Abstracts of Interest
Selected by:
Violet Harvey
Abstract: 1710.10288
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Title: Gamma-Ray Flux from Dark Matter Near the Galactic Center
(Submitted on 27 Oct 2017)
Abstract: The High Altitude Water Cherenkov (HAWC) gamma-ray observatory is a wide field-of-view observatory sensitive to 500 GeV - 100 TeV gamma rays and cosmic rays. With its observations over 2/3 of the sky every day, the HAWC observatory is sensitive to a wide variety of astrophysical sources, including possible gamma rays from dark matter. Dark matter annihilation and decay in the Milky Way Galaxy should produce gamma-ray signals across many degrees on the sky. The HAWC instantaneous field-of-view of 2 sr enables observations of extended regions on the sky, such as those from dark matter in the Galactic halo. Here we show limits on the dark matter annihilation cross-section and decay lifetime from HAWC observations of the Galactic halo with 15 months of data. These are some of the most robust limits on TeV and PeV dark matter, largely insensitive to the dark matter morphology. These limits begin to constrain models in which PeV IceCube neutrinos are explained by dark matter which primarily decays into hadrons.
Abstract: 1710.10367
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Title: Deep Crustal Heating by Neutrinos from the Surface of Accreting Neutron Stars
(Submitted on 28 Oct 2017)
Abstract: We present a new mechanism for deep crustal heating in accreting neutron stars. Charged pions ($\pi^+$) are produced in nuclear collisions on the neutron star surface during active accretion and upon decay they provide a flux of neutrinos into the neutron star crust. For massive and/or compact neutron stars, neutrinos deposit $\approx 1\textrm{--} 2 \, \mathrm{MeV}$ of heat per accreted nucleon into the inner crust. The strength of neutrino heating is comparable to the previously known sources of deep crustal heating, such as from pycnonuclear fusion reactions, and is relevant for studies of cooling neutron stars. We model the thermal evolution of a transient neutron star in a low-mass X-ray binary, and in the particular case of the neutron star MXB~1659-29 we show that additional deep crustal heating requires a higher thermal conductivity for the neutron star inner crust. A better knowledge of pion production cross sections near threshold would improve the accuracy of our predictions.
Abstract: 1710.10471
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Title: Refurbishing Voyager 1 & 2 Planetary Radio Astronomy (PRA) Data
(Submitted on 28 Oct 2017)
Abstract: Voyager/PRA (Planetary Radio Astronomy) data from digitized tapes archived at CNES have been reprocessed and recalibrated. The data cover the Jupiter and Saturn flybys of both Voyager probes. We have also reconstructed goniopolarimetric datasets (flux and polarization) at full resolution. These datasets are currently not available to the scientific community, but they are of primary interest for the analysis of the Cassini data at Saturn, and the Juno data at Jupiter, as well as for the preparation of the JUICE mission. We present the first results derived from the re-analysis of this dataset.
Abstract: 1710.10630
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Title: Dark matter in galaxies
(Submitted on 29 Oct 2017)
Abstract: Dark matter in galaxies, its abundance, and its distribution remain a subject of long-standing discussion, especially in view of the fact that neither dark matter particles nor dark matter bodies have yet been found. Experts' opinions range from a very large number of completely dark galaxies exist to nonbaryonic dark matter does not exist at all in any significant amounts. We discuss astronomical evidence for the existence of dark matter and its connection with visible matter and examine attempts to estimate its mass and distribution in galaxies from photometry, dynamics, gravitational lensing, and other observations (the cosmological aspects of the existence of dark matter are not considered in this review). In our view, the presence of dark matter in and around galaxies is a well-established fact. We conclude with an overview of mechanisms by which a dark halo can influence intragalactic processes.
Abstract: 1710.10671
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Title: The fate of close encounters between binary stars and binary supermassive black holes
(Submitted on 29 Oct 2017)
Abstract: The evolution of main sequence binaries that reside in the Galactic Centre can be heavily influenced by the central supermassive black hole (SMBH). Due to these perturbative effects, the stellar binaries in dense environments are likely to experience mergers, collisions or ejections through secular and/or non-secular interactions. More direct interactions with the central SMBH are thought to produce hypervelocity stars (HVSs) and tidal disruption events (TDEs). In this paper, we use N-body simulations to study the dynamics of stellar binaries orbiting a central SMBH primary with an outer SMBH secondary orbiting this inner triple. The effects of the secondary SMBH on the event rates of HVSs, TDEs and stellar mergers are investigated, as a function of the SMBH-SMBH binary mass ratio. Our numerical experiments reveal that, relative to the isolated SMBH case, the TDE and HVS rates are enhanced for, respectively, the smallest and largest mass ratio SMBH-SMBH binaries. This suggests that the observed event rates of TDEs and HVSs have the potential to serve as a diagnostic of the mass ratio of a central SMBH-SMBH binary. The presence of a secondary SMBH also allows for the creation of hypervelocity binaries. Observations of these systems could thus constrain the presence of a secondary SMBH in the Galactic Centre.
