Abstracts of Interest
Selected by:
Jarryd Day
Abstract: 1908.11375
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Title:The Missing Link in Gravitational-Wave Astronomy: Discoveries waiting in the decihertz range
(Submitted on 29 Aug 2019)
Abstract: The gravitational-wave astronomical revolution began in 2015 with LIGO's observation of the coalescence of two stellar-mass black holes. Over the coming decades, ground-based detectors like LIGO will extend their reach, discovering thousands of stellar-mass binaries. In the 2030s, the space-based LISA will enable gravitational-wave observations of the massive black holes in galactic centres. Between LISA and ground-based observatories lies the unexplored decihertz gravitational-wave frequency band. Here, we propose a Decihertz Observatory to cover this band, and complement observations made by other gravitational-wave observatories. The decihertz band is uniquely suited to observation of intermediate-mass ($\sim 10^2-10^4$ M$_\odot$) black holes, which may form the missing link between stellar-mass and massive black holes, offering a unique opportunity to measure their properties. Decihertz observations will be able to detect stellar-mass binaries days to years before they merge and are observed by ground-based detectors, providing early warning of nearby binary neutron star mergers, and enabling measurements of the eccentricity of binary black holes, providing revealing insights into their formation. Observing decihertz gravitational-waves also opens the possibility of testing fundamental physics in a new laboratory, permitting unique tests of general relativity and the Standard Model of particle physics. Overall, a Decihertz Observatory will answer key questions about how black holes form and evolve across cosmic time, open new avenues for multimessenger astronomy, and advance our understanding of gravitation, particle physics and cosmology.
Abstract: 1908.11397
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Full Text: [ PostScript, PDF]
Title:Extending the susy model to core-collapse supernovae
(Submitted on 29 Aug 2019 (v1), last revised 2 Sep 2019 (this version, v2))
Abstract: A notable feature of the two standard models for thermonuclear and core-collapse supernovae is that, although these two models are fundamentally different, the respective supernova types have quite similar rates and appearances. For instance, both types occur one to several times per century per typical galaxy and both types seed the universe with the heavy elements essential to life. In spite of this, neither standard model provides a reasonably problem-free description of its target phenomenon. A major obstacle to providing a unified picture of supernovae would seem to be the fact that type Ia supernovae occur typically with gigayear delay times after the cessation of carbon fusion while the core-collapse explosions occur only days after such fusion cessation. In this article we study the possibility of extending the successful supersymmetric model for type Ia supernovae to core-collapse events. The question is whether and under what assumptions a phase transition to an exact supersymmetric background can efficiently explain both type Ia and core collapse supernovae.
Abstract: 1908.11408
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Title:The Spectrum of the Crab Nebula and Highest Energy Photons Measured by HAWC
(Submitted on 29 Aug 2019)
Abstract: HAWC has developed new energy algorithms using an artificial neural network for event-by-event reconstruction of Very High Energy (VHE) primary gamma ray energies. Unlike previous estimation methods for HAWC photons, these estimate photon energies with good energy precision and accuracy in a range from 1 TeV to greater than 100 TeV. Photon emission at the highest energies is of interest in understanding acceleration mechanisms of astrophysical sources and where the acceleration might cut off. We apply the new HAWC reconstruction to present the preliminary measurement of the highest energies at which photons are emitted by the Crab Nebula and by six additional sources in the galactic plane which emit above 50 TeV. We have observed photons above 200 TeV at 95% confidence. We also compare fits to the HAWC Crab spectrum with other measurements and theoretical models of the Crab spectrum.
Abstract: 1908.11410
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Full Text: [ PostScript, PDF]
Title:High angular resolution gravitational wave astronomy
(Submitted on 29 Aug 2019)
Abstract: Since the very beginning of astronomy the location of objects on the sky has been a fundamental observational quantity that has been taken for granted. While precise two dimensional positional information is easy to obtain for observations in the electromagnetic spectrum, the positional accuracy of current and near future gravitational wave detectors is limited to between tens and hundreds of square degrees, which makes it extremely challenging to identify the host galaxies of gravitational wave events or to confidently detect any electromagnetic counterparts. Gravitational wave observations provide information on source properties and distances that is complementary to the information in any associated electromagnetic emission and that is very hard to obtain in any other way. Observing systems with multiple messengers thus has scientific potential much greater than the sum of its parts. A gravitational wave detector with higher angular resolution would significantly increase the prospects for finding the hosts of gravitational wave sources and triggering a multi-messenger follow-up campaign. An observatory with arcminute precision or better could be realised within the Voyage 2050 programme by creating a large baseline interferometer array in space and would have transformative scientific potential. Precise positional information of standard sirens would enable precision measurements of cosmological parameters and offer new insights on structure formation; a high angular resolution gravitational wave observatory would allow the detection of a stochastic background and resolution of the anisotropies within it; it would also allow the study of accretion processes around black holes; and it would have tremendous potential for tests of modified gravity and the discovery of physics beyond the Standard Model.
