Abstracts of Interest
Selected by:
Fabien Voisin
Abstract: 1710.03020
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Title: All-sky Search for High-Energy Neutrinos from Gravitational Wave Event GW170104 with the ANTARES Neutrino Telescope
(Submitted on 9 Oct 2017)
Abstract: Advanced LIGO detected a significant gravitational wave signal (GW170104) originating from the coalescence of two black holes during the second observation run on January 4$^{\textrm{th}}$, 2017. An all-sky high-energy neutrino follow-up search has been made using data from the ANTARES neutrino telescope, including both upgoing and downgoing events in two separate analyses. No neutrino candidates were found within $\pm500$ s around the GW event time nor any time clustering of events over an extended time window of $\pm3$ months. The non-detection is used to constrain isotropic-equivalent high-energy neutrino emission from GW170104 to less than $\sim4\times 10^{54}$ erg for a $E^{-2}$ spectrum.
Abstract: 1710.02889
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Title: KASCADE-Grande Limits on the Isotropic Diffuse Gamma-Ray Flux between 100 TeV and 1 EeV
(Submitted on 8 Oct 2017)
Abstract: KASCADE and KASCADE-Grande were multi-detector installations to measure individual air showers of cosmic rays at ultra-high energy. Based on data sets measured by KASCADE and KASCADE-Grande, 90% C.L. upper limits to the flux of gamma-rays in the primary cosmic ray flux are determined in an energy range of ${10}^{14} - {10}^{18}$ eV. The analysis is performed by selecting air showers with a low muon content as expected for gamma-ray-induced showers compared to air showers induced by energetic nuclei. The best upper limit of the fraction of gamma-rays to the total cosmic ray flux is obtained at $3.7 \times {10}^{15}$ eV with $1.1 \times {10}^{-5}$. Translated to an absolute gamma-ray flux this sets constraints on some fundamental astrophysical models, such as the distance of sources for at least one of the IceCube neutrino excess models.
Abstract: 1710.02803
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Full Text: [ PostScript, PDF]
Title: Diffuse gamma-ray emission in the vicinity of young star cluster Westerlund 2
(Submitted on 8 Oct 2017)
Abstract: We report the results of our analysis of the publicly available data obtained by the Large Area Telescope (LAT) on board of the Fermi satellite towards the direction of the young massive star cluster Westerlund 2. We found significant extended gamma-ray emission in the vicinity of Westerlund 2 with a hard power-law energy spectrum extending from 1 GeV to 250 GeV with a photon index of 2.0 +/- 0.1. We argue that amongst several alternatives, the luminous stars in Westerlund 2 are likely sites of acceleration of particles responsible for the diffuse gamma-ray emission of the surrounding interstellar medium. In particular, the young star cluster Westerlund 2 can provide sufficient non-thermal energy to account for the gamma-ray emission. In this scenario, since the gamma-ray production region is significantly larger than the area occupied by the star cluster, we conclude that the gamma-ray production is caused by hadronic interactions of the accelerated protons and nuclei with the ambient gas. In that case, the total energy budget in relativistic particles is estimated of the order of 1e50 erg.
Abstract: 1710.03170
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Title: 3D Kinetic Pulsar Magnetosphere Models: Exploring Self Consistency
(Submitted on 9 Oct 2017)
Abstract: We present 3D global kinetic pulsar magnetosphere models, where the charged particle trajectories and the corresponding electromagnetic fields are treated self-consistently. For our study, we have developed a cartesian 3D relativistic particle-in-cell code that incorporates the radiation reaction forces. We describe our code and discuss the related technical issues, treatments, and assumptions. Injecting particles up to large distances in the magnetosphere, we apply arbitrarily low to high particle injection rates and get an entire spectrum of solutions from close to the Vacuum-Retarded-Dipole to close to the Force-Free solution, respectively. For high particle injection rates (close to FF solutions) significant accelerating electric field components are confined only near the equatorial current sheet outside the light-cylinder. The self-consistent nature of our models and a judicious interpretation of them allow the calculation of the particle emission and consequently the derivation of the corresponding realistic high-energy sky-maps and spectra. Using model parameters that cover the entire range of spin-down powers of \emph{Fermi} young and millisecond pulsars, we compare the corresponding model $\gamma$-ray light-curves, cutoff energies, and total $\gamma$-ray luminosities with those observed by \emph{Fermi} to discover a dependence of the particle injection-rate, $\mathcal{F}$, on the spin-down power, $\dot{\mathcal{E}}$, indicating an increase of $\mathcal{F}$ with $\dot{\mathcal{E}}$. Our models guided by \emph{Fermi} observations provide field-structures and particle distributions that are not only consistent with each other but also able to reproduce a broad range of the observed $\gamma$-ray phenomenology of both young and millisecond pulsars.
Abstract: 1710.04024
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Title: Ultra-High Energy Neutrino Afterglows of nearby Long Duration Gamma-Ray Bursts
(Submitted on 11 Oct 2017)
Abstract: Detection of ultra-high energy (UHE, $\gtrsim 1$ PeV) neutrinos from astrophysical sources will be a major advancement in identifying and understanding the sources of UHE cosmic rays (CRs) in nature. Long duration gamma-ray burst (GRB) blast waves have been considered as potential acceleration sites of UHECRs. These CRs are expected to interact with GRB afterglow photons, which is synchrotron radiation from relativistic electrons co-accelerated with CRs in the blast wave, and naturally produce UHE neutrinos. Fluxes of these neutrinos are uncertain, however, and crucially depend on the observed afterglow modeling. We have selected a sample of 23 long duration GRBs within redshift 0.5 for which adequate electromagnetic afterglow data are available and which could produce high flux of UHE afterglow neutrinos, being nearby. We fit optical, X-ray and $\gamma$-ray afterglow data with an adiabatic blast wave model in a constant density interstellar medium and in a wind environment where the density of the wind decreases as inverse square of the radius from the center of the GRB. The blast wave model parameters extracted from these fits are then used for calculating UHECR acceleration and $p\gamma$ interactions to produce UHE neutrino fluxes from these GRBs. We have also explored the detectability of these neutrinos by currently running and upcoming large area neutrino detectors, such as the Pierre Auger Observatory, IceCube Gen-2 and KM3NeT observatories. We find that our realistic flux models from nearby GRBs will be unconstrained in foreseeable future.
