Multiwavelength Analysis of Dark Matter Annihilation and RX-DMFIT [HEAP]

Dark matter (DM) particles are predicted by several well motivated models to yield Standard Model particles through self-annihilation that can potentially be detected by astrophysical observations. In particular, the production of charged particles from DM annihilation in astrophysical systems that contain magnetic fields yields radio emission through synchrotron radiation and X-ray emission through inverse Compton scattering of ambient photons. We introduce RX-DMFIT, a tool used for calculating the expected secondary emission from DM annihilation. RX-DMFIT includes a wide range of customizable astrophysical and particle parameters and incorporates important astrophysics including the diffusion of charged particles, relevant radiative energy losses, and magnetic field modelling. We demonstrate the use and versatility of RX-DMFIT by analyzing the potential radio and X-ray signals for a variety of DM particle models and astrophysical environments including galaxy clusters, dwarf spheroidal galaxies and normal galaxies. We then apply RX-DMFIT to a concrete example using Segue I radio data to place constraints for a range of assumed DM annihilation channels. For WIMP models with $M_{\chi} \leq 100$GeV and assuming weak diffusion, we find that the the leptonic $\mu^+\mu^-$ and $\tau^+\tau^-$ final states provide the strongest constraints, placing limits on the DM particle cross-section well below the thermal relic cross-section, while even for the $b\bar{b}$ channel we find limits close to the thermal relic cross-section. Our analysis shows that radio emission provides a highly competitive avenue for dark matter searches.

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A. McDaniel, T. Jeltema, S. Profumo, et. al.
Mon, 29 May 17

Comments: 21 pages, 9 figures, 2 tables

Theoretical Description Of GRB 160625B with Wind-to-ISM Transition and Implications for a Magnetized Outflow [HEAP]

GRB 160625B, one of the brightest bursts in recent years, was simultaneously observed by Fermi and Swift satellites, and ground-based optical telescopes in three different events separated by long periods of time. In this paper the non-thermal multiwavelength observations of GRB 160625B are described and a transition phase from wind-type-like medium to interstellar medium between the early (event II) and the late (event III) afterglow is found. The multiwavelength observations of the early afterglow are consistent with the afterglow evolution in a stellar wind medium whereas the observations of the late afterglow are consistent with the afterglow evolution in ISM. The wind-to-ISM transition is calculated to be at $\sim$ 830 s when the jet has decelerated, at a distance of $\sim$ 2.2 $\times 10^{17}$ cm from the progenitor. Using the standard external shock model, the synchrotron and synchrotron self-Compton emission from reverse shock is required to model the GeV $\gamma$-ray and early optical observations in the early afterglow, and synchrotron radiation from the adiabatic forward shock to describe the X-ray and late optical observations in the late afterglow. The derived values of the magnetization parameter, the slope of the fast decay of the optical flash and the inferred magnetic fields suggest that Poynting flux-dominated jet models with arbitrary magnetization could account for the spectral properties exhibited by GRB 160625B.

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N. Fraija, P. Veres, B. Zhang, et. al.
Mon, 29 May 17

Comments: 9 pages, 1 figure, 3 tables. Submitted to ApJ

Shape stability of pasta phases: Lasagna case [HEAP]

The stability of periodically placed slabs (lasagna phase) by exact geometrical methods is examined for the first time. Although the calculations are done in the framework of compressible liquid drop model the obtained results do not depend on model parameters. It appears the shape of slabs is stable in the whole range of volume fraction and perturbation wavelengths. The conclusion questions about the transition mechanism to other shapes of pasta phases.

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S. Kubis and W. Wojcik
Mon, 29 May 17

Comments: 6 pages, 3 figures

Classifying initial conditions of long GRBs modeled with Radiation Relativistic Hydrodynamics [IMA]

We present a method to classify initial conditions of a Long Gamma Ray Bursts model sourced by a single relativistic shock. It is based on the use of Artificial Neural Networks (ANNs) that are trained with Light Curves (LC) generated with Radiation Relativistic Hydrodynamics simulations. The model we use consists in a single shock with a highly relativistic injected beam into a stratified surrounding medium with profile 1/r2. In the process we only consider the Bremsstrahlung radiation and Thomson scattering process. The initial conditions we use to train the ANN are three: the rest mass density, Lorentz factor and radiation energy density of the beam that produces the relativistic shock, together with the LC generated during the process. The classification selects the location of a box in the 3d parameter space that better fits a given LC, and in order to decrease the uncertainty of the parameters this box is refined and the classification selects a new box of smaller size.

