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J.P. Magué & B. Ménard



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[1]  arXiv:1507.08656 [pdf, ps, other]
Title: Boosting the Annihilation Boost: Semi-Analytic Model of Tidal Effects on Dark Matter Subhalos
Comments: 7 pages, 3 figures, 1 table
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

In the cold dark matter paradigm, structures form hierarchically, implying that large structures contain smaller substructures. These subhalos will enhance signatures of dark matter annihilation such as gamma rays. In the literature, typical estimates of this boost factor are based on field-halo modelling, where halos are assumed to be virialized without any mass loss.However, since subhalos accreted in the gravitational potential of their host lose mass through tidal stripping and dynamical friction, they have a quite characteristic density profile, different from that of the field halos of the same mass. In this work, we quantify the effect of tidal stripping on the boost factor, by developing a semi-analytic model that combines mass-accretion history of both the host and subhalos as well as subhalo accretion rates. We find that compared with the field-halo models, the boost factor increases by a factor 2-3 for host halos ranging from sub-galaxy to cluster masses. The results are particularly relevant for indirect dark matter searches in the extragalactic gamma-ray sky.

[2]  arXiv:1507.08661 [pdf, other]
Title: Confirmation of the Planetary Microlensing Signal and Star and Planet Mass Determinations for Event OGLE-2005-BLG-169
Comments: 21 pages, including 5 figures, published in ApJ
Journal-ref: 2015, ApJ, 808, 169
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

We present Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) observations of the source and lens stars for planetary microlensing event OGLE-2005-BLG-169, which confirm the relative proper motion prediction due to the planetary light curve signal observed for this event. This (and the companion Keck result) provide the first confirmation of a planetary microlensing signal, for which the deviation was only 2%. The follow-up observations determine the flux of the planetary host star in multiple passbands and remove light curve model ambiguity caused by sparse sampling of part of the light curve. This leads to a precise determination of the properties of the OGLE-2005-BLG-169Lb planetary system. Combining the constraints from the microlensing light curve with the photometry and astrometry of the HST/WFC3 data, we find star and planet masses of M_* = 0.69+- 0.02 M_solar and m_p = 14.1 +- 0.9 M_earth. The planetary microlens system is located toward the Galactic bulge at a distance of D_L = 4.1 +- 0.4 kpc, and the projected star-planet separation is a_perp = 3.5 +- 0.3 AU, corresponding to a semi-major axis of a = 4.0 (+2.2 -0.6) AU.

[3]  arXiv:1507.08662 [pdf, other]
Title: Chaotic Dispersal of Tidal Debris
Comments: 47 pages, 14 figures, submitted to MNRAS
Subjects: Astrophysics of Galaxies (astro-ph.GA)

Several long, dynamically cold stellar streams have been observed around the Milky Way Galaxy, presumably formed from the tidal disruption of globular clusters. In integrable potentials---where all orbits are dynamically regular---tidal debris phase-mixes close to the orbit of the progenitor system. However, cosmological simulations of structure formation suggest that the Milky Way's dark matter halo is expected not to be fully integrable; an appreciable fraction of orbits will be chaotic. This paper examines the influence of chaos on the phase-space morphology of cold tidal streams. We find very stark results: Streams in chaotic regions look very different from those in regular regions. We find that streams (simulated using test particle ensembles of nearby orbits) can be sensitive to chaos on a much shorter time-scale than any standard prediction (from the Lyapunov or frequency-diffusion times). For example, on a weakly chaotic orbit with a chaotic timescale predicted to be >1000 orbital periods (>1000 Gyr), the resulting stellar stream is, after just a few 10's of orbits, substantially more diffuse than any formed on a nearby but regular orbit. We find that the enhanced diffusion of the stream stars can be understood by looking at the variance in orbital frequencies of orbit ensembles centered around the parent (progenitor) orbit. Our results suggest that long, cold streams around our Galaxy must exist only on regular (or very nearly regular) orbits; they potentially provide a map of the regular regions of the Milky Way potential. This suggests a promising new direction for the use of tidal streams to constrain the distribution of dark matter around our Galaxy.

[4]  arXiv:1507.08664 [pdf, other]
Title: One-point statistics of the Lagrangian displacement field
Comments: 4 pages, 3 figures, 1 table. Addendum to "One-point remapping of Lagrangian perturbation theory in the mildly non-linear regime of cosmic structure formation" (arXiv:1305.4642), published by JCAP
Journal-ref: JCAP04 (2015) 026
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

This document is an addendum to "One-point remapping of Lagrangian perturbation theory in the mildly non-linear regime of cosmic structure formation" (arXiv:1305.4642).

[5]  arXiv:1507.08665 [pdf, other]
Title: Cosmological Axion and neutrino mass constraints from Planck 2015 temperature and polarization data
Comments: 5 pages, 1 figure
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Astrophysical Phenomena (astro-ph.HE)

Axions currently provide the most compelling solution to the strong CP problem. These particles may be copiously produced in the early universe, including via thermal processes. Therefore, relic axions constitute a hot dark matter component and their masses are strongly degenerate with those of the three active neutrinos, as they leave identical signatures in the different cosmological observables. In addition, thermal axions, while still relativistic states, also contribute to the relativistic degrees of freedom, parameterised via $N_{eff}$. We present the cosmological bounds on the relic axion and neutrino masses, exploiting the full Planck mission data, which include polarization measurements. In the mixed hot dark matter scenario explored here, we find the tightest and more robust constraint to date on the sum of the three active neutrino masses, $\sum m_\nu <0.136$ eV at $95\%$ CL, obtained in the well-known linear perturbation regime. The Planck Sunyaev-Zeldovich cluster number count data further tightens this bound, providing a $95\%$ CL upper limit of $\sum m_\nu <0.126$ eV in this very same mixed hot dark matter model, a value which is very close to the expectations in the inverted hierarchical neutrino mass scenario. Using this same combination of data sets we find the most stringent bound to date on the thermal axion mass, $m_a<0.529$ eV at $95\%$ CL.

