arXiv subjects

G. B. Taylor

Publications and source records attributed to G. B. Taylor.

At least 19 recordsLinked to original sources

arXiv2025

Design and Commissioning of an LWA Swarm Station: The Long Wavelength Array -- North Arm

Modern radio interferometers are designed with increasingly sprawling geographical footprints, offering enhanced sensitivity and resolution. However, managing such extensive facilities presents operational challenges that can potentially impede or delay scientific progress. One solution to such obstacles is the `swarm telescope' concept which enables collaborative use of individual telescope systems, overseen by separate institutions, to create a more powerful and manageable facility. We present the design, construction, and commissioning of the Long Wavelength Array -- North Arm (LWA-NA) station, a prototype 64-element LWA Swarm telescope. LWA-NA is a cost-efficient, rapidly deployable platform for radio astronomy, and serves as a pathfinder for the larger LWA Swarm project.

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arXiv2025

Exploring Compact Symmetric Objects with Complex Morphologies

Compact symmetric objects (CSOs) are a unique class of jetted active galactic nuclei (AGN) defined by sub-kpc radio emission, showing radio structure on both sides of the central engine. CSOs tend to exhibit little to no relativistic beaming, thereby allowing us to determine their physical characteristics, such as the magnetic field strength and particle energy density. Selected with a literature search, we describe VLBI observations, imaging, and analyses of 167 CSO candidates. We identified 65 new bona fide CSOs, thus almost doubling the number of known bona fide CSOs to 144. With our greater breadth of sources, we confirm that edge-dimmed CSOs (CSO-1s) may represent a more diverse population than originally expected. We highlight a number of CSOs with complex morphologies, including candidates for supermassive binary black holes (SBBHs) and CSOs that appear to have morphologies akin to wide-angle tail (WAT) galaxies, which could perhaps indicate that some CSOs are experiencing a galactic merger.

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arXiv2024

The Radio Spectra of High Luminosity Compact Symmetric Objects (CSO-2s): Implications for Studies of Compact Jetted Active Galactic Nuclei

This paper addresses, for the first time, a key aspect of the phenomenology of Compact Symmetric Objects (CSOs) -- the characteristics of their radio spectra. We present a radio-spectrum description of a complete sample of high luminosity CSOs (CSO-2s), which shows that they exhibit the \textit{complete} range of spectral types, including flat-spectrum sources ($α\ge -0.5$), steep-spectrum sources ($α< -0.5$), and peaked-spectrum sources. We show that there is no clear correlation between spectral type and size, but there is a correlation between the high-frequency spectral index and both object type and size. We also show that, to avoid biasing the data and to understand the various classes of jetted-AGN involved, the complete range of spectral types should be included in studying the general phenomenology of compact jetted-AGN, and that complete samples must be used, selected over a wide range of frequencies. We discuss examples that demonstrate these points. We find that the high-frequency spectral indices of CSO-2s span $-1.3 <α_{\rm hi} < -0.3$, and hence that radio spectral signatures cannot be used to discriminate definitively between CSO-2s, binary galactic nuclei, and millilensed objects, unless they have $α_{\rm hi} >-0.3$.

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arXiv2024

Not So Fast: A New Catalog of Meteor Persistent Trains

This paper presents the results of a nearly two year long campaign to detect and analyze meteor persistent trains (PTs) - self-emitting phenomena which can linger up to an hour after their parent meteor. The modern understanding of PTs has been primarily developed from the Leonid storms at the turn of the century; our goal was to assess the validity of these conclusions using a diverse sample of meteors with a wide range of velocities and magnitudes. To this end, year-round observations were recorded by the Widefield Persistent Train camera, 2nd edition (WiPT2) and were passed through a pipeline to filter out airplanes and flag potential meteors. These were classified by visual inspection based on the presence and duration of trains. Observed meteors were cross-referenced with the Global Meteor Network (GMN) database, which independently detects and calculates meteor parameters, enabling statistical analysis of PT-leaving meteors. There were 4726 meteors codetected by the GMN, with 636 of these leaving trains. Among these were a large population of slow, dim meteors that left PTs; these slower meteors had a greater train production rate relative to their faster counterparts. Unlike prior research, we did not find a clear magnitude cutoff or a strong association with fast meteor showers. Additionally, we note several interesting trends not previously reported, which include PT eligibility being primarily determined by a meteor's terminal height and an apparent dynamical origin dependence that likely reflects physical meteoroid properties.

