Publications


A STRINGENT LIMIT on the AMPLITUDE of ALFVÉNIC PERTURBATIONS in HIGH-BETA LOW-COLLISIONALITY PLASMAS

Astrophysical Journal Letters 830 (2016)

J Squire, E Quataert, AA Schekochihin

© 2016. The American Astronomical Society. All rights reserved.It is shown that low-collisionality plasmas cannot support linearly polarized shear-Alfvén fluctuations above a critical amplitude δB⊥/B0 ∼ B-1/2, where β is the ratio of thermal to magnetic pressure. Above this cutoff, a developing fluctuation will generate a pressure anisotropy that is sufficient to destabilize itself through the parallel firehose instability. This causes the wave frequency to approach zero, interrupting the fluctuation before any oscillation. The magnetic field lines rapidly relax into a sequence of angular zig-zag structures. Such a restrictive bound on shear-Alfvén-wave amplitudes has far-reaching implications for the physics of magnetized turbulence in the high-β conditions prevalent in many astrophysical plasmas, as well as for the solar wind at ∼1 au where β ≳ 1.


The violent white dwarf merger scenario for the progenitors of Type Ia supernovae

Monthly Notices of the Royal Astronomical Society 461 (2016) 3653-3662

DD Liu, B Wang, P Podsiadlowski, Z Han

© 2016 The Authors.Recent observations suggest that some Type Ia supernovae (SNe Ia) originate from the merging of two carbon-oxygen white dwarfs (CO WDs). Meanwhile, recent hydrodynamical simulations have indicated that the accretion-induced collapse may be avoided under certain conditions when double WDs merge violently. However, the properties of SNe Ia from this violent merger scenario are highly dependent on a particular mass-accretion stage, the so-called WD + He subgiant channel, during which the primary WD is able to increase its mass by accreting He-rich material from an He subgiant before the systems evolves into a doubleWD system. In this paper, we aim to study this particular evolutionary stage systematically and give the properties of violentWDmergers. By employing the Eggleton stellar evolution code, we followed a large number of binary calculations and obtained the regions in parameter space for producing violent mergers based on the WD + He subgiant channel. According to these simulations, we found that the primary WDs can increase their mass by ∼0.10-0.45M⊙ during the massaccretion stage. We then conducted a series of binary population synthesis calculations and found that the Galactic SN Ia birthrate from this channel is about 0.01-0.4 × 10-3 yr-1. This suggests that the violent WD mergers from this channel may only contribute to ∼0.3-10 per cent of all SNe Ia in our Galaxy. The delay times of violent WD mergers from this channel are ≥1.7Gyr, contributing to the SNe Ia in old populations. We also found that the WD + He subgiant channel is the dominant way for producing violent WD mergers that may be able to eventually explode as SNe Ia.


Searches for Sterile Neutrinos with the IceCube Detector.