Abstract: 1908.11440
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Title:Radio Flares from Collisions of Neutron Stars with Interstellar Asteroids
(Submitted on 26 Aug 2019 (v1), last revised 2 Sep 2019 (this version, v2))
Abstract: We propose that collisions between neutron stars and interstellar asteroids, such as `Oumuamua, could power observable radio flares in the Milky Way galaxy. We find the rate of such events at $\sim 1 \mathrm{\; Jy}$ to be $\sim 10 \mathrm{\; day^{-1}}$.
Abstract: 1908.11456
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Title:Studies of the Time Structure of Extended Air Showers for Direction Reconstruction with the HAWC Outrigger Array
(Submitted on 29 Aug 2019)
Abstract: The High Altitude Water Cherenkov (HAWC) gamma-ray observatory is a ground-based air shower array designed to detect Cherenkov light produced in water by secondary particles from atmospheric air showers. In order to improve the sensitivity at the highest energies, especially for the shower cores falling outside the main array, 345 smaller Water Cherenkov Detectors (WCDs) were installed around the main array, the outrigger array. This extension increased the instrumented area of HAWC by a factor of four. With the increased size of the array, and the ability to detect shower particles further away from the core, understanding of the time structure of the shower front is crucial for accurate direction reconstruction and mandates proper modeling. In this contribution, we present a model of the shower front as expected to be observed by the outriggers obtained from Monte-Carlo simulations. Applying this model to shower reconstruction, the improvements on air shower parameter are studied.
Abstract: 1908.11469
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Title:Science Case of a Scintillator and Radio Surface Array at IceCube
(Submitted on 29 Aug 2019)
Abstract: The upgrade of IceTop, the surface array of IceCube, by a hybrid array of scintillation and radio detectors is motivated by a rich science case. The scintillators will lower the threshold for the measurement of air showers to about 100 TeV, provide a more efficient veto of air showers for neutrino measurements, and improve the separation of the electromagnetic and muonic shower components due to the different responses of scintillators and ice-Cherenkov tanks. Furthermore, the scintillators will enable the calibration and compensation of the effect of snow accumulation above IceTop. The radio antennas will provide a calorimetric measurement of the electromagnetic shower component and a direct sensitivity to the shower maximum. Consequently, the combination of the existing ice-Cherenkov detectors in the ice and at the surface with the new scintillation and radio detectors at the surface will enable unprecedented accuracy for event-by-event mass classification in the PeV to EeV range. This will transform IceCube into the most accurate instrument for high-energy Galactic cosmic rays in the Southern Hemisphere. Hence, the hybrid array will make an important contribution to the main science case of IceCube of understanding the origin of cosmic rays. In addition to its cosmic-ray science goals, the hybrid array provides essential R&D for IceCube-Gen2 which will feature a larger surface array, sophisticated timing and communication technology, and elevated surface structures. Moreover, the hybrid array will improve the understanding of the atmospheric background to the neutrino measurements and opens new scientific opportunities, such as the searches for PeV gamma rays from the Galactic Center and for mass-dependent anisotropies.
Abstract: 1908.11485
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Title:Constraints on the Diffuse Gamma-Ray Background with HAWC
(Submitted on 30 Aug 2019)
Abstract: The Diffuse Gamma-Ray Background (DGB) above 100 GeV at high-latitudes is expected to be produced by unresolved extragalactic objects such as active galactic nuclei, isotropic Galactic gamma-rays, and possible emission from dark matter annihilations or decays in the Galactic dark matter halo. The DGB has been observed up to nearly 1 TeV, but has yet to be detected at higher energies. Detections or stringent limits on the DGB above this energy would have strong multimessenger consequences, such as constraining the origin of astrophysical neutrinos observed in IceCube. The High Altitude Water Cherenkov (HAWC) observatory has its highest sensitivity to gamma rays above 1 TeV and observes over 2/3 of the sky each day. With its high energy reach and large areal coverage, HAWC can significantly improve searches of the DGB at TeV energies. We will investigate parameter cuts to the HAWC dataset to better isolate gamma-ray air showers from background hadronic showers. This, combined with new background estimation techniques will improve the HAWC sensitivity to the DGB. We will present a limit on the DGB with HAWC as well as its implications for multimessenger and dark matter studies.