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F. Rivera-Paleo, C. Nunez, F. Guzman, et. al.
Fri, 26 May 17

Comments: 8 pages, 9 figures, accepted for publication in Physical Review D

Measurement of Energy Spectrum of Ultra-High Energy Cosmic Rays [HEAP]

Ultra-High Energy Cosmic Rays (UHECRs) are charged particles of energies above $10^{18}$ eV that originate outside of the Galaxy. Because the flux of the UHECRs at Earth is very small, the only practical way of observing UHECRs is by measuring the extensive air showers (EAS) produced by UHECRs in the atmosphere. This is done by using air fluorescence detectors and giant arrays of particle detectors on the ground. The Pierre Auger Observatory (Auger) and Telescope Array (TA) are two large cosmic ray experiments which use such techniques and cover 3000 km$^2$ and 700 km$^2$ areas on the ground, respectively. In this paper, we present the UHECR spectrum reported by the TA, using an exposure of 6300 km$^2$ sr yr accumulated over 7 years of data taking, and the corresponding result of Auger, using 10 years of data with a total exposure exceeding 50000 km$^2$ sr yr. We review the astrophysical interpretation of the two measurements, and discuss their systematic uncertainties.

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V. Verzi, D. Ivanov and Y. Tsunesada
Fri, 26 May 17

Comments: 31 pages, 19 figures, accepted for publication in Prog. Theor. Exp. Phys

The origin of radio pulsar polarisation [HEAP]

Polarisation of radio pulsar profiles involves a number of poorly understood, intriguing phenomena, such as the existence of comparable amounts of orthogonal polarisation modes (OPMs), strong distortions of polarisation angle (PA) curves into shapes inconsistent with the rotating vector model (RVM), and the strong circular polarisation V which can be maximum (instead of zero) at the OPM jumps. It is shown that the existence of comparable OPMs and of the large V results from a coherent addition of phase-delayed waves in natural propagation modes, which are produced by an incident linearly polarised signal. The coherent mode summation implies opposite polarisation properties to those known from the incoherent case, in particular, the OPM jumps occur at peaks of V , whereas V changes sign at a maximum of the linear polarisation fraction L/I. These features are indispensable to interpret various observed polarisation effects. It is shown that statistical properties of the emission mechanism and of propagation effects can be efficiently parametrised in a simple model of coherent mode addition, which is successfully applied to complex polarisation phenomena, such as the stepwise PA curve of PSR B1913+16 and the strong distortions of the PA curve within core components of pulsars B1933+16 and B1237+25. The inclusion of coherent mode addition opens the possibility for a number of new polarisation effects, such as inversion of relative modal strength, twin minima in L/I coincident with peaks in V , 45 deg PA jumps in weakly polarised emission, and loop-shaped core PA distortions. The empirical treatment of the coherency of mode addition makes it possible to advance the understanding of pulsar polarisation beyond the RVM model.

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J. Dyks
Fri, 26 May 17

Comments: 21 pages, 20 figures, submitted to MNRAS

An XMM-Newton and NuSTAR study of IGR J18214-1318: a non-pulsating high-mass X-ray binary with a neutron star [HEAP]

IGR J18214-1318, a Galactic source discovered by the International Gamma-Ray Astrophysics Laboratory, is a high-mass X-ray binary (HMXB) with a supergiant O-type stellar donor. We report on the XMM-Newton and NuSTAR observations that were undertaken to determine the nature of the compact object in this system. This source exhibits high levels of aperiodic variability, but no periodic pulsations are detected with a 90% confidence upper limit of 2% fractional rms between 0.00003-88 Hz, a frequency range that includes the typical pulse periods of neutron stars (NSs) in HMXBs (0.1-10$^3$ s). Although the lack of pulsations prevents us from definitively identifying the compact object in IGR J18214-1318, the presence of an exponential cutoff with e-folding energy $\lesssim30$ keV in its 0.3-79 keV spectrum strongly suggests that the compact object is an NS. The X-ray spectrum also shows a Fe K$\alpha$ emission line and a soft excess, which can be accounted for by either a partial-covering absorber with $N_{\mathrm{H}}\approx10^{23}$ cm$^{-2}$ which could be due to the inhomogeneous supergiant wind, or a blackbody component with $kT=1.74^{+0.04}{-0.05}$ keV and $R{BB}\approx0.3$ km, which may originate from NS hot spots. Although neither explanation for the soft excess can be excluded, the former is more consistent with the properties observed in other supergiant HMXBs. We compare IGR J18214-1318 to other HMXBs that lack pulsations or have long pulsation periods beyond the range covered by our observations.

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F. Fornasini, J. Tomsick, M. Bachetti, et. al.
Fri, 26 May 17

Comments: 15 pages, 12 figures, 4 tables