Physical review letters 117 (2016) 071801-

MG Aartsen, K Abraham, M Ackermann, J Adams, JA Aguilar, M Ahlers, M Ahrens, D Altmann, K Andeen, T Anderson, I Ansseau, G Anton, M Archinger, C Argüelles, TC Arlen, J Auffenberg, S Axani, X Bai, SW Barwick, V Baum, R Bay, JJ Beatty, J Becker Tjus, KH Becker, S BenZvi, P Berghaus, D Berley, E Bernardini, A Bernhard, DZ Besson, G Binder, D Bindig, E Blaufuss, S Blot, DJ Boersma, C Bohm, M Börner, F Bos, D Bose, S Böser, O Botner, J Braun, L Brayeur, HP Bretz, A Burgman, J Casey, M Casier, E Cheung, D Chirkin, A Christov, K Clark, L Classen, S Coenders, GH Collin, JM Conrad, DF Cowen, AH Cruz Silva, J Daughhetee, JC Davis, M Day, JP de André, C De Clercq, E Del Pino Rosendo, H Dembinski, S De Ridder, P Desiati, KD de Vries, G de Wasseige, M de With, T DeYoung, JC Díaz-Vélez, V di Lorenzo, H Dujmovic, JP Dumm, M Dunkman, B Eberhardt, T Ehrhardt, B Eichmann, S Euler, PA Evenson, S Fahey, AR Fazely, J Feintzeig, J Felde, K Filimonov, C Finley, S Flis, CC Fösig, T Fuchs, TK Gaisser, R Gaior, J Gallagher, L Gerhardt, K Ghorbani, W Giang, L Gladstone, T Glüsenkamp, A Goldschmidt, G Golup, JG Gonzalez, D Góra, D Grant, Z Griffith, A Haj Ismail, A Hallgren, F Halzen, E Hansen, K Hanson, D Hebecker, D Heereman, K Helbing, R Hellauer, S Hickford, J Hignight, GC Hill, KD Hoffman, R Hoffmann, K Holzapfel, A Homeier, K Hoshina, F Huang, M Huber, W Huelsnitz, K Hultqvist, S In, A Ishihara, E Jacobi, GS Japaridze, M Jeong, K Jero, BJ Jones, M Jurkovic, A Kappes, T Karg, A Karle, U Katz, M Kauer, A Keivani, JL Kelley, A Kheirandish, M Kim, T Kintscher, J Kiryluk, T Kittler, SR Klein, G Kohnen, R Koirala, H Kolanoski, L Köpke, C Kopper, S Kopper, DJ Koskinen, M Kowalski, K Krings, M Kroll, G Krückl, C Krüger, J Kunnen, S Kunwar, N Kurahashi, T Kuwabara, M Labare, JL Lanfranchi, MJ Larson, D Lennarz, M Lesiak-Bzdak, M Leuermann, L Lu, J Lünemann, J Madsen, G Maggi, KB Mahn, S Mancina, M Mandelartz, R Maruyama, K Mase, R Maunu, F McNally, K Meagher, M Medici, M Meier, A Meli, T Menne, G Merino, T Meures, S Miarecki, E Middell, L Mohrmann, T Montaruli, M Moulai, R Nahnhauer, U Naumann, G Neer, H Niederhausen, SC Nowicki, DR Nygren, A Obertacke Pollmann, A Olivas, A Omairat, A O'Murchadha, T Palczewski, H Pandya, DV Pankova, JA Pepper, C Pérez de Los Heros, C Pfendner, D Pieloth, E Pinat, J Posselt, PB Price, GT Przybylski, M Quinnan, C Raab, M Rameez, K Rawlins, M Relich, E Resconi, W Rhode, M Richman, B Riedel, S Robertson, C Rott, T Ruhe, D Ryckbosch, D Rysewyk, L Sabbatini, J Salvado, SE Sanchez Herrera, A Sandrock, J Sandroos, S Sarkar, K Satalecka, P Schlunder, T Schmidt, S Schöneberg, A Schönwald, D Seckel, S Seunarine, D Soldin, M Song, GM Spiczak, C Spiering, M Stamatikos, T Stanev, A Stasik, A Steuer, T Stezelberger, RG Stokstad, A Stößl, R Ström, NL Strotjohann, GW Sullivan, M Sutherland, H Taavola, I Taboada, J Tatar, S Ter-Antonyan, A Terliuk, G Tešić, S Tilav, PA Toale, MN Tobin, S Toscano, D Tosi, M Tselengidou, A Turcati, E Unger, M Usner, S Vallecorsa, J Vandenbroucke, N van Eijndhoven, S Vanheule, M van Rossem, J van Santen, J Veenkamp, M Voge, M Vraeghe, C Walck, A Wallace, N Wandkowsky, C Weaver, C Wendt, S Westerhoff, BJ Whelan, K Wiebe, L Wille, DR Williams, L Wills, H Wissing, M Wolf, TR Wood, E Woolsey, K Woschnagg, DL Xu, XW Xu, Y Xu, JP Yanez, G Yodh, S Yoshida, M Zoll

The IceCube neutrino telescope at the South Pole has measured the atmospheric muon neutrino spectrum as a function of zenith angle and energy in the approximate 320 GeV to 20 TeV range, to search for the oscillation signatures of light sterile neutrinos. No evidence for anomalous ν_{μ} or ν[over ¯]_{μ} disappearance is observed in either of two independently developed analyses, each using one year of atmospheric neutrino data. New exclusion limits are placed on the parameter space of the 3+1 model, in which muon antineutrinos experience a strong Mikheyev-Smirnov-Wolfenstein-resonant oscillation. The exclusion limits extend to sin^{2}2θ_{24}≤0.02 at Δm^{2}∼0.3  eV^{2} at the 90% confidence level. The allowed region from global analysis of appearance experiments, including LSND and MiniBooNE, is excluded at approximately the 99% confidence level for the global best-fit value of |U_{e4}|^{2}.


