Publications


Axion detection through resonant photon-photon collisions

Physical Review D American Physical Society (APS) 101 (2020) 95018

K Beyer, G Marocco, R Bingham, G Gregori


A Search for MeV to TeV Neutrinos from Fast Radio Bursts with IceCube

The Astrophysical Journal: an international review of astronomy and astronomical physics American Astronomical Society (2020)

GW Sullivan, T Stürwald, K Tollefson, T Stuttard, L Tomankova, A Terliuk, F Tenholt, I Taboada, S Tilav, M Tselengidou, S Toscano, CF Turley, A Turcati, R Turcotte, C Tönnis, A Trettin, CF Tung, D Tosi, J Vandenbroucke, MAU Elorrieta, NV Eijndhoven, WV Driessche, S Vanheule, E Unger, M Usner

We present two searches for IceCube neutrino events coincident with 28 fast radio bursts (FRBs) and one repeating FRB. The first improves upon a previous IceCube analysis -- searching for spatial and temporal correlation of events with FRBs at energies greater than roughly 50 GeV -- by increasing the effective area by an order of magnitude. The second is a search for temporal correlation of MeV neutrino events with FRBs. No significant correlation is found in either search, therefore, we set upper limits on the time-integrated neutrino flux emitted by FRBs for a range of emission timescales less than one day. These are the first limits on FRB neutrino emission at the MeV scale, and the limits set at higher energies are an order-of-magnitude improvement over those set by any neutrino telescope.


Trapped orbits and solar-neighbourhood kinematics

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 495 (2020) 895-904

J Binney


Angle-action variables for orbits trapped at a Lindblad resonance

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 495 (2020) 886-894

J Binney


Structure of a massive common envelope in the common-envelope wind model for Type Ia supernovae

ASTRONOMY & ASTROPHYSICS 633 (2020) ARTN A41

R Song, X Meng, P Podsiadlowski, Y Cui


Corrections to weighted opacities and energy exchange rate in 3-T radiation-hydrodynamics

High Energy Density Physics Elsevier BV 35 (2020) 100734

KW McLean, SJ Rose


Impact of main ion pressure anisotropy on stellarator impurity transport

Nuclear Fusion IOP Publishing (2019)

I Calvo, FI Parra, JL Velasco, JM García-Regaña

Main ions influence impurity dynamics through a variety of mechanisms; in particular, via impurity-ion collisions. To lowest order in an expansion in the main ion mass over the impurity mass, the impurity-ion collision operator only depends on the component of the main ion distribution that is odd in the parallel velocity. These lowest order terms give the parallel friction of the impurities with the main ions, which is typically assumed to be the main cause of collisional impurity transport. Next-order terms in the mass ratio expansion of the impurity-ion collision operator, proportional to the component of the main ion distribution that is even in the parallel velocity, are usually neglected. However, in stellarators, the even component of the main ion distribution can be very large. In this article, such next-order terms in the mass ratio expansion of the impurity-ion collision operator are retained, and analytical expressions for the neoclassical radial flux of trace impurities are calculated in the Pfirsch-Schl\"uter, plateau and $1/\nu$ regimes. The new terms provide a drive for impurity transport that is physically very different from parallel friction: they are associated to anisotropy in the pressure of the main ions, which translates into impurity pressure anisotropy. It is argued that main ion pressure anisotropy must be taken into account for a correct description of impurity transport in certain realistic stellarator plasmas. Examples are given by numerically evaluating the analytical expressions for the impurity flux.


