Abstracts of Interest
Selected by:
Andrew Curzons
Abstract: 1809.08610
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Title: Highly-boosted dark matter and cutoff for cosmic-ray neutrino through neutrino portal
(Submitted on 23 Sep 2018)
Abstract: We study the cutoff for the cosmic-ray neutrino, set by the scattering with cosmic background neutrinos into dark sector particles through a neutrino portal interaction. We find that a large interaction rate is still viable, when the dark sector particles are mainly coupled to the ${\tau}$-neutrino, so that the neutrino mean free path can be reduced to be O(10) Mpc over a wide energy range. If stable enough, the dark sector particle, into whom most of the cosmic-ray neutrino energy is transferred, can travel across the Universe and reach to the earth. The energy of them can be as large as O(EeV) if originates from a cosmogenic neutrino.
Abstract: 1809.08249
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Full Text: [ PostScript, PDF]
Title: Constraining the limiting brightness temperature and Doppler factors for the largest sample of radio bright blazars
(Submitted on 21 Sep 2018)
Abstract: Relativistic effects dominate the emission of blazar jets complicating our understanding of their intrinsic properties. Although many methods have been proposed to account for them, the variability Doppler factor method has been shown to describe the blazar populations best. We use a Bayesian hierarchical code called {\it Magnetron} to model the light curves of 1029 sources observed by the Owens Valley Radio Observatory's 40-m telescope as a series of flares with an exponential rise and decay, and estimate their variability brightness temperature. Our analysis allows us to place the most stringent constraints on the equipartition brightness temperature i.e., the maximum achieved intrinsic brightness temperature in beamed sources which we found to be $\rm \langle T_{eq}\rangle=2.78\times10^{11}K\pm26\%$. Using our findings we estimated the variability Doppler factor for the largest sample of blazars increasing the number of available estimates in the literature by almost an order of magnitude. Our results clearly show that $\gamma$-ray loud sources have faster and higher amplitude flares than $\gamma$-ray quiet sources. As a consequence they show higher variability brightness temperatures and thus are more relativistically beamed, with all of the above suggesting a strong connection between the radio flaring properties of the jet and $\gamma$-ray emission.
Abstract: 1809.08398
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Full Text: [ PostScript, PDF]
Title: Charged-current scattering off $^{16}$O nucleus as a detection channel for supernova neutrinos
(Submitted on 22 Sep 2018)
Abstract: Event spectra of the neutrino-$^{16}$O charged-current reactions in Super-Kamiokande are evaluated for a future supernova neutrino burst. Since these channels are expected to be useful for diagnosing a neutrino spectrum with high average energy, the evaluations are performed not only for an ordinary supernova neutrino model but also for a model of neutrino emission from a black-hole-forming collpase. Using shell model results, whose excitation energies are consistent with the experimental data, the cross sections of the $^{16}$O($\nu_e, e^-$)X and $^{16}$O($\bar\nu_e, e^+$)X reactions for each nuclear state with a different excitation energy are employed in this study. It is found that, owing to the components of the reaction with higher excitation energy, the event spectrum becomes 4-7 MeV softer than that in the case without considering the excitation energies. In addition, a simplified approach to evaluate the event spectra is proposed for convenience and its validity is examined.
Abstract: 1809.08492
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Title: Using UHE Cosmic Rays to Probe the CBR and Test Standard Model Particle Physics
(Submitted on 22 Sep 2018)
Abstract: Tipler has shown that if we assume that the particle physics Standard Model and DeWitt-Wheeler quantum gravity (equivalent to Feynman-Weinberg quantum gravity) are a Theory of Everything, then in the very early universe, the Cosmic Background Radiation (CBR) could not have coupled to right handed electrons and quarks. Tipler further showed that if this property of CBR has continued, the Sunyaev-Zel'dovich (SZ) effect would be observed to be too low by a factor of two. WMAP and PLANCK observed this. Tipler showed that this CBR property would also mean the Ultra High Energy Cosmic Rays (UHECR) would propagate a factor of ten further than standard theory predicts, since most of the cross section for pion production when a UHECR hits a CBR photon is due to a quark spin flip, and such a flip cannot occur if a CBR particle cannot couple to right-handed quarks. We show that taking this additional propagation distance into account allows us to identify the sources of 86\% of the UHECR seen by the Pierre Auger Collaboration. We can also identify the sources of 9 of the 11 UHECR seen by the AGASA observatory, and the source of the 320 EeV UHECR seen by the Fly's Eye instrument. We propose observations to test the theory underlying the UHECR identifications, beginning with measuring the redshifts of five galaxies whose apparent visual magnitude we estimate to be about 15, and whose positions we give to within one arcsecond. The particle physics Standard Model identifies the Dark Energy and Dark Matter.