Sensitivity of detachment extent to magnetic configuration and external parameters

Nuclear Fusion 56 (2016)

B Lipschultz, FI Parra, IH Hutchinson

© 2016 IAEA, Vienna.Divertor detachment may be essential to reduce heat loads to magnetic fusion tokamak reactor divertor surfaces. Yet in experiments it is difficult to control the extent of the detached, low pressure, plasma region. At maximum extent the front edge of the detached region reaches the X-point and can lead to degradation of core plasma properties. We define the 'detachment window' in a given position control variable C (for example, the upstream plasma density) as the range in C within which the front location can be stably held at any position from the target to the X-point; increased detachment window corresponds to better control. We extend a 1D analytic model [1] to determine the detachment window for the following control variables: the upstream plasma density, the impurity concentration and the power entering the scrape-off layer (SOL). We find that variations in magnetic configuration can have strong effects; increasing the ratio of the total magnetic field at the X-point to that at the target,Bx/Bt, (total flux expansion, as in the super-x divertor configuration) strongly increases the detachment window for all control variables studied, thus strongly improving detachment front control and the capability of the divertor plasma to passively accommodate transients while still staying detached. Increasing flux tube length and thus volume in the divertor, through poloidal flux expansion (as in the snowflake or x-divertor configurations) or length of the divertor, also increases the detachment window, but less than the total flux expansion does. The sensitivity of the detachment front location, zh, to each control variable, C, defined as , depends on the magnetic configuration. The size of the radiating volume and the total divertor radiation increase ∝ (Bx/Bt)2 and ∝ Bx/Bt, respectively, but not by increasing divertor poloidal flux expansion or field line length. We believe this model is applicable more generally to any thermal fronts in flux tubes with varying magnetic field, and similar sources and sinks, such as detachment fronts in stellarator divertors and solar prominences in coronal loops.


Proton imaging of an electrostatic field structure formed in laser-produced counter-streaming plasmas

Journal of Physics: Conference Series 688 (2016)

T Morita, NL Kugland, W Wan, R Crowston, RP Drake, F Fiuza, G Gregori, C Huntington, T Ishikawa, M Koenig, C Kuranz, MC Levy, D Martinez, J Meinecke, F Miniati, CD Murphy, A Pelka, C Plechaty, R Presura, N Quirós, BA Remington, B Reville, JS Ross, DD Ryutov, Y Sakawa, L Steele, H Takabe, Y Yamaura, N Woolsey, HS Park

© Published under licence by IOP Publishing Ltd.We report the measurements of electrostatic field structures associated with an electrostatic shock formed in laser-produced counter-streaming plasmas with proton imaging. The thickness of the electrostatic structure is estimated from proton images with different proton kinetic energies from 4.7 MeV to 10.7 MeV. The width of the transition region is characterized by electron scale length in the laser-produced plasma, suggesting that the field structure is formed due to a collisionless electrostatic shock.


A laboratory model of post-Newtonian gravity with high power lasers and 4th generation light sources

Classical and Quantum Gravity 33 (2016)

G Gregori, MC Levy, MA Wadud, BJB Crowley, R Bingham

© 2016 IOP Publishing Ltd.Using the post-Newtonian formalism of gravity, we attempt to calculate the x-ray Thomson scattering cross section of electrons that are accelerated in the field of a high intensity optical laser. We show that our results are consistent with previous calculations, suggesting that the combination of high power laser and 4th generation light sources may become a powerful platform to test models exploring high order corrections to the Newtonian gravity.


Search for astrophysical tau neutrinos in three years of IceCube data

PHYSICAL REVIEW D 93 (2016)

