Determination of cosmic-ray primary mass on an event-by-event basis using radio detection [HEAP]

We present a new methodology to discriminate between light and heavy ultra-high energy cosmic-ray primaries on an event-by-event basis using information from the radio detection of extensive air showers at MHz frequencies. Similarly to other methods to determine primary cosmic ray composition, the one presented here is based on comparisons between detected radio signals and Monte Carlo simulations for multiple primary cosmic ray compositions. Unlike other methods that first reconstruct the depth of maximum shower development $X_{\rm max}$ to relate it to the nature of the primaries, we instead infer the cosmic-ray composition directly. The method is most effective in the case of inclined showers that arrive at large zenith angles with respect to the vertical to the ground, where methods based on the determination of $X_{\rm max}$ lose accuracy. We show that a $90\%$ discrimination efficiency can be reached for zenith angles above $\theta \simeq 65^{\circ}$, even when typical uncertainties in radio detection are taken into account. Our methodology can be applied in large and sparse radio arrays, designed with the large radio footprint of inclined showers in mind, to significantly increase the statistics of ultra-high energy cosmic-ray composition studies.

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W. Carvalho and J. Alvarez-Muniz
Tue, 12 Dec 17

Comments: N/A

Synergy of stochastic and systematic energization of plasmas during turbulent reconnection [HEAP]

The important characteristic of turbulent reconnection is that it combines large scale magnetic disturbances $(\delta B/B \sim 1)$ with randomly distributed Unstable Current Sheets (UCSs). Many well known non linear MHD structures (strong turbulence, current sheet(s), shock(s)) lead asymptotically to the state of turbulent reconnection. We analyze in this article, for the first time, the energization of electrons and ions in a {\bf large scale} environment that {\bf combines} large amplitude disturbances propagating with sub-Alfv\’enic speed with UCSs. The magnetic disturbances interact stochastically (second order Fermi) with the charged particles and they play a crucial role in the heating of the particles, while the UCS interact systematically (first order Fermi) and play a crucial role in the formation of the high energy tail. The synergy of stochastic and systematic acceleration provided by the mixture of magnetic disturbances and UCSs influences the energetics of the thermal and non-thermal particles, the power law index, and the time the particles remain inside the energy release volume. We show that this synergy can explain the observed very fast and impulsive particle acceleration and the slightly delayed formation of a super-hot particle population.

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T. Pisokas, L. Vlahos and H. Isliker
Tue, 12 Dec 17

Comments: 6 pages, 3 figures, Accepted for publication in ApJ

Conformal Higgs Gravity [CL]

It is shown that gravitation emerges naturally from the standard model of particle physics if local scale invariance is imposed in the context of a single conformal theory. Doing so resolves major puzzles afflicting the standard models of particle physics and cosmology, clearly indicating these to be artifacts stemming from universally applying the system of units selected here and now. Slip-free scalar (but not vector or tensor) modes of metric perturbations can be gauged away and are thus spurious degrees of freedom. In the approach adopted here gravitation is viewed as a collective phenomenon, with its characteristic Planck scale devoid of fundamental meaning; consequently, mass hierarchy and Higgs mass instability concerns are avoided altogether. On cosmological scales, the dynamical vacuum-like Higgs self-coupling energy accounts for dark energy, and its near equality with nonrelativistic matter is simply a result of the choice of standard units.

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M. Shimon
Tue, 12 Dec 17

Comments: Submitted for publication

$ν$CO$N$CEPT: Cosmological neutrino simulations from the non-linear Boltzmann hierarchy [CEA]

In this paper the non-linear effect of massive neutrinos on cosmological structures is studied in a conceptually new way. We have solved the non-linear continuity and Euler equations for the neutrinos on a grid in real space in $N$-body simulations, and closed the Boltzmann hierarchy at the non-linear Euler equation using the stress and pressure perturbations from linear theory. By comparing with state-of-the art cosmological neutrino simulations, we are able to simulate the non-linear neutrino power spectrum very accurately. This translates into a negligible error in the matter power spectrum, and so our CONCEPT code is ideally suited for extracting the neutrino mass from future high precision non-linear observational probes such as Euclid.

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J. Dakin, J. Brandbyge, S. Hannestad, et. al.
Tue, 12 Dec 17

Comments: 28 pages, 10 figures

AGB subpopulations in the nearby globular cluster NGC 6397 [SSA]

It has been well established that Galactic Globular clusters (GCs) harbour more than one stellar population, distinguishable by the anti-correlations of light element abundances (C-N, Na-O, and Mg-Al). These studies have been extended recently to the asymptotic giant branch (AGB). Here we investigate the AGB of NGC 6397 for the first time. We have performed an abundance analysis of high-resolution spectra of 47 RGB and 8 AGB stars, deriving Fe, Na, O, Mg and Al abundances. We find that NGC 6397 shows no evidence of a deficit in Na-rich AGB stars, as reported for some other GCs – the subpopulation ratios of the AGB and RGB in NGC 6397 are identical, within uncertainties. This agrees with expectations from stellar theory. This GC acts as a control for our earlier work on the AGB of M 4 (with contrasting results), since the same tools and methods were used.

