Astronomical time series often have non-uniform sampling in time, or irregular cadences, with long gaps separating clusters of observations. Some of these data sets are also explicitly non-Gaussian with respect to the expected model fit, or the simple mean. The standard Lomb-Scargle periodogram is based on the least squares solution for a set of test periods and, therefore, is easily corrupted by a subset of statistical outliers or an intrinsically non-Gaussian population. It can produce completely misleading results for heavy-tailed distribution of residuals. We propose a robust 1-norm periodogram technique, which is based on the principles of robust statistical estimation. This technique can be implemented in weighted or unweighted options. The method is described in detail and compared with the classical least squares periodogram on a set of astrometric VLBI measurements of the ICRF quasar IERS B0642+449. It is uniformly applied to a collection of 259 ICRF3 quasars each with more than 200 epoch VLBI measurements, resulting in a list of 49 objects with quasi-periodic position changes above the 3 sigma level, which warrant further investigation.

Published analyses of very long baseline interferometry data for the sources included in the third International Celestial Reference Frame catalog have revealed object-specific, excess astrometric variability and quasi-coherent trajectories as functions of time. A fraction of these sources show markedly elongated distributions of positions on the sky measured with diurnal observations. Here we apply a novel statistical and data-processing method to the diurnal position measurements stretching over 40 yr to quantify the degree of elongation and its position angle, for each source with more than 200 data points. We find that 49% of the examined sources have distribution elongations in excess of 1.3. Robust uncertainties of the directions of maximal astrometric dispersion are computed by the bootstrapping method, and the results are compared with a larger catalog of radio jet directions by A. V. Plavin et al. (2022). Nearly one-half of the sources with smaller position angle uncertainties are found to have astrometric position excursions from their mean positions aligned with the radio jet structures within +/- 30 degrees.

We present recent 2-port vector network analyzer (VNA) measurements of the complete set of scattering parameters for the antenna used within the Long Wavelength Array (LWA) and the associated front end electronics (FEEs). Full scattering parameter measurements of the antenna yield not only the reflection coefficient for each polarization, S11 and S22, but also the coupling between polarizations, S12 and S21. These had been previously modeled using simulations, but direct measurements had not been obtained until now. The measurements are used to derive a frequency dependent impedance mismatch factor (IMF) which represents the fraction of power that is passed through the antenna-FEE interface and not reflected due to a mismatch between the impedance of the antenna and the impedance of the FEE. We also present results from a two-antenna experiment where each antenna is hooked up to a separate port on the VNA. This allows for cross-antenna coupling to be measured for all four possible polarization combinations. Finally, we apply the newly measured IMF and FEE forward gain corrections to LWA data to investigate how well they remove instrumental effects.

We summarize the second radio synchrotron background workshop, which took place on 2022 June 15–17 in Barolo, Italy. This meeting was convened because available measurements of the diffuse radio zero level continue to suggest that it is several times higher than can be attributed to known Galactic and extragalactic sources and processes, rendering it the least well-understood electromagnetic background at present and a major outstanding question in astrophysics. The workshop agreed on the next priorities for investigations of this phenomenon, which include searching for evidence of the radio Sunyaev–Zel’dovich effect, carrying out cross-correlation analyses of radio emission with other tracers, and supporting the completion of the 310 MHz absolutely calibrated sky map project.

We present recent improvements to the search for the global Cosmic Dawn signature using the Long Wavelength Array station located on the Sevilleta National Wildlife Refuge in New Mexico, USA (LWA–SV). These improvements are both in the methodology of the experiment and the hardware of the station. An improved observing strategy along with more sophisticated temperature calibration and foreground modeling schemes have led to improved residual RMS limits. A large improvement over previous work using LWA–SV is the use of a novel achromatic beamforming technique which has been developed for LWA–SV. We present results from an observing campaign which contains 29 days of observations between March 10, 2021 and April 10, 2021. The reported residual RMS limits are six times above the amplitude of the potential signal reported by the Experiment to Detect the Global EoR Signature (EDGES) collaboration.

The search for the spectral signature of hydrogen from the formation of the first stars, known as Cosmic Dawn or First Light, is an ongoing effort around the world. The signature should present itself as a decrease in the temperature of the 21-cm transition relative to that of the Cosmic Microwave Background and is believed to reside somewhere below 100 MHz. A potential detection was published by the Experiment to Detect the Global EoR Signal (EDGES) collaboration with a profile centered around 78 MHz of both unexpected depth and width (Bowman et. al 2018; arXiv:1810.05912). If validated, this detection will have profound impacts on the current paradigm of structure formation within $\Lambda$CDM cosmology. We present an attempt to detect the spectral signature reported by the EDGES collaboration with the Long Wavelength Array station located on the Sevilleta National Wildlife Refuge in New Mexico, USA (LWA-SV). LWA-SV differs from other instruments in that it is a 256 element antenna array and offers beamforming capabilities that should help with calibration and detection. We report first limits from LWA-SV and look toward future plans to improve these limits.

There exists a well known connection between gamma-ray emission and millisecond pulsars (MSPs) and there is also some evidence for a connection between gamma-ray emission and black widow and redback pulsar systems. These black widow and redback pulsar systems have been shown to have periodic dispersion measure (DM) variations on timescales near that of the binary period. This variation in DM arises from the pulse traveling through material present within the systems. The exact conditions which separate “normal” MSP systems from black widows and redbacks are not well understood. We have observed four binary pulsar systems, two of which show gamma-ray emission, which have known white dwarf companions in order to search for similar periodic DM variations. The expected DM variations are small as white dwarfs contribute little material to the system due to their strong gravity and theoretically weak stellar winds. The low frequencies observed by the Long Wavelength Array (LWA) make us highly sensitive to DM variations. We report changes in DM nearly 3 orders of magnitude smaller than seen in black widow systems, but find no periodic variations.