Role of collisionality and radiative cooling in supersonic plasma jet collisions of different materials

Physical Review E American Physical Society 101 (2020) 023205

Collins, Valenzuela, Speliotopoulos, Aybar, Conti, Beg, Tzeferacos, Khiar, G Gregori

Currently there is considerable interest in creating scalable laboratory plasmas to study the mechanisms behind the formation and evolution of astrophysical phenomena such as Herbig-Haro objects and supernova remnants. Laboratory-scaled experiments can provide a well diagnosed and repeatable supplement to direct observations of these extraterrestrial objects if they meet similarity criteria demonstrating that the same physics govern both systems. Here, we present a study on the role of collision and cooling rates on shock formation using colliding jets from opposed conical wire arrays on a compact pulsed-power driver. These diverse conditions were achieved by changing the wire material feeding the jets, since the ion-ion mean free path (λmfp-ii) and radiative cooling rates (Prad) increase with atomic number. Low Z carbon flows produced smooth, temporally stable shocks. Weakly collisional, moderately cooled aluminum flows produced strong shocks that developed signs of thermal condensation instabilities and turbulence. Weakly collisional, strongly cooled copper flows collided to form thin shocks that developed inconsistently and fragmented. Effectively collisionless, strongly cooled tungsten flows interpenetrated, producing long axial density perturbations.


Time-integrated Neutrino Source Searches with 10 years of IceCube Data

Physical Review Letters American Physical Society (2020)

S Robertson, M Rongen, C Rott, T Ruhe, D Ryckbosch, D Rysewyk, I Safa, SES Herrera, A Sandrock, J Sandroos, M Santander, SUBIR Sarkar, S SARKAR, K Satalecka, M Schaufel, H Schieler, P Schlunder, T Schmidt, A Schneider, J Schneider, FG Schröder, L Schumacher, S Sclafani, D Seckel, S Seunarine

This paper presents the results from point-like neutrino source searches using ten years of IceCube data collected between Apr.~6, 2008 and Jul.~10, 2018. We evaluate the significance of an astrophysical signal from a point-like source looking for an excess of clustered neutrino events with energies typically above $\sim1\,$TeV among the background of atmospheric muons and neutrinos. We perform a full-sky scan, a search within a selected source catalog, a catalog population study, and three stacked Galactic catalog searches. The most significant point in the Northern hemisphere from scanning the sky is coincident with the Seyfert II galaxy NGC 1068, which was included in the source catalog search. The excess at the coordinates of NGC 1068 is inconsistent with background expectations at the level of $2.9\,\sigma$ after accounting for statistical trials. The combination of this result along with excesses observed at the coordinates of three other sources, including TXS 0506+056, suggests that, collectively, correlations with sources in the Northern catalog are inconsistent with background at 3.3$\,\sigma$ significance. These results, all based on searches for a cumulative neutrino signal integrated over the ten years of available data, motivate further study of these and similar sources, including time-dependent analyses, multimessenger correlations, and the possibility of stronger evidence with coming upgrades to the detector.


The spectral evolution of disc dominated tidal disruption events

Monthly Notices of the Royal Astronomical Society 492 (2020) 5655-5674

A Mummery, SA Balbus

We perform a detailed numerical and analytical study of the properties of observed light curves from relativistic thin discs, focussing on observational bands most appropriate for comparison with tidal disruption events (TDEs). We make use of asymptotic expansion techniques applied to the spectral emission integral, using time-dependent disc temperature profiles appropriate for solutions of the relativistic thin disc equation. Rather than a power law associated with bolometric disc emission L ∼ t−n, the observed X-ray flux from disc-dominated TDEs will typically have the form of a power law multiplied by an exponential (see equation 91). While precise details are somewhat dependent on the nature of the ISCO stress and disc-observer orientational angle, the general form of the time-dependent flux is robust and insensitive to the exact disc temperature profile. We present numerical fits to the UV and X-ray light curves of ASASSN-14li, a particularly well observed TDE. This modelling incorporates strong gravity optics. The full 900 d of ASASSN-14li X-ray observations are very well fit by a simple relativistic disc model, significantly improving upon previous work. The same underlying model also fits the final 1000 d of ASASSN-14li observations in three different UV bandpasses. Finally, we demonstrate that the analytic formulae reproduce the properties of full numerical modelling at both UV and X-ray wavelengths with great fidelity.