MG Aartsen, K Abraham, M Ackermann, J Adams, JA Aguilar, M Ahlers, M Ahrens, D Altmann, T Anderson, I Ansseau, M Archinger, C Arguelles, TC Arlen, J Auffenberg, X Bai, SW Barwick, V Baum, R Bay, JJ Beatty, JB Tjus, K-H Becker, E Beiser, S BenZvi, P Berghaus, D Berley, E Bernardini, A Bernhard, DZ Besson, G Binder, D Bindig, M Bissok, E Blaufuss, J Blumenthal, DJ Boersma, C Bohm, M Boerner, F Bos, D Bose, S Boeser, O Botner, J Braun, L Brayeur, H-P Bretz, N Buzinsky, J Casey, M Casier, E Cheung, D Chirkin, A Christov, K Clark, L Classen, S Coenders, DF Cowen, AHC Silva, J Daughhetee, JC Davis, M Day, JPAM de Andre, C De Clercq, EDP Rosendo, H Dembinski, S De Ridder, P Desiati, KD de Vries, G de Wasseige, M de With, T De Young, JC Diaz-Velez, V di Lorenzo, JP Dumm, M Dunkman, R Eagan, B Eberhardt, T Ehrhardt, B Eichmann, S Euler, PA Evenson, O Fadiran, S Fahey, AR Fazely, A Fedynitch, J Feintzeig, J Felde, K Filimonov, C Finley, T Fischer-Wasels, S Flis, C-C Foesig, T Fuchs, TK Gaisser, R Gaior, J Gallagher, L Gerhardt, K Ghorbani, D Gier, L Gladstone, M Glagla, T Gluesenkamp, A Goldschmidt, G Golup, JG Gonzalez, D Gora, D Grant, JC Groh, A Gross, C Ha, C Haack, AH Ismail, A Hallgren, F Halzen, E Hansen, B Hansmann, K Hanson, D Hebecker, D Heereman, K Helbing, R Hellauer, S Hickford, J Hignight, GC Hill, KD Hoffman, R Hoffmann, K Holzapfel, A Homeier, K Hoshina, F Huang, M Huber, W Huelsnitz, PO Hulth, K Hultqvist, S In, A Ishihara, E Jacobi, GS Japaridze, K Jero, M Jurkovic, A Kappes, T Karg, A Karle, M Kauer, A Keivani, JL Kelley, J Kemp, A Kheirandish, J Kiryluk, J Klaes, SR Klein, G Kohnen, R Koirala, H Kolanoski, R Konietz, L Koepke, C Kopper, S Kopper, DJ Koskinen, M Kowalski, K Krings, G Kroll, M Kroll, J Kunnen, N Kurahashi, T Kuwabara, M Labare, JL Lanfranchi, MJ Larson, M Lesiak-Bzdak, M Leuermann, J Leuner, L Lu, J Luenemann, J Madsen, G Maggi, KBM Mahn, R Maruyama, K Mase, HS Matis, R Maunu, F McNally, K Meagher, M Medici, A Meli, T Menne, G Merino, T Meures, S Miarecki, E Middell, E Middlemas, L Mohrmann, T Montaruli, R Morse, R Nahnhauer, U Naumann, G Neer, H Niederhausen, SC Nowicki, DR Nygren, A Obertacke, A Olivas, A Omairat, A O'Murchadha, T Palczewski, H Pandya, DV Pankova, L Paul, CPDL Heros, C Pfendner, D Pieloth, E Pinat, J Posselt, PB Price, GT Przybylski, J Puetz, M Quinnan, C Raab, L Raedel, M Rameez, K Rawlins, R Reimann, M Relich, E Resconi, W Rhode, M Richman, S Richter, B Riedel, S Robertson, M Rongen, C Rott, T Ruhe, D Ryckbosch, SM Saba, L Sabbatini, H-G Sander, A Sandrock, J Sandroos, S Sarkar, K Schatto, F Scheriau, M Schimp, T Schmidt, M Schmitz, S Schoenen, S Schoeneberg, A Schoenwald, L Schulte, D Seckel, S Seunarine, MWE Smith, D Soldin, M Song, GM Spiczak, C Spiering, M Stahlberg, M Stamatikos, T Stanev, NA Stanisha, A Stasik, T Stezelberger, RG Stokstad, A Stoessl, R Stroem, NL Strotjohann, GW Sullivan, M Sutherland, H Taavola, I Taboada, J Tatar, S Ter-Antonyan, A Terliuk, G Tesic, S Tilav, PA Toale, MN Tobin, S Toscano, D Tosi, M Tselengidou, A Turcati, E Unger, M Usner, S Vallecorsa, J Vandenbroucke, N van Eijndhoven, S Vanheule, J van Santen, J Veenkamp, M Vehring, M Voge, M Vraeghe, C Walck, A Wallace, M Wallraff, N Wandkowsky, C Weaver, C Wendt, S Westerhoff, BJ Whelan, N Whitehorn, K Wiebe, CH Wiebusch, L Wille, DR Williams, H Wissing, M Wolf, TR Wood, K Woschnagg, DL Xu, XW Xu, Y Xu, JP Yanez, G Yodh, S Yoshida, M Zoll, I Collaboration


Numerical study of neutron beam divergence in a beam-fusion scenario employing laser driven ions

Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 829 (2016) 176-180

A Alejo, A Green, H Ahmed, APL Robinson, M Cerchez, R Clarke, D Doria, S Dorkings, J Fernandez, P McKenna, SR Mirfayzi, K Naughton, D Neely, P Norreys, C Peth, H Powell, JA Ruiz, J Swain, O Willi, M Borghesi, S Kar

© 2016 Elsevier B.V.The most established route to create a laser-based neutron source is by employing laser accelerated, low atomic-number ions in fusion reactions. In addition to the high reaction cross-sections at moderate energies of the projectile ions, the anisotropy in neutron emission is another important feature of beam-fusion reactions. Using a simple numerical model based on neutron generation in a pitcher–catcher scenario, anisotropy in neutron emission was studied for the deuterium–deuterium fusion reaction. Simulation results are consistent with the narrow-divergence (∼70° full width at half maximum) neutron beam recently served in an experiment employing multi-MeV deuteron beams of narrow divergence (up to 30° FWHM, depending on the ion energy) accelerated by a sub-petawatt laser pulse from thin deuterated plastic foils via the Target Normal Sheath Acceleration mechanism. By varying the input ion beam parameters, simulations show that a further improvement in the neutron beam directionality (i.e. reduction in the beam divergence) can be obtained by increasing the projectile ion beam temperature and cut-off energy, as expected from interactions employing higher power lasers at upcoming facilities.