Abstract: 1710.10732
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Title: Relativistic Spacecraft Propelled by Directed Energy
(Submitted on 30 Oct 2017)
Abstract: Achieving relativistic flight to enable extrasolar exploration is one of the dreams of humanity and the long term goal of our NASA Starlight program. We derive a fully relativistic solution for the motion of a spacecraft propelled by radiation pressure from a directed energy system. Depending on the system parameters, low mass spacecraft can achieve relativistic speeds; thereby enabling interstellar exploration. The diffraction of the directed energy system plays an important role and limits the maximum speed of the spacecraft. We consider 'photon recycling' as a possible method to achieving higher speeds. We also discuss recent claims that our previous work on this topic is incorrect and show that these claims arise from an improper treatment of causality.
Abstract: 1710.10791
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Title: Supernovae Ia in 2017: a long time delay from merger/accretion to explosion
(Submitted on 30 Oct 2017)
Abstract: I use recent observational and theoretical studies of type Ia supernovae (SNe Ia) to further constrain the viable SN Ia scenarios and to argue that there must be a substantial time delay between the end of the merger of the WD with a companion or the end of mass accretion on to the WD and its terminal explosion. This merger/accretion to explosion delay (MED) is required to allow the binary system to lead to a more or less spherical explosion and to prevent a pre-explosion ionizing radiation. Considering these recent results and the required MED, I conclude that the core degenerate scenario is the most favorable one, followed by the double degenerate scenario. Although the single degenerate scenario is viable as well, it is unlikely to account for common (normal) SN Ia. As all scenarios require substantial MED, the MED has turned from a disadvantage of the core degenerate scenario to a challenge that theory should overcome.
Abstract: 1710.10816
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Title: Gaia: on the road to DR2
(Submitted on 30 Oct 2017 (v1), last revised 3 Nov 2017 (this version, v2))
Abstract: The second Gaia data release (DR2) is scheduled for April 2018. While Gaia DR1 had increased the number of stars with parallaxes by a factor 20 with respect to the Hipparcos catalogue, Gaia DR2 will bring another factor 500 increase, with parallaxes (and proper motions) for more than a billion stars. In addition, Gaia DR2 will deliver improved accuracy and precision for the astrometric and photometric data, $G$, $G_\mathrm{BP}$, $G_\mathrm{RP}$ magnitudes, radial velocities, identification and characterisation of variable stars and asteroids as well as stellar parameters for stars down to $G = 17$ mag. On behalf of the teams of the Gaia-DPAC consortium, these proceedings give a foretaste of Gaia DR2, 6 months before the release.
Abstract: 1710.11130
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Title: The most ancient spiral galaxy: a 2.6-Gyr-old disk with a tranquil velocity field
(Submitted on 30 Oct 2017)
Abstract: We report an integral-field spectroscopic (IFS) observation of a gravitationally lensed spiral galaxy A1689B11 at redshift $z=2.54$. It is the most ancient spiral galaxy discovered to date and the second kinematically confirmed spiral at $z\gtrsim2$. Thanks to gravitational lensing, this is also by far the deepest IFS observation with the highest spatial resolution ($\sim$ 400 pc) on a spiral galaxy at a cosmic time when the Hubble sequence is about to emerge. After correcting for a lensing magnification of 7.2 $\pm$ 0.8, this primitive spiral disk has an intrinsic star formation rate of 22 $\pm$ 2 $M_{\odot}$ yr$^{-1}$, a stellar mass of 10$^{9.8 \pm 0.3}$$M_{\odot}$ and a half-light radius of $r_{1/2}=2.6 \pm 0.7$ kpc, typical of a main-sequence star-forming (SF) galaxy at $z\sim2$. However, the H\alpha\ kinematics show a surprisingly tranquil velocity field with an ordered rotation ($V_{\rm c}$ = 200 $\pm$ 12 km/s) and uniformly small velocity dispersions ($V_{\rm \sigma, mean}$ = 23 $\pm$ 4 km/s and $V_{\rm \sigma, outer-disk}$ = 15 $\pm$ 2 km/s). The low gas velocity dispersion is similar to local spiral galaxies and is consistent with the classic density wave theory where spiral arms form in dynamically cold and thin disks. We speculate that A1689B11 belongs to a population of rare spiral galaxies at $z\gtrsim2$ that mark the formation epoch of thin disks. Future observations with JWST will greatly increase the sample of these rare galaxies and unveil the earliest onset of spiral arms.
Abstract: 1710.11134
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Title: Is Life Most Likely Around Sun-like Stars?
(Submitted on 30 Oct 2017)
Abstract: We consider the habitability of Earth-analogs around stars of different masses, which is regulated by the stellar lifetime, stellar wind-induced atmospheric erosion, and biologically active ultraviolet (UV) irradiance. By estimating the timescales associated with each of these items, we show that they collectively impose limits on the habitability of Earth-analogs. We conclude that planets orbiting most M-dwarfs are not likely to host life, and that the highest probability of complex biospheres is for planets around K- and G-type stars. Our analysis suggests that the current existence of life near the Sun is slightly unusual, but not significantly anomalous.