Abstract: 1908.11564
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Full Text: [ PostScript, PDF]
Title:Electronics Development for the New Photo-Detectors (PDOM and D-Egg) for IceCube-Upgrade
(Submitted on 30 Aug 2019)
Abstract: The planned IceCube-Upgrade will enhance the capability of IceCube in the detection of GeV-scale neutrino physics and enable an improved measurement of the properties of the glacial ice. Three types of new optical sensors will be deployed during the Upgrade: PDOM, D-Egg, and mDOM. Since the design of the PDOM and D-Egg are very similar, the development of the front-end electronics for the two optical sensors has been merged. The photo-electron signals detected by the PMTs are digitized with high-speed ultra-low power ADCs and processed in an FPGA, before being sent to the data acquisition system located on the surface of the South-Pole glacier. The almost final revision of the front-end electronics is equipped with the common microcontroller unit and the communication daughter board for simplifying the communication scheme for the three different modules. This contribution focuses on the design of the front-end electronics and presents first results from the performance tests.
Abstract: 1908.11703
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Full Text: [ PostScript, PDF]
Title:Thirteen facts that you need to know on multiple populations in globular clusters
(Submitted on 30 Aug 2019)
Abstract: I review the methods, mostly developed in the last decade, that are commonly used to identify and characterize multiple populations (MPs) in Globular Clusters based on photometry. I summarize the results from the recent surveys of MPs with the Hubble Space Telescope and ground-based facilities and provide a list of the main properties of MPs as inferred from these studies.
Abstract: 1909.00075
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Full Text: [ PostScript, PDF]
Title:Monitoring radio galaxies at TeV energies with HAWC
(Submitted on 30 Aug 2019)
Abstract: With an instantaneous field of view of 2 sr and a duty cycle > 95%, the High Altitude Water Cherenkov (HAWC) Gamma-Ray Observatory is a perfect instrument for monitoring variable TeV sources. Because radio galaxies are a type of Active Galactic Nuclei (AGN) with their jets misaligned with respect to our line of sight, they may help us to probe the physics of very-high-energy (VHE) emission processes in these objects. Three out of four radio galaxies that have been detected at TeV energies by other facilities are located within the field of view of the HAWC Observatory: M87, NGC 1275, and 3C 264. A search for TeV gamma rays at their locations yields no statistically significant excess of counts. We present corresponding upper limits for each radio galaxy and light curves covering 3 years of data taken with HAWC.
Abstract: 1909.00078
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Full Text: [ PostScript, PDF]
Title:Searches for neutrinos from fast radio bursts with IceCube
(Submitted on 30 Aug 2019)
Abstract: Although IceCube has discovered a diffuse astrophysical neutrino flux, the underlying sources of these neutrinos remain unknown. Transient astrophysical objects, such as fast radio bursts (FRBs), could explain a large percentage of the measured flux. We present the analysis techniques of IceCube searches for MeV to TeV neutrinos from FRBs. As no significant correlation between IceCube neutrinos and FRBs has been found, we present the first limit on MeV neutrino emission from FRBs and the most constraining limits for neutrinos with GeV to TeV energies. We also describe the prospects for future IceCube neutrino searches coinciding with FRB detections from next generation radio interferometers.
Abstract: 1909.00261
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Full Text: [ PostScript, PDF]
Title:A parameterized catalog of radio galaxies as ultra-high energy cosmic ray sources
(Submitted on 31 Aug 2019)
Abstract: Many attempts have been made to provide catalogs of potential sources of ultra-high energy cosmic ray (UHECR) particles based on various astronomical tracers, such as observed radio or gamma-ray emission. A closer look reveals, however, that they all suffer from significant bias and selection effects. We present here a demo-version of a catalog for one often-discussed UHECR source class, radio galaxies (or radio-loud AGN), which is based on a complete theoretical description of jet-energetics, particle acceleration physics, relativistic beaming effects and nuclear composition, parametrized by a comprehensible set of adjustable physical quantities. In addition to the bright radio galaxies Centaurus A, Virgo A, Fornax A and Cygnus A discussed in previous work, we find several sources with blazar-like properties that can contribute on a similar level if relativistic beaming effects are considered. We present a simple method to test the basic properties of the catalog for any choice of parameters (without the need to run expensive simulations), and find that in the canonical case the anisotropy signals expected from radio galaxies promise to be in good agreement with current observational findings. In particular, radio galaxies can reproduce almost exactly the direction of the dipole above 8 EeV detected by the Pierre Auger Observatory if we assume that extragalactic magnetic fields are strong (>1nG) only in structures, but very weak in voids. We plan to provide a completed and improved version of this catalog in electronic form, to be used in more detailed UHECR propagation simulations. For immediate applications, we suggest a complete set of 16 strong UHECR sources which can contribute to UHECR anisotropy on the level which can be currently probed by experiment, and note that 6 of them have not been considered in any previous studies.