Age-velocity dispersion relations and heating histories in disc galaxies

Monthly Notices of the Royal Astronomical Society 462 (2016) 1697-1713

M Aumer, J Binney, R Schönrich

© 2016 The Authors.We analyse the heating of stellar discs by non-axisymmetric structures and giant molecular clouds (GMCs) in N-body simulations of growing disc galaxies. The analysis resolves long-standing discrepancies between models and data by demonstrating the importance of distinguishing between measured age-velocity dispersion relations (AVRs) and the heating histories of the stars that make up the AVR. We fit both AVRs and heating histories with formulae ∝tβ and determine the exponents βR and βz derived from in-plane and vertical AVRs and β~R and β~z from heating histories. Values of βz are in almost all simulations larger than values of β~z, whereas values of βR are similar to or mildly larger than values of β~R. Moreover, values of βz (β~z) are generally larger than values of βR (β~R). The dominant cause of these relations is the decline over the life of the disc in importance of GMCs as heating agents relative to spiral structure and the bar. We examine how age errors and biases in solar neighbourhood surveys influence the measured AVR: they tend to decrease β values by smearing out ages and thus measured dispersions. We compare AVRs and velocity ellipsoid shapes σz/σR from simulations to solar neighbourhood data. We conclude that for the expected disc mass and dark halo structure, combined GMC and spiral/bar heating can explain the AVR of the Galactic thin disc. Strong departures of the disc mass or the dark halo structure from expectation spoil fits to the data.


Pressure-anisotropy-driven microturbulence and magnetic-field evolution in shearing, collisionless plasma

Monthly Notices of the Royal Astronomical Society 459 (2016) 2701-2720

S Melville, AA Schekochihin, MW Kunz

© 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.The non-linear state of a high-beta collisionless plasma is investigated where an imposed shear amplifies or diminishes a uniform mean magnetic field, driving pressure anisotropies and, therefore, firehose or mirror instabilities. To mimic the local behaviour of a macroscopic flow, the shear is switched off or reversed after one shear time, so a new macroscale configuration is superimposed on previous microscale state. A threshold plasma beta is found: when β ≪ Ω/S (ion cyclotron frequency/shear rate), the emergence/disappearance of firehose or mirror fluctuations is quasi-instantaneous compared to the shear time (lending some credence to popular closures that assume this). This follows from the free decay of these fluctuations being constrained by the same marginal-stability conditions as their growth in the unstable regime, giving the decay time ~β/Ω ≪ S-1. In contrast, when β ≳ Ω/S, the old microscale state only disappears on the shear time-scale. In this 'ultra-high-beta' regime, driven firehose fluctuations grow secularly to order-unity amplitudes, compensating for the decrease of the mean field and thus pinning the pressure anisotropy at marginal stability without scattering particles - unlike what happens at moderate β. After the shear reverses, the shearing away of these fluctuations compensates for the increase of the mean field and thus prevents growth of the pressure anisotropy, so the system stays close to the firehose threshold, does not go mirror-unstable, the total magnetic energy barely changing at all. Implications for various astrophysical situations, especially the origin of cosmic magnetism, are discussed: collisionless effects appear mostly beneficial to fast magnetic-field generation.


