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  1. ABSTRACT

    Magnetars have been considered as progenitors of magnetar giant flares (MGFs) and fast radio bursts (FRBs). We present detailed studies on afterglow emissions caused by bursts that occur in their wind nebulae and surrounding baryonic ejecta. In particular, following the bursts-in-bubble model, we analytically and numerically calculate spectra and light curves of such afterglow emission. We scan parameter space for the detectability of radio signals, and find that a burst with ∼1045 erg is detectable with the Very Large Array or other next-generation radio facilities. The detection of multiwavelength afterglow emission from MGFs and/or FRBs is of great significance for their localization and revealing their progenitors, and we estimate the number of detectable afterglow events.

     
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  2. Abstract

    Early-time light curves/spectra of some hydrogen-rich supernovae (SNe) provide solid evidence of the existence of confined, dense circumstellar matter (CSM) surrounding dying massive stars. We numerically and analytically study the radiative acceleration of CSM in such systems, where the radiation is mainly powered by the interaction between the SN ejecta and the CSM. We find that the acceleration of the unshocked dense CSM ahead of the shock is larger for massive and compact CSM, with velocities reaching up to ∼103km s−1for a CSM of order 0.1Mconfined within ∼1015cm. We show that the dependence of the acceleration on the CSM density helps us explain the diversity of the CSM velocity inferred from the early spectra of some Type II SNe. For explosions in even denser CSM, radiative acceleration can affect the dissipation of strong collisionless shocks formed after the shock breakout, which would affect early nonthermal emission expected from particle acceleration.

     
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  3. ABSTRACT

    Very high energy (VHE) γ-rays ($\gtrsim\!\! 0.1\rm ~TeV$) and neutrinos are crucial for identifying accelerators of ultra-high-energy cosmic rays (UHECRs), but this is challenging especially for UHECR nuclei. In this work, we develop a numerical code to solve the transport equation for UHECRs and their secondaries, where both nuclear and electromagnetic cascades are taken into account self-consistently, considering steady UHECR accelerators such as radio galaxies. In particular, we focus on Centaurus A, which has been proposed as one of the most promising UHECR sources in the local Universe. Motivated by observations of extended VHE γ-ray emission from its kiloparsec-scale jet by the High Energy Stereoscopic System (H.E.S.S.), we study interactions between UHECRs accelerated in the large-scale jet and various target photon fields including blazar-like beamed core emission, and present a quantitative study on VHE γ-ray signatures of UHECR nuclei, including the photodisintegration and Bethe–Heitler pair production processes. We show that VHE γ-rays from UHECR nuclei could be detected by the ground-based γ-ray telescopes given that the dominant composition of UHECRs consists of intermediate-mass (such as oxygen) nuclei.

     
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  4. Abstract

    Recent multimessenger studies have provided evidence for high-energy neutrino sources that are opaque to GeV–TeV gamma rays. We present model-independent studies on the connection between neutrinos and gamma rays in the active galaxy NGC 1068, and find that the neutrinos most likely come from regions within ∼30–100 Schwarzschild radii. This is especially the case if neutrinos are produced via the photomeson production process, although the constraints could be alleviated if hadronuclear interactions are dominant. We consider the most favorable neutrino production regions, and discuss coronae, jets, winds, and their interactions with dense material. The results strengthen the importance of understanding dissipation mechanisms near the coronal region and the outflow base. There could be a connection between active galactic nuclei with near-Eddington accretion and tidal disruptions events, in that neutrinos are produced in the obscured vicinity of supermassive black holes.

     
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  5. Abstract

    The detection of the hyper-bright gamma-ray burst (GRB) 221009A enables us to explore the nature of the GRB emission and the origin of very high-energy gamma rays. We analyze the Fermi Large Area Telescope (Fermi-LAT) data of this burst and investigate the GeV–TeV emission in the framework of the external reverse-shock model. We show that the early ∼1–10 GeV emission can be explained by the external inverse-Compton mechanism via upscattering MeV gamma rays by electrons accelerated at the reverse shock, in addition to the synchrotron self-Compton component. The predicted early optical flux could have been brighter than that of the naked-eye GRB 080319B. We also show that proton synchrotron emission from accelerated ultrahigh-energy cosmic rays (UHECRs) is detectable and could potentially explain ≳TeV photons detected by LHAASO or constrain the UHECR acceleration mechanism. Our model suggests that the detection of(10TeV)photons with energies up to ∼18 TeV is possible for reasonable models of the extragalactic background light without invoking new physics and predicts anticorrelations between MeV photons and TeV photons, which can be tested with the LHAASO data.

     
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  6. Abstract

    We discuss implications that can be obtained by searches for neutrinos from the brightest gamma-ray burst (GRB), GRB 221009A. We derive constraints on GRB model parameters such as the cosmic-ray loading factor and dissipation radius, taking into account both neutrino spectra and effective areas. The results are strong enough to constrain proton acceleration near the photosphere, and we find that the single burst limits are comparable to those from stacking analysis. Quasi-thermal neutrinos from subphotospheres and ultra-high-energy neutrinos from external shocks are not yet constrained. We show that GeV–TeV neutrinos originating from neutron collisions are detectable, and urge dedicated analysis on these neutrinos with DeepCore and IceCube as well as ORCA and KM3NeT.