Abstract: 1710.11177
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Title: Modified Gravity (MOG), the speed of gravitational radiation and the event GW170817/GRB170817A
(Submitted on 30 Oct 2017)
Abstract: Modified gravity (MOG) is a covariant, relativistic, alternative gravitational theory whose field equations are derived from an action that supplements the spacetime metric tensor with vector and scalar fields. Both gravitational (spin 2) and electromagnetic waves travel on null geodesics of the theory's one metric. Despite a recent claim to the contrary, MOG satisfies the weak equivalence principle and is consistent with observations of the neutron star merger and gamma ray burster event GW170817/GRB170817A.
Abstract: 1711.00060
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Title: Proton-Air Cross Section and Composition of Ultra High Energy Cosmic Rays Observed by Telescope Array
(Submitted on 31 Oct 2017 (v1), last revised 2 Nov 2017 (this version, v2))
Abstract: Ultra high energy cosmic rays (UHECRs) provide a natural source of particles accelerated to energies beyond those that can be attained in the laboratory. UHECRs have been observed with energies exceeding $10^{20}$ eV, which is equivalent to 433 TeV in the center-of-momentum frame. Using this natural source of particles physicists can extend the measurement of the $pp$ cross section an order of magnitude above what is achievable in the lab, possibly identifying hints of new physics. The proton-air cross section and other properties of UHECR QCD physics are also important in their own right to the study of the sources and composition of UHECRs, but hadronic modelling at these energies is still reliant upon phenomenological and the theoretical extrapolations based upon terrestrial accelerator data. UHECR data can be used to improve these extrapolations of the proton-air cross section, but large uncertainties remain for other hadronic model parameters. We present the most recent measurement of the inelastic proton-air cross section at $\sqrt{s} = 95$ TeV measured by Telescope Array using high quality $X_{\mathrm{max}}$ data collected in hybrid observing mode. This measurement is also used to infer the total proton-proton cross section.
Abstract: 1711.00494
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Title: SPIDERMAN: an open-source code to model phase curves and secondary eclipses
(Submitted on 1 Nov 2017)
Abstract: We present SPIDERMAN, a fast code for calculating exoplanet phase curves and secondary eclipses with arbitrary surface brightness distributions in two dimensions.
Using a geometrical algorithm, the code solves exactly the area of sections of the disc of the planet that are occulted by the star. The code is written in C with a user-friendly Python interface, and is optimised to run quickly, with no loss in numerical precision. Approximately 1000 models can be generated per second in typical use, making Markov Chain Monte Carlo analyses practicable. The modular nature of the code allows easy comparison of the effect of multiple different brightness distributions for the dataset.
As a test case we apply the code to archival data on the phase curve of WASP-43b using a physically motivated analytical model for the two dimensional brightness map. The model provides a good fit to the data; however, it overpredicts the temperature of the nightside. We speculate that this could be due to the presence of clouds on the nightside of the planet, or additional reflected light from the dayside. When testing a simple cloud model we find that the best fitting model has a geometric albedo of $0.32 \pm0.02$ and does not require a hot nightside. We also test for variation of the map parameters as a function of wavelength and find no statistically significant correlations.
Abstract: 1711.00578
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Title: ALMA Discovery of Dust Belts Around Proxima Centauri
(Submitted on 2 Nov 2017)
Abstract: Proxima Centauri, the star closest to our Sun, is known to host at least one terrestrial planet candidate in a temperate orbit. Here we report the ALMA detection of the star at 1.3 mm wavelength and the discovery of a belt of dust orbiting around it at distances ranging between 1 and 4 au, approximately. Given the low luminosity of the Proxima Centauri star, we estimate a characteristic temperature of about 40 K for this dust, which might constitute the dust component of a small-scale analog to our solar system Kuiper belt. The estimated total mass, including dust and bodies up to 50 km in size, is of the order of 0.01 Earth masses, which is similar to that of the solar Kuiper belt. Our data also show a hint of warmer dust closer to the star. We also find signs of two additional features that might be associated with the Proxima Centauri system, which, however, still require further observations to be confirmed: an outer extremely cold (about 10 K) belt around the star at about 30 au, whose orbital plane is tilted about 45 degrees with respect to the plane of the sky; and additionally, we marginally detect a compact 1.3 mm emission source at a projected distance of about 1.2 arcsec from the star, whose nature is still unknown.
Abstract: 1711.01251
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Title: The ANTARES Collaboration: Contributions to ICRC 2017 Part I: Neutrino astronomy (diffuse fluxes and point sources)
(Submitted on 3 Nov 2017)
Abstract: Papers on neutrino astronomy (diffuse fluxes and point sources, prepared for the 35th International Cosmic Ray Conference (ICRC 2017, Busan, South Korea) by the ANTARES Collaboration
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