Abstract: 1909.00356
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Full Text: [ PostScript, PDF]
Title:Origin of ultra-high energy cosmic rays: The cosmological manifesto
(Submitted on 1 Sep 2019)
Abstract: A spectre is haunting physics---the spectre of non-thermal processes. Manifesting itself in astroparticle physics, all classical disciplines of physics and astronomy have entered into a holy alliance to exorcise this spectre: While astronomers try to destroy it with ignorance, convinced that only thermal processes are of importance to the dynamics of the Universe, particle physicists obscure it in the clouds of mystified admiration, simply because the Universe works on energy scales which are far above of their own technical and economical capabilities. It is high time to understand the energy scales of astroparticle physics in those of the Universe itself, by linking the existence of their basic essence, cosmic rays, via a universal mechanism to the ground reservoir of all non-thermal energy, gravitation. By this we meet the nursery tale of the enigmatic, mysterious sources of cosmic rays with a set of numbers naturally derived from cosmological parameters, which manifest themselves in a large range of astrophysical objects that stand in rank and file along a diagonal in the famous Hillas-plot, and in fact only have in common that they efficiently convert gravitational energy. While this manifesto, promoting the cosmological revolution in astroparticle physics, does not release us from detailed modelling of cosmic ray and multimessenger sources in order to understand all the details delivered by current experiments, it does help to clear up our view on the problem and to avoid some common fallacies and misconceptions.
Abstract: 1909.00501
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Full Text: [ PostScript, PDF]
Title:Suzaku Observation of Diffuse X-Ray Emission from a Southwest Region of the Carina Nebula
(Submitted on 2 Sep 2019)
Abstract: A southwest region of the Carina nebula was observed with the Suzaku observatory for 47 ks in 2010 December. This region shows distinctively soft X-ray emission in the Chandra campaign observations. Suzaku clearly detects the diffuse emission above known foreground and background components between 0.4-5 keV at the surface brightness of 3.3x10^-14 erg s^{-1} arcmin^{-2}. The spectrum requires two plasma emission components with kT~0.2 and 0.5 keV, which suffer interstellar absorption of N_H~1.9x10^{21} cm^{-2}. Multiple absorption models assuming two temperature plasmas at ionization equilibrium or non-equilibrium are tested but there is no significant difference in terms of chi^2/d.o.f.. These plasma temperatures are similar to those of the central and eastern parts of the Carina nebula measured in earlier Suzaku observations, but the surface brightness of the hot component is significantly lower than those of the other regions. This means that these two plasma components are physically separated and have different origins. The elemental abundances of O, Ne and Mg with respect to Fe favor that the diffuse plasma originates from core-collapsed supernovae or massive stellar winds.
Abstract: 1909.00622
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Full Text: [ PostScript, PDF]
Title:Exploring the pattern of the Galactic HI foreground of GRBs with the ATCA
(Submitted on 2 Sep 2019)
Abstract: The afterglow of a gamma ray burst (GRB) can give us valuable insight into the properties of its host galaxy. To correctly interpret the spectra of the afterglow we need to have a good understanding of the foreground interstellar medium (ISM) in our own Galaxy. The common practice to correct for the foreground is to use neutral hydrogen (HI) data from the Leiden/Argentina/Bonn (LAB) survey. However, the poor spatial resolution of the single dish data may have a significant effect on the derived column densities. To investigate this, we present new high-resolution HI observations with the Australia Telescope Compact Array (ATCA) towards 4 GRBs. We combine the interferometric ATCA data with single dish data from the Galactic All Sky Survey (GASS) and derive new Galactic HI column densities towards the GRBs. We use these new foreground column densities to fit the Swift XRT X-ray spectra and calculate new intrinsic hydrogen column density values for the GRB host galaxies. We find that the new ATCA data shows higher Galactic HI column densities compared to the previous single dish data, which results in lower intrinsic column densities for the hosts. We investigate the line of sight optical depth near the GRBs and find that it may not be negligible towards one of the GRBs, which indicates that the intrinsic hydrogen column density of its host galaxy may be even lower. In addition, we compare our results to column densities derived from far-infrared data and find a reasonable agreement with the HI data.
Abstract: 1909.00670
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Full Text: [ PostScript, PDF]
Title:The Origins of the Highest Energy Particles in Nature: where we are and where we go next
(Submitted on 2 Sep 2019)
Abstract: In his Nobel Prize lecture Victor Hess urged that different instruments, working together, should be used to solve the problem of the origin of cosmic rays. I review some of the key developments that have opened up the new fields of direct and indirect multi-messenger astronomy and that are guiding us to the solution of this riddle. I then discuss, very briefly, some of the new instruments that are shortly to come on line and give examples to show the long lead-times from conception to implementation that occur in this field. I conclude with some remarks about very ambitious future projects. The paper is not intended as a review: rather it is an attempt to set down issues discussed in the Hess Memorial Public Lecture given at the 2019 ICRC in Madison, Wisconsin and accessible at this http URL.
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