Abstract: 1809.09054
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Full Text: [ PostScript, PDF]
Title: Outflow and Emission Model of Pulsar Wind Nebulae with the Back-reaction of Particle Diffusion
(Submitted on 24 Sep 2018)
Abstract: We present a new pulsar wind nebula (PWN) model solving both advection and diffusion of non-thermal particles in a self-consistent way to satisfy the momentum and energy conservation laws. Assuming spherically symmetric (1--D) steady outflow, we calculate the emission spectrum integrating over the entire nebula and the radial profile of the surface brightness. We find that the back reaction of the particle diffusion modifies the flow profile. The photon spectrum and the surface brightness profile are different from the model calculations without the back reaction of the particle diffusion. Our model is applied to the two well-studied PWNe 3C 58 and G21.5-0.9. By fitting the spectra of these PWNe, we determine the parameter sets and calculate the radial profiles of X-ray surface brightness. For both the objects, obtained profiles of X-ray surface brightness and photon index are well consistent with observations. Our model suggests that particles escaped from the nebula significantly contribute to the gamma-ray flux. A $\gamma$-ray halo larger than the radio nebula is predicted in our model.
Abstract: 1809.08682
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Full Text: [ PostScript, PDF]
Title: How to tell an accreting boson star from a black hole
(Submitted on 23 Sep 2018)
Abstract: Radio-astronomical observations of the supermassive black-hole candidate in the galactic center will soon offer the possibility to study gravity in its strongest regimes and to test different models for these compact objects. Studies based on semi-analytic models and strong-field images of stationary plasma configurations around boson stars have stressed the difficulty to distinguish them from black holes. We here report on the first general-relativistic magnetohydrodynamic simulations of accretion onto a nonrotating boson star and employ general-relativistic radiative-transfer calculations to revisit the appearance of an accreting boson star. We find that the absence of an event horizon in a boson star leads to important differences in the dynamics of the accretion and results in both the formation of a small torus in the interior of the boson star and in the absence of an evacuated high-magnetization funnel in the polar regions. Synthetic reconstructed images considering realistic astronomical observing conditions show that differences in the appearance of the two compact object are large enough to be detectable. These results, which also apply to other horizonless compact objects, strengthen confidence in the ability to determine the presence of an event horizon via radio observations and highlight the importance of self-consistent multidimensional simulations to study the compact object at the galactic center.
Abstract: 1809.09125
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Full Text: [ PostScript, PDF]
Title: High-accuracy mass, spin, and recoil predictions of generic black-hole merger remnants
(Submitted on 24 Sep 2018)
Abstract: We present accurate fits for the remnant properties of generically precessing binary black holes, trained on large banks of numerical-relativity simulations. We use Gaussian process regression to interpolate the remnant mass, spin, and recoil velocity in the 7-dimensional parameter space of precessing black-hole binaries. For precessing systems, our errors in estimating the remnant mass, spin magnitude, and kick magnitude are lower than those of existing fitting formulae by at least an order of magnitude. In addition, we also model the remnant spin and kick directions. Improvement is also reported for aligned-spin systems. Being trained directly on precessing simulations, our fits are free from ambiguities regarding the initial frequency at which precessing quantities are defined. As a byproduct, we also provide error estimates for all fitted quantities, which can be consistently incorporated into current and future gravitational-wave parameter-estimation analyses. Our model(s) are made publicly available through a fast and easy-to-use Python module called surfinBH.
Abstract: 1809.09610
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Full Text: [ PostScript, PDF]
Title: Constraining high-energy neutrinos from choked-jet supernovae with IceCube high-energy starting events
(Submitted on 25 Sep 2018)
Abstract: Different types of core-collapse supernovae (SNe) have been considered as candidate sources of high-energy cosmic neutrinos. Stripped-envelope SNe, including energetic events like hypernovae and super-luminous SNe, are of particular interest. They may harbor relativistic jets, which are capable of explaining the diversity among gamma-ray bursts (GRBs), low-luminosity GRBs, ultra-long GRBs, and broadline Type Ib/c SNe. Using the six-year IceCube data on high-energy starting events (HESEs), we perform an unbinned maximum likelihood analysis to search for spatial and temporal coincidences with 222 samples of SNe Ib/c. We find that the present data are consistent with the background only hypothesis, by which we place new upper constraints on the isotropic-equivalent energy of cosmic rays, ${\mathcal E}_{\rm cr}\lesssim{10}^{52}~{\rm erg}$, in the limit that all SNe are accompanied by on-axis jets. Our results demonstrate that not only upgoing muon neutrinos but also HESE data enable us to constrain the potential contribution of these SNe to the diffuse neutrino flux observed in IceCube. We also discuss implications for the next-generation neutrino detectors such as IceCube-Gen2.