Detection of very-high-energy gamma-ray emission from the colliding wind binary eta Car with HESS

ASTRONOMY & ASTROPHYSICS 635 (2020)

H Abdalla, R Adam, F Aharonian, FA Benkhali, EO Anguner, M Arakawa, C Arcaro, C Armand, T Armstrong, H Ashkar, M Backes, VB Martins, M Barnard, Y Becherini, D Berge, K Bernloehr, R Blackwell, M Bottcher, C Boisson, J Bolmont, S Bonnefoy, J Bregeon, M Breuhaus, F Brun, P Brun, M Bryan, M Buchele, T Bulik, T Bylund, S Caroff, A Carosi, S Casanova, M Cerruti, T Chand, S Chandra, A Chen, S Colafrancesco, G Cotter, M Curylo, ID Davids, J Davies, C Deil, J Devin, P dewilt, L Dirson, A Djannati-Atai, A Dmytriiev, A Donath, V Doroshenko, J Dyks, K Egberts, F Eichhorn, G Emery, J-P Ernenwein, S Eschbach, K Feijen, S Fegan, A Fiasson, G Fontaine, S Funk, M Fussling, S Gabici, YA Gallant, F Gate, G Giavitto, L Giunti, D Glawion, JF Glicenstein, D Gottschall, M-H Grondin, J Hahn, M Haupt, G Heinzelmann, G Henri, G Hermann, JA Hinton, W Hofmann, C Hoischen, TL Holch, M Holler, M Horbe, D Horns, D Huber, H Iwasaki, M Jamrozy, D Jankowsky, F Jankowsky, A Jardin-Blicq, V Joshi, I Jung-Richardt, MA Kastendieck, KKP Nski, M Katsuragawa, U Katz, D Khangulyan, B Khelifi, J King, S Klepser, W Kluzniak, N Komin, K Kosack, D Kostunin, M Kreter, G Lamanna, A Lemiere, M Lemoine-Goumard, J-P Lenain, E Leser, C Levy, T Lohse, I Lypova, J Mackey, J Majumdar, D Malyshev, D Malyshev, V Marandon, P Marchegiani, A Marcowith, A Mares, G Marti-Devesa, R Marx, G Maurin, PJ Meintjes, R Moderski, M Mohamed, L Mohrmann, C Moore, P Morris, E Moulin, J Muller, T Murach, S Nakashima, K Nakashima, M de Naurois, H Ndiyavala, F Niederwanger, J Niemiec, L Oakes, P O'Brien, H Odaka, S Ohm, EDO Wilhelmi, M Ostrowski, M Panter, RD Parsons, C Perennes, P-O Petrucci, B Peyaud, Q Piel, S Pita, V Poireau, AP Noel, DA Prokhorov, H Prokoph, G Puhlhofer, M Punch, A Quirrenbach, S Raab, R Rauth, A Reimer, O Reimer, Q Remy, M Renaud, F Rieger, L Rinchiuso, C Romoli, G Rowell, B Rudak, E Ruiz-Velasco, V Sahakian, S Sailer, S Saito, DA Sanchez, A Santangelo, M Sasaki, M Scalici, R Schlickeiser, F Schussler, A Schulz, HM Schutte, U Schwanke, S Schwemmer, M Seglar-Arroyo, M Senniappan, AS Seyffert, N Shafi, K Shiningayamwe, R Simoni, A Sinha, H Sol, A Specovius, S Spencer, M Spir-Jacob, L Stawarz, R Steenkamp, C Stegmann, C Steppa, T Takahashi, T Tavernier, AM Taylor, R Terrier, D Tiziani, M Tluczykont, L Tomankova, C Trichard, M Tsirou, N Tsuji, R Tuffs, Y Uchiyama, DJ van der Walt, C van Eldik, C van Rensburg, B van Soelen, G Vasileiadis, J Veh, C Venter, P Vincent, J Vink, HJ Volk, T Vuillaume, Z Wadiasingh, SJ Wagner, J Watson, F Werner, R White, A Wierzcholska, R Yang, H Yoneda, M Zacharias, R Zanin, AA Zdziarski, A Zech, J Zorn, N Zywucka, HESS Collaboration


