Space-based Observations Research Articles

The Purport of Space Telescopes in Supernova Research

The violent stellar explosions known as supernovae have received especially strong attention in both the research community and the general public recently. With the advent of space telescopes, the study of these extraordinary events has switched gears and it has become one of the leading fields in modern astrophysics. In this paper, we review some of the recent developments, focusing mainly on studies related to space-based observations.

Design and performance characterization of a new LISA-like (laser interferometer space antenna-like) gravitational reference sensor and torsion pendulum testbed.

In this paper, we present the design and performance of the upgraded University of Florida torsion pendulum facility for testing inertial sensor technology related to space-based gravitational wave observatories and geodesy missions. In particular, much work has been conducted on inertial sensor technology related to the Laser Interferometer Space Antenna (LISA) space gravitational wave observatory mission. A significant upgrade to the facility was the incorporation of a newly designed and fabricated LISA-like gravitational reference sensor (GRS) based on the LISA Pathfinder GRS. Its LISA-like geometry has allowed us to make noise measurements that are more representative of those in LISA and has allowed for the characterization of the mechanisms of noise induced on a LISA GRS and their underlying physics. Noise performance results and experiments exploring the effect of temperature gradients across the sensor will also be discussed. The LISA-like sensor also includes unique UV light injection geometries for UV LED based charge management. Pulsed and DC charge management experiments have been conducted using the University of Florida charge management group's technology readiness level 4 charge management device. These experiments have allowed for the testing of charge management system hardware and techniques as well as characterizations of the dynamics of GRS test mass charging. The work presented here demonstrates the upgraded torsion pendulum's ability to act as an effective testbed for GRS technology.

Hybrid Optimization Algorithm in the Photometric Inversion of Periods for Asteroids

Asteroids, as the primitive building blocks for the formation of our solar system, could reveal its evolution mechanism, and have attracted more and more attention from the public and professional institutions in recent years. Their physical properties, such as rotational period, spin axis and overall shape, can be inverted from ground- and space-based photometric observations. Since the inversion process is very time-consuming, this paper combines the genetic algorithm with the Levenberg–Marquardt (LM) algorithm, and presents a hybrid optimization algorithm based on a Cellinoid shape model for the inversion of rotational periods, which greatly improves the inversion efficiency. The proposed hybrid algorithm is applied to the synthetic lightcurves generated for an assumed Cellinoid shape model and the inverted rotational period results are consistent with the preset ones with a reduced search time, compared with the LM algorithm. Finally, multiple numerical experiments on the periods are performed on lightcurves and sparse observations of real asteroids to confirm that the proposed method can perform well in improving computational efficiency.

Orbital kinematics of conjuncting objects in Low-Earth Orbit and opportunities for autonomous observations

As satellites and debris continue to proliferate in Low Earth Orbit (LEO), collision avoidance maneuvers are becoming routine for operational spacecraft, causing increasingly discontinuous operations. Despite the congested environment, collisions are still very unlikely events and most satellites would never actually need to maneuver during their lifetime. Maneuvers are currently performed far more than necessary because of the limited accuracy of the tracking data used for assessing collision risks, which leads to overestimates. A little explored solution is to equip satellites with sensors that enable them, whenever at risk of collision, to autonomously track the hazardous objects and refine their positional knowledge before making a maneuver decision. Unlike what is possible from ground, satellites can collect data and estimate the collision risk even shortly before a potential collision (e.g., one orbit before), improving the final prediction accuracy and reducing false alarm rates. Moreover, while most surveillance data is currently obtained through ground-based sensors, space-based observations can provide unique information as they do not suffer from atmospheric issues (e.g., diffractions, aberrations). Here, the feasibility of observing hazardous objects directly from at-risk satellites before potential collisions is corroborated by demonstrating that objects in LEO usually pass close together several times before the closest approach, providing short observation opportunities. A thorough characterization of these observing windows is performed by reconstructing and analyzing the trajectory evolution for thousands of historical conjunction events, starting from Two-Line Element (TLE) sets and using a Simplified General Perturbations 4 model (SGP4) for the propagation. Statistical analysis is performed to assess the average number and duration of the observation opportunities, the relative distances and velocities involved, and other relevant features. Results show that a satellite with a detection range of 500 km would be able in more than 80% of the cases to observe a high-risk object twice and for at least 10 s before the potential collision.

