Publications


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.


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


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

Physical Review E American Physical Society 101 (2020) 023205

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

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 Oxford University Press (OUP) 492 (2020) 5655-5674

SA Balbus, A Mummery

<jats:title>ABSTRACT</jats:title> <jats:p>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.</jats:p>


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.


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.


Origins of Type Ibn SNe 2006jc/2015G in interacting binaries and implications for pre-SN eruptions

Monthly Notices of the Royal Astronomical Society Oxford University Press (2019)

N-C Sun, PA Crowther, P Podsiadlowski, R Hirai

Type Ibn supernovae (SNe Ibn) are intriguing stellar explosions whose spectra exhibit narrow helium lines with little hydrogen. They trace the presence of circumstellar material (CSM) formed via pre-SN eruptions of their stripped-envelope progenitors. Early work has generally assumed that SNe Ibn come from massive Wolf-Rayet (WR) stars via single star evolution. In this paper, we report ultraviolet (UV) and optical observations of two nearby Type Ibn SNe 2006jc and 2015G conducted with the Hubble Space Telescope (HST) at late times. A point source is detected at the position of SN 2006jc, and we confirm the conclusion of Maund et al. that it is the progenitor’s binary companion. Its position on the Hertzsprung-Russell (HR) diagram corresponds to a star that has evolved off the main sequence (MS); further analysis implies a low initial mass for the companion star (M2 ≤ 12.3+2.3−1.5 M⊙) and a secondary-to-primary initial mass ratio very close to unity (q = M2/M1 ∼ 1); the SN progenitor’s hydrogen envelope had been stripped through binary interaction. We do not detect the binary companion of SN 2015G. For both SNe, the surrounding stellar populations have relatively old ages and argue against any massive WR stars as their progenitors. These results suggest that SNe Ibn may have lower-mass origins in interacting binaries. As a result, they also provide evidence that the giant eruptions commonly seen in massive luminous blue variables (LBVs) can also occur in much lower-mass, stripped-envelope stars just before core collapse.


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


Is there really a `Hubble tension'?

arXiv (2019)

SUBIR Sarkar, M Rameez

Errors in redshift measurements as small as $\Delta z \sim 0.0001$ can have significant impact on the value of inferred cosmological parameters such as $H_0$ (Davis et al. 2019). We have earlier reported that the redshifts of over 100 Type Ia supernovae (SNe Ia) which are in common between the SDSSII-SNLS3 Joint Lightcurve Analysis (JLA) catalogue (Betoule et al. 2014) and the subsequent Pantheon compilation (Scolnic et al. 2018) are discrepant - some by as much as $\Delta z \sim 0.1$ (Rameez 2019a). We study the impact of this on the inferred value of $H_0$ using calibrations of the supernova absolute magnitude via the 'local distance ladder' (Riess et al. 2016). For supernovae with $\Delta z > 0.025$, the JLA redshifts favour $H_0 \sim 72$~km~s$^{-1}$Mpc$^{-1}$, while the Pantheon redshifts favour $H_0 \sim 68$~km~s$^{-1}$Mpc$^{-1}$. For comparison the value inferred (assuming the flat $\Lambda$CDM model) from the Planck data on CMB anisotropies is $H_0 \sim 67.4 \pm 0.5$~km~s$^{-1}$Mpc$^{-1}$ (Aghanim et al. 2018). Thus the systematic uncertainties that apparently still plague the distance ladder measurement of $H_0$ undermine the significance of the discrepancy claimed by Riess et al. (2019).


Wakefields in a cluster plasma

Physical Review Special Topics: Accelerators and Beams American Physical Society 22 (2019) 113501

L Ceurvorst, N Bourgeois, R Pattathil, P Norreys, M Mayr, J Sadler, M Kasim, B Spiers, K Glize, A Savin, F Keeble, A Ross, R Wang, R Bingham, P Burrows, M Wing, D Symes, R Aboushelbaya, R Fonseca, J Holloway, N Ratan, R Trines

We report the first comprehensive study of large amplitude Langmuir waves in a plasma of nanometer-scale clusters. Using an oblique angle single-shot frequency domain holography diagnostic, the shape of these wakefields is captured for the first time. The wavefronts are observed to curve backwards, in contrast to the forwards curvature of wakefields in uniform plasma. Due to the expansion of the clusters, the first wakefield period is longer than those trailing it. The features of the data are well described by fully relativistic two-dimensional particle-in-cell simulations and by a quasianalytic solution for a one-dimensional, nonlinear wakefield in a cluster plasma.


Evidence for anisotropy of cosmic acceleration

Astronomy and Astrophysics: a European journal EDP Sciences (2019)

J Colin, R Mohayaee, M Rameez, S Sarkar

Observations reveal a `bulk flow' in the local Universe which is faster and extends to much larger scales than is expected around a typical observer in the standard $\Lambda$CDM cosmology. This is expected to result in a scale-dependent dipolar modulation of the acceleration of the expansion rate inferred from observations of objects within the bulk flow. From a maximum-likelihood analysis of the Joint Lightcurve Analysis (JLA) catalogue of Type Ia supernovae we find that the deceleration parameter, in addition to a small monopole, indeed has a much bigger dipole component aligned with the CMB dipole which falls exponentially with redshift $z$: $q_0 = q_\mathrm{m} + \vec{q}_\mathrm{d}.\hat{n}\exp(-z/S)$. The best fit to data yields $q_\mathrm{d} = -8.03$ and $S = 0.0262~(\Rightarrow d \sim 100~\mathrm{Mpc})$, rejecting isotropy ($q_\mathrm{d} = 0$) with $3.9\sigma$ statistical significance, while $q_\mathrm{m} = -0.157$ and consistent with no acceleration ($q_\mathrm{m} = 0$) at $1.4\sigma$. Thus the cosmic acceleration deduced from supernovae may be an artefact of our being non-Copernican observers, rather than evidence for a dominant component of `dark energy' in the Universe.


