Abstracts of Interest
Selected by:
Sally Robertson
Abstract: 1710.02144
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Title: An Empirical Study of Contamination in Deep, Rapid, and Wide-Field Optical Follow-Up of Gravitational Wave Events
(Submitted on 5 Oct 2017 (v1), last revised 9 Oct 2017 (this version, v2))
Abstract: We present an empirical study of contamination in deep, rapid, and wide-field optical follow-up searches of GW sources from aLIGO. We utilize dedicated observations during four nights of imaging with DECam. Our search covered $\sim56$ deg$^2$, with two visits per night separated by $\approx 3$~hours, in $i$- and $z$-band, followed by an additional set of $griz$ images three weeks later to serve as reference images for subtraction, and for the purpose of identifying galaxy and stellar counterparts for any transient sources. We achieve $5\sigma$ point-source limiting magnitudes of $i \approx 23.5$ and $z \approx 22.4$ mag in the coadded single-epoch images. We conduct a search for transient objects that can mimic the $i-z$ color behavior of both red ($i-z > 0.5$~mag) and blue ($i-z < 0$~mag) kilonova emission, finding 11 and 10 contaminants, respectively. Independent of color, we identify 48 transients of interest. Additionally, we leverage the rapid cadence of our observations to search for sources with characteristic timescales of $\approx1$ day and $\approx3$ hours, finding no potential contaminants. We assess the efficiency of our pipeline and search methodology with injected point sources, finding that we are 90\% (60\%) efficient when searching for red (blue) kilonova-like sources to a limiting magnitude of $i \lesssim 22.5$ mag. Applying these efficiencies, we derive sky rates for kilonova contaminants in the red and blue regimes of $\mathcal{R}_{\rm red} \approx 0.16$ deg$^{-2}$ and $\mathcal{R}_{\rm blue} \approx 0.80$ deg$^{-2}$. The total contamination rate, independent of color, is $\mathcal{R}_{\rm all} \approx 1.79$ deg$^{-2}$. We compare our derived results to optical follow-up searches of the GW events GW150914 and GW151226 and comment on the outlook for GW follow-up searches as additional GW detectors (e.g., KAGRA, LIGO India) come online in the next decade.
Abstract: 1710.01690
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Title: Equation of State Dependent Dynamics and Multimessenger Signals from Stellar-mass Black Hole Formation
(Submitted on 4 Oct 2017)
Abstract: We investigate axisymmetric black hole (BH) formation and its gravitational wave and neutrino signals with self-consistent core-collapse supernova simulations of a non-rotating $40 M_\odot$ progenitor star using the isotropic diffusion source approximation for the transport of electron flavor neutrinos and anti-neutrinos and a modified gravitational potential for general relativistic effects. We consider four different neutron star equations of state: LS220, SFHo, BHB$\Lambda\phi$ and DD2, and study the impact of the equation of state on BH formation dynamics and gravitational wave emission. We find that the BH formation time is sensitive to the equation of state and is delayed in multiple dimensions due to the finite entropy effects, that enlarge the maximum proto-neutron star (PNS) mass and PNS convection. Depending on the equation of state, our simulations show the possibility that shock revival can occur along with the collapse of the PNS to a BH. The gravitational waveforms contain four major features: 1) a low frequency signal from core-bounce and prompt convection, 2) a strong signal from the PNS g-mode oscillation, 3) a high frequency signal from the PNS inner core convection, 4) signals from the standing accretion shock instability and convection. The peak frequency at the onset of BH formation reaches to $\sim 2.3$~kHz. The characteristic amplitude of a 10~kpc object at peak frequency is detectable but close to the noise threshold of the Advanced LIGO and KAGRA, suggesting that the next generation gravitational wave detector will need to improve the sensitivity at kHz domain to better observe stellar mass BH formation from core-collapse supernovae or failed supernovae.