Rapid search for massive black hole binary coalescences using deep learning

The coalescences of massive black hole binaries are one of the main targets of space-based gravitational wave observatories. Such gravitational wave sources are expected to be accompanied by electromagnetic emissions. Low latency detection of the massive black hole mergers provides a start point for a global-fit analysis to explore the large parameter space of signals simultaneously being present in the data but at great computational cost. To alleviate this issue, we present a deep learning method for rapidly searching for signals of massive black hole binaries in gravitational wave data. Our model is capable of processing a year of data, simulated from the LISA data challenge, in only several seconds, while identifying all coalescences of massive black hole binaries with no false alarms. We further demonstrate that the model shows robust resistance to a wide range of generalization cases, including various waveform families and updated instrumental configurations. This method offers an effective approach that combines advances in artificial intelligence to open a new pathway for space-based gravitational wave observations.

Wireless Picosecond Time Synchronization for Distributed Antenna Arrays

Distributed antenna arrays have been proposed for many applications ranging from space-based observatories to automated vehicles. Achieving good performance in distributed antenna systems requires stringent synchronization at the wavelength and information levels to ensure that the transmitted signals arrive coherently at the target, or scattered and received signals can be appropriately processed via distributed algorithms. In this article, we address the challenge of high-precision time synchronization to align the operations of elements in a distributed antenna array and overcome time-varying bias between platforms primarily due to oscillator drift. We use a spectrally sparse two-tone waveform, which obtains approximately optimal time estimation accuracy, in a two-way time transfer process. We also describe a technique for determining the true time delay using the ambiguous two-tone matched filter output, and we compare the time synchronization precision of the two-tone waveform with the more common linear frequency modulation (LFM) waveform. We experimentally demonstrate wireless time synchronization using a single-pulse 40-MHz two-tone waveform over a 90-cm 5.8-GHz wireless link in a laboratory setting, obtaining a timing precision of 2.26 ps.

Severe L-band scintillation over low-to-mid latitudes caused by an extreme equatorial plasma bubble: joint observations from ground-based monitors and GOLD

The occurrence of plasma irregularities and ionospheric scintillation over the Caribbean region have been reported in previous studies, but a better understanding of the source and conditions leading to these events is still needed. In December 2021, three ground-based ionospheric scintillation and Total Electron Content monitors were installed at different locations over Puerto Rico to better understand the occurrence of ionospheric irregularities in the region and to quantify their impact on transionospheric signals. Here, the findings for an event that occurred on March 13–14, 2022 are reported. The measurements made by the ground-based instrumentation indicated that ionospheric irregularities and scintillation originated at low latitudes and propagated, subsequently, to mid-latitudes. Imaging of the ionospheric F-region over a wide range of latitudes provided by the GOLD mission confirmed, unequivocally, that the observed irregularities and the scintillation were indeed caused by extreme equatorial plasma bubbles, that is, bubbles that reach abnormally high apex heights. The joint ground- and space-based observations show that plasma bubbles reached apex heights exceeding 2600 km and magnetic dip latitudes beyond 28°. In addition to the identification of extreme plasma bubbles as the source of the ionospheric perturbations over low-to-mid latitudes, GOLD observations also provided experimental evidence of the background ionospheric conditions leading to the abnormally high rise of the plasma bubbles and to severe L-band scintillation. These conditions are in good agreement with the theoretical hypothesis previously proposed.Graphical

The effects of Galactic model uncertainties on LISA observations of double neutron stars

ABSTRACT Observations of binaries containing pairs of neutron stars using the upcoming space-based gravitational wave observatory, LISA, have the potential to improve our understanding of neutron star physics and binary evolution. In this work, we assess the effect of changing the model of the Milky Way’s kinematics and star formation history on predictions of the population of double neutron stars that will be detected and resolved by LISA. We conclude that the spatial distribution of these binaries is insensitive to the choice of Galactic models, compared to the stochastic variation induced by the small sample size. In particular, the time-consuming computation of the binaries’ Galactic orbits is not necessary. The distributions of eccentricity and gravitational-wave frequency are, however, affected by the choice of star formation history. Binaries with eccentricities e > 0.1, which can be measured by LISA observations, are mostly younger than $100\, {\rm Myr}$. We caution that comparisons between different predictions for LISA observations need to use consistent star formation histories, and that the Galactic star formation history should be taken into account in the analysis of the observations themselves. The lack of strong dependence on Galactic models means that LISA detection of double neutron star binaries may provide a relatively clean probe of massive binary star evolution.