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arXiv2024

Spatially Resolved Observations of Meteor Radio Afterglows with the OVRO-LWA

We conducted an all-sky imaging transient search with the Owens Valley Radio Observatory Long Wavelength Array (OVRO-LWA) data collected during the Perseid meteor shower in 2018. The data collection during the meteor shower was motivated to conduct a search for intrinsic radio emission from meteors below 60 MHz known as the meteor radio afterglows (MRAs). The data collected were calibrated and imaged using the core array to obtain lower angular resolution images of the sky. These images were input to a pre-existing LWA transient search pipeline to search for MRAs as well as cosmic radio transients. This search detected 5 MRAs and did not find any cosmic transients. We further conducted peeling of bright sources, near-field correction, visibility differencing and higher angular resolution imaging using the full array for these 5 MRAs. These higher angular resolution images were used to study their plasma emission structures and monitor their evolution as a function of frequency and time. With higher angular resolution imaging, we resolved the radio emission size scales to less than 1 km physical size at 100 km heights. The spectral index mapping of one of the long duration event showed signs of diffusion of plasma within the meteor trails. The unpolarized emission from the resolved radio components suggest resonant transition radiation as the possible radiation mechanism of MRAs.

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arXiv2023

Compact Symmetric Objects -- I Towards a Comprehensive Bona Fide Catalog

Compact Symmetric Objects (CSOs) are jetted Active Galactic Nuclei (AGN) with overall projected size <1 kpc. The classification was introduced to distinguish these objects from the majority of compact jetted-AGN in centimeter wavelength very long baseline interferometry observations, where the observed emission is relativistically boosted towards the observer. The original classification criteria for CSOs were: (i) evidence of emission on both sides of the center of activity, and (ii) overall size <1 kpc. However some relativistically boosted objects with jet axes close to the line of sight appear symmetric and have been mis-classified as CSOs, thereby undermining the CSO classification. This is because two essential CSO properties, pointed out in the original papers, have been neglected: (iii) low variability, and (iv) low apparent speeds along the jets. As a first step towards creating a comprehensive catalog of ``bona fide'' CSOs, we identify 79 bona fide CSOs, including 15 objects claimed as confirmed CSOs here for the first time, that match the CSO selection criteria. This sample of bona fide CSOs can be used for astrophysical studies of CSOs without contamination by mis-classified CSOs. We show that the fraction of CSOs in complete flux density limited AGN samples with S$_{\rm 5\,GHz}$ >700 mJy is between $(6.8\pm1.6)$% and $(8.5\pm1.8)$%.

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arXiv2023

Compact Symmetric Objects -- II Confirmation of a Distinct Population of High-Luminosity Jetted Active Galaxies

Compact Symmetric Objects (CSOs) are compact (<1 kpc), jetted Active Galactic Nuclei (AGN), whose jet axes are not aligned close to the line of sight, and whose observed emission is not predominantly relativistically boosted towards us. Two classes of CSOs have previously been identified: approximately one fifth are edge-dimmed and designated as CSO 1s, while the rest are edge brightened and designated as CSO 2s. This paper focuses almost exclusively on CSO 2s. Using complete samples of CSO 2s we present three independent lines of evidence, based on their relative numbers, redshift distributions, and size distributions, which show conclusively that the vast majority (> 99%) of CSO 2s do not evolve into larger-scale radio sources. These CSO 2s belong to a distinct population of jetted-AGN, which should be characterized as ``short-lived'' compared to the classes of larger jetted-AGN, as opposed to ``young''. We show that there is a sharp upper cutoff in the CSO 2 size distribution at $\approx 500$ pc. The distinct differences between most CSO 2s and other jetted-AGN provides a crucial new time domain window on the formation and evolution of relativistic jets in AGN and the supermassive black holes that drive them.

