with blazars. Among them, PKS B1424-418, GB6 J1040+0617 and PKS 1502+106 are low synchrotron peaked sources, which are usually believed to have the broad line region in the vicinity of the central black hole. They are considered as counterparts of IceCube event 35, IceCube-141209A and IceCube-190730A, respectively. By considering the proton-proton (pp) interactions between the dense gas clouds in the broad line region and the relativistic protons in the jet, we show that the pp model that is applied in this work can not only reproduce the multi-waveband spectral energy distribution but also suggest a considerable annual neutrino detection rate. We also discuss the emission from the photopion production and Bethe-Heitler pair production with a sub-Eddington jet power that is suggested in our model and find that it has little effect on the spectrum of total emission for all of three sources.
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Nava, L., L. Sironi, G. Ghisellini, A. Celotti, and G. Ghirlanda. "Afterglow emission in gamma-ray bursts – I. Pair-enriched ambient medium and radiative blast waves." Monthly Notices of the Royal Astronomical Society 433, no. 3 (June 17, 2013): 2107–21. http://dx.doi.org/10.1093/mnras/stt872.
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Zhang, Lian, Hua-Yu Wang, Ning Wang, Can Tao, Xue-Lin Zhai, Ping-Zhun Ma, Ying Zhong, and Hai-Tao Liu. "Broadband enhancement of spontaneous emission by optical dipole nanoantenna on metallic substrate: An intuitive model of surface plasmon polariton." Acta Physica Sinica 71, no. 11 (2022): 118101. http://dx.doi.org/10.7498/aps.70.20212290.
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<sec>Optical nanoantennas can achieve electromagnetic-field enhancement under far-field excitation or spontaneous-emission enhancement under excitation by radiating emitters. Among them, nanoantennas on a metallic substrate (i.e. the so-called nanoparticle-on-mirror antennas) have aroused great research interest due to their ease in forming metallic gaps of sizes down to a few nanometers or even subnanometer. Here we propose an optical dipole nanoantenna on a metallic substrate with a broadband enhancement of spontaneous emission. Its total and radiative emission-rate enhancement factors can reach up to 5454 and 1041, respectively. In the near-infrared band, the wavelength range of spontaneous-emission enhancement (Purcell factor over 1000) can reach 260nm. By changing the width of the slit between the two antenna arms and also the length of the antenna arms, the spontaneous-emission enhancement bandwidth and enhancement factors can be adjusted, respectively, which brings great freedom and simplicity to the design process. The antenna can achieve a strong far-field radiation within a central anglular zone (polar angle <i>θ</i>≤60°) corresponding to a certain numerical aperture of objective lens, and therefore can increase the intensity of the fluorescence collected by the objective lens. Based on the above performances, the antenna can provide a broadband enhancement of spontaneous emission for fluorescent molecules or quantum dots (whose fluorescence spectrum usually covers a certain wavelength range), which is of great significance for the applications such as in high-speed and super-bright nanoscale light sources and high-sensitivity fluorescent-molecule sensing.</sec><sec>To clarify the underlying physical mechanisms, we build up a semi-analytical model by considering an intuitive excitation and multiple-scattering process of surface plasmon polaritons (SPPs) that propagate along the antenna arms. All the parameters used in the model (such as the SPP scattering coefficients) are obtained via rigorous calculations based on the first principle of Maxwell's equations without any fitting process, which ensures that the model has a solid electromagnetic foundation and can provide quantitative predictions. The SPP model can comprehensively reproduce all the radiation properties of the antenna, such as the total radiative emission rate and the far-field radiation pattern. Two phase-matching conditions are derived from the model for predicting the antenna resonance, and show that under these conditions, the SPPs on the antenna arms form a pair of Fabry-Perot resonance and therefore are enhanced, and the enhanced SPPs propagate to the emitter in the nanogap (or scattered into the free space), so as to enhance the total spontaneous emission rate (or the far-field radiative emission rate). Besides, this pair of Fabry-Perot resonance results in a pair of resonance peaks close to each other, then enhancing the spontaneous emission with a broadband.</sec>
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Dundovic, A., C. Evoli, D. Gaggero, and D. Grasso. "Simulating the Galactic multi-messenger emissions with HERMES." Astronomy & Astrophysics 653 (September 2021): A18. http://dx.doi.org/10.1051/0004-6361/202140801.
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Context. The study of nonthermal processes such as synchrotron emission, inverse Compton scattering, bremsstrahlung, and pion production is crucial to understanding the properties of the Galactic cosmic-ray population, to shed light on their origin and confinement mechanisms, and to assess the significance of exotic signals possibly associated to new physics. Aims. We present a public code called HERMES which is designed generate sky maps associated to a variety of multi-messenger and multi-wavelength radiative processes, spanning from the radio domain all the way up to high-energy gamma-ray and neutrino production. Methods. We describe the physical processes under consideration, the code concept and structure, and the user interface, with particular focus on the python-based interactive mode. In particular, present the modular and flexible design that allows the user to easily extend the numerical package according to their needs. Results. In order to demonstrate the capabilities of the code, we describe the details of a comprehensive set of sky maps and spectra associated to all physical processes included in the code. We comment in particular on the radio, gamma-ray, and neutrino maps, and mention the possibility of studying signals stemming from dark matter annihilation. Conclusions. HERMES can be successfully applied to constrain the properties of the Galactic cosmic-ray population, improve our understanding of the diffuse Galactic radio, gamma-ray, and neutrino emission, and search for signals associated to particle dark matter annihilation or decay.