Three-Dimensional Reconstruction of Coronal Features: A Python Tool for Geometric Triangulation

The determination of the three-dimensional (3D) geometry of coronal features is important for understanding the magnetic structuring of the solar atmosphere. In this context, the length of a coronal loop, which is subject to standing transverse oscillations, is a crucial parameter in coronal seismology for the correct estimation of the phase speed of the wave and, consequently, of the Alfvén speed and coronal magnetic-field strength. Simultaneous space-based observations of the solar corona from different vantage points, e.g. one from the Solar Dynamics Observatory (SDO) and the second from the Solar TErrestrial RElations Observatory (STEREO), have permitted the reconstruction of the geometry of coronal loops. Nisticò, Verwichte, and Nakariakov (Entropy15, 4520, 2013) proposed a method based on principal component analysis for fitting an ensemble of 3D points that sample a coronal loop. This method was shown to retrieve easily the main geometric parameters that define a loop, such as the loop axes and the loop plane. In this article, an extension of that work is presented that includes a Python tool for performing geometric triangulation of coronal features seen by two different observers.

Constraining the Cosmic Merger History of Intermediate-mass Black Holes with Gravitational Wave Detectors

Intermediate-mass black holes (IMBHs) have not been detected beyond any reasonable doubt through either dynamical or accretion signatures. Gravitational waves (GWs) represent an unparalleled opportunity to survey the sky and detect mergers of IMBHs, making it possible for the first time to constrain their formation, growth, and merger history across cosmic time. While the current network LIGO–Virgo–KAGRA is significantly limited in detecting mergers of IMBH binaries, the next generation of ground-based observatories and space-based missions promise to shed light on the IMBH population through the detection of several events per year. Here, we assess this possibility by determining the optimal network of the next generation of GW observatories to reconstruct the IMBH merger history across cosmic time. We show that Voyager, the Einstein Telescope, and Cosmic Explorer will be able to constrain the distribution of the primary masses of merging IMBHs up to ∼103 M ⊙ and with mass ratio ≳0.1, while LISA will complementary do so at higher mass and smaller mass ratios. Therefore, a network of next-generation ground-based and space-based observatories will potentially reconstruct the merger history of IMBHs. Moreover, IMBHs with masses ≲5 × 103 M ⊙ could be observed in multiband up to a redshift of z ≈ 4, ushering in a new era of GW astronomy.

Construction and Validation of a Geometry-based Mathematical Model for the Hard X-Ray Imager

Quantitative and analytical analysis of the modulation process of the collimator is a great challenge, and is also of great value to the design and development of Fourier transform imaging telescopes. The Hard X-ray Imager (HXI), as one of the three payloads onboard the Advanced Space-based Solar Observatory (ASO-S) mission, adopts modulating Fourier-Transformation imaging technique and will be used to explore the mechanism of energy release and transmission in solar flare activities. As an important step to reconstruct the images of solar flares, accurate modulation functions of HXI are needed. In this paper, a mathematical model is developed to analyze the modulation function under a simplified condition first. Then its behavior under six degrees of freedom is calculated after adding the rotation matrix and translation change to the model. In addition, unparalleled light and extended sources are also considered so that our model can be used to analyze the X-ray beam experiment. Next, applied to the practical HXI conditions, the model has been confirmed not only by Geant4 simulations but also by some verification experiments. Furthermore, how this model helps to improve the image reconstruction process after the launch of ASO-S is also presented.