[6]  arXiv:1507.08667 [pdf, ps, other]
Title: Eccentric Jupiters via Disk-Planet Interactions
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

Numerical hydrodynamics calculations are performed to determine conditions under which giant planet eccentricities can be excited by parent gas disks. Unlike in other studies, Jupiter-mass planets are found to have their eccentricities amplified --- provided their orbits start eccentric. We disentangle the web of co-rotation, co-orbital, and external resonances to show that this finite-amplitude instability is consistent with that predicted analytically. Ellipticities can grow until they reach of order the disk's aspect ratio, beyond which the external Lindblad resonances that excite eccentricity are weakened by the planet's increasingly supersonic epicyclic motion. Forcing the planet to still larger eccentricities causes catastrophic eccentricity damping as the planet collides into gap walls. If the eccentricity driving documented here survives in 3D, it may explain the low-to-moderate eccentricities $\lesssim 0.1$ exhibited by many giant planets (including Jupiter and Saturn), especially those without planetary or stellar companions.

[7]  arXiv:1507.08669 [pdf, ps, other]
Title: RESOLVE Survey Photometry and Volume-limited Calibration of the Photometric Gas Fractions Technique
Comments: (29 pages, 15 figures, accepted for publication in ApJ; a data table is available at this http URL and a code for predicting individual galaxy G/S probability distributions (pred_loggs_dist.pro) is available at this https URL
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We present custom-processed UV, optical, and near-IR photometry for the RESOLVE survey, a volume-limited census of stellar, gas, and dynamical mass within two subvolumes of the nearby universe (RESOLVE-A and -B), complete down to baryonic mass ~10^9.1-9.3 Msun. In contrast to standard pipeline photometry (e.g., SDSS), our photometry uses optimal background subtraction, avoids suppressing color gradients, and includes systematic errors. With these improvements, we measure brighter magnitudes, larger radii, bluer colors, and a real increase in scatter around the red sequence. Combining stellar masses from our photometry with the RESOLVE-A HI mass census, we create volume-limited calibrations of the photometric gas fractions (PGF) technique, which predicts gas-to-stellar mass ratios (G/S) from galaxy colors and optional additional parameters. We analyze G/S-color residuals vs. potential third parameters, finding that axial ratio is the best independent and physically meaningful third parameter. We define a "modified color" from planar fits to G/S as a function of both color and axial ratio. In the complete galaxy population, upper limits on G/S bias linear and planar fits. We therefore model the entire PGF probability density field, enabling iterative statistical modeling of upper limits and prediction of full G/S probability distributions for individual galaxies, with two-component structure for red colors. We use the RESOLVE-B 21cm census to test several PGF calibrations, finding that most systematically under- or overestimate gas masses, but the full probability density method performs well.

[8]  arXiv:1507.08671 [pdf, other]
Title: Gamma-Ray Bursts as Sources of Strong Magnetic Fields
Comments: 51 pages; 12 figures; invited topical review, to be published in "The Strongest Magnetic Fields in the Universe" (Space Sciences Series of ISSI, Springer), Space Science Reviews
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Gamma-Ray Bursts (GRBs) are the strongest explosions in the Universe, which due to their extreme character likely involve some of the strongest magnetic fields in nature. This review discusses the possible roles of magnetic fields in GRBs, from their central engines, through the launching, acceleration and collimation of their ultra-relativistic jets, to the dissipation and particle acceleration that power their $\gamma$-ray emission, and the powerful blast wave they drive into the surrounding medium that generates their long-lived afterglow emission. An emphasis is put on particular areas in which there have been interesting developments in recent years.

[9]  arXiv:1507.08676 [pdf, ps, other]
Title: The QUEST-La Silla AGN Variability Survey
Comments: Accepted for publication in ApJ
Subjects: Astrophysics of Galaxies (astro-ph.GA); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We present the characterization and initial results from the QUEST-La Silla AGN variability survey. This is an effort to obtain well sampled optical light curves in extragalactic fields with unique multi-wavelength observations. We present photometry obtained from 2010 to 2012 in the XMM-COSMOS field, which was observed over 150 nights using the QUEST camera on the ESO-Schmidt telescope. The survey uses a broadband filter, the $Q$-band, similar to the union of the $g$ and the $r$ filters, achieving an intrinsic photometric dispersion of $0.05$ mag, and a systematic error of $0.05$ mag in the zero-point. Since some detectors of the camera show significant non-linearity, we use a linear correlation to fit the zero-points as a function of the instrumental magnitudes, thus obtaining a good correction to the non-linear behavior of these detectors. We obtain good photometry to an equivalent limiting magnitude of $r\sim 20.5$. Studying the optical variability of X-ray detected sources in the XMM-COSMOS field, we find that the survey is $\sim75-80$% complete to magnitudes $r\sim20$, and $\sim67$% complete to a magnitude $r\sim21$. The determination and parameterization of the structure function (${SF}_{norm}(\tau) = A \tau^{\gamma}$) of the variable sources shows that most BL AGN are characterized by $A > 0.1$ and $\gamma > 0.025$. It is further shown that variable NL AGN and GAL sources occupying the same parameter space in $A$ and $\gamma$ are very likely to correspond to obscured or low luminosity AGN. Our samples are, however, small, and we expect to revisit these results using larger samples with longer light curves obtained as part of our ongoing survey.

[10]  arXiv:1507.08680 [pdf, other]
Title: AMS-02 electrons and positrons: astrophysical interpretation and Dark Matter constraints
Comments: 9 pages and 4 figure, Proceedings of the 34th International Cosmic Ray Conference (ICRC 2015), The Hague (The Netherlands)
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics - Phenomenology (hep-ph)

We present here a quantitative analysis of the recent AMS-02 data with the purpose of investigating the interplay between astrophysical sources and Dark Matter in their interpretation. First, we show that AMS-02 leptonic measurements are in a remarkably good agreement with the hypothesis that all electrons and positrons are the outcome of primary or secondary astrophysical processes. Then, we add Dark Matter to the picture, in order to establish which are the informations on its annihilation cross section (or lifetime) that can be inferred by fitting AMS-02 data within a scenario in which Dark Matter and astrophysical sources jointly contribute to the different leptonic observables. In particular, by performing a Markov Chain Monte Carlo sampling of the parameters space of the theory, we attempt at characterizing the significance of a possible Dark Matter contribution to the observed data and we derive robust upper limits on the Dark Matter annihilation/decay rate.