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arXiv2023

Compact Symmetric Objects -- III Evolution of the High-Luminosity Branch and a Possible Connection with Tidal Disruption Events

We use a sample of 54 Compact Symmetric Objects (CSOs) to confirm that there are two unrelated CSO classes: an edge-dimmed, low-luminosity class (CSO~1), and an edge-brightened, high-luminosity class (CSO~2). Using blind tests, we show that CSO~2s consist of three sub-classes: CSO 2.0, having prominent hot-spots at the leading edges of narrow jets and/or narrow lobes; CSO~2.2, without prominent hot-spots, and with broad jets and/or lobes; and CSO~2.1, which exhibit mixed properties. Most CSO 2s do not evolve into larger jetted-AGN, but spend their whole life-cycle as CSOs of size $\lesssim$500 pc and age $\lesssim$5000 yr. The minimum energies needed to produce the radio luminosity and structure in CSO~2s range from $\sim~10^{-4}\,M_\odot{c}^2$ to $\sim7\,M_\odot{c}^2$. We show that the transient nature of most CSO~2s, and their birthrate, can be explained through ignition in the tidal disruption events of giant stars. We also consider possibilities of tapping the spin energy of the supermassive black hole, and tapping the energy of the accretion disk. Our results demonstrate that CSOs constitute a large family of AGN in which we have thus far studied only the brightest. More comprehensive CSO studies, with higher sensitivity, resolution, and dynamic range, will revolutionize our understanding of AGN and the central engines that power them.

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arXiv2023

Cannonball or Bowling Ball: A Proper Motion and Parallax for PSR J0002+6216

We report the results of careful astrometric measurements of the Cannonball pulsar J0002+6216 carried out over three years using the High Sensitivity Array (HSA). We significantly refine the proper motion to $μ=35.3\pm0.6$ mas yr$^{-1}$ and place new constraints on the distance, with the overall effect of lowering the velocity and increasing the inferred age to $47.60\pm0.80$ kyr. Although the pulsar is brought more in line with the standard natal kick distribution, this new velocity has implications for the morphology of the pulsar wind nebula that surrounds it, the density of the interstellar medium through which it travels, and the age of the supernova remnant (CTB 1) from which it originates.

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arXiv2023

Resolving the bow shock and tail of the cannonball pulsar PSR J0002+6216

We present X-ray and radio observations of the recently-discovered bow shock pulsar wind nebula associated with PSR J0002+6216, characterizing the PWN morphology, which was unresolved in previous studies. The multi-frequency, multi-epoch Very Large Array radio observations reveal a cometary tail trailing the pulsar and extending up to 5.3', with multiple kinks along the emission. The presented radio continuum images from multi-configuration broadband VLA observations are one of the first results from the application of multi-term multi-frequency synthesis deconvolution in combination with the awproject gridder implemented in the Common Astronomy Software Applications package (CASA). The X-ray emission observed with Chandra extends to only 21'', fades quickly, and has some hot spots present along the extended radio emission. These kinks could indicate the presence of density variation in the local ISM or turbulence. The bow shock standoff distance estimates a small bow shock region with a size 0.003-0.009 pc, consistent with the pulsar spin-down power of Edot=1.51x10^35 ergs/s estimated from timing. The high-resolution radio image reveals the presence of an asymmetry in the bow shock region which is also present in the X-ray image. The broadband radio image shows an unusually steep spectrum along with a flat-spectrum sheath, which could indicate varying opacity or energy injection into the region. Spatially-resolved X-ray spectra provide marginal evidence of synchrotron cooling along the extended tail. Our analysis of the X-ray data also shows that this pulsar has a low spin-down power and one of the lowest X-ray efficiencies observed in these objects.