Abstract: 1809.09615
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Full Text: [ PostScript, PDF]
Title: The ANITA Anomalous Events as Signatures of a Beyond Standard Model Particle, and Supporting Observations from IceCube
(Submitted on 25 Sep 2018)
Abstract: The ANITA collaboration have reported observation of two anomalous events that appear to be $\varepsilon_{\rm cr} \approx 0.6$ EeV cosmic ray showers emerging from the Earth with exit angles of $27^\circ$ and $35^\circ$, respectively. While EeV-scale upgoing showers have been anticipated as a result of astrophysical tau neutrinos converting to tau leptons during Earth passage, the observed exit angles are much steeper than expected in Standard Model (SM) scenarios. Indeed, under conservative extrapolations of the SM interactions, there is no particle that can propagate through the Earth with probability $p > 10^{-6}$ at these energies and exit angles. We explore here whether "beyond the Standard Model" (BSM) particles are required to explain the ANITA events, if correctly interpreted, and conclude that they are. Seeking confirmation or refutation of the physical phenomenon of sub-EeV Earth-emergent cosmic rays in data from other facilities, we find support for the reality of the ANITA events, and three candidate analog events, among the Extremely High Energy Northern Track neutrinos of the IceCube Neutrino Observatory. Properties of the implied BSM particle are anticipated, at least in part, by those predicted for the "stau" slepton ($\tilde{\tau}_R$) in some supersymmetric models of the fundamental interactions, wherein the stau manifests as the next-to-lowest mass supersymmetric partner particle.
Abstract: 1809.10259
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Full Text: [ PostScript, PDF]
Title: Astrophysical neutrino production and impact of associated uncertainties in photo-hadronic interactions of UHECRs
(Submitted on 26 Sep 2018)
Abstract: High energy neutrinos can be produced by interactions of ultra-high energy cosmic rays (UHECRs) in the dense radiation fields of their sources as well as off the cosmic backgrounds when they propagate through the universe. Multi-messenger interpretations of current measurements deeply rely on the understanding of these interactions. In order to efficiently produce neutrinos in the sources of UHECRs, at least a moderate level of interactions is needed, which means that a nuclear cascade develops if nuclei are involved. On the other hand, the available cross-section data and interaction models turn out to make poor predictions for most nuclei heavier than protons. We show the impact of these uncertainties in state-of-the-art photo-disintegration models and motivate nuclear cross-section measurements. Further, we discuss extensions for photo-meson models currently used in astrophysics and demonstrate the importance of understanding the details of UHECR interaction with the Glashow resonance.
Abstract: 1809.10285
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Full Text: [ PostScript, PDF]
Title: Observing the Energetic Universe at Very High Energies with the VERITAS Gamma Ray Observatory
(Submitted on 27 Sep 2018)
Abstract: Very high energy gamma-ray observations offer indirect methods for studying the highest energy cosmic rays in our Universe. The origin of cosmic rays at energies greater than $10^{18}$ eV remains a mystery, and many questions in particle astrophysics exist. The VERITAS observatory in southern Arizona, USA, carries out an extensive observation program of the gamma-ray sky at energies above 85 GeV. Observations of Galactic and extragalactic sources in the TeV band provide clues to the highly energetic processes occurring in these objects, and could provide indirect evidence for the origin of cosmic rays and the sites of particle acceleration in the Universe. VERITAS has now been operational for ten years with the complete array of four atmospheric Cherenkov telescopes. In this review, we present the status of VERITAS, and give few results from three of its key scientific programs: extragalactic science, Galactic physics, and study of fundamental physics and cosmology.
Abstract: 1809.10683
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Full Text: [ PostScript, PDF]
Title: Simultaneous Spectral and Spatial Modelling of Young Pulsar Wind Nebulae
(Submitted on 27 Sep 2018)
Abstract: We model the morphology and spectrum of a pulsar wind nebula using a leptonic emission code. This code is a time-dependent, multi-zone model that investigates the changes in the particle spectrum as they traverse the nebula. We calculate the synchrotron and inverse Compton emissivities at different positions in the nebula, obtaining the surface brightness versus the radius, and also the size of the nebula as a function of energy. We incorporate a time and spatially-dependent $B$-field, spatially-dependent bulk particle speed implying convection and adiabatic losses, diffusion, as well as radiative losses. We calibrate our new model using two independent models. We then apply the model to PWN G0.9+0.1 and show that simultaneously fitting the spectral energy distribution and the energy-dependent source size may lead to constraints on several model parameters pertaining to the spatial properties of the PWN.
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