arXiv subjects

Steven Tingay

Publications and source records attributed to Steven Tingay.

At least 19 recordsLinked to original sources

arXiv2025

The Growing Impact of Unintended Starlink Broadband Emission on Radio Astronomy in the SKA-Low Frequency Range

We present the largest survey to date characterising intended and unintended emission from Starlink satellites across the SKA-Low frequency range. This survey analyses ~76 million full sky images captured over ~29 days of observing with an SKA-Low prototype station - the Engineering Development Array 2 - at the site of SKA-Low. We report 112,534 individual detections of 1,806 unique Starlink satellites, some emitting broadband emission and others narrowband emission. Our analysis compares observations across different models of Starlink satellite, with 76% of all v2-mini Ku and 71% of all v2-mini Direct to Cell satellites identified. It is shown that in the worst cases, some datasets have a detectable Starlink satellite in ~30% of all images acquired. Emission from Starlink satellites is detected in primary and secondary frequency ranges protected by the International Telecommunication Union, with 13 satellites identified between 73.00 - 74.60 MHz and 703 identified between 150.05 - 153.00 MHz. We also detect the reflections of terrestrial FM radio off different models of Starlink satellites at 99.70 MHz. The polarisation of the broadband emission shows the flux density of two orthogonal polarisations is anti-correlated with temporally shifting spectral structure observed. We compare our results to previous EDA2 and LOFAR results and provide open public access to our final data products to assist in quantifying future changes in this emission.

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arXiv2024

Enhanced detection and identification of satellites using an all-sky multi-frequency survey with prototype SKA-Low stations

With the low Earth orbit environment becoming increasingly populated with artificial satellites, rockets, and debris, it is important to understand the effects they have on radio astronomy. In this work, we undertake a multi-frequency, multi-epoch survey with two SKA-Low station prototypes located at the SKA-Low site, to identify and characterise radio frequency emission from orbiting objects and consider their impact on radio astronomy observations. We identified 152 unique satellites across multiple passes in low and medium Earth orbits from 1.6 million full-sky images across 13 selected ${\approx}1$ MHz frequency bands in the SKA-Low frequency range, acquired over almost 20 days of data collection. Our algorithms significantly reduce the rate of satellite misidentification, compared to previous work, validated through simulations to be $<1\%$. Notably, multiple satellites were detected transmitting unintended electromagnetic radiation, as well as several decommissioned satellites likely transmitting when the Sun illuminates their solar panels. We test alternative methods of processing data, which will be deployed for a larger, more systematic survey at SKA-Low frequencies in the near future. The current work establishes a baseline for monitoring satellite transmissions, which will be repeated in future years to assess their evolving impact on radio astronomy observations.

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arXiv2024

An image-based blind search for Fast Radio Bursts in 88 hours of data from the EoR0 Field, with the Murchison Widefield Array

This work is part of ongoing efforts to detect Fast Radio Bursts (FRBs) using the Murchison Widefield Array (MWA) in a spectral window below 300 MHz. We used an image-based method based on the pilot study of Tingay et al. 2015, scaled up via massively parallel processing using a commercial supercomputer. We searched 87.6 hours of 2-second snapshot images, each covering 1165 square degrees of the EoR0 field, over a dispersion measure range of 170 to 1035 pc cm$^{-3}$. The large amount of data necessitated the construction of a series of filters to classify and reject the large number of false positives. Our search was more sensitive than any previous blind search using the MWA telescope, but we report no FRB detections, a result which is consistent with the extrapolation into the low-frequency domain of the results of Sokolowski et al. (2024). We obtain upper bounds on the event rate ranging from <1783 sky$^{-1}$day$^{-1}$ at a fluence of 392 Jy ms, to <31 sky$^{-1}$day$^{-1}$ at 8400 Jy ms, for our spectral window of 167-198 MHz. Our method was shown to be computationally efficient and scalable by the two or three orders of magnitude required to seriously test the model of Sokolowski et al. Our process is especially sensitive to detections of satellites and meteor trails and may find applications in the identification of these transients. We comment on future surveys using this method, with both the MWA and the SKA.