Development of an analysis to probe the neutrino mass ordering with atmospheric neutrinos using three years of IceCube DeepCore data: IceCube Collaboration

European Physical Journal C 80 (2020)

MG Aartsen, M Ackermann, J Adams, JA Aguilar, M Ahlers, M Ahrens, C Alispach, K Andeen, T Anderson, I Ansseau, G Anton, C Argüelles, J Auffenberg, S Axani, P Backes, H Bagherpour, X Bai, A Barbano, SW Barwick, V Baum, R Bay, JJ Beatty, KH Becker, JB Tjus, S BenZvi, D Berley, E Bernardini, DZ Besson, G Binder, D Bindig, E Blaufuss, S Blot, C Bohm, M Börner, S Böser, O Botner, E Bourbeau, J Bourbeau, F Bradascio, J Braun, HP Bretz, S Bron, J Brostean-Kaiser, A Burgman, RS Busse, T Carver, C Chen, E Cheung, D Chirkin, K Clark, L Classen, GH Collin, JM Conrad, P Coppin, P Correa, DF Cowen, R Cross, P Dave, JPAM de André, C De Clercq, JJ DeLaunay, H Dembinski, K Deoskar, S De Ridder, P Desiati, KD de Vries, G de Wasseige, M de With, T DeYoung, A Diaz, JC Díaz-Vélez, H Dujmovic, M Dunkman, E Dvorak, B Eberhardt, T Ehrhardt, B Eichmann, P Eller, JJ Evans, PA Evenson, S Fahey, AR Fazely, J Felde, K Filimonov, C Finley, A Franckowiak, E Friedman, A Fritz, TK Gaisser, J Gallagher, E Ganster, S Garrappa, L Gerhardt, K Ghorbani, T Glauch, T Glüsenkamp, A Goldschmidt, JG Gonzalez, D Grant, Z Griffith

© 2020, The Author(s). The Neutrino Mass Ordering (NMO) remains one of the outstanding questions in the field of neutrino physics. One strategy to measure the NMO is to observe matter effects in the oscillation pattern of atmospheric neutrinos above ∼1GeV, as proposed for several next-generation neutrino experiments. Moreover, the existing IceCube DeepCore detector can already explore this type of measurement. We present the development and application of two independent analyses to search for the signature of the NMO with three years of DeepCore data. These analyses include a full treatment of systematic uncertainties and a statistically-rigorous method to determine the significance for the NMO from a fit to the data. Both analyses show that the dataset is fully compatible with both mass orderings. For the more sensitive analysis, we observe a preference for normal ordering with a p-value of pIO= 15.3 % and CL s= 53.3 % for the inverted ordering hypothesis, while the experimental results from both analyses are consistent within their uncertainties. Since the result is independent of the value of δCP and obtained from energies Eν≳5GeV, it is complementary to recent results from long-baseline experiments. These analyses set the groundwork for the future of this measurement with more capable detectors, such as the IceCube Upgrade and the proposed PINGU detector.


Design and Performance of the first IceAct Demonstrator at the South Pole

Journal of Instrumentation IOP Publishing (2020)

GW Sullivan, I Taboada, A Taketa, S Ter-Antonyan, HKM Tanaka, F Tenholt, A Terliuk, S Tilav, K Tollefson, L Tomankova, C Tönnis, S Toscano, D Tosi, M Tselengidou, A Turcati, A Trettin, CF Tung, R Turcotte, CF Turley, MAU Elorrieta, B Ty, E Unger, J Vandenbroucke, M Usner, WV Driessche