Simulating MOS science on the ELT: Ly alpha forest tomography

ASTRONOMY & ASTROPHYSICS 632 (2019) ARTN A94

JEG Devriendt, P Petitjean, Y Dubois, E Gendron, F Hammer, S Morris, L Kaper, R Sanchez-Janssen, SD Vergani, N Pirzkal, A Slyz, Y Yang, J Japelj, C Laigle, H Rahmani, C Pichon, M Puech

Mapping of the large-scale structure through cosmic time has numerous applications in the studies of cosmology and galaxy evolution. At $z > 2$, the structure can be traced by the neutral intergalactic medium (IGM) by way of observing the Ly$\alpha$, forest towards densely-sampled lines-of-sight of bright background sources, such as quasars and star forming galaxies. We investigate the scientific potential of MOSAIC, a planned multi-object spectrograph on the European Extremely Large Telescope (ELT), for the 3D mapping of the IGM at $z \gtrsim 3$. We simulate a survey of $3 \lesssim z \lesssim 4$ galaxies down to a limiting magnitude of $m_{r}\sim 25.5$ mag in an area of 1 degree$^2$ in the sky. Galaxies and their spectra (including the line-of-sight Ly$\alpha$ absorption) are taken from the lightcone extracted from the Horizon-AGN cosmological hydrodynamical simulation. The quality of the reconstruction of the original density field is studied for different spectral resolutions and signal-to-noise ratios of the spectra. We demonstrate that the minimum $S/N$ (per resolution element) of the faintest galaxies that such survey has to reach is $S/N = 4$. We show that a survey with such sensitivity enables a robust extraction of cosmic filaments and the detection of the theoretically-predicted galaxy stellar mass and star-formation rate gradients towards filaments. By simulating the realistic performance of MOSAIC we obtain $S/N(T_{\rm obs}, R, m_{r})$ scaling relations. We estimate that $\lesssim 35~(65)$ nights of observation time are required to carry out the survey with the instrument's high multiplex mode and with the spectral resolution of $R=1000~(2000)$. A survey with a MOSAIC-concept instrument on the ELT is found to enable the mapping of the IGM at $z > 3$ on Mpc scales, and as such will be complementary to and competitive with other planned IGM tomography surveys. [abridged]


Inverse problem instabilities in large-scale modelling of matter in extreme conditions

Physics of Plasmas AIP Publishing 26 (2019) 112706

MF Kasim, TP Galligan, J Topp-Mugglestone, G Gregori, S Vinko

Our understanding of physical systems often depends on our ability to match complex computational modeling with the measured experimental outcomes. However, simulations with large parameter spaces suffer from inverse problem instabilities, where similar simulated outputs can map back to very different sets of input parameters. While of fundamental importance, such instabilities are seldom resolved due to the intractably large number of simulations required to comprehensively explore parameter space. Here, we show how Bayesian inference can be used to address inverse problem instabilities in the interpretation of x-ray emission spectroscopy and inelastic x-ray scattering diagnostics. We find that the extraction of information from measurements on the basis of agreement with simulations alone is unreliable and leads to a significant underestimation of uncertainties. We describe how to statistically quantify the effect of unstable inverse models and describe an approach to experimental design that mitigates its impact.


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.


Dependence on ion temperature of shallow-angle magnetic presheaths with adiabatic electrons

Journal of Plasma Physics Cambridge University Press 85 (2019) 795850601

A Geraldini, F Parra, F Militello


A response to Rubin & Heitlauf: "Is the expansion of the universe accelerating? All signs \emph{still} point to yes"

arXiv (2019)

J Colin, SUBIR Sarkar, R Mohayaee, M Rameez

We have shown (Colin et al. 2019) that the acceleration of the Hubble expansion rate inferred from Type Ia supernovae is essentially a dipole with 3.9$\sigma$ significance, approximately aligned with the CMB dipole, while its monopole component which may be interpreted as due to a Cosmological Constant (or more generally dark energy) is consistent with zero at 1.4$\sigma$. This is challenged by Rubin & Heitlauf (2019) who assert that we incorrectly assumed the supernova light-curve parameters to be independent of redshift, and erred further in considering their measured redshifts (in the heliocentric frame) rather than transforming them to the CMB frame (in which the universe supposedly looks isotropic). We emphasize that our procedure is justified and that their criticism serves only to highlight the rather "arbitrary corrections" that are made to the data in order to infer isotropic cosmic acceleration. This is a vivid illustration of the 'Cosmological Fitting Problem' faced by observers who live in an inhomogeneous universe but still use the maximally symmetric FLRW cosmolgy to interpret observations.


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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