Abstract: 1710.01353
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Title: Simulations of ultra-high Energy Cosmic Rays in the local Universe and the origin of Cosmic Magnetic Fields
(Submitted on 3 Oct 2017)
Abstract: We simulate the propagation of cosmic rays at ultra-high energies, $\gtrsim 10^{18}$ eV, in models of extragalactic magnetic fields in constrained simulations of the local Universe. We use constrained initial conditions with the cosmological magnetohydrodynamics code ENZO. The resulting models of the distribution of magnetic fields in the local Universe are used in the CRPROPA code to simulate the propagation of ultra-high energy cosmic rays. We investigate the impact of six different magneto-genesis scenarios, both primordial and astrophysical, on the propagation of cosmic rays over cosmological distances. Moreover, we study the influence of different source distributions around the Milky Way. Our study shows that different scenarios of magneto-genesis do not have a large impact on the anisotropy measurements of ultra-high energy cosmic rays. However, at high energies above the GZK-limit, there is anisotropy caused by the distribution of nearby sources, independent of the magnetic field model. This provides a chance to identify cosmic ray sources with future full-sky measurements and high number statistics at the highest energies. We further compare to the dipole signal recently reported by the Pierre Auger Collaboration. None of our source models could mimic the observed signal. Our results hint on a strong dipolar component in the distribution of sources necessary to account for that signal.
Abstract: 1710.01179
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Title: The IceCube Neutrino Observatory - Contributions to ICRC 2017 Part I: Searches for the Sources of Astrophysical Neutrinos
(Submitted on 3 Oct 2017)
Abstract: Papers on the searches for the sources of astrophysical neutrinos, submitted to the 35th International Cosmic Ray Conference (ICRC 2017, Busan, South Korea) by the IceCube Collaboration
Abstract: 1710.01191
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Title: The IceCube Neutrino Observatory - Contributions to ICRC 2017 Part II: Properties of the Atmospheric and Astrophysical Neutrino Flux
(Submitted on 3 Oct 2017)
Abstract: Papers on the properties of the atmospheric and astrophysical neutrino flux submitted to the 35th International Cosmic Ray Conference (ICRC 2017, Busan, South Korea) by the IceCube Collaboration
Abstract: 1710.01194
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Title: The IceCube Neutrino Observatory - Contributions to ICRC 2017 Part III: Cosmic Rays
(Submitted on 3 Oct 2017)
Abstract: Papers on cosmic-ray measurements submitted to the 35th International Cosmic Ray Conference (ICRC 2017, Busan, South Korea) by the IceCube Collaboration
Abstract: 1710.00890
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Title: All-particle cosmic ray energy spectrum measured by the HAWC experiment from 10 to 500 TeV
(Submitted on 2 Oct 2017)
Abstract: We report on the measurement of the all-particle cosmic ray energy spectrum with the High Altitude Water Cherenkov (HAWC) Observatory in the energy range 10 to 500 TeV. HAWC is a ground based air-shower array deployed on the slopes of Volcan Sierra Negra in the state of Puebla, Mexico, and is sensitive to gamma rays and cosmic rays at TeV energies. The data used in this work were taken from 234 days between June 2016 to February 2017. The primary cosmic-ray energy is determined with a maximum likelihood approach using the particle density as a function of distance to the shower core. Introducing quality cuts to isolate events with shower cores landing on the array, the reconstructed energy distribution is unfolded iteratively. The measured all-particle spectrum is consistent with a broken power law with an index of $-2.49\pm0.01$ prior to a break at $(45.7\pm0.1$) TeV, followed by an index of $-2.71\pm0.01$. The spectrum also respresents a single measurement that spans the energy range between direct detection and ground based experiments. As a verification of the detector response, the energy scale and angular resolution are validated by observation of the cosmic ray Moon shadow's dependence on energy.
Abstract: 1710.01040
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Title: A multi-messenger study of the total galactic high-energy neutrino emission
(Submitted on 3 Oct 2017)
Abstract: A detailed multi-messenger study of the high-energy emission from the Galactic plane is possible nowadays thanks to the observations provided by gamma and neutrino telescopes and could be mandatory in order to obtain a consistent scenario. We show the potential of this approach by using the total gamma flux from the inner galactic region measured by HESS at $1\,{\rm TeV}$ and in the longitude range $-75^\circ < l < 60^\circ$. By comparing the observational data with the expected diffuse galactic emission, we highlight the existence of an extended hot region of the gamma sky where the cumulative sources contribution dominates over the diffuse component. This region approximately coincides with the portion of the galactic plane from which a $\sim 2 \sigma$ excess of showers is observed in IceCube high energy starting events. In the assumption that hadronic mechanisms are responsible for the observed gamma emission, we estimate the total galactic contribution (i.e. including both diffuse and the source components) to the IceCube neutrino signal as a function of the spectral index and energy cutoff of the sources, taking also into account the upper limit on a galactic component provided by Antares.