In this paper we describe the first results of a compact imaging air-Cherenkov telescope, IceAct, operating in coincidence with the IceCube Neutrino Observatory (IceCube) at the geographic South Pole. An array of IceAct telescopes (referred to as the IceAct project) is under consideration as part of the IceCube-Gen2 extension to IceCube. Surface detectors in general will be a powerful tool in IceCube-Gen2 for distinguishing astrophysical neutrinos from the dominant backgrounds of cosmic-ray induced atmospheric muons and neutrinos: the IceTop array is already in place as part of IceCube, but has a high energy threshold. Although the duty cycle will be lower for the IceAct telescopes than the present IceTop tanks, the IceAct telescopes may prove to be more effective at lowering the detection threshold for air showers. Additionally, small imaging air-Cherenkov telescopes in combination with IceTop, the deep IceCube detector or other future detector systems might improve measurements of the composition of the cosmic ray energy spectrum. In this paper we present measurements of a first 7-pixel imaging air Cherenkov telescope demonstrator, proving the capability of this technology to measure air showers at the South Pole in coincidence with IceTop and the deep IceCube detector.


X-ray-line coincidence photopumping in a potassium-chlorine mixed plasma

Physical Review A American Physical Society (APS) 101 (2020) 53431

L Hobbs, D Burridge, M Hill, D Hoarty, C Brown, R Charles, G Cooper, S James, L Wilson, W Babbage, P Hatfield, P Beiersdorfer, J Nilsen, H Scott, S Rose


Search for PeV Gamma-Ray Emission from the Southern Hemisphere with 5 Years of Data from the IceCube Observatory

The Astrophysical Journal: an international review of astronomy and astronomical physics American Astronomical Society (2020)

H Bagherpour, C Argüelles, J Auffenberg, T Anderson, I Ansseau, P Backes, G Anton, S Axani, X Bai, E Bernardini, DZ Besson, E Blaufuss, D Bindig, S BenZvi, D Berley, JB Tjus, G Binder, S Blot, J Brostean-Kaiser, RS Busse, D Chirkin, A Burgman, J Buscher, T Carver, E Cheung

The measurement of diffuse PeV gamma-ray emission from the Galactic plane would provide information about the energy spectrum and propagation of Galactic cosmic rays, and the detection of a point-like source of PeV gamma rays would be strong evidence for a Galactic source capable of accelerating cosmic rays up to at least a few PeV. This paper presents several un-binned maximum likelihood searches for PeV gamma rays in the Southern Hemisphere using 5 years of data from the IceTop air shower surface detector and the in-ice array of the IceCube Observatory. The combination of both detectors takes advantage of the low muon content and deep shower maximum of gamma-ray air showers, and provides excellent sensitivity to gamma rays between $\sim$0.6 PeV and 100 PeV. Our measurements of point-like and diffuse Galactic emission of PeV gamma rays are consistent with background, so we constrain the angle-integrated diffuse gamma-ray flux from the Galactic Plane at 2 PeV to $2.61 \times 10^{-19}$ cm$^{-2}$ s$^{-1}$ TeV$^{-1}$ at 90% confidence, assuming an E$^{-3}$ spectrum, and we estimate 90% upper limits on point-like emission at 2 PeV between 10$^{-21}$ - 10$^{-20}$ cm$^{-2}$ s$^{-1}$ TeV$^{-1}$ for an E$^{-2}$ spectrum, depending on declination. Furthermore, we exclude unbroken power-law emission up to 2 PeV for several TeV gamma-ray sources observed by H.E.S.S., and calculate upper limits on the energy cutoffs of these sources at 90% confidence. We also find no PeV gamma rays correlated with neutrinos from IceCube's high-energy starting event sample. These are currently the strongest constraints on PeV gamma-ray emission.