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arXiv2022

A Combined Radio Multi-Survey Catalog of Fermi Unassociated Sources

Approximately one-third of existing $γ$-ray sources identified by the $\textit{Fermi Gamma-Ray Space Telescope}$ are considered to be unassociated, with no known counterpart at other frequencies/wavelengths. These sources have been the subject of intense scrutiny and observational effort during the observatory's mission lifetime, and here we present a method of leveraging existing radio catalogs to examine these sources without the need for specific dedicated observations, which can be costly and complex. Via the inclusion of many sensitive low-frequency catalogs we specifically target steep spectrum sources such as pulsars. This work has found steep-spectrum radio sources contained inside 591 $\textit{Fermi}$ unassociated fields, with at least 21 of them being notable for having pulsar-like $γ$-ray properties as well. We also identify a number of other fields of interest based on various radio and $γ$-ray selections.

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arXiv2022

Pulsar Observations at Low Frequencies: Applications to Pulsar Timing and Solar Wind Models

Efforts are underway to use high-precision timing of pulsars in order to detect low-frequency gravitational waves. A limit to this technique is the timing noise generated by dispersion in the plasma along the line of sight to the pulsar, including the solar wind. The effects due to the solar wind vary with time, influenced by the change in solar activity on different time scales, ranging up to $\sim 11$ years for a solar cycle. The solar wind contribution depends strongly on the angle between the pulsar line of sight and the solar disk, and is a dominant effect at small separations. Although solar wind models to mitigate these effects do exist, they do not account for all the effects of the solar wind and its temporal changes. Since low-frequency pulsar observations are most sensitive to these dispersive delays, they are most suited to test the efficacy of these models and identify alternative approaches. Here, we investigate the efficacy of some solar wind models commonly used in pulsar timing using long-term, high-cadence data on 6 pulsars taken with the Long Wavelength Array, and compare them with an operational solar wind model. Our results show that stationary models of the solar wind correction are insufficient to achieve the timing noise desired by pulsar timing experiments, and we need to use non-stationary models, which are informed by other solar wind observations, to obtain accurate timing residuals.

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arXiv2022

New Tests of Millilensing in the Blazar PKS 1413+135

Symmetric Achromatic Variability (SAV) is a rare form of radio variability in blazars that has been attributed to gravitational millilensing by a ~$10^2 - 10^5$ $M_\odot$ mass condensate. Four SAVs have been identified between 1980 and 2020 in the long-term radio monitoring data of the blazar PKS 1413+135. We show that all four can be fitted with the same, unchanging, gravitational lens model. If SAV is due to gravitational millilensing, PKS 1413+135 provides a unique system for studying active galactic nuclei with unprecedented microarcsecond resolution, as well as for studying the nature of the millilens itself. We discuss two possible candidates for the putative millilens: a giant molecular cloud hosted in the intervening edge-on spiral galaxy, and an undetected dwarf galaxy with a massive black hole. We find a significant dependence of SAV crossing time on frequency, which could indicate a fast shock moving in a slower underlying flow. We also find tentative evidence for a 989-day periodicity in the SAVs, which, if real, makes possible the prediction of future SAVs: the next three windows for possible SAVs begin in August 2022, May 2025, and February 2028.

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arXiv2021

Improvements to the Search for Cosmic Dawn Using the Long Wavelength Array

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 modelling 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 $10^{\rm{th}}$, 2021 and April $10^{\rm{th}}$ 2021. The reported residual RMS limits are 6 times above the amplitude of the potential signal reported by the Experiment to Detect the Global EoR Signature (EDGES) collaboration.

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arXiv2021

Broadband Imaging to Study the Spectral Distribution of Meteor Radio Afterglows

We present observations of 86 meteor radio afterglows (MRAs) using the new broadband imager at the Long Wavelength Array Sevilleta (LWA-SV) station. The MRAs were detected using the all-sky images with a bandwidth up to 20 MHz. We fit the spectra with both a power law and a log-normal function. When fit with a power law, the spectra varied from flat to steep and the derived spectral index distribution from the fit peaked at -1.73. When fit with a log-normal function, the spectra exhibits turnovers at frequencies between 30-40 MHz, and appear to be a better functional fit to the spectra. We compared the spectral parameters from the two fitting methods with the physical properties of MRAs. We observe a weak correlation between the log-normal turnover frequency and the altitude of MRAs. The spectral indices from the power law fit do not show any strong correlations with the physical properties of MRAs. However, the full width half maximum (FWHM) duration of MRAs is correlated with the local time, incidence angle, luminosity and optically derived kinetic energy of parent meteoroid. Also, the average luminosity of MRAs seems to be correlated with the kinetic energy of parent meteoroid and the altitude at which they occur.

