Next-generation Ground Research Articles

Current and future cosmological impact of microwave background temperature measurements

The redshift dependence of the cosmic microwave background temperature, T(z)=T0(1+z), is a key prediction of standard cosmology, but this relation is violated in many extensions thereof. Current astrophysical facilities can probe it in the redshift range 0≤z≤6.34. We extend recent work by Gelo et al. (2022) showing that for several classes of models (all of which aim to provide alternative mechanisms for the recent acceleration of the universe) the constraining power of these measurements is comparable to that of other background cosmology probes. Specifically, we discuss constraints on two classes of models not considered in the earlier work: a model with torsion and a recently proposed phenomenological dynamical dark energy model which can be thought of as a varying speed of light model. Moreover, for both these models and also for those in the earlier work, we discuss how current constraints may be improved by next-generation ground and space astrophysical facilities. Overall, we conclude that these measurements have a significant cosmological impact, mainly because they often constrain combinations of model parameters that are orthogonal, in the relevant parameter space, to those of other probes.

Global Impact of Emerging Internetwork Fields on the Low Solar Atmosphere

Small-scale, newly emerging internetwork (IN) magnetic fields are considered a viable source of energy and mass for the solar chromosphere and possibly the corona. Multiple studies show that single events of flux emergence can indeed locally heat the low solar atmosphere through interactions of the upward propagating magnetic loops and the preexisting ambient field lines. However, the global impact of the newly emerging IN fields on the solar atmosphere is still unknown. In this paper, we study the spatiotemporal evolution of IN bipolar flux features and analyze their impact on the energetics and dynamics of the quiet-Sun atmosphere. We use high-resolution, multiwavelength, coordinated observations obtained with the Interface Region Imaging Spectrograph, Hinode, and the Solar Dynamics Observatory to identify emerging IN magnetic fields and follow their evolution. Our observational results suggest that only the largest IN bipoles are capable of heating locally the low solar atmosphere, while the global contribution of these bipoles appears to be marginal. However, the total number of bipoles detected and their impact estimated in this work is limited by the sensitivity level, spatial resolution, and duration of our observations. To detect smaller and weaker IN fields that would maintain the basal flux, and examine their contribution to the chromospheric heating, we will need higher resolution, higher sensitivity, and longer time series obtained with current and next-generation ground- and space-based telescopes.

The Fibre Resolved OpticAl and Near-Ultraviolet Czerny–Turner Imaging Spectropolarimeter (francis)

The solar physics community is entering a golden era that is ripe with next-generation ground- and space-based facilities, advanced spectral inversion techniques, and realistic simulations that are becoming more computationally streamlined and efficient. With ever-increasing resolving power stemming from the newest observational telescopes, it becomes more challenging to obtain (near-)simultaneous measurements at high spatial, temporal and spectral resolutions, while operating at the diffraction limit of these new facilities. Hence, in recent years there has been increased interest in the capabilities integral field units (IFUs) offer towards obtaining the trifecta of high spatial, temporal and spectral resolutions contemporaneously. To date, IFUs developed for solar physics research have focused on mid-optical and infrared measurements. Here, we present an IFU prototype that has been designed for operation within the near-ultraviolet to mid-optical wavelength range, which enables key spectral lines (e.g., Ca ii H/K, Hβ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$\\beta $\\end{document}, Sr ii, Na i D1/D2, etc.) to be studied, hence providing additional spectral coverage to the instrument suites developed to date. The IFU was constructed as a low-budget proof-of-concept for the upcoming 2 m\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$2\ ext{ m}$\\end{document} class Indian National Large Solar Telescope and employs circular cross-section fibres to guide light into a Czerny–Turner configuration spectrograph, with the resulting spectra captured using a high quantum efficiency scientific CMOS camera. Mapping of each input fibre allows for the reconstruction of two-dimensional spectral images, with frame rates exceeding 20 s−1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$20\ ext{ s}^{-1}$\\end{document} possible while operating in a non-polarimetric configuration. Initial commissioning of the instrument was performed at the Dunn Solar Telescope, USA, during August 2022. The science verification data presented here highlights the suitability of fibre-fed IFUs operating at near-ultraviolet wavelengths for solar physics research. Importantly, the successful demonstration of this type of instrument paves the way for further technological developments to make a future variant suitable for upcoming ground-based and space-borne telescope facilities.