     
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  7. ABSTRACT

    Relativistic jets originating from protomagnetar central engines can lead to long duration gamma-ray bursts (GRBs) and are considered potential sources of ultra-high-energy cosmic rays and secondary neutrinos. We explore the propagation of such jets through a broad range of progenitors, from stars which have shed their envelopes to supergiants which have not. We use a semi-analytical spin-down model for the strongly magnetized and rapidly rotating protoneutron star (PNS) to investigate the role of central engine properties such as the surface dipole field strength, initial rotation period, and jet opening angle on the interactions and dynamical evolution of the jet-cocoon system. With this model, we determine the properties of the relativistic jet, the mildly relativistic cocoon, and the collimation shock in terms of system parameters such as the time-dependent jet luminosity, injection angle, and density profile of the stellar medium. We also analyse the criteria for a successful jet breakout, the maximum energy that can be deposited into the cocoon by the relativistic jet, and structural stability of the magnetized outflow relative to local instabilities. Lastly, we compute the high-energy neutrino emission as these magnetized outflows burrow through their progenitors. Precursor neutrinos from successful GRB jets are unlikely to be detected by IceCube, which is consistent with the results of previous works. On the other hand, we find that high-energy neutrinos may be produced for extended progenitors like blue and red supergiants, and we estimate the detectability of neutrinos with next generation detectors such as IceCube-Gen2.

     
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  8. Abstract

    We present a bottom-up calculation of the flux of ultrahigh-energy cosmic rays (UHECRs) and high-energy neutrinos produced by powerful jets of active galactic nuclei (AGNs). By propagating test particles in 3D relativistic magnetohydrodynamic jet simulations, including a Monte Carlo treatment of sub-grid pitch-angle scattering and attenuation losses due to realistic photon fields, we study the spectrum and composition of the accelerated UHECRs and estimate the amount of neutrinos produced in such sources. We find that UHECRs may not be significantly affected by photodisintegration in AGN jets where theespressomechanism efficiently accelerates particles, consistent with Auger’s results that favor a heavy composition at the highest energies. Moreover, we present estimates andupper boundsfor the flux of high-energy neutrinos expected from AGN jets. In particular, we find that (i) source neutrinos may account for a sizable fraction, or even dominate, the expected flux of cosmogenic neutrinos; (ii) neutrinos from theβ-decay of secondary neutrons produced in nucleus photodisintegration end up in the teraelectronvolt to petaelectronvolt band observed by IceCube, but can hardly account for the observed flux; (iii) UHECRs accelerated via theespressomechanism lead to nearly isotropic neutrino emission, which suggests that nearby radio galaxies may be more promising as potential sources. We discuss our results in light of multimessenger astronomy and current/future neutrino experiments.

     
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  9. ABSTRACT

    Primordial black holes (PBHs) formed in the early Universe constitute an attractive candidate for dark matter. Within the gaseous environment of the interstellar medium, PBHs with accretion discs naturally launch outflows such as winds and jets. We discuss for the first time how PBHs with significant spin can sustain powerful relativistic jets and generate associated cocoons. Jets and winds can efficiently deposit their kinetic energies and heat the surrounding gas through shocks. Focusing on the Leo T dwarf galaxy, we demonstrate that these effects form novel tests and set new limits on PBHs over a significant ∼10−2 –106 M⊙ mass range, including the parameter space associated with gravitational wave observations by the LIGO and VIRGO Collaborations. Observing the morphology of emission will allow to distinguish between jet and wind contributions, and hence establishes a new method for identifying spinning PBHs.

     
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  10. ABSTRACT

    It has been suggested that strongly magnetized and rapidly rotating protoneutron stars (PNSs) may produce long duration gamma-ray bursts (GRBs) originating from stellar core collapse. We explore the steady-state properties and heavy element nucleosynthesis in neutrino-driven winds from such PNSs whose magnetic axis is generally misaligned with the axis of rotation. We consider a wide variety of central engine properties such as surface dipole field strength, initial rotation period, and magnetic obliquity to show that heavy element nuclei can be synthesized in the radially expanding wind. This process is facilitated provided the outflow is Poynting-flux dominated such that its low entropy and fast expansion time-scale enables heavy nuclei to form in a more efficient manner as compared to the equivalent thermal GRB outflows. We also examine the acceleration and survival of these heavy nuclei and show that they can reach sufficiently high energies ≳ 1020 eV within the same physical regions that are also responsible for powering gamma-ray emission, primarily through magnetic dissipation processes. Although these magnetized outflows generally fail to achieve the production of elements heavier than lanthanides for our explored electron fraction range 0.4–0.6, we show that they are more than capable of synthesizing nuclei near and beyond iron peak elements.

     
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