Gravitational waves from no-scale supergravity

In this paper we study four concrete models, based on no-scale supergravity with SU(2,1)/SU(2) times U(1) symmetry. We modify either the Kähler potential or the superpotential, which are related to the no-scale theory with this symmetry. In this scenario, the induced Gravitational Waves, are calculated to be detectable by the future space-based observations such as LISA, BBO and DECIGO. The models under study are interrelated, as they all yield the Starobinsky effective-like scalar potential in the unmodified case. We evaluate numerically the scalar power spectrum and the stochastic background of the Gravitational Waves, satisfying the observational Planck cosmological constraints for inflation.

A Review of Orbital Mechanics for Space-Based Gravitational Wave Observatories

The confirmation of gravitational waves in recent years has set off a new upsurge of exploring the extreme interactions critical to the origin and evolution of stars, galaxies, and the universe. The detection of gravitational waves in space is expected to cover the largest number and the greatest variety of gravitational wave sources, which is more compelling and valuable than the initial detection on the ground. Orbital dynamics and control are the keys to realizing the detection of gravitational waves in space. This paper reviews the orbital mechanics for space-based gravitational wave observatories. The principle and typical gravitational wave observation mission concepts are first introduced and classified summarized. Then, the orbital mechanics of the space-based gravitational wave observatories in different spatial locations are reviewed. On the basis of the characteristics of different observatories, 2 groups of methods related to the observatory configuration design and optimization are summarized: the constellation configuration design and optimization method similar to the geocentric configuration and libration point configuration, the formation design and optimization method similar to heliocentric configuration. The prospects of space-based gravitational wave observatories are finally put forward, which shall provide a reference for future research on space-based gravitational wave observatories.

Cosmic topology. Part I. Limits on orientable Euclidean manifolds from circle searches

The Einstein field equations of general relativity constrain the local curvature at every point in spacetime, but say nothing about the global topology of the Universe. Cosmic microwave background anisotropies have proven to be the most powerful probe of non-trivial topology since, within ΛCDM, these anisotropies have well-characterized statistical properties, the signal is principally from a thin spherical shell centered on the observer (the last scattering surface), and space-based observations nearly cover the full sky. The most generic signature of cosmic topology in the microwave background is pairs of circles with matching temperature and polarization patterns. No such circle pairs have been seen above noise in the WMAP or Planck temperature data, implying that the shortest non-contractible loop around the Universe through our location is longer than 98.5% of the comoving diameter of the last scattering surface. We translate this generic constraint into limits on the parameters that characterize manifolds with each of the nine possible non-trivial orientable Euclidean topologies, and provide a code which computes these constraints. In all but the simplest cases, the shortest non-contractible loop in the space can avoid us, and be shorter than the diameter of the last scattering surface by a factor ranging from 2 to at least 6. This result implies that a broader range of manifolds is observationally allowed than widely appreciated. Probing these manifolds will require more subtle statistical signatures than matched circles, such as off-diagonal correlations of harmonic coefficients.

Structured H-infinity design for the LISA mission accelerometer mode

This article presents the application of the structured H∞ control approach to the design of the LISA mission accelerometer mode. This joint ESA/NASA mission will be the first space-based gravitational wave observatory and is characterized by very stringent scientific constraints resulting in unprecedented control challenges in terms of precision, accuracy, and complexity. The results presented in here were the first demonstration step performed within an ESA study tasked with surveying, trading-off, and applying advanced control techniques to LISA. In addition to showing the methodological gains and design capabilities of the structured H∞ approach, the effects of hardware changes as well as control switching were also analyzed for the designed controllers providing good insight on the way forward to reduce the associated transients. The results presented in this article laid the groundwork, and design process, to subsequently design and validate the full LISA accelerometer mode.