Turbulent dynamo in a collisionless plasma

PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA 113 (2016) 3950-3953

F Rincon, F Califano, AA Schekochihin, F Valentini


Torus mapper: a code for dynamical models of galaxies

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 456 (2016) 1982-1998

J Binney, PJ McMillan


THE SEARCH FOR TRANSIENT ASTROPHYSICAL NEUTRINO EMISSION WITH ICECUBE-DEEPCORE

ASTROPHYSICAL JOURNAL 816 (2016) ARTN 75

MG Aartsen, K Abraham, M Ackermann, J Adams, JA Aguilar, M Ahlers, M Ahrens, D Altmann, T Anderson, I Ansseaus, M Archinger, C Arguelles, TC Arlen, J Auffenberg, X Bai, SW Barwick, V Baum, R Bay, JJ Beatty, JB Tjus, K-H Becker, E Beiser, S Benzvi, P Berghaus, D Berley, E Bernardini, A Bernhard, DZ Besson, G Binder, D Bindig, M Bissoki, E Blaufuss, J Blumenthal, DJ Boersma, C Bohm, M Boerner, F Bos, D Bose, S Boeser, O Botner, J Braun, L Brayeur, H-P Bretz, N Buzinsky, J Casey, M Casier, E Cheung, D Chirkin, A Christov, K Clark, L Classen, S Coenders, DF Cowen, AHC Silva, J Daughhetee, JC Davis, M Day, JPAM de Andre, C De Clercq, E del Pino Rosendo, H Dembinski, S De Ridder, P Desiati, KD de Vries, G de Wasseige, M de With, T DeYoung, JC Diaz-Velez, V di Lorenzo, JP Dumm, M Dunkman, R Eagan, B Eberhardt, T Ehrhardt, B Eichmann, S Euler, PA Evenson, O Fadiran, S Fahey, AR Fazely, A Fedynitch, J Feintzeig, J Felde, K Filimonov, C Finley, T Fischer-Wasels, S Flis, C-C Foesig, T Fucus, TK Gaisser, R Gaior, J Gallagher, L Gerhardt, K Ghorbani, D Gier, L Gladstone, M Glagla, T Gluesenkamp, A Goldschmidt, G Golup, JG Gonzalez, D Gora, D Grant, JC Groii, A Gross, C Ha, C Haack, AH Ismail, A Hallgren, F Halzen, E Hansen, B Hansmann, K Hanson, D Hebecker, D Heereman, K Helbing, R Hellauer, S Hickford, J Hignigiit, GC Hill, KD Hoffman, R Hoffmann, K Holzapfel, A Homeier, K Hoshina, F Huang, M Huber, W Huelsnitz, PO Hulth, K Hultqvist, S In, A Ishihara, E Jacobi, GS Japaridze, K Jero, M Jurkovic, A Kappes, T Karg, A Karle, M Kauer, A Keivani, JL Kelley, J Kemp, A Kheirandish, J Kiryluk, J Klaes, SR Klein, G Kohnen, R Koirala, H Kolanoski, R Konietz, L Koepke, C Kopper, S Kopper, DJ Koskinen, M Kowalski, K Krings, G Kroll, M Kroll, J Kunnen, N Kurahashi, T Kuwabara, M Labare, JL Lanfranchi, MJ Larson, M Lesiak-Bzdak, M Leuermann, J Leuner, L Lu, J Lunemann, J Madsen, G Maggi, KBM Mahn, R Maruyama, K Mase, HS Matis, R Maunu, F McNally, K Meagher, M Medici, A Meli, T Menne, G Merino, T Meuress, S Miarecki, E Middell, E Middlemas, L Mohrmann, T Montaruli, R Morse, R Nahnhauer, U Naumann, G Neer, H Niederhausen, SC Nowicki, DR Nygren, A Obertacke, A Olivas, A Omairat, A O'Murchadha, T Palczewski, H Pandya, DV Pankova, L Paul, JA Pepper, C Perez de los Heros, C Pfendner, D Pieloth, E Pinat, J Posselt, PB Price, GT Przybylski, J Puetz, M Quinnan, C Raab, L Raedel, M Rameez, K Rawlins, R Reimann, M Relich, E Resconi, W Rhode, M Richman, S Richter, B Riedel, S Robertson, M Rongen, C Rott, T Ruhe, D Ryckbosch, SM Saba, L Sabbatini, H-G Sander, A Sandrock, J Sandroos, S Sarkar, K Schatto, F Scheriau, M Schimp, T Schmidt, M Schmitz, S Schoenen, S Schoeneberg, A Schoenwald, L Schulte, D Seckel, S Seunarine, MWE Smith, D Soldin, M Song, GM Spiczak, C Spiering, M Stahlberg, M Stamatikos, T Stanev, NA Stanisha, A Stasik, T Stezelberger, RG Stokstad, A Stoessl, R Strom, NL Strotjohann, GW Sullivan, M Sutherland, H Taavola, I Taboada, J Tatar, S Ter-Antonyan, A Terliuk, G Tesic, S Tilav, PA Toale, MN Tobin, S Toscano, D Tosi, M Tselengidou, A Turcati, E Unger, M Usner, S Vallecorsa, J Vandenbroucke, N van Eundhoven, S Vanheule, J van Santen, J Veenkamp, M Vehring, M Voge, M Vraeghe, C Walck, A Wallace, M Wallraff, N Wandkowsky, C Weaver, C Wendt, S Westerhoff, BJ Whelan, N Whitehorn, K Wiebe, CH Wiebusch, L Wille, DR Williams, H Wissing, M Wolf, TR Wood, K Woschnagg, DL Xu, XW Xu, Y Xu, JP Yanez, G Yodh, S Yoshida, M Zoll


High-energy neutrino follow-up search of gravitational wave event GW150914 with ANTARES and IceCube

Physical Review D 93 (2016)