Stability of the fundamental quasinormal mode in time-domain observations against small perturbations

Black hole spectroscopy with gravitational waves is an important tool to measure the mass and spin of astrophysical black holes and to test their Kerr nature. Next-generation ground- and space-based detectors will observe binary black hole mergers with large signal-to-noise ratios and perform spectroscopy routinely. It was recently shown that small perturbations due, e.g., to environmental effects (the "flea") to the effective potential governing gravitational-wave generation and propagation in black hole exteriors (the "elephant") can lead to arbitrarily large changes in the black hole's quasinormal spectrum, including the fundamental mode, which is expected to dominate the observed signal. This raises an important question: is the black hole spectroscopy program robust against perturbations? We clarify the physical behavior of time-domain signals under small perturbations in the potential, and we show that changes in the amplitude of the fundamental mode in the prompt ringdown signal are parametrically small. This implies that the fundamental quasinormal mode extracted from the observable time-domain signal is stable against small perturbations. The stability of overtones deserves further investigation.

Probing Gamma-Ray Burst VHE Emission with the Southern Wide-Field-of-View Gamma-Ray Observatory

Recent observations have confirmed that Gamma-Ray Burst (GRB) afterglows produce Very High-Energy radiation (VHE, E>100GeV). This highly anticipated discovery opens new scenarios in the interpretation of GRBs and in their role as probes of Extragalactic Background Light (EBL) and Lorentz Invariance Violation (LIV). However, some fundamental questions about the actual nature of VHE emission in GRBs and its evolution during the burst are still unsolved. These questions will be difficult to address, even with future imaging Cherenkov telescopes, such as the Cherenkov Telescope Array (CTA). Here we investigate the prospects of gamma-ray sky monitoring with Extensive Air Showers arrays (EAS) to address these problems. We discuss the theoretical aspects connected with VHE radiation emission and the implications that its temporal evolution properties have on the interpretation of GRBs. By revisiting the high-energy properties of some Fermi-LAT detected GRBs, we estimate the typical fluxes expected in the VHE band and compare them with a range of foreseeable instrument performances, based on the Southern Wide Field-of-view Gamma-ray Observatory concept (SWGO). We focus our analysis on how different instrument capabilities affect the chances to explore the burst onset and early evolution in VHE, providing invaluable complementary information with respect to Cherenkov telescope observations. We show that under the assumption of conditions already observed in historical events, the next-generation ground monitoring detectors can actually contribute to answer several key questions.

Unveiling the origin of the gamma-ray emission in NGC 1068 with the Cherenkov Telescope Array

Several observations are revealing the widespread occurrence of mildly relativistic wide-angle AGN winds strongly interacting with the gas of their host galaxy. Such winds are potential cosmic-ray accelerators, as supported by gamma-ray observations of the nearby Seyfert galaxy NGC 1068 with the Fermi gamma-ray space telescope. The non-thermal emission produced by relativistic particles accelerated by the AGN-driven wind observed in the circum-nuclear molecular disk of such galaxy is invoked to produce the gamma-ray spectrum. The AGN wind model predicts a hard spectrum that extend in the very high energy band which differs significantly from those corresponding to other models discussed in the literature, like starburst or AGN jet. We present dedicated simulations of observations through the Cherenkov Telescope Array (CTA), the next-generation ground based gamma-ray observatory, of the very high energy spectrum of the Seyfert galaxy NGC 1068 assuming the AGN wind and the AGN jet models. We demonstrate that, considering 50 hours of observations, CTA can be effectively used to constrain the two different emission models, providing important insight into the physics governing the acceleration of particles in non-relativistic AGN-driven outflows. This analysis strongly motivates observations of Seyfert and starburst galaxies with CTA in order to test source population models of the extragalactic gamma-ray and neutrino backgrounds.