[11]  arXiv:1507.08687 [pdf, ps, other]
Title: Molecular line formation in the extremely metal-poor star BD+44 493
Authors: Wako Aoki
Comments: 7 figures, 2 tables, to appear in ApJ
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Molecular absorption lines of OH (99 lines) and CH (105 lines) are measured for the carbon-enhanced metal-poor star BD+44 493 with [Fe/H]=-3.8. The abundances of oxygen and carbon determined from individual lines based on an 1D-LTE analysis exhibit significant dependence on excitation potentials of the lines; d log e/d chi ~ -0.15 - -0.2 dex/eV, where e and chi are elemental abundances from individual spectral lines and their excitation potentials, respectively. The dependence is not explained by the uncertainties of stellar parameters, but suggests that the atmosphere of this object possesses a cool layer that is not reproduced by the 1D model atmosphere. This result agrees with the predictions by 3D model calculations. Although absorption lines of neutral iron exhibit similar trend, it is much weaker than found in molecular lines and that predicted by 3D LTE models.

[12]  arXiv:1507.08702 [pdf, other]
Title: Magnetic Field Amplification via Protostellar Disc Dynamos
Comments: 15 pages, 13 figures
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR)

We model the generation of a magnetic field in a protostellar disc using an \alpha-dynamo and perform axisymmetric magnetohydrodynamics (MHD) simulations of a T Tauri star. We find that for small values of the dimensionless dynamo parameter $\alpha_d$ the poloidal field grows exponentially at a rate ${\sigma} \propto {\Omega}_K \sqrt{\alpha_d}$ , before saturating to a value $\propto \sqrt{\alpha_d}$ . The dynamo excites dipole and octupole modes, but quadrupole modes are suppressed, because of the symmetries of the seed field. Initial seed fields too weak to launch MHD outflows are found to grow sufficiently to launch winds with observationally relevant mass fluxes of order $10^{-9} M_{\odot}/\rm{yr}$ for T Tauri stars. For large values of $\alpha_d$ magnetic loops are generated over the entire disc. These quickly come to dominate the disc dynamics and cause the disc to break up due to the magnetic pressure.

[13]  arXiv:1507.08724 [pdf, other]
Title: Bayesian redshift-space distortions correction from galaxy redshift surveys
Comments: 6 pages, 3 figures
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We present a Bayesian reconstruction method which maps a galaxy distribution from redshift-space to real-space inferring the distances of the individual galaxies. The method is based on sampling density fields assuming a lognormal prior with a likelihood given by the negative binomial distribution function modelling stochastic bias. We assume a deterministic bias given by a power law relating the dark matter density field to the expected halo or galaxy field. Coherent redshift-space distortions are corrected in a Gibbs-sampling procedure by moving the galaxies from redshift-space to real-space according to the peculiar motions derived from the recovered density field using linear theory with the option to include tidal field corrections from second order Lagrangian perturbation theory. The virialised distortions are corrected by sampling candidate real-space positions (being in the neighbourhood of the observations along the line of sight), which are compatible with the bulk flow corrected redshift-space position adding a random dispersion term in high density collapsed regions. The latter are defined according to the eigenvalues of the Hessian. This approach presents an alternative method to estimate the distances to galaxies using the three dimensional spatial information, and assuming isotropy. Hence the number of applications is very broad. In this work we show the potential of this method to constrain the growth rate up to $k$ ~ 0.3 $h$ Mpc$^{-1}$. Furthermore it could be useful to correct for photo-metric redshift errors, and to obtain improved BAO reconstructions.

[14]  arXiv:1507.08737 [pdf, other]
Title: Vorticity, Shocks and Magnetic Fields in Subsonic, ICM-like Turbulence
Comments: 46 pages, 14 figures. Accepted for publication in the Astrophysical Journal
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We analyze high resolution simulations of compressible, MHD turbulence with properties resembling conditions in galaxy clusters. The flow is driven to turbulence Mach number $\mathcal{M}_t \sim 1/2$ in an isothermal medium with an initially very weak, uniform seed magnetic field ($\beta = P_g/P_B = 10^6$). Since cluster turbulence is likely to result from a mix of sheared (solenoidal) and compressive forcing processes, we examine the distinct turbulence properties for both cases. In one set of simulations velocity forcing is entirely solenoidal ($\nabla\cdot \delta {\vec u} = 0$), while in the other it is entirely compressive ($\nabla\times \delta {\vec u} = 0$). Both cases develop a mixture of solenoidal and compressive turbulent motions, since each generates the other. The development of compressive turbulent motions leads to shocks, even when the turbulence is solenoidally forced and subsonic. Shocks, in turn, produce and amplify vorticity, which is especially important in compressively forced turbulence. To clarify those processes we include a pair of appendices that look in detail at vorticity evolution in association with shocks. From our simulation analyses we find that magnetic fields amplified to near saturation levels in predominantly solenoidal turbulence can actually enhance vorticity on small scales by concentrating and stabilizing shear. The properties, evolution rates and relative contributions of the kinetic and magnetic turbulent elements depend strongly on the character of the forcing. Specifically, shocks are stronger, but vorticity evolution and magnetic field amplification are slower and weaker when the turbulence is compressively forced. We identify a simple relation to estimate characteristic shock strengths in terms of the turbulence Mach number and the character of the forcing. Our results will be helpful in understanding flow motions in galaxy clusters.

[15]  arXiv:1507.08739 [pdf]
Title: Magnetospherically driven optical and radio aurorae at the end of the stellar main sequence
Comments: Accepted for publication in the 30 July 2015 issue of Nature. 27 pages, 2 figures, 2 extended data figures
Journal-ref: Nature 523 (2015) 568-571
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Aurorae are detected from all the magnetized planets in our Solar System, including Earth. They are powered by magnetospheric current systems that lead to the precipitation of energetic electrons into the high-latitude regions of the upper atmosphere. In the case of the gas-giant planets, these aurorae include highly polarized radio emission at kilohertz and megahertz frequencies produced by the precipitating electrons, as well as continuum and line emission in the infrared, optical, ultraviolet and X-ray parts of the spectrum, associated with the collisional excitation and heating of the hydrogen-dominated atmosphere. Here we report simultaneous radio and optical spectroscopic observations of an object at the end of the stellar main sequence, located right at the boundary between stars and brown dwarfs, from which we have detected radio and optical auroral emissions both powered by magnetospheric currents. Whereas the magnetic activity of stars like our Sun is powered by processes that occur in their lower atmospheres, these aurorae are powered by processes originating much further out in the magnetosphere of the dwarf star that couple energy into the lower atmosphere. The dissipated power is at least four orders of magnitude larger than what is produced in the Jovian magnetosphere, revealing aurorae to be a potentially ubiquitous signature of large-scale magnetospheres that can scale to luminosities far greater than those observed in our Solar System. These magnetospheric current systems may also play a part in powering some of the weather phenomena reported on brown dwarfs.