Abstract: 1710.03930
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Title: Galactic Outflows by Alfvénic Poynting Flux: Application to Fermi Bubbles
(Submitted on 11 Oct 2017)
Abstract: We investigate roles of magnetic activity in the Galactic bulge region in driving large-scale outflows of size ~ 10 kpc. Magnetic buoyancy and breakups of channel flows formed by magnetorotational instability excite Poynting flux by the magnetic tension force. A three-dimensional global numerical simulation shows that the average luminosity of such Alfvenic Poynting flux is 10^{40} - 10^{41} erg s^{-1}. We examine the energy and momentum transfer from the Poynting flux to the gas by solving time-dependent hydrodynamical simulations with explicitly taking into account low-frequency Alfvenic waves of period of 0.5 Myr in a one-dimensional vertical magnetic flux tube. The Alfvenic waves propagate upward into the Galactic halo, and they are damped through the propagation along meandering magnetic field lines. If the turbulence is nearly trans-Alfvenic, the wave damping is significant, which leads to the formation of an upward propagating shock wave. At the shock front, the temperature >~ 5 x 10^6 K, the density ~ 1 cm^{-3}, and the outflow velocity ~ 400-500 km/s at a height ~10 kpc, which reasonably explain the basic physical properties of the thermal component of the Fermi bubbles.
Abstract: 1710.04250
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Full Text: [ PostScript, PDF]
Title: Fermi non-detections of four X-ray jet sources and implications for the IC/CMB mechanism
(Submitted on 11 Oct 2017)
Abstract: Since its launch in 1999, the Chandra X-ray observatory has discovered several dozen X-ray jets associated with powerful quasars. In many cases the X-ray spectrum is hard and appears to come from a second spectral component. The most popular explanation for the kpc-scale X-ray emission in these cases has been inverse-Compton (IC) scattering of Cosmic Microwave Background (CMB) photons by relativistic electrons in the jet (the IC/CMB model). Requiring the IC/CMB emission to reproduce the observed X-ray flux density inevitably predicts a high level of gamma-ray emission which should be detectable with the Fermi Large Area Telescope (LAT). In previous work, we found that gamma-ray upper limits from the large scale jets of 3C 273 and PKS 0637-752 violate the predictions of the IC/CMB model. Here we present Fermi/LAT flux density upper limits for the X-ray jets of four additional sources: PKS 1136-135, PKS 1229-021, PKS 1354+195, and PKS 2209+080, and show that these limits violate the IC/CMB predictions at a very high significance level. We also present new Hubble Space Telescope (HST) observations of the quasar PKS 2209+080 showing a newly detected optical jet, and Atacama Large Millimeter/submillimeter Array (ALMA) band 3 and 6 observations of all four sources, which provide key constraints on the spectral shape that enable us to rule out the IC/CMB model.
Abstract: 1710.04657
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Title: Revealing black holes with Gaia
(Submitted on 12 Oct 2017)
Abstract: We estimate the population of black holes with luminous stellar companions (BH-LCs) in the Milky Way (MW) observable by Gaia. We evolve a realistic distribution of BH-LC progenitors from zero-age to the current epoch taking into account relevant physics, including binary stellar evolution, BH-formation physics, and star formation rate, to estimate the BH-LC population in the MW today. We predict that Gaia will discover between 3,800 and 12,000 BH-LCs by the end of its 5 yr mission, depending on BH natal kick strength and observability constraints. We find that the overall yield, and distributions of eccentricities and masses of observed BH-LCs can provide important constraints on the strength of BH natal kicks. Gaia-detected BH-LCs are expected to have very different orbital properties compared to those detectable via radio, X-ray, or gravitational wave observations.
Abstract: 1710.04820
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Title: A Suzaku View of Accretion Powered X-ray Pulsar GX 1+4
(Submitted on 13 Oct 2017)
Abstract: We present results obtained from a Suzaku observation of the accretion powered X-ray pulsar GX 1+4. Broad-band continuum spectrum of the pulsar was found to be better described by a simple model consisting of a blackbody component and an exponential cutoff power-law than the previously used compTT continuum model. Though the pulse profile had a sharp dip in soft X-rays ($<$10 keV), phase-resolved spectroscopy confirmed that the dimming was not due to increase in photoelectric absorption. Phase-sliced spectral analysis showed the presence of a significant spectral modulation beyond 10 keV except for the dip phase. A search for the presence of cyclotron resonance scattering feature in the Suzaku spectra yielded a negative result. Iron K-shell (K$_\alpha$ and K$_\beta$) emission lines from nearly neutral iron ions ($<$Fe III) were clearly detected in the source spectrum. A significant K$_\alpha$ emission line from almost neutral Ni atoms was detected for the first time in this source. We estimated the iron abundance of $\sim$80 % of the solar value and Ni/Fe abundance ratio of about two times of the solar value. We searched for a iron Ly$_\alpha$ emission line and found a significant improvement in the spectral fitting by inclusion of this line.
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