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1. Gravitational lensing in the presence of plasma scattering with application to Fast Radio Bursts

   https://doi.org/10.1093/mnras/stad160  

   Kumar, Pawan; Beniamini, Paz (January 2023, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT We describe how gravitational lensing of fast radio bursts (FRBs) is affected by a plasma screen in the vicinity of the lens or somewhere between the source and the observer. Wave passage through a turbulent medium affects gravitational image magnification, lensing probability (particularly for strong magnification events), and the time delay between images. The magnification is suppressed because of the broadening of the angular size of the source due to scattering by the plasma. The time delay between images is modified as the result of different dispersion measures (DM) along photon trajectories for different images. Each of the image light curves is also broadened due to wave scattering so that the images could have distinct temporal profiles. The first two effects are most severe for stellar and sub-stellar mass lens, and the last one (scatter broadening) for lenses and plasma screens at cosmological distances from the source/observer. This could limit the use of FRBs to measure their cosmic abundance. On the other hand, when the time delay between images is large, such that the light curve of a transient source has two or more well-separated peaks, the different DMs along the wave paths of different images can probe density fluctuations in the IGM on scales ≲10−6 rad and explore the patchy reionization history of the universe using lensed FRBs at high redshifts. Different rotation measures (RM) along two-image paths can convert linearly polarized radiation from a source to partial circular polarization. 

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2. A Search for Lensed Lyα Emitters within the Early HETDEX Data Set

   https://doi.org/10.3847/1538-4357/ac9186  

   Laseter, Isaac H.; Finkelstein, Steven L.; Bagley, Micaela J.; Davis, Dustin M.; Gebhardt, Karl; Gronwall, Caryl; Ciardullo, Robin; Zeimann, Gregory R.; Cooper, Erin Mentuch; Farrow, Daniel (November 2022, The Astrophysical Journal)

   Abstract The Hobby–Eberly Telescope Dark Energy Experiment (HETDEX) is a large-volume spectroscopic survey without preselection of sources, searching ∼540 deg²for Lyαemitting galaxies (LAEs) at 1.9 <z< 3.5. Taking advantage of such a wide-volume survey, we perform a pilot study using early HETDEX data to search for lensed Lyαemitters (LAEs). After performing a proof of concept using a previously known lensed LAE covered by HETDEX, we perform a search for previously unknown lensed LAEs in the HETDEX spectroscopic sample. We present a catalog of 26 potential LAEs lensed by foreground, red, non-star-forming galaxies atz∼ 0.4–0.7. We estimate the magnification for each candidate system, finding 12 candidates to be within the strong lensing regime (magnificationμ> 2). Follow-up observations of these potential lensed LAEs have the potential to confirm their lensed nature and explore these distant galaxies in more detail. 

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3. Dark Energy Survey Year 3 results: magnification modelling and impact on cosmological constraints from galaxy clustering and galaxy–galaxy lensing

   https://doi.org/10.1093/mnras/stad1594  

   Elvin-Poole, J.; MacCrann, N.; Everett, S.; Prat, J.; Rykoff, E_S; De Vicente, J.; Yanny, B.; Herner, K.; Ferté, A.; Valentino, E_Di; et al (June 2023, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT We study the effect of magnification in the Dark Energy Survey Year 3 analysis of galaxy clustering and galaxy–galaxy lensing, using two different lens samples: a sample of luminous red galaxies, redMaGiC, and a sample with a redshift-dependent magnitude limit, MagLim. We account for the effect of magnification on both the flux and size selection of galaxies, accounting for systematic effects using the Balrog image simulations. We estimate the impact of magnification on the galaxy clustering and galaxy–galaxy lensing cosmology analysis, finding it to be a significant systematic for the MagLim sample. We show cosmological constraints from the galaxy clustering autocorrelation and galaxy–galaxy lensing signal with different magnifications priors, finding broad consistency in cosmological parameters in ΛCDM and wCDM. However, when magnification bias amplitude is allowed to be free, we find the two-point correlation functions prefer a different amplitude to the fiducial input derived from the image simulations. We validate the magnification analysis by comparing the cross-clustering between lens bins with the prediction from the baseline analysis, which uses only the autocorrelation of the lens bins, indicating that systematics other than magnification may be the cause of the discrepancy. We show that adding the cross-clustering between lens redshift bins to the fit significantly improves the constraints on lens magnification parameters and allows uninformative priors to be used on magnification coefficients, without any loss of constraining power or prior volume concerns. 

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4. Observing flow of He II with unsupervised machine learning

   https://doi.org/10.1038/s41598-022-21906-w  

   Wen, X.; McDonald, L.; Pierce, J.; Guo, W.; Fitzsimmons, M_R (November 2022, Scientific Reports)

   Abstract Time dependent observations of point-to-point correlations of the velocity vector field (structure functions) are necessary to model and understand fluid flow around complex objects. Using thermal gradients, we observed fluid flow by recording fluorescence of$${\text{He}}_{2}^{*}$$ ${\text{He}}_2^{\ast }$excimers produced by neutron capture throughout a ~ cm³volume. Because the photon emitted by an excited excimer is unlikely to be recorded by the camera, the techniques of particle tracking (PTV) and particle imaging (PIV) velocimetry cannot be applied to extract information from the fluorescence of individual excimers. Therefore, we applied an unsupervised machine learning algorithm to identify light from ensembles of excimers (clusters) and then tracked the centroids of the clusters using a particle displacement determination algorithm developed for PTV. 

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5. Temporal evolution of the light emitted by a thin, laser-ionized plasma source

   https://doi.org/10.1063/5.0180416  

   Lee, Valentina; Ariniello, Robert; Doss, Christopher; Wolfinger, Kathryn; Stoltz, Peter; Hansel, Claire; Gessner, Spencer; Cary, John; Litos, Michael (January 2024, Physics of Plasmas)

   We present an experimental and simulation-based investigation of the temporal evolution of light emission from a thin, laser-ionized helium plasma source. We demonstrate an analytic model to calculate the approximate scaling of the time-integrated, on-axis light emission with the initial plasma density and temperature, supported by the experiment, which enhances the understanding of plasma light measurement for plasma wakefield accelerator (PWFA) plasma sources. Our model simulates the plasma density and temperature using a split-step Fourier code and a particle-in-cell code. A fluid simulation is then used to model the plasma and neutral density, and the electron temperature as a function of time and position. We then show the numerical results of the space-and-time-resolved light emission and that collisional excitation is the dominant source of light emission. We validate our model by measuring the light emitted by a laser-ionized plasma using a novel statistical method capable of resolving the nanosecond-scale temporal dynamics of the plasma light using a cost-effective camera with microsecond-scale timing jitter. This method is ideal for deployment in the high radiation environment of a particle accelerator that precludes the use of expensive nanosecond-gated cameras. Our results show that our models can effectively simulate the dynamics of a thin, laser-ionized plasma source. In addition, this work provides a detailed understanding of the plasma light measurement, which is one of the few diagnostic signals available for the direct measurement of PWFA plasma sources. 

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