Improving QZSS Precise Orbit Determination using Space-based and Ground-based Observations

Improving QZSS Precise Orbit Determination using Space-based and Ground-based Observations

GD 99: Re-investigation of an old ZZ Ceti companion

Context. Thanks to photometric space missions, we have access to more and more information on the properties of white dwarf stars, especially pulsating ones. In the case of pulsators, we have the opportunity to get an insight into their otherwise hidden interiors by the means of asteroseismology. In addition to space-based observations, we also take advantage of the opportunity to study the pulsations of white dwarf stars from the ground, either as observations that are complementary to space-based measurements or individual observing runs on selected targets across long timescales. Aims. We aim to investigate long-term, single-site observations of the bright, yet scarcely studied ZZ Ceti star, GD 99. Our main goals are to determine as many eigenmodes for asteroseismology as possible and then to carry out a seismic analysis of this target. Methods. We performed a Fourier analysis of the light curves obtained in different epochs. After finding the normal modes of the pulsation, we ran the 2018 version of the White Dwarf Evolution Code to build model grids for the period fits. We compared the seismic distance of the best-fit model with the geometric value provided by Gaia measurements. Results. We find that GD 99 is rich in pulsation modes in the ∼200 − 1100 s period range, as we detected seven new periods. Together with the literature data, we were able to use 11 modes for the asteroseismic fits. We accepted an asteroseismic model solution with Teff = 13 500 K and M* = 0.80 M⊙ as a best fit; however, this suggests a hotter and more massive star than we might have expected based on the spectroscopic values. We also estimated the rotational rate of the star to be 13.17 h, based on TESS observations.

Influences of various space current systems on the geomagnetic field in near-Earth space

Ground and space-based observations of the geomagnetic field are usually a superposition of different sources from the Earth’s core, lithosphere, ocean, ionosphere, and magnetosphere, and also from field-aligned currents coupling the ionosphere and magnetosphere—the meridional currents that connect the two hemispheres and the induced currents due to the variations of fields over time. The fluctuation of magnetic fields generated by these highly dynamic space currents greatly limits the accuracy of the geomagnetic models. In order to better accomplish the scientific objectives of Macau Science Satellite-1 (MSS-1), and to improve existing geomagnetic field models, we present here for the first time a self-consistent coupling of solar wind, magnetosphere, and ionosphere, which represents the most developed numerical simulation method for space physics research so far, making it possible to quantify the contribution of different current systems to the total observed magnetic field (<italic><bold>B</bold></italic>). The results show that numerical simulation can capture main magnetic disturbance characteristics with significant precision. Partial ring current is a major contributor to the latitudinal magnetic perturbation near the equator. Magnetopause and magnetotail currents affect the radial magnetic perturbation around the mid-latitudes. Field-aligned and Pedersen currents produce significant longitudinal and latitudinal magnetic perturbations at high latitudes.

Moist Convection in the Giant Planet Atmospheres

The outer planets of our Solar System display a myriad of interesting cloud features, of different colors and sizes. The differences between the types of observed clouds suggest a complex interplay between the dynamics and chemistry at play in these atmospheres. Particularly, the stark difference between the banded structures of Jupiter and Saturn vs. the sporadic clouds on the ice giants highlights the varieties in dynamic, chemical and thermal processes that shape these atmospheres. Since the early explorations of these planets by spacecrafts, such as Voyager and Voyager 2, there are many outstanding questions about the long-term stability of the observed features. One hypothesis is that the internal heat generated during the formation of these planets is transported to the upper atmosphere through latent heat release from convecting clouds (i.e., moist convection). In this review, we present evidence of moist convective activity in the gas giant atmospheres of our Solar System from remote sensing data, both from ground- and space-based observations. We detail the processes that drive moist convective activity, both in terms of the dynamics as well as the microphysical processes that shape the resulting clouds. Finally, we also discuss the effects of moist convection on shaping the large-scale dynamics (such as jet structures on these planets).

What the Upper Atmospheres of Giant Planets Reveal

The upper atmospheres of the Giant Planets, Jupiter, Saturn, Uranus and Neptune are transition regions between meteorological layers and outer space. As a result of their exceptionally rarefied nature, they are highly sensitive and therefore revealing probes of the forcing exerted both from above and below. This review provides an overview of these upper atmospheres and the major processes that take place within them, including their powerful auroras, the giant planet ‘energy crisis’ and the decay of Saturn’s rings into the planet. We discuss the many remote-sensing tools that have been used to understand them, for example, large ground-based observatories such as the Keck telescope, space-based observatories such as the Hubble Space Telescope and orbiters such as the Cassini spacecraft. Looking into the future, we discuss the possibilities afforded by the latest and next generation of observatories and space missions, such as the James Webb Space Telescope.