[16]  arXiv:1507.08740 [pdf, other]
Title: Hard X-ray Morphological and Spectral Studies of The Galactic Center Molecular Cloud Sgr B2: Constraining Past Sgr A* Flaring Activity
Comments: 17 pages, 6 figures, submitted to ApJ
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Galactic Center (GC) molecular cloud Sgr B2 is the best manifestation of an X-ray reflection nebula (XRN) reprocessing a past giant outburst from the supermassive black hole Sgr A*. Alternatively, Sgr B2 could be illuminated by low-energy cosmic ray electrons (LECRe) or protons (LECRp). In 2013, NuSTAR for the first time resolved Sgr B2 hard X-ray emission on sub-arcminute scales. Two prominent features are detected above 10 keV - a newly emerging cloud G0.66-0.13 and the central 90" radius region containing two compact cores Sgr B2(M) and Sgr B2(N) surrounded by diffuse emission. It is inconclusive whether the remaining level of Sgr B2 emission is still decreasing or has reached a constant background level. A decreasing Fe K$\alpha$ emission can be best explained by XRN while a constant background emission can be best explained by LECRp. In the XRN scenario, the 3-79 keV Sgr B2 spectrum can well constrain the past Sgr A* outburst, resulting in an outburst spectrum with a peak luminosity of $L_{3-79\rm~keV} \sim 5\times10^{38} \rm~erg~s^{-1}$ derived from the maximum Compton-scattered continuum and the Fe K$\alpha$ emission consistently. The XRN scenario is preferred by the fast variability of G0.66-0.13, which could be a molecular clump located in the Sgr B2 envelope reflecting the same Sgr A* outburst. In the LECRp scenario, we derived the required CR ion power $dW/dt=(1-4)\times10^{39}\rm~erg~s^{-1}$ and the CR ionization rate $\zeta_{H}=(6-10)\times 10^{-15}\rm~H^{-1}~s^{-1}$. The Sgr B2 background level X-ray emission will be a powerful tool to constrain GC CR population.

[17]  arXiv:1507.08770 [pdf, other]
Title: Turning off the lights: Supernova SN1987A 30 years on
Authors: Richard de Grijs
Comments: Invited "News and Views" article, Nature Physics, August 2015; 2 pages, 1 figure
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); High Energy Astrophysical Phenomena (astro-ph.HE)

Decades-long repeat observations of supernova SN1987A offer us unique, real-time insights into the violent death of a massive star and its long-term environmental effects, until its eventual switch-off.

[18]  arXiv:1507.08774 [pdf, other]
Title: CARMA Observations of Galactic Cold Cores: Searching for Spinning Dust Emission
Comments: Accepted for publication in MNRAS
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We present the first search for spinning dust emission from a sample of 34 Galactic cold cores, performed using the CARMA interferometer. For each of our cores we use photometric data from the Herschel Space Observatory to constrain N_{H}, T_{d}, n_{H}, and G_{0}. By computing the mass of the cores and comparing it to the Bonnor-Ebert mass, we determined that 29 of the 34 cores are gravitationally unstable and undergoing collapse. In fact, we found that 6 cores are associated with at least one young stellar object, suggestive of their proto-stellar nature. By investigating the physical conditions within each core, we can shed light on the cm emission revealed (or not) by our CARMA observations. Indeed, we find that only 3 of our cores have any significant detectable cm emission. Using a spinning dust model, we predict the expected level of spinning dust emission in each core and find that for all 34 cores, the predicted level of emission is larger than the observed cm emission constrained by the CARMA observations. Moreover, even in the cores for which we do detect cm emission, we cannot, at this stage, discriminate between free-free emission from young stellar objects and spinning dust emission. We emphasise that, although the CARMA observations described in this analysis place important constraints on the presence of spinning dust in cold, dense environments, the source sample targeted by these observations is not statistically representative of the entire population of Galactic cores.

[19]  arXiv:1507.08778 [pdf, ps, other]
Title: Cold galaxies
Authors: Michael Rowan-Robinson (Imperial College London), David L. Clements (Imperial College London)
Comments: 9 pages, 15 figures. Accepted for publication MNRAS
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We use 350 mu angular diameter estimates from Planck to test the idea that some galaxies contain exceptionally cold (10-13 K) dust, since colder dust implies a lower surface brightness radiation field illuminating the dust, and hence a greater physical extent for a given luminosity. The galaxies identified from their spectral energy distributions as containing cold dust do indeed show the expected larger 350 mu diameters. For a few cold dust galaxies where Herschel data are available we are able to use submillimetre maps or surface brightness profiles to locate the cold dust, which as expected generally lies outside the optical galaxy.

[20]  arXiv:1507.08786 [pdf, other]
Title: Filaments in the Lupus molecular clouds
Comments: 16 pages, 16 figures
Subjects: Astrophysics of Galaxies (astro-ph.GA); Solar and Stellar Astrophysics (astro-ph.SR)

We have studied the filaments extracted from the column density maps of the nearby Lupus 1, 3, and 4 molecular clouds, derived from photometric maps observed with the Herschel satellite. Filaments in the Lupus clouds have quite low column densities, with a median value of $\sim$1.5$\times$10$^{21}$ cm$^{-2}$ and most have masses per unit length lower than the maximum critical value for radial gravitational collapse. Indeed, no evidence of filament contraction has been seen in the gas kinematics. We find that some filaments, that on average are thermally subcritical, contain dense cores that may eventually form stars. This is an indication that in the low column density regime, the critical condition for the formation of stars may be reached only locally and this condition is not a global property of the filament. Finally, in Lupus we find multiple observational evidences of the key role that the magnetic field plays in forming filaments, and determining their confinement and dynamical evolution.