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B. MacLean, S. Campbell, G. Silva, et. al.
Tue, 12 Dec 17

Comments: 10 pages, 7 figures, 8 tables (2 online-only). Accepted for publication in MNRAS

ALMA Twenty-six arcmin$^2$ Survey of GOODS-S at One-millimeter (ASAGAO): X-ray AGN Properties of Millimeter-Selected Galaxies [HEAP]

We investigate the X-ray active galactic nucleus (AGN) properties of millimeter galaxies in the Great Observatories Origins Deep Survey South (GOODS-S) field detected with the Atacama Large Millimeter/submillimeter Array (ALMA), by utilizing the Chandra 7-Ms data, the deepest X-ray survey to date. Our millimeter galaxy sample comes from the ASAGAO survey covering 26 arcmin$^2$ (12 sources at a 1.2-mm flux-density limit of $\approx$0.6 mJy), supplemented by the deeper but narrower 1.3-mm survey of a part of the ASAGAO field by Dunlop et al.\ (2017). Fourteen out of the total 25 millimeter galaxies have Chandra counterparts. The observed AGN fractions at $z=1.5-3$ is found to be 90$^{+8}{-19}$\% and $57^{+23}{-25}$\% for the ultra/luminous infrared galaxies with $\log L_{\rm IR}/L_{\odot} = 12-12.8$ and $\log L_{\rm IR}/L_{\odot} = 11.5-12$, respectively. The majority ($\sim$2/3) of the ALMA and/or Herschel detected X-ray AGNs at $z=1.5-3$ appear to be star-formation dominant populations, having $L_{\rm X}$/ $L_{\rm IR}$ ratios smaller than the “simultaneous evolution” value expected from the local black-hole mass to stellar mass ($M_{\rm BH}$-$M_$) relation. On the basis of the $L_{\rm X}$ and stellar mass relation, we infer that a large fraction of star-forming galaxies at $z=1.5-3$ have black hole masses smaller than those expected from the local $M_{\rm BH}$-$M_$ relation. This is opposite to previous reports on luminous AGN at same redshifts detected in wider and shallower surveys, which are subject to selection biases against lower luminosity AGN. Our results are consistent with an evolutionary scenario that star formation occurs first, and an AGN-dominant phase follows later, in objects finally evolving into galaxies with classical bulges.

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Y. Ueda, B. Hatsukade, K. Kohno, et. al.
Tue, 12 Dec 17

Comments: 14 pages including 5 figures and 1 table, accepted for publication in ApJ

Simultaneous, Multi-Wavelength Variability Characterization of the Free-Floating Planetary Mass Object PSO J318.5-22 [EPA]

We present simultaneous HST WFC3 + Spitzer IRAC variability monitoring for the highly-variable young ($\sim$20 Myr) planetary-mass object PSO J318.5-22. Our simultaneous HST + Spitzer observations covered $\sim$2 rotation periods with Spitzer and most of a rotation period with HST. We derive a period of 8.6$\pm$0.1 hours from the Spitzer lightcurve. Combining this period with the measured $v sin i$ for this object, we find an inclination of 56.2$\pm 8.1^{\circ}$. We measure peak-to-trough variability amplitudes of 3.4$\pm$0.1$\%$ for Spitzer Channel 2 and 4.4 – 5.8$\%$ (typical 68$\%$ confidence errors of $\sim$0.3$\%$) in the near-IR bands (1.07-1.67 $\mu$m) covered by the WFC3 G141 prism — the mid-IR variability amplitude for PSO J318.5-22 one of the highest variability amplitudes measured in the mid-IR for any brown dwarf or planetary mass object. Additionally, we detect phase offsets ranging from 200–210$^{\circ}$ (typical error of $\sim$4$^{\circ}$) between synthesized near-IR lightcurves and the Spitzer mid-IR lightcurve, likely indicating depth-dependent longitudinal atmospheric structure in this atmosphere. The detection of similar variability amplitudes in wide spectral bands relative to absorption features suggests that the driver of the variability may be inhomogeneous clouds (perhaps a patchy haze layer over thick clouds), as opposed to hot spots or compositional inhomogeneities at the top-of-atmosphere level.

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B. Biller, J. Vos, E. Buenzli, et. al.
Tue, 12 Dec 17

Comments: 48 pages, 22 figures, accepted to AJ