arXiv subjects

Tiege McCarthy

Publications and source records attributed to Tiege McCarthy.

6 recordsLinked to original sources

arXiv2026

Comprehensive VLBI observations of Galileo satellites with the AuScope array

Interest in the topic of geodetic co-location in space and space ties has recently intensified within the geodetic community, particularly following the approval of the European Space Agency's (ESA) Genesis mission. From the perspective of Very Long Baseline Interferometry (VLBI), observations of Earth-orbiting satellites are not standard practice yet. To enable VLBI support for future colocation satellite missions, such observations must be integrated into the VLBI processing chain. In this study, we present comprehensive VLBI observations of Galileo navigation satellites conducted with the Australian AuScope VLBI array. Using the 12-m antennas in Hobart, Katherine and Yarragadee equipped with VLBI Global Observing System (VGOS) instrumentation, Galileo E1 and E6 signals were observed in test experiments and a series of four full-scale 24-hour observing sessions. We present the estimation of VLBI station coordinates from observations to navigation satellites, thereby demonstrating, for the first time, inter-technique ties between the VLBI and Global Navigation Satellite System (GNSS) frame. We describe the processing strategy, including correlation, fringe fitting, precision assessment and satellite tracking approach. Delay observables achieve precisions of a few picoseconds in the E1 band and several tens of picoseconds in the E6 band for 1-s integration times. However, unmodelled signals on the order of several hundred picoseconds are found in the residual delays. Estimated station coordinates agree with a priori values at the metre level, while baseline lengths agree at the sub-metre level. These results demonstrate the feasibility of large-scale VLBI observations to GNSS satellites and provide critical groundwork for future co-location satellite missions such as Genesis.

physics.geo-ph↗

arXiv2025

The impact of observation losses on IVS-R1/R4 VLBI sessions

Global VLBI observations, to measure Earth orientation and station positions, are organised into 24-hour sessions. Each session has a bespoke schedule created, optimised for the particular time period and the station network that is available during it. Due to various factors, whether it be station outages, sensitivity issues or source effects, not all scheduled observations are available, or of sufficient quality, to be included in the final geodetic analysis. In this paper we derive statistics about the number of missing observations, as well as their effect on the expected precision of geodetic parameters such as station positions and Earth Orientation Parameters. We investigate the impact of observation loss on the weekly rapid turnaround IVS-R1 and IVS-R4 geodetic VLBI sessions over a decade period from 2014 - 2023. Across our 1030 sessions we find on average 25.3\% of observations scheduled do not make it to analysis. This results in median performance losses, when compared to the scheduled versions, of 18.8%, 19.2%, 12.1/11.3% and 28.7/22.9% for UT1-UTC, 3D station position, X/Y nutation and x/y polar motion respectively. We find that the estimation of X/Y nutation is particularly robust to typical observation loss seen from these 24-hour sessions. Conversely, we see high-rates of critical degradation in performance (a doubling of the scheduled repeatability) for other geodetic parameters at observations losses of between 15 - 19%, which is less than the median loss of 25.3% that we find across this 10-year period.

physics.geo-ph↗

arXiv2024

An experiment to observe GNSS signals with the Australian VGOS array

This paper introduces a new instrument enabling a novel combination of Earth measuring techniques: direct observations with the radio astronomical instruments to satellites of the global navigation satellite systems. Inter-technique biases are a major error source in the terrestrial reference frame. Combining two major space-geodetic techniques, GNSS and VLBI, through observations to identical sensors has been considered infeasible due to their seemingly incompatible operating frequencies. The newly accessible L-band capability of the Australian VGOS telescopes is shown here, invalidating this prevailing opinion. A series of test observations demonstrates geodetic VLBI observations to GPS satellites for a continental-wide IVS telescope array, with the potential for observations at a critical scale. We anticipate immediate impact for the geodetic community, through first-ever inter-technique ties between VLBI and GNSS in the Australian region and via the opportunity for critical test observations towards the Genesis mission, geodesy's flagship project in the area of space ties set for launch in 2028.