Probing the Magnetic Field in the GW170817 Outflow Using HESS Observations

ASTROPHYSICAL JOURNAL LETTERS 894 (2020) ARTN L16

H Abdalla, R Adam, F Aharonian, FA Benkhali, EO Anguner, M Arakawa, C Arcaro, C Armand, T Armstrong, H Ashkar, M Backes, V Baghmanyan, V Barbosa-Martins, A Barnacka, M Barnard, Y Becherini, D Berge, K Bernloehr, R Blackwell, M Bottcher, C Boisson, J Bolmont, S Bonnefoy, J Bregeon, M Breuhaus, F Brun, P Brun, M Bryan, M Buechele, T Bulik, T Bylund, S Caroff, A Carosi, S Casanova, M Cerruti, T Chand, S Chandra, A Chen, G Cotter, M Curylo, ID Davids, J Davies, C Deil, J Devin, P deWilt, L Dirson, A Djannati-Ata, A Dmytriiev, A Donath, V Doroshenko, J Dyks, K Egberts, F Eichhorn, G Emery, J-P Ernenwein, S Eschbach, K Feijen, S Fegan, A Fiasson, G Fontaine, S Funk, M Fuessling, S Gabici, YA Gallant, G Giavitto, L Giunti, D Glawion, JF Glicenstein, D Gottschall, M-H Grondin, J Hahn, M Haupt, G Heinzelmann, G Hermann, JA Hinton, W Hofmann, C Hoischen, TL Holch, M Holler, M Horbe, D Horns, D Huber, H Iwasaki, M Jamrozy, D Jankowsky, F Jankowsky, A Jardin-Blicq, V Joshi, I Jung-Richardt, MA Kastendieck, K Katarzynski, M Katsuragawa, U Katz, D Khangulyan, B Khelifi, S Klepser, W Kluzniak, N Komin, R Konno, K Kosack, D Kostunin, M Kreter, G Lamanna, A Lemiere, M Lemoine-Goumard, J-P Lenain, E Leser, C Levy, T Lohse, I Lypova, J Mackey, J Majumdar, D Malyshev, V Marandon, P Marchegiani, A Marcowith, A Mares, G Marti-Devesa, R Marx, G Mauring, PJ Meintjes, R Moderski, M Mohamed, L Mohrmann, C Moore, P Morriss, E Moulin, J Muller, T Murach, S Nakashima, K Nakashima, M de Naurois, H Ndiyavala, F Niederwanger, J Niemiec, L Oakes, P O'Brien, HG Odaka, S Ohm, EDO Wilhelmi, M Ostrowski, M Panter, RD Parsons, B Peyaud, Q Piel, S Pita, V Poireau, AP Noel, DA Prokhorov, H Prokoph, G Puehlhofer, M Punch, A Quirrenbach, S Raab, R Rauth, A Reimer, O Reimer, Q Remy, M Renaud, F Rieger, L Rinchiuso, C Romoli, G Rowell, B Rudak, E Ruiz-Velasco, V Sahalcian, S Sailer, S Saito, DA Sanchez, A Santangelo, M Sasaki, M Scalici, R Schlickeiser, F Schuessler, A Schulz, HM Schutte, U Schwanke, S Schwemmer, M Seglar-Arroyo, M Senniappan, AS Seyffert, N Shafi, K Shiningayamwe, R Simoni, A Sinha, H Sol, A Specovius, S Spencer, M Spir-Jacob, L Stawarz, R Steenkamp, C Stegmann, C Steppa, T Takahashi, T Tavernier, AM Taylor, R Terrier, D Tiziani, M Tluczykont, L Tomankova, C Trichard, M Tsirou, N Tsuji, R Tuffs, Y Uchiyama, DJ van der Walt, C van Eldik, C van Rensburg, B van Soelen, G Vasileiadis, J Veh, C Venter, P Vincent, J Vink, HJ Voelk, T Vuillaume, Z Wadiasingh, SJ Wagner, J Watson, F Werner, R White, A Wierzcholska, R Yang, H Yoneda, M Zacharias, R Zanin, AA Zdziarski, A Zech, J Zorn, N Zywucka, X Rodrigues, HESS Collaboration