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arXiv2021

Radio Counterpart Candidates to 4FGL-DR2 Unassociated Sources

For the duration of the Fermi Gamma-Ray Space Telescope's mission, approximately one-third of the point sources detected have been noted as "unassociated," meaning that they seem to have no known counterpart at any other wavelength/frequency. This mysterious part of the gamma-ray sky is perhaps one of the largest unknowns in current astronomical pursuits, and as such has been probed extensively by various techniques at various frequencies. Radio frequencies have been perhaps one of the most fruitful, producing a large fraction of the identified and associated Active Galactic Nuclei (AGN) and pulsars noted in each update of the point source catalogs. Here we present a catalog of 7432 radio counterpart candidates for unassociated gamma-ray fields in the 2nd Data Release of the 4th Fermi Point Source Catalog (4FGL-DR2). A description of the catalog and source types is provided followed by a discussion that demonstrates how the results of this work will aid new associations and identifications. As part of this work, we also present a first catalog derived from "quicklook" images of the Very Large Array Sky Survey (VLASS).

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arXiv2020

The Relativistic Jet Orientation and Host Galaxy of the Peculiar Blazar PKS 1413+135

PKS 1413+135 is one of the most peculiar blazars known. Its strange properties led to the hypothesis almost four decades ago that it is gravitationally lensed by a mass concentration associated with an intervening galaxy. It exhibits symmetric achromatic variability, a rare form of variability that has been attributed to gravitational milli-lensing. It has been classified as a BL Lac object, and is one of the rare objects in this class with a visible counterjet. BL Lac objects have jet axes aligned close to the line of sight. It has also been classified as a compact symmetric object, which have jet axes not aligned close to the line of sight. Intensive efforts to understand this blazar have hitherto failed to resolve even the questions of the orientation of the relativistic jet, and the host galaxy. Answering these two questions is important as they challenge our understanding of jets in active galactic nuclei and the classification schemes we use to describe them. We show that the jet axis is aligned close to the line of sight and PKS 1413+135 is almost certainly not located in the apparent host galaxy, but is a background object in the redshift range $0.247 < z < 0.5$. The intervening spiral galaxy at $z = 0.247$ provides a natural host for the putative lens responsible for symmetric achromatic variability and is shown to be a Seyfert 2 galaxy. We also show that, as for the radio emission, a "multizone" model is needed to account for the high-energy emission.

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arXiv2020

On the relation between mini-halos and AGN feedback in clusters of galaxies

A variety of large-scale diffuse radio structures have been identified in many clusters with the advent of new state-of-the-art facilities in radio astronomy. Among these diffuse radio structures, radio mini-halos are found in the central regions of cool core clusters. Their origin is still unknown and they are challenging to discover; less than thirty have been published to date. Based on new VLA observations, we confirmed the mini-halo in the massive strong cool core cluster PKS 0745$-$191 ($z=0.1028$) and discovered one in the massive cool core cluster MACS J1447.4+0827 ($z=0.3755$). Furthermore, using a detailed analysis of all known mini-halos, we explore the relation between mini-halos and AGN feedback processes from the central galaxy. We find evidence of strong, previously unknown correlations between mini-halo radio power and X-ray cavity power, and between mini-halo and the central galaxy radio power related to the relativistic jets when spectrally decomposing the AGN radio emission into a component for past outbursts and one for on-going accretion. Overall, our study indicates that mini-halos are directly connected to the central AGN in clusters, following previous suppositions. We hypothesize that AGN feedback may be one of the dominant mechanisms giving rise to mini-halos by injecting energy into the intra-cluster medium and reaccelerating an old population of particles, while sloshing motion may drive the overall shape of mini-halos inside cold fronts. AGN feedback may therefore not only play a vital role in offsetting cooling in cool core clusters, but may also play a fundamental role in re-energizing non-thermal particles in clusters.

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