[21]  arXiv:1507.08801 [pdf, ps, other]
Title: Concurrent Formation of Carbon and Silicate Dust in Nova V1280 Sco
Comments: 47 pages, 20 figures. Submitted to the Astrophysical Journal
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We present infrared multi-epoch observations of the dust forming nova V1280 Sco over $\sim$2000 days from the outburst. The temporal evolution of the infrared spectral energy distributions at 1272, 1616 and 1947 days can be explained by the emissions produced by amorphous carbon dust of mass (6.6--8.7)$\times$10$^{-8}$M$_{\odot}$ with a representative grain size of 0.01$~\mu$m and astronomical silicate dust of mass (3.4--4.3)$\times$10$^{-7}$M$_{\odot}$ with a representative grain size of 0.3--0.5$~\mu$m. Both of these dust species travel farther away from the white dwarf without an apparent mass evolution throughout those later epochs. The dust formation scenario around V1280 Sco suggested from our analyses is that the amorphous carbon dust is formed in the nova ejecta followed by the formation of silicate dust in the expanding nova ejecta or as a result of the interaction between the nova wind and the circumstellar medium.

[22]  arXiv:1507.08806 [pdf, ps, other]
Title: The white dwarf population of NGC 6397
Comments: 9 pages, 6 figures, accepted for publication in A&A
Subjects: Astrophysics of Galaxies (astro-ph.GA); Solar and Stellar Astrophysics (astro-ph.SR)

NGC 6397 is one of the most interesting, well observed and theoretically studied globular clusters. The existing wealth of observations allows us to study the reliability of the theoretical white dwarf cooling sequences of low metallicity progenitors,to determine its age and the percentage of unresolved binaries, and to assess other important characteristics of the cluster, like the slope of the initial mass function, or the fraction of white dwarfs with hydrogen deficient atmospheres. We present a population synthesis study of the white dwarf population of NGC 6397. In particular, we study the shape of the color-magnitude diagram, and the corresponding magnitude and color distributions. We do this using an up-to-date Monte Carlo code that incorporates the most recent and reliable cooling sequences and an accurate modeling of the observational biases. We find a good agreement between our theoretical models and the observed data. In particular, we find that this agreement is best for those cooling sequences that take into account residual hydrogen burning. This result has important consequences for the evolution of progenitor stars during the thermally-pulsing asymptotic giant branch phase, since it implies that appreciable third dredge-up in low-mass, low-metallicity progenitors is not expected to occur. Using a standard burst duration of 1.0 Gyr, we obtain that the age of the cluster is 12.8+0.50-0.75 Gyr. Larger ages are also compatible with the observed data, but then realistic longer durations of the initial burst of star formation are needed to fit the luminosity function. We conclude that a correct modeling of the white dwarf opulation of globular clusters, used in combination with the number counts of main sequence stars provides an unique tool to model the properties of globular clusters.

[23]  arXiv:1507.08809 [pdf, ps, other]
Title: Eccentricity Evolution Through Accretion of Protoplanets
Comments: Accepted for publication in ApJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

Most of super-Earths detected by the radial velocity (RV) method have significantly smaller eccentricities than the eccentricities corresponding to velocity dispersion equal to their surface escape velocity ("escape eccentricities"). If orbital instability followed by giant impacts among protoplanets that have migrated from outer region is considered, it is usually considered that eccentricities of the merged bodies become comparable to those of orbital crossing bodies, which are excited up to their escape eccentricities by close scattering. However, the eccentricity evolution in the {\it in situ} accretion model has not been studied in detail. Here, we investigate the eccentricity evolution through {\it N}-body simulations. We have found that the merged planets tend to have much smaller eccentricities than the escape eccentricities due to very efficient collision damping. If the protoplanet orbits are initially well separated and their eccentricities are securely increased, an inner protoplanet collides at its apocenter with an outer protoplanet at its pericenter. The eccentricity of the merged body is the smallest for such configuration. Orbital inclinations are also damped by this mechanism and planets tend to share a same orbital plane, which is consistent with {\it Kepler} data. Such efficient collision damping is not found when we start calculations from densely packed orbits of the protoplanets. If the protoplanets are initially in the mean-motion resonances, which corresponds to well separated orbits, the {\it in situ} accretion model well reproduces the features of eccentricities and inclinations of multiple super-Earths/Earth systems discovered by RV and {\it Kepler} surveys.

[24]  arXiv:1507.08843 [pdf, ps, other]
Title: Host Galaxy Properties and Black Hole Mass of Swift J164449.3+573451 from Multi-Wavelength Long-Term Monitoring and HST Data
Comments: 12 pages, 10 figures, published in APJ
Journal-ref: The Astrophysical Journal, 808:96 (11pp), 2015 July 20
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We study the host galaxy properties of the tidal disruption object, Swift J164449.3+573451 using long-term optical to near-infrared (NIR) data. First, we decompose the galaxy surface brightness distribution and analyze the morphology of the host galaxy using high resolution \emph{HST} WFC3 images. We conclude that the host galaxy is a bulge-dominant galaxy that is well described by a single S\'{e}rsic model with S\'{e}rsic index $n=3.43\pm0.05$. Adding a disk component, the bulge to total host galaxy flux ratio (B/T) is $0.83\pm0.03$, which still indicates a bulge-dominant galaxy. Second, we estimate multi-band fluxes of the host galaxy through long-term light curves. Our long-term NIR light curves reveal the pure host galaxy fluxes $\sim500$ days after the burst. We fit spectral energy distribution (SED) models to the multi-band fluxes from the optical to NIR of the host galaxy and determine its properties. The stellar mass, the star formation rate, and the age of stellar population are $\log(M_{\star}/M_{\odot}) = 9.14^{+0.13}_{-0.10}$, $0.03^{+0.28}_{-0.03}\, M_{\odot}$/yr, and $0.63^{+0.95}_{-0.43}$ Gyr. Finally, we estimate the mass of the central super massive black hole which is responsible for the tidal disruption event. The black hole mass is estimated to be $10^{6.7\pm0.4}\, M_{\odot}$ from $M_{\mathrm{BH}}$ - $M_{\star,\mathrm{bul}}$ and $M_{\mathrm{BH}}$ - $L_{\mathrm{bul}}$ relations for the $K$ band, although a smaller value of $\sim10^5\, M_{\odot}$ cannot be excluded convincingly if the host galaxy harbors a pseudobulge.