Demonstration of femtosecond broadband X-rays from laser wakefield acceleration as a source for pump-probe X-ray absorption studies

High Energy Density Physics Elsevier BV 35 (2020) 100729

K Krushelnick, RA Baggott, TZ Zhao, JM Cole, E Hill, SJ Rose, A Maksimchuk, J Nees, AGR Thomas, SPD Mangles, V Yanovsky, JC Wood, R Watt, AE Hussein, K Behm


Experimental characterization of the interaction zone between counter propagating Taylor Sedov blast waves

Physics of Plasmas AIP Publishing 27 (2020) 022111

B Albertazzi, P Mabey, T Michel, G Rigon, Marques, S Pikuz, S Ryazantsev, E Falize, L Van Box Som, J Meinecke, N Ozaki, A Ciardi, G Gregori, M Koenig

Astronomical observations reveal that the interaction between shock waves and/or blast waves with astrophysical objects (molecular clouds, stars, jets winds etc.) is a common process which leads to a more intricate structure of the Interstellar medium (ISM). In particular, when two isolated massive stars are relatively close and explode, the resulting Supernovae Remnants (SNR) can interact. The impact zone presents fascinating complex hydrodynamic physics which depends on the age of the SNRs, their relative evolution stage and the distance between the two stars. In this letter, we investigate experimentally the interaction region (IR) formed when two blast waves (BW) collide during their Taylor-Sedov expansion phase. The two BWs are produced by the laser irradiation (1 ns, ∼ 500 J) of 300 µm diameter carbon rods and propagate in different gases (Ar and N) at different pressures. The physical parameters, such as density and temperature of the IR are measured for the first time using a set of optical diagnostics (interferometry, schlieren, time-resolved optical spectroscopy etc.). This allows us to determine precisely the thermodynamic conditions of the IR. A compression ratio of r ∼ 1.75 is found and a 17-20 % increase of temperature is measured compared to the shell of a single blast wave. Moreover, we observe the generation of vorticity, inducing strong electron density gradients, in the IR at long times after the interaction. This could in principle generate magnetic fields through the Biermann Battery effect.


Reionization history constraints from neural network based predictions of high-redshift quasar continua

Monthly Notices of the Royal Astronomical Society Oxford University Press 493 (2020) 4256–4275-

D Ďurovčíková, H Katz, SEI Bosman, FB Davies, J Devriendt, A Slyz

Observations of the early Universe suggest that reionization was complete by z ∼ 6, however, the exact history of this process is still unknown. One method for measuring the evolution of the neutral fraction throughout this epoch is via observing the Lyα damping wings of high-redshift quasars. In order to constrain the neutral fraction from quasar observations, one needs an accurate model of the quasar spectrum around Lyα, after the spectrum has been processed by its host galaxy but before it is altered by absorption and damping in the intervening IGM. In this paper, we present a novel machine learning approach, using artificial neural networks, to reconstruct quasar continua around Lyα. Our QSANNDRA algorithm improves the error in this reconstruction compared to the state-of-the-art PCA-based model in the literature by 14.2% on average, and provides an improvement of 6.1% on average when compared to an extension thereof. In comparison with the extended PCA model, QSANNDRA further achieves an improvement of 22.1% and 16.8% when evaluated on low-redshift quasars most similar to the two high-redshift quasars under consideration, ULAS J1120+0641 at z = 7.0851 and ULAS J1342+0928 at z = 7.5413, respectively. Using our more accurate reconstructions of these two z > 7 quasars, we estimate the neutral fraction of the IGM using a homogeneous reionization model and find x¯H1=0.25+0.05−0.05 at z = 7.0851 and x¯H1=0.60+0.11−0.11 at z = 7.5413. Our results are consistent with the literature and favour a rapid end to reionization.


Axion-like-particle decay in strong electromagnetic backgrounds

Journal of High Energy Physics Springer 2019 (2019) 162

B King, BM Dillon, K Beyer, G Gregori

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