physics.geo-ph↗

arXiv2021

Molecular line search toward the flaring 6.7-GHz methanol masers of G24.33+0.13 and G359.6-0.243: rare maser transitions detected

We have performed a molecular line search toward the flaring 6.7-GHz masers G24.33+0.13 and G359.62-0.24 using the Australia Telescope Compact Array. We present spectra of the 6.7-GHz class~II methanol and 22.2-GHz water masers toward these sources and provide comparison with other recent flaring events these sources have experienced. We also detect the fourth example of a 23.4-GHz class~I methanol maser, and the eleventh example of a 4.8-GHz formaldehyde maser toward G24.33+0.13. Alongside these results, we observe the previously detected ammonia (3,3) emission and report upper limits on the presence of various other cm-wavelength methanol, ammonia and OH transitions. Our results are consistent with the flaring of G24.33+0.13 being driven by a variable accretion rate in the host high-mass young stellar object.

astro-ph.GA↗

arXiv2021

Variability in extragalactic class I methanol masers: New maser components toward NGC4945 and NGC253

We have used the Australia Telescope Compact Array (ATCA) to make new observations of the 36.2-GHz ($4_{-1}\rightarrow3_0$E) methanol transition toward NGC 4945 and NGC 253. These observations have revealed the presence of new maser components toward these galaxies, and have provided the first clear evidence for variability in extragalactic class~I methanol masers. Alongside the new observations of NGC 4945 and NGC 253, we present the results of recent 36.2-GHz methanol maser searches toward 12 galaxies, placing upper limits on the emission from the 36.2-GHz class~I transition and the 37.7-GHz ($7_{2}\rightarrow8_1$E) class~II maser line toward these sources. Flux density values for the 7-mm continuum emission toward these sources are also reported where applicable. A re-analysis of the published 36.2-GHz methanol observations of Arp 220 undertaken as part of the search revealed some issues with previous imaging procedures. The re-analysis, combined with non-detections in independent follow-up observations suggest that there is no 36.2-GHz methanol emission toward Arp 220 stronger than 3.5 mJy in a 10 km s$^{-1}$ channel (5$σ$ upper limit).

astro-ph.GA↗

arXiv2018

84-GHz methanol masers, their relationship to 36-GHz methanol masers and their molecular environments

We present observations of the 36- (4_-1 -> 3_0E) and 84-GHz (5_-1 -> 4_0 E) class I methanol maser transitions towards a sample of 94 known class I sites. These observations resulted in 93 and 92 detections in the 84- and 36-GHz transitions. While the majority of the 36-GHz sources have been previously reported, many of the sites are observed in the 84-GHz transition for the first time. The near-simultaneous observations of the two transitions revealed strikingly similar spectral profiles and a mean and median 36- to 84-GHz integrated flux density ratio of 2.6 and 1.4. Alongside the 36- and 84-GHz observations, we included rare class II methanol masers at 37.7-, 38.3-, 38.5-, 86.6- and 86.9-GHz, a number of recombination lines, and thermal molecular transitions. We detect one new site of 86.6- and 86.9-GHz methanol masers, as well as six maser candidates in one or more of 37.7-, 38.3-, 38.5-, 86.6- and 86.9-GHz methanol maser transitions. We detect a relatively higher rate of HC3N compared to that reported by MALT90 (once the respective detection limits were taken into account) who targeted dense dust clumps, suggesting that the class I methanol maser targets incorporate a relatively higher number of warm protostellar sources. We further find that there are similar relationships between the integrated flux density of both class I transitions with the integrated intensity of HC3N, HNC, HCO+, HNC, SiO and H13CO+. We suggest that this indicates that the integrated flux density of the 36- and 84-GHz transitions are closely linked to the available gas volume.

astro-ph.GA↗