[25]  arXiv:1507.08845 [pdf, other]
Title: The absolute age of the globular cluster M15 using near-infrared adaptive optics images from PISCES/LBT
Comments: 13 pages, 8 figures, ApJ accepted
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Astrophysics of Galaxies (astro-ph.GA)

We present deep near-infrared (NIR) J, Ks photometry of the old, metal-poor Galactic globular cluster M\,15 obtained with images collected with the LUCI1 and PISCES cameras available at the Large Binocular Telescope (LBT). We show how the use of First Light Adaptive Optics system coupled with the (FLAO) PISCES camera allows us to improve the limiting magnitude by ~2 mag in Ks. By analyzing archival HST data, we demonstrate that the quality of the LBT/PISCES color magnitude diagram is fully comparable with analogous space-based data. The smaller field of view is balanced by the shorter exposure time required to reach a similar photometric limit. We investigated the absolute age of M\,15 by means of two methods: i) by determining the age from the position of the main sequence turn-off; and ii) by the magnitude difference between the MSTO and the well-defined knee detected along the faint portion of the MS. We derive consistent values of the absolute age of M15, that is 12.9+-2.6 Gyr and 13.3+-1.1 Gyr, respectively.

[26]  arXiv:1507.08853 [pdf, other]
Title: Planck 2015 results. III. LFI systematic uncertainties
Comments: Submitted to A&A
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We present the current accounting of systematic effect uncertainties for the Low Frequency Instrument (LFI) that are relevant to the 2015 release of the Planck cosmological results, showing the robustness and consistency of our data set, especially for polarization analysis. We use two complementary approaches: (i) simulations based on measured data and physical models of the known systematic effects; and (ii) analysis of difference maps containing the same sky signal ("null-maps"). The LFI temperature data are limited by instrumental noise. At large angular scales the systematic effects are below the cosmic microwave background (CMB) temperature power spectrum by several orders of magnitude. In polarization the systematic uncertainties are dominated by calibration uncertainties and compete with the CMB $E$-modes in the multipole range 10-20. Based on our model of all known systematic effects, we show that these effects introduce a slight bias of around $0.2\,\sigma$ on the reionization optical depth derived from the 70 GHz $EE$ spectrum using the 30 and 353\,GHz channels as foreground templates. At 30 GHz the systematic effects are smaller than the Galactic foreground at all scales in temperature and polarization, which allows us to consider this channel as a reliable template of synchrotron emission. We assess the residual uncertainties due to LFI effects on CMB maps and power spectra after component separation and show that these effects are smaller than the CMB at all scales. We also assess the impact on non-Gaussianity studies and find it to be negligible. Some residuals still appear in null maps from particular sky survey pairs, particularly at 30 GHz, suggesting possible straylight contamination due to an imperfect knowledge of the beam far sidelobes.

[27]  arXiv:1507.08856 [pdf, ps, other]
Title: Effects of granulation on the visibility of solar oscillations
Authors: J. Schou
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Context. The interaction of solar oscillations with near surface convection is poorly understood. These interactions are likely the cause of several problems in helio- and astero-seismology, including the so-called surface effect and apparently unphysical travel time shifts as a function of center to limb distance. There is thus a clear need for further theoretical understanding and observational tests.
Aims. The aim is to determine how the observed modes are affected by the convection.
Methods. I use HMI velocity and intensity images to construct k-$\omega$ diagrams showing how the oscillation amplitude and phase depend on the local granulation intensity.
Results. There is a clear and significant dependence of the observed properties of the oscillations on the local convection state.

[28]  arXiv:1507.08869 [pdf, other]
Title: Detection of two power-law tails in the probability distribution functions of massive GMCs
Authors: N. Schneider (1,2), S. Bontemps (1), P. Girichidis (3), T. Rayner (4), F. Motte (5), P. Andre (5), D. Russeil (6), A. Abergel (7), L. Anderson (8), D. Arzoumanian (7), M. Benedettini (9), T. Csengeri (10), P. Didelon (5), J. D. Francesco (11), M. Griffin (4), T. Hill (12), R. S. Klessen (13), V. Ossenkopf (2), S. Pezzuto (9), A. Rivera-Ingraham (14), L. Spinoglio (9), P. Tremblin (15,5), A. Zavagno (5) ((1) LAB Univ. Bordeaux, France, (2) I. Physik. Institut, University of Cologne, Germany, (3) MPA Garching, Germany, (4) School of Physics and Astronomy, Cardiff, UK, (5) IRFU/SAp CEA/DSM, Gif-sur-Yvette, France, (6) AIX Marseille Univ. LAM, Marseille, France, (7) IAS Orsay, France, (8) Department of Physics and Astronomy, West Virginia University, USA, (9) IAPS, INAF, Roma, Italy, (10) MPifR Bonn, Germany, (11) NRC, Herzberg Institute of Astrophysics, Victoria, Canada, (12) Joint ALMA Observatory, Santiago, Chile, (13) Universitaet Heidelberg, Zentrum fuer Astronomie, Heidelberg, Germany, (14) SA/ESAC, Madrid, Spain, (15) Astrophysics Group, University of Exeter, UK)
Comments: MNRAS Letters, accepted 20.7.2015, in press
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We report the novel detection of complex high-column density tails in the probability distribution functions (PDFs) for three high-mass star-forming regions (CepOB3, MonR2, NGC6334), obtained from dust emission observed with Herschel. The low column density range can be fit with a lognormal distribution. A first power-law tail starts above an extinction (Av) of ~6-14. It has a slope of alpha=1.3-2 for the rho~r^-alpha profile for an equivalent density distribution (spherical or cylindrical geometry), and is thus consistent with free-fall gravitational collapse. Above Av~40, 60, and 140, we detect an excess that can be fitted by a flatter power law tail with alpha>2. It correlates with the central regions of the cloud (ridges/hubs) of size ~1 pc and densities above 10^4 cm^-3. This excess may be caused by physical processes that slow down collapse and reduce the flow of mass towards higher densities. Possible are: 1. rotation, which introduces an angular momentum barrier, 2. increasing optical depth and weaker cooling, 3. magnetic fields, 4. geometrical effects, and 5. protostellar feedback. The excess/second power-law tail is closely linked to high-mass star-formation though it does not imply a universal column density threshold for the formation of (high-mass) stars.