A next-generation ground array for the detection of ultrahigh-energy cosmic rays: the Fluorescence detector Array of Single-pixel Telescopes (FAST)

The origin and nature of ultrahigh-energy cosmic rays (UHECRs) is one of the most intriguing and important mysteries in astroparticle physics. The two largest observatories currently in operation, the Telescope Array Experiment in central Utah, USA, and the Pierre Auger Observatory in western Argentina, have been steadily observing UHECRs in both hemispheres for over a decade. We highlight the latest results from both of these experiments, and address the requirements for a next-generation UHECR observatory. The Fluorescence detector Array of Single-pixel Telescopes (FAST) is a design concept for a next-generation UHECR observa-tory, addressing the requirements for a large-area, low-cost detector suitable for measuring the properties of the highest energy cosmic rays with an unprecedented aperture. We have developed a full-scale prototype consisting of four 200 mm photomultiplier-tubes at the focus of a segmented mirror of 1.6 m in diameter. Over the last three years, we installed three such prototypes at the Black Rock Mesa site of the Telescope Array Experiment. These telescopes have been steadily taking data since installation. We report on preliminary results of the full-scale FAST prototypes, including measurements of distant ultraviolet lasers and UHECRs. Futhermore, we discuss our plan to install an additional identical FAST prototype at the Pierre Auger Observatory. Possible benefits to the Telescope Array and the Pierre Auger Observatory include a comparison of the transparency of the atmosphere above both experiments, a study of the systematic uncertainty associated with their existing fluorescence detectors, and a cross-calibration of their energy and Xmax scales.

On the sensitivity of atmospheric Cherenkov telescope arrays for regions with presence of multiple gamma-ray sources

The potential of a next-generation ground based gamma-ray telescope array has been investigated. In addition to the ideal Gaussian shaped PSF, more realistic non-Gaussian PSFs with tails have been considered and their impact on the detector performance has been studied. The capability of the instrument to resolve multiple sources has been analyzed and the corresponding detector sensitivity estimated. These scenarios are particularly interesting in the framework of Galactic objects, where the observation of more than one source in the same field of view (FoV) is very likely to happen.