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Svensson, Roland. "Physical Processes in Active Galactic Nuclei." International Astronomical Union Colloquium 89 (1986): 324–45. http://dx.doi.org/10.1017/s0252921100086152.
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AbstractActive galactic nuclei (AGNs) emit continuum radiation evenly spread over up to ten decades in frequency from the radio into the gamma-ray range. Plausible emission mechanisms and their characteristics are reviewed. In the deep potential wells around black holes the mean energy per proton can reach 100 MeV. Part or all of this energy may be channeled to all electrons equally (thermal plasma) or, preferentially, into only a small fraction of the electrons (nonthermal plasma). In the former case thermal Comptonization of soft photons may be the dominant emission mechanism, while in the latter case the synchrotron and the inverse Compton scattering process (synchro-self-Compton) are likely to dominate.When the compactness parameter L (hν≈mc2 )/R. (power L, radius R) exceeds about 1030 ergs cm−1s−1 or L>Lc ≡ 1030R ergs s−1, then electron-positron pair production takes place due to photon-photon interactions causing the source to shroud itself with an electron-positron atmosphere. The efficiency of pair cascades in converting injected energy into electron-positron rest mass can reach levels of about 10% in static pair atmospheres. The emerging radiation is strongly modified by the pair atmosphere causing the spectrum to soften and to have characteristic breaks.For emission coming from a region near the Schwarzschild radius, L>10-3LEdd is sufficient to cause prolific pair production. Radiation pressure then drives a mildly relativistic pair wind with Compton drag limiting the Lorentz factor to be less then 10. The pair rest mass power is at most of the order of Lc.Most results so far on static pair atmospheres and pair winds are either qualitative or based on simple analytical models. Needed numerical treatments of both time dependent and steady radiative transfer of both the continuum and the annihilation line radiation in mildly relativistic flows are relevant not only for AGNs but also for gamma ray bursts and galactic black hole sources.
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Zhdankin, Vladimir, Dmitri A. Uzdensky, Gregory R. Werner, and Mitchell C. Begelman. "Kinetic turbulence in shining pair plasma: intermittent beaming and thermalization by radiative cooling." Monthly Notices of the Royal Astronomical Society 493, no. 1 (January 31, 2020): 603–26. http://dx.doi.org/10.1093/mnras/staa284.
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ABSTRACT High-energy astrophysical systems frequently contain collision-less relativistic plasmas that are heated by turbulent cascades and cooled by emission of radiation. Understanding the nature of this radiative turbulence is a frontier of extreme plasma astrophysics. In this paper, we use particle-in-cell simulations to study the effects of external inverse Compton radiation on turbulence driven in an optically thin, relativistic pair plasma. We focus on the statistical steady state (where injected energy is balanced by radiated energy) and perform a parameter scan spanning from low magnetization to high magnetization (0.04 ≲ σ ≲ 11). We demonstrate that the global particle energy distributions are quasi-thermal in all simulations, with only a modest population of non-thermal energetic particles (extending the tail by a factor of ∼2). This indicates that non-thermal particle acceleration (observed in similar non-radiative simulations) is quenched by strong radiative cooling. The quasi-thermal energy distributions are well fit by analytic models in which stochastic particle acceleration (due to, e.g. second-order Fermi mechanism or gyroresonant interactions) is balanced by the radiation reaction force. Despite the efficient thermalization of the plasma, non-thermal energetic particles do make a conspicuous appearance in the anisotropy of the global momentum distribution as highly variable, intermittent beams (for high magnetization cases). The beamed high-energy particles are spatially coincident with intermittent current sheets, suggesting that localized magnetic reconnection may be a mechanism for kinetic beaming. This beaming phenomenon may explain rapid flares observed in various astrophysical systems (such as blazar jets, the Crab nebula, and Sagittarius A*).
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Faran, Tamar, and Re'em Sari. "Shock Breakout from Stellar Envelopes: The Relativistic Limit." Astrophysical Journal 943, no. 2 (January 27, 2023): 97. http://dx.doi.org/10.3847/1538-4357/aca7fd.
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Abstract We calculate the observed luminosity and spectrum following the emergence of a relativistic shock wave from a stellar edge. Shock waves propagating at 0.6 < Γsh β sh, where Γsh is the shock Lorentz factor, and β sh is its associated reduced velocity, heat the stellar envelope to temperatures exceeding ∼50 keV, allowing for a vigorous production of electron and positron pairs. Pairs significantly increase the electron-scattering optical depth and regulate the temperature through photon generation, producing distinct observational signatures in the escaping emission. Assuming Wien equilibrium, we find analytic expressions for the temperature and pair density profiles in the envelope immediately after shock passage, and compute the emission during the expansion phase. Our analysis shows that, in pair-loaded regions, photons are produced at a roughly uniform rest-frame energy of ∼200 keV, and reinforce previous estimates that the shock breakout signal will be detected as a short burst of energetic γ-ray photons, followed by a longer phase of X-ray emission. We test our model on a sample of low-luminosity gamma-ray bursts using a closure relation between the γ-ray burst duration, the radiation temperature, and the γ-ray isotropic equivalent energy, and find that some of the events are consistent with the relativistic shock breakout model. Finally, we apply our results to explosions in white dwarfs and neutron stars, and find that typical type Ia supernovae emit ∼1041 erg in the form of ∼1 MeV photons.