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arXiv2024

Evolutionary Map of the Universe (EMU): Observations of Filamentary Structures in the Abell S1136 Galaxy Cluster

We present radio observations of the galaxy cluster Abell S1136 at 888 MHz, using the Australian Square Kilometre Array Pathfinder radio telescope, as part of the Evolutionary Map of the Universe Early Science program. We compare these findings with data from the Murchison Widefield Array, XMM-Newton, the Wide-field Infrared Survey Explorer, the Digitised Sky Survey, and the Australia Telescope Compact Array. Our analysis shows the X-ray and radio emission in Abell S1136 are closely aligned and centered on the BCG, while the X-ray temperature profile shows a relaxed cluster with no evidence of a cool core. We find that the diffuse radio emission in the centre of the cluster shows more structure than seen in previous low-resolution observations of this source, which appeared formerly as an amorphous radio blob, similar in appearance to a radio halo; our observations show the diffuse emission in the Abell S1136 galaxy cluster contains three narrow filamentary structures visible at 888 MHz, between$\sim 80$ and 140 kpc in length; however the properties of the diffuse emission do not fully match that of a radio (mini-)halo or (fossil) tailed radio source.

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arXiv2023

Detection of intended and unintended emissions from Starlink satellites in the SKA-Low frequency range, at the SKA-Low site, with an SKA-Low station analog

Intended and unintended radio emissions from satellites can interfere with sensitive radio telescopes in the frequency ranges of key experiments in astrophysics and cosmology. We detect strong intended and unintended electromagnetic radiation from Starlink satellites at the site of the future SKA-Low facility in Western Australia, using an SKA-low prototype station known as the Engineering Development Array version 2 (EDA2). We aim to show that Starlink satellites are easily detectable utilising a configuration of low frequency radio antennas representative of an SKA-Low 'station' and that our results complement similar findings with the LOFAR telescope. Utilising the EDA2 at frequencies of 137.5 MHz and 159.4 MHz, we detect trains of Starlink satellites on 2023-03-17/18 and 2021-11-16/17, respectively, via the formation of all-sky images with a frequency resolution of 0.926 MHz and a time resolution of 2 s. Time differencing techniques are utilised to isolate and characterise the transmissions from Starlink and other satellites. We observe Starlink satellites reaching intensities of $10^6$ Jy/beam, with the detected transmissions exhibiting a range of behaviours, from periodic bursts to steady transmission. The results are notable because they demonstrate that Starlink satellites are detected in the SKA-Low frequency range, transmitting both intentionally and unintentionally. Follow-up work and discussion are needed to identify the cause of this unintentional radiation as it has the potential to interfere with SKA-Low science. Our results indicate that both intended and unintended radiation from Starlink satellites will be detrimental to key SKA science goals without mitigation. Continued conversation with SpaceX could potentially result in future mitigations which the EDA2 instrument could efficiently monitor and characterise at the SKA-Low site.

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arXiv2022

DUG Insight: A software package for big-data analysis and visualisation, and its demonstration for passive radar space situational awareness using radio telescopes

As the demand for software to support the processing and analysis of massive radio astronomy datasets increases in the era of the SKA, we demonstrate the interactive workflow building, data mining, processing, and visualisation capabilities of DUG Insight. We test the performance and flexibility of DUG Insight by processing almost 68,000 full sky radio images produced from the Engineering Development Array (EDA2) over the course of a three day period. The goal of the processing was to passively detect and identify known Resident Space Objects (RSOs: satellites and debris in orbit) and investigate how radio interferometry could be used to passively monitor aircraft traffic. These signals are observable due to both terrestrial FM radio signals reflected back to Earth and out-of-band transmission from RSOs. This surveillance of the low Earth orbit and airspace environment is useful as a contribution to space situational awareness and aircraft tracking technology. From the observations, we made 40 detections of 19 unique RSOs within a range of 1,500 km from the EDA2. This is a significant improvement on a previously published study of the same dataset and showcases the flexible features of DUG Insight that allow the processing of complex datasets at scale. Future enhancements of our DUG Insight workflow will aim to realise real-time acquisition, detect unknown RSOs, and continue to process data from SKA-relevant facilities.