[29]  arXiv:1507.08895 [pdf, ps, other]
Title: Thermodynamic Spectrum of Solar Flares Based on SDO/EVE Observations: Techniques and First Results
Comments: 39 pages, 19 figures, 4 tables
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

SDO/EVE provide rich information of the thermodynamic processes of solar activities, particularly of solar flares. Here, we develop a method to construct thermodynamic spectrum (TDS) charts based on the EVE spectral lines. Reading from the charts, we are able to easily recognize if there is a late phase following a main phase of a flare, and able to learn the begin, peak and end times of the flare as well as the drift of the temperature, i.e., the cooling rate, of the heated plasma during the flare. Through four M-class flares of different types, we illustrate which thermodynamic information can be revealed from the TDS charts. Further, we investigate the TDS charts of all the flares greater than M5.0, and some interesting results are achieved. First, there are two distinct drift patterns, called Type I and Type II. For Type I flares, the enhanced emission drifts from high to low temperture, whereas for Type II flares, the drift is somewhat reversed, suggesting a more violent and durable heating during Type II flares than Type I flares. Second, for late-phase flares, the peak intensity ratio of the late phase to the main phase read from the TDS chart is roughly correlated with the flare class identified by GOES SXR, and the flares with a stronger late phase are all confined. We believe that the re-deposition of the energy carried by a flux rope, that unsuccessfully erupts out, into thermal emissions is responsible for the strong late phase found in a confined flare. These results provide us new clues to advance our understanding of the thermodynamic processes of solar flares and associated solar eruptions, e.g., coronal mass ejections.

[30]  arXiv:1507.08902 [pdf, ps, other]
Title: Grain size constraints on HL Tau with polarization signature
Comments: 6 pages, 5 figures, submitted to ApJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)

We report a new interpretation of the millimeter-wave polarization of the protoplanetary disk around HL Tau with self-polarization. We successfully reproduce the observed polarization signature with self-scattered light of dust grains. The detected polarization can be explained only if dust grains have a maximum size of around 150 ${\rm \mu m}$. This is a strong constraint on grain size in the early stage of a circumstellar disk. The obtained grain size contradicts to previously expected grain size, which is millimeter. The inferred grain size is too small to be trapped at gas pressure bumps, and therefore it requires planet formation theory to explain the mechanism to stop the grain growth or it might suggest the dust grains are no longer spherical but highly porous.

[31]  arXiv:1507.08914 [pdf]
Title: Confirmation of the OGLE-2005-BLG-169 planet signature and characteristics with lens-source proper motion detection
Comments: 9 pages, 5 figures
Journal-ref: ApJ, 808, 170, 2015
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

We present Keck NIRC2 high angular resolution adaptive optics observations of the microlensing event OGLE-2005-BLG-169, taken 8.21 years after the discovery of this planetary system. For the first time for a microlensing planetary event, the source and the lens are completely resolved, providing a precise measurement of their heliocentric relative proper motion, $\mu_{\rm{rel},\rm{helio}}=7.44 \pm 0.17$ mas yr$^{-1}$. This confirms and refines the initial model presented in the discovery paper and rules out a range of solutions that were allowed by the microlensing light curve. This is also the first time that parameters derived from a microlensing planetary signal are confirmed, both with Keck measurements, presented in this paper, and independent measurements obtained with the Hubble Space Telescope in I, V and B bands, presented in a companion paper. Hence, this new measurement of $\mu_{\rm{rel},\rm{helio}}$, as well as the measured brightness of the lens in H band, enabled the mass and distance of the system to be updated: a Uranus-mass planet ($m_\rm{p}=13.2\pm 1.3 M_\oplus$) orbiting a K5-type main sequence star ($M_*=0.65\pm 0.05 M_\odot$) separated by $a_\perp=3.4\pm 0.3$ AU, at the distance $D_\rm{L}=4.0\pm 0.4$ kpc from us.

[32]  arXiv:1507.08932 [pdf, other]
Title: Calibrating the absolute amplitude scale for air showers measured at LOFAR
Comments: Prepared for submission to JINST
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); High Energy Astrophysical Phenomena (astro-ph.HE)

Air showers induced by cosmic rays create nanosecond pulses detectable at radio frequencies. These pulses have been measured successfully in the past few years at the LOw- Frequency ARray (LOFAR) and are used to study the properties of cosmic rays. For a complete understanding of this phenomenon and the underlying physical processes, an absolute calibration of the detecting antenna system is needed. We present three approaches that were used to check and improve the antenna model of LOFAR and to provide an absolute calibration for air shower measurements. Two methods are based on calibrated reference sources and one on a calibration approach using the diffuse radio emission of the Galaxy, optimized for short data-sets. An accuracy of 35% in amplitude is reached. The absolute calibration is also compared to predictions from air shower simulations. These results are used to set an absolute energy scale for air shower measurements and can be used as a basis for an absolute scale for the measurement of astronomical transients with LOFAR.

[33]  arXiv:1507.08950 [pdf, ps, other]
Title: An HI View of Galaxy Conformity: HI-rich Environment around HI-excess Galaxies
Comments: 15 pages, 13 figures. Accepted for publication in MNRAS
Subjects: Astrophysics of Galaxies (astro-ph.GA)

Using data taken as part of the Bluedisk project we study the connection between neutral hydrogen (HI) in the environment of spiral galaxies and that in the galaxies themselves. We measure the total HI mass present in the environment in a statistical way by studying the distribution of noise peaks in the HI data cubes obtained for 40 galaxies observed with WSRT. We find that galaxies whose HI mass fraction is high relative to standard scaling relations have an excess HI mass in the surrounding environment as well. Gas in the environment consists of gas clumps which are individually below the detection limit of our HI data. These clumps may be hosted by small satellite galaxies and\or be the high-density peaks of a more diffuse gas distribution in the inter-galactic medium. We interpret this result as an indication for a picture in which the HI-rich central galaxies accrete gas from an extended gas reservoir present in their environment.