Toward a Protected Future Force

A significant challenge facing planners of America's future ground forces is the question of how to think about survivability. With a great deal of emphasis placed on strategic mobility--both in speed of deployment and in logistical efficiency--the manned ground vehicles of the US Army's Future Combat Systems (FCS) will be considerably lighter than the tanks and infantry fighting vehicles currently fielded in Army units. This poses a problem: without the ability to wield the armor protection of the Abrams main battle tank, FCS vehicles (1) will have more inherent vulnerability to enemy direct-fire weapons than the vehicles that they will eventually replace. This problem is not just tactical and operational in nature; it has strategic implications, and if it is not addressed effectively, the ability of the Army to meet its required aims will be put at risk. The US Army plans to introduce its next-generation ground force quickly, starting with an experimental battalion by the end of the decade and a full brigade--called a Unit of Action--in 2014. (2) The Future Force, formerly called the Objective Force, is anticipated to be a highly mobile, light armored force with previously unheard-of intelligence-surveillance-reconnaissance (ISR) capabilities, emphasizing maneuver and stand-off precision firepower to eliminate enemy forces from long range. The Army's plan does allow for a conventional armored counterattack corps based on existing tanks and fighting vehicles through at least 2030, but the centerpiece of the Army will be the FCS-equipped Units of Action. The FCS Family of Vehicles--Survivability without Protection? The survivability of the Future depends on two factors: the technological measures taken to protect the force and the methods of employment of the Units of Action. According to the Army's Concepts for the Objective Force white paper: The agility of our formations combined with the common operating picture is critical to maximize survivability. Ground and air platforms will leverage the best combination of low observable, reduced electronic signature, ballistic protection, long-range acquisition, early discrete targeting, shoot first every time, and target destruction every time we pull the trigger. Objective survivability will be linked to its inherently offensive orientation, as well as its speed and lethality. (3) The inherent protection of the 16- to 20-ton FCS manned ground vehicle will be relatively low, primarily the result of its light weight. Future Combat Systems vehicles will be equipped with a variety of technical countermeasures intended to enhance their survivability in the event of contact with the enemy, but the underlying basis for their ability to survive on the battlefield is their ability to locate the enemy in all terrain types and then kill of outmaneuver the enemy without being effectively engaged. The extent to which armor will play a role in FCS survivability was outlined in a presentation given at the 23d Army Science Conference in December 2002. (4) The presentation outlines the Army's vision of a holistic approach to survivability: it intends to employ methods of preventing American vehicles from being effectively engaged through a combination of technical defenses and creative employment of forces. For example, to avoid detection, the Army will maneuver its forces out of contact with the enemy, it will employ vehicles with reduced signatures, and it will attempt to blind the enemy through targeting its command and control and ISR assets. Similar methods will be employed at each of the other levels of engagement--once detected, methods will be used to prevent Army vehicles from being acquired, and then hit, and then penetrated, and then destroyed. This is typically given in a diagram with concentric circles, the outermost being Detected and the innermost being Killed. …

Advanced structure methodologies for next-generation ground vehicles. Part 2: Case study

In the first paper of this two-part study, basic theories were introduced for several new methodologies developed in the Automotive Research Center (a US Army TACOM Center of Excellence for Modelling and Simulation of Ground Vehicles at the University of Michigan) for the simulation and design of advanced structures and materials for next-generation ground vehicles. These new methodologies include: (1) an advanced topology optimisation technique for innovative conceptual design of vehicle structures and materials; (2) a systematic design optimisation process with efficient analysis and sensitivity analysis capabilities for detailed design modifications to improve the vibration and noise characteristics of a complex vehicle structure; (3) a reduced-order modelling technique that can be used to systematically generate low-order models for the prediction of vehicle vibration, power flow, and the effects of parameter uncertainties; and (4) an efficient and accurate energy boundary element analysis method for high-frequency noise analysis outside the vehicle. In this second paper, an extensive case study is presented to demonstrate how the methodologies presented in the first paper can be applied to a vehicle system. A pick-up truck equipped with an advanced hybrid propulsion system is considered in this paper, and various example design and prediction problems are discussed, which provide proof-of-concept for the methodologies developed.

Advanced structure methodologies for next-generation ground vehicles. Part 1: Basic theories

One of the major objectives of the Automotive Research Center (a US Army TACOM Center of Excellence for the modelling and simulation of ground vehicles at the University of Michigan) is to develop new methodologies for advanced structures and materials for next-generation ground vehicles. Several major developments in this area are detailed in this paper. First, an advanced topology optimisation technique is presented, which provides a tool for laying out new, conceptually advanced designs for vehicle structures, or substructures, to achieve the lower weight and higher performance requirements for next-generation ground vehicles. Second, a 'sizing' design optimisation process is presented for detailed design changes in order to improve the vibro-acoustic response of a complex vehicle structure. This process incorporates efficient analysis and sensitivity analysis capabilities for vibro-acoustic systems. In addition, a component-based technique is presented for generating reduced-order models of a vehicle structure in order to lower the computational costs of vibration analysis. This technique is also extended to analysing vibration transmission in a complex vehicle structural system to determine the power flow among components and the effect of parameter uncertainties. Finally, an energy boundary element analysis method is presented for efficient and accurate high-frequency noise analysis, which extends the capability for predicting the acoustic field around the vehicle due to various sources.