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arXiv2022

Performance of a Small Array of Imaging Air Cherenkov Telescopes sited in Australia

As TeV gamma-ray astronomy progresses into the era of the Cherenkov Telescope Array (CTA), there is a desire for the capacity to instantaneously follow up on transient phenomena and continuously monitor gamma-ray flux at energies above $10^{12}$ eV. To this end, a worldwide network of Imaging Air Cherenkov Telescopes (IACTs) is required to provide triggers for CTA observations and complementary continuous monitoring. An IACT array sited in Australia would contribute significant coverage of the Southern Hemisphere sky. Here, we investigate the suitability of a small IACT array and how different design factors influence its performance. Monte Carlo simulations were produced based on the Small-Sized Telescope (SST) and Medium-Sized Telescope (MST) designs from CTA. Angular resolution improved with larger baseline distances up to 277m between telescopes, and energy thresholds were lower at 1000m altitude than at 0m. The $\sim$300 GeV energy threshold of MSTs proved more suitable for observing transients than the $\sim$1.2 TeV threshold of SSTs. An array of four MSTs at 1000m was estimated to give a 5.7$\sigma$ detection of an RS Ophiuchi-like nova eruption from a 4-hour observation. We conclude that an array of four MST-class IACTs at an Australian site would ideally complement the capabilities of CTA.

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arXiv2022

Establishing the Capabilities of the Murchison Widefield Array as a Passive Radar for the Surveillance of Space

This paper describes the use of the Murchison Widefield Array, a low-frequency radio telescope at a radio-quiet Western Australian site, as a radar receiver forming part of a continent-spanning multistatic radar network for the surveillance of space. This paper details the system geometry employed, the orbit-specific radar signal processing, and the orbit determination algorithms necessary to ensure resident space objects are detected, tracked, and propagated. Finally, the paper includes the results processed after a short collection campaign utilising several FM radio transmitters across the country, up to a maximum baseline distance of over 2500 km. The results demonstrate the Murchison Widefield Array is able to provide widefield and persistent coverage of objects in low Earth orbit.

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arXiv2021

VLBI properties of compact interplanetary scintillators detected by the Murchison Widefield Array

Interplanetary scintillation (IPS) provides an approach for identifying the presence of sub-arcsec structures in radio sources, and very long baseline interferometry (VLBI) technique can help verify whether the IPS sources have fine structures on milli-arcsec (mas) scales. We searched the available VLBI archive for the 244 IPS sources detected by the Murchison Widefield Array at 162~MHz and found 63 cross-matches. We analysed the VLBI data of the 63 sources and characterised the compactness index in terms of the ratio $R$ of the VLBI-measured flux density at 4.3~GHz to the flux density estimated using the Very Large Array Sky Survey (VLASS) at 3~GHz and NRAO VLA Sky Survey (NVSS) at 1.4~GHz ($S_{\rm VLBI}/S_{\rm SA}$). Eleven sources are identified as blazars according to their flat spectra and strong variability. They show high compactness indices with $R>0.4$, compact core-jet structure, and a broad distribution of normalised scintillation index (NSI). Other sources show diverse morphologies (compact core, core and one-sided jet, core and two-sided jets), but there is a correlation between $R$ and NSI with a correlation coefficient $r=0.47$. A similar $R$--NSI correlation is found in sources showing single steep power-law or convex spectra. After excluding blazars (which are already known to be compact sources) from the VLBI-detected IPS sources, a strong correlation is found between the compactness and scintillation index of the remaining samples, indicating that stronger scintillating sources are more compact. This pilot study shows that IPS offers a convenient method to identify compact radio sources without the need to invoke high-resolution imaging observations, which often require significant observational time.

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arXiv2020

Archival VLBA observations of the Cygnus A Nuclear Radio Transient (Cyg A-2) Strengthen the Tidal Disruption Event Interpretation

We have analyzed archival VLBA data for Cygnus A between 2002 and 2013, to search for radio emission from the transient discovered in 2015 by \citet{per18} approximately 0.4\arcsec~ from the nucleus of Cygnus A (Cyg A-2). \citet{per18} use VLA and VLBA archival data (between 1989 and 1997) to show that the transient rises in flux density by a factor of at least five in less than approximately 20 years. With the additional data presented here, we revise the rise time to between approximately four years and six years, based on a new detection of the source at 15.4 GHz from October 2011. Our results strengthen the interpretation of Cyg A-2 as the result of a Tidal Disruption Event (TDE), as we can identify the location of the compact object responsible for the TDE and can estimate the angular expansion speed of the resulting radio emitting structures, equivalent to an apparent expansion speed of $<0.9c$. While our results are consistent with recent X-ray analyses, we can rule out a previously suggested date of early 2013 for the timing of the TDE. We favour a timing between early 2009 and late 2011. Applying the model of \citet{nak11}, we suggest a TDE causing a mildly relativistic outflow with a (density-dependent) total energy $>10^{49}$ erg. Due to the improved temporal coverage of our archival measurements, we find that it is unlikely that Cyg A-2 has previously been in a high luminosity radio state over the last 30 years.