[34]  arXiv:1507.08960 [pdf, other]
Title: Testing light-traces-mass in Hubble Frontier Fields Cluster MACS-J0416.1-2403
Comments: submitted to MNRAS, 9 pages, 6 figures
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We reconstruct the projected mass distribution of a massive merging Hubble Frontier Fields cluster MACSJ0416 using the genetic algorithm based free-form technique called Grale. The reconstructions are constrained by 149 lensed images identified by Jauzac et al. using HFF data. No information about cluster galaxies or light is used, which makes our reconstruction unique in this regard. Using visual inspection of the maps, as well as galaxy-mass correlation functions we conclude that overall light does follow mass. Furthermore, the fact that brighter galaxies are more strongly clustered with mass is an important confirmation of the standard biasing scenario in galaxy clusters. On the smallest scales, approximately less than a few arcseconds the resolution afforded by 149 images is still not sufficient to confirm or rule out galaxy-mass offsets of the kind observed in ACO 3827. We also compare the mass maps of MACSJ0416 obtained by three different groups: Grale, and two parametric Lenstool reconstructions from the CATS and Sharon/Johnson teams. Overall, the three agree well; one interesting discrepancy between Grale and Lenstool galaxy-mass correlation functions occurs on scales of tens of kpc and may suggest that cluster galaxies are more biased tracers of mass than parametric methods generally assume.

[35]  arXiv:1507.08972 [pdf, other]
Title: Baryon Acoustic Oscillations from the SDSS DR10 galaxies angular correlation function
Comments: 9 pages, 5 figures
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc)

The 2-point angular correlation function $w(\theta)$ (2PACF), where $\theta$ is the angular separation between pairs of galaxies, provides the transversal Baryon Acoustic Oscillation (BAO) signal almost model-independently. In this paper we use 409,337 luminous red galaxies in the redshift range $z = [0.440,0.555]$ obtained from the tenth data release of the Sloan Digital Sky Survey (SDSS DR10) to estimate $\theta_{\rm{BAO}}(z)$ from the 2PACF at six redshift {shells}. Since noise and systematics can hide the BAO signature in the $w - \theta$ plane, we also discuss some criteria to localize the acoustic bump. We identify two sources of model-dependence in the analysis, namely, the value of the acoustic scale from Cosmic Microwave Background (CMB) measurements and the correction in the $\theta_{\rm{BAO}}(z)$ position due to projection effects. Constraints on the dark energy equation-of-state parameter w$(z)$ from the $\theta_{\rm{BAO}}(z)$ diagram are derived, as well as from a joint analysis with current CMB measurements. We find that the standard $\Lambda$CDM model as well as some of its extensions are in good agreement with these $\theta_{\rm{BAO}}(z)$ measurements.

[36]  arXiv:1507.08977 [pdf, other]
Title: NuSTAR observations of the young, energetic radio pulsar PSR B1509-58
Comments: 10 pages, 8 figures, 6 tables, submitted to ApJ
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

We report on Nuclear Spectroscopic Telescope Array (NuSTAR) hard X-ray observations of the young rotation-powered radio pulsar PSR B1509$-$58 in the supernova remnant MSH 15$-$52. We confirm the previously reported curvature in the hard X-ray spectrum, showing that a log parabolic model provides a statistically superior fit to the spectrum compared with the standard power law. The log parabolic model describes the NuSTAR data, as well as previously published gamma-ray data obtained with COMPTEL and AGILE, all together spanning 3 keV through 500 MeV. Our spectral modelling allows us to constrain the peak of the broadband high energy spectrum to be at 2.6$\pm$0.8 MeV, an improvement of nearly an order of magnitude over previous measurements. In addition, we calculate NuSTAR spectra in 26 pulse phase bins and confirm previously reported variations of photon indices with phase. Finally, we measure the pulsed fraction of PSR B1509$-$58 in the hard X-ray energy band for the first time. Using the energy resolved pulsed fraction results, we estimate that the pulsar's DC component has a photon index value between 1.26 and 1.96. Our results support a model in which the pulsar's lack of GeV emission is due to viewing geometry, with the X-rays originating from synchrotron emission from secondary pairs in the magnetosphere.

[37]  arXiv:1507.08991 [pdf, other]
Title: Performance of two Askaryan Radio Array stations and first results in the search for ultra-high energy neutrinos
Comments: 21 pages, 34 figures, 1 table, includes supplementary material
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Instrumentation and Methods for Astrophysics (astro-ph.IM)

Ultra-high energy neutrinos are interesting messenger particles since, if detected, they can transmit exclusive information about ultra-high energy processes in the Universe. These particles, with energies above $10^{16}\mathrm{eV}$, interact very rarely. Therefore, detectors that instrument several gigatons of matter are needed to discover them. The ARA detector is currently being constructed at South Pole. It is designed to use the Askaryan effect, the emission of radio waves from neutrino-induced cascades in the South Pole ice, to detect neutrino interactions at very high energies. With antennas distributed among 37 widely-separated stations in the ice, such interactions can be observed in a volume of several hundred cubic kilometers. Currently 3 deep ARA stations are deployed in the ice of which two have been taking data since the beginning of the year 2013. In this publication, the ARA detector "as-built" and calibrations are described. Furthermore, the data reduction methods used to distinguish the rare radio signals from overwhelming backgrounds of thermal and anthropogenic origin are presented. Using data from only two stations over a short exposure time of 10 months, a neutrino flux limit of $3 \cdot 10^{-6} \mathrm{GeV} / (\mathrm{cm^2 \ s \ sr})$ is calculated for a particle energy of 10^{18}eV, which offers promise for the full ARA detector.

[38]  arXiv:1507.08995 [pdf, other]
Title: Search for gamma-ray emission from the Coma Cluster with six years of Fermi-LAT data
Comments: 9 pages, 4 figures, 2 tables, submitted to ApJ; corresponding authors: S. Zimmer, J. Conrad, O. Reimer & Y. Rephaeli
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

We present results from gamma-ray observations of the Coma cluster incorporating 6 years of Fermi-LAT data and the newly released "Pass 8" event-level analysis. Our analysis of the region reveals low-significance residual structures within the virial radius of the cluster that are too faint for a detailed investigation with the current data. Using a likelihood approach that is free of assumptions on the spectral shape we derive upper limits on the gamma-ray flux that is expected from energetic particle interactions in the cluster. We also consider a benchmark spatial and spectral template motivated by models in which the observed radio halo is mostly emission by secondary electrons. In this case, the median expected and observed upper limits for the flux above 100 MeV are 1.7x10-9 ph/cm2/s and 4.2x10-9 ph/cm2/s respectively. These bounds are comparable to several recent predictions for the hadronic gamma-ray emission in such secondary models, although direct comparisons are sensitive to assumptions regarding the magnetic field strength and other factors. The minimal expected gamma-ray flux from radio and star-forming galaxies within the Coma cluster is roughly an order of magnitude below the median sensitivity of our analysis.