S Adrián-Martínez, A Albert, M André, M Anghinolfi, G Anton, M Ardid, JJ Aubert, T Avgitas, B Baret, J Barrios-Martí, S Basa, V Bertin, S Biagi, R Bormuth, MC Bouwhuis, R Bruijn, J Brunner, J Busto, A Capone, L Caramete, J Carr, S Celli, T Chiarusi, M Circella, A Coleiro, R Coniglione, H Costantini, P Coyle, A Creusot, A Deschamps, G De Bonis, C Distefano, C Donzaud, D Dornic, D Drouhin, T Eberl, I El Bojaddaini, D Elsässer, A Enzenhöfer, K Fehn, I Felis, LA Fusco, S Galatà, P Gay, S Geißelsöder, K Geyer, V Giordano, A Gleixner, H Glotin, R Gracia-Ruiz, K Graf, S Hallmann, H Van Haren, AJ Heijboer, Y Hello, JJ Hernández-Rey, J Hößl, J Hofestädt, C Hugon, G Illuminati, CW James, M De Jong, M Jongen, M Kadler, O Kalekin, U Katz, D Kießling, A Kouchner, M Kreter, I Kreykenbohm, V Kulikovskiy, C Lachaud, R Lahmann, D Lefèvre, E Leonora, S Loucatos, M Marcelin, A Margiotta, A Marinelli, JA Martínez-Mora, A Mathieu, K Melis, T Michael

© 2016 American Physical Society.We present the high-energy-neutrino follow-up observations of the first gravitational wave transient GW150914 observed by the Advanced LIGO detectors on September 14, 2015. We search for coincident neutrino candidates within the data recorded by the IceCube and Antares neutrino detectors. A possible joint detection could be used in targeted electromagnetic follow-up observations, given the significantly better angular resolution of neutrino events compared to gravitational waves. We find no neutrino candidates in both temporal and spatial coincidence with the gravitational wave event. Within ±500 s of the gravitational wave event, the number of neutrino candidates detected by IceCube and Antares were three and zero, respectively. This is consistent with the expected atmospheric background, and none of the neutrino candidates were directionally coincident with GW150914. We use this nondetection to constrain neutrino emission from the gravitational-wave event.


AWAKE: A Proton-Driven Plasma Wakefield Acceleration Experiment at CERN

Nuclear and Particle Physics Proceedings 273-275 (2016) 175-180

C Bracco, LD Amorim, R Assmann, F Batsch, R Bingham, G Burt, B Buttenschön, A Butterworth, A Caldwell, S Chattopadhyay, S Cipiccia, LC Deacon, S Doebert, U Dorda, E Feldbaumer, RA Fonseca, V Fedossev, B Goddard, J Grebenyuk, O Grulke, E Gschwendtner, J Hansen, C Hessler, W Hofle, J Holloway, D Jaroszynski, M Jenkins, L Jensen, S Jolly, R Jones, MF Kasim, N Lopes, K Lotov, SR Mandry, M Martyanov, M Meddahi, O Mete, V Minakov, J Moody, P Muggli, Z Najmudin, PA Norreys, E Öz, A Pardons, A Petrenko, A Pukhov, K Rieger, O Reimann, AA Seryi, E Shaposhnikova, P Sherwood, LO Silva, A Sosedkin, R Tarkeshian, RMGM Trines, FM Velotti, J Vieira, H Vincke, C Welsch, M Wing, G Xia

© 2015 Elsevier B.V..The AWAKE Collaboration has been formed in order to demonstrate proton-driven plasma wakefield acceleration for the first time. This acceleration technique could lead to future colliders of high energy but of a much reduced length when compared to proposed linear accelerators. The CERN SPS proton beam in the CNGS facility will be injected into a 10 m plasma cell where the long proton bunches will be modulated into significantly shorter micro-bunches. These micro-bunches will then initiate a strong wakefield in the plasma with peak fields above 1 GV/m that will be harnessed to accelerate a bunch of electrons from about 20 MeV to the GeV scale within a few meters. The experimental program is based on detailed numerical simulations of beam and plasma interactions. The main accelerator components, the experimental area and infrastructure required as well as the plasma cell and the diagnostic equipment are discussed in detail. First protons to the experiment are expected at the end of 2016 and this will be followed by an initial three-four years experimental program. The experiment will inform future larger-scale tests of proton-driven plasma wakefield acceleration and applications to high energy colliders.


Characteristics of betatron radiation from direct-laser-accelerated electrons

Physical Review E - Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics (2016)

PA Norreys


Bursty star formation feedback and cooling outflows

Monthly Notices of the Royal Astronomical Society 462 (2016) 994-1001

T Suarez, A Pontzen, HV Peiris, A Slyz, J Devriendt

© 2016 The Authors.We study how outflows of gas launched from a central galaxy undergoing repeated starbursts propagate through the circum-galactic medium (CGM), using the simulation code RAMSES. We assume that the outflow from the disc can be modelled as a rapidly moving bubble of hot gas at ~1 kpc above disc, then ask what happens as it moves out further into the halo around the galaxy on ~100 kpc scales. To do this, we run 60 two-dimensional simulations scanning over parameters of the outflow. Each of these is repeated with and without radiative cooling, assuming a primordial gas composition to give a lower bound on the importance of cooling. In a large fraction of radiative-cooling cases we are able to form rapidly outflowing cool gas from in situ cooling of the flow. We show that the amount of cool gas formed depends strongly on the 'burstiness' of energy injection; sharper, stronger bursts typically lead to a larger fraction of cool gas forming in the outflow. The abundance ratio of ions in the CGMmay therefore change in response to the detailed historical pattern of star formation. For instance, outflows generated by star formation with short, intense bursts contain up to 60 per cent of their gas mass at temperatures <5 × 104 K; for near-continuous star formation, the figure is < ≈ 5 per cent. Further study of cosmological simulations, and of idealized simulations with e.g. metal-cooling, magnetic fields and/or thermal conduction, will help to understand the precise signature of bursty outflows on observed ion abundances.


Radio Galaxy Zoo: Discovery of a poor cluster through a giant wide-angle tail radio galaxy

Monthly Notices of the Royal Astronomical Society 460 (2016) 2376-2384

JK Banfield, H Andernach, AD Kapińska, L Rudnick, MJ Hardcastle, G Cotter, S Vaughan, TW Jones, I Heywood, JD Wing, OI Wong, T Matorny, IA Terentev, R López-Sánchez, RP Norris, N Seymour, SS Shabala, KW Willett

© 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.We have discovered a previously unreported poor cluster of galaxies (RGZ-CL J0823.2+0333) through an unusual giant wide-angle tail radio galaxy found in the Radio Galaxy Zoo project. We obtained a spectroscopic redshift of z = 0.0897 for the E0-type host galaxy, 2MASX J08231289+0333016, leading to Mr = -22.6 and a 1.4 GHz radio luminosity density of L1.4 = 5.5 × 1024 W Hz-1. These radio and optical luminosities are typical for wide-angle tailed radio galaxies near the borderline between Fanaroff-Riley classes I and II. The projected largest angular size of ≈8 arcmin corresponds to 800 kpc and the full length of the source along the curved jets/trails is 1.1 Mpc in projection. X-ray data from the XMM-Newton archive yield an upper limit on the X-ray luminosity of the thermal emission surrounding RGZ J082312.9+033301 at 1.2-2.6 × 1043 erg s-1 for assumed intracluster medium temperatures of 1.0-5.0 keV. Our analysis of the environment surrounding RGZ J082312.9+033301 indicates that RGZ J082312.9+033301 lies within a poor cluster. The observed radio morphology suggests that (a) the host galaxy is moving at a significant velocity with respect to an ambient medium like that of at least a poor cluster, and that (b) the source may have had two ignition events of the active galactic nucleus with 107 yr in between. This reinforces the idea that an association between RGZ J082312.9+033301 and the newly discovered poor cluster exists.


Rejuvenation of stellar mergers and the origin of magnetic fields in massive stars

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 457 (2016) 2355-2365

FRN Schneider, P Podsiadlowski, N Langer, N Castro, L Fossati


Characterizing stellar halo populations - I. An extended distribution function for halo K giants

Monthly Notices of the Royal Astronomical Society 460 (2016) 1725-1738

P Das, J Binney

© 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.We fit an extended distribution function (EDF) to K giants in the Sloan Extension for Galactic Understanding and Exploration survey. These stars are detected to radii ~80 kpc and span a wide range in [Fe/H]. Our EDF, which depends on [Fe/H] in addition to actions, encodes the entanglement of metallicity with dynamics within the Galaxy's stellar halo. Our maximum-likelihood fit of the EDF to the data allows us to model the survey's selection function. The density profile of the K giants steepens with radius from a slope ~-2 to ~-4 at large radii. The halo's axis ratio increases with radius from 0.7 to almost unity. The metal-rich stars are more tightly confined in action space than the metal-poor stars and form a more flattened structure. A weak metallicity gradient ~-0.001 dex kpc-1, a small gradient in the dispersion in [Fe/H] of ~0.001 dex kpc-1, and a higher degree of radial anisotropy in metal-richer stars result. Lognormal components with peaks at ~-1.5 and ~-2.3 are required to capture the overall metallicity distribution, suggestive of the existence of two populations of K giants. The spherical anisotropy parameter varies between 0.3 in the inner halo to isotropic in the outer halo. If the Sagittarius stream is included, a very similar model is found but with a stronger degree of radial anisotropy throughout.

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