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arXiv2020

A survey of spatially and temporally resolved radio frequency interference in the FM band at the Murchison Radio-astronomy Observatory

We present the first survey of radio frequency interference (RFI) at the future site of the low frequency Square Kilometre Array (SKA), the Murchison Radio-astronomy Observatory (MRO), that both temporally and spatially resolves the RFI. The survey is conducted in a 1 MHz frequency range within the FM band, designed to encompass the closest and strongest FM transmitters to the MRO (located in Geraldton, approximately 300 km distant). Conducted over approximately three days using the second iteration of the Engineering Development Array in an all-sky imaging mode, we find a range of RFI signals. We are able to categorise the signals into: those received directly from the transmitters, from their horizon locations; reflections from aircraft (occupying approximately 13% of the observation duration); reflections from objects in Earth orbit; and reflections from meteor ionisation trails. In total we analyse 33,994 images at 7.92 s time resolution in both polarisations with angular resolution of approximately 3.5 deg., detecting approximately forty thousand RFI events. This detailed breakdown of RFI in the MRO environment will enable future detailed analyses of the likely impacts of RFI on key science at low radio frequencies with the SKA.

astro-ph.IM↗

arXiv2020

Simulations of orbital debris clouds due to breakup events and their characterisation using the Murchison Widefield Array radio telescope

In this paper we consider the use of wide field of view radar sensors such as the Murchison Widefield Array (MWA), a low frequency radio telescope designed for astrophysics and cosmology, for rapid response observations of the debris clouds produced by collisions between objects in Earth orbit. With an increasing density of objects in Low Earth Orbit, including legacy assets used by the astronomy community over decades, the risk of new debris clouds forming is also increasing. The MWA constitutes a wide field, rapid response passive radar system and we explore its likely performance in the detection and characterisation of debris clouds. In general, astronomy facilities such as the MWA can play a role in protecting the space environment for the future. In order to undertake this work, we adapt the NASA EVOLVE 4.0 breakup model, utilising the EVOLVE outputs to produce representative dynamic debris clouds. We find that the MWA is likely to detect a large fraction (>70%) of modelled debris cloud fragments for collision masses between 100 kg and 1000 kg for orbits in the lower part of LEO, if the MWA can achieve close to optimal detection sensitivity. Useful detection fractions are still achieved for more conservative assumptions. The detection fraction of fragments decreases as a function of altitude and inversely with collision mass. Encouragingly, we find that the wide field nature of the MWA allows the full evolving debris clouds to be observed in a single observation, with only $\sim2\%$ of the debris fragments escaping the sensitive portion of the field of view after 100 seconds, for all collision masses and altitudes. These results show that the MWA is an intrinsically useful facility for the rapid characterisation of debris clouds, but that work is required to achieve the data processing within an appropriate timeframe to provide rapid alerts.

astro-ph.EP↗

arXiv2020

Dark matter annihilation in $\omega$ Centauri: Astrophysical implications derived from the MWA radio data

We present an analysis of Murchison Widefield Array radio telescope data from $\omega$ Cen, possibly a stripped dwarf spheroidal galaxy core captured by our Galaxy. Recent interpretations of Fermi-LAT $\gamma$-ray data by Brown {\it et al.} (2019) and Reynoso-Cordova {\it et al.} (2019) suggest that $\omega$ Cen may contain significant Dark Matter. We utilise their best-fit Dark Matter annihilation models, and an estimate of the magnetic field strength in $\omega$ Cen, to calculate the expected radio synchrotron signal from annihilation, and show that one can usefully rule out significant parts of the magnetic field - diffusion coefficient plane using our current observational limits on the radio emission. Improvement by a factor of 10-100 on these limits could constrain the models even more tightly.

astro-ph.HE↗

arXiv2020

Orbit Determination Before Detect: Orbital Parameter Matched Filtering for Uncued Detection

This paper presents a novel algorithm to incorporate orbital parameters into radar ambiguity function expressions by extending the standard ambiguity function to match Keplerian two-body orbits. A coherent orbital matched-filter will maximise a radar's sensitivity to objects in orbit, as well as provide rapid initial orbit determination from a single detection. This paper then shows how uncued detection searches can be practically achieved by incorporating radar parameters into the orbital search-space, especially for circular orbits. Simulated results are compared to results obtained from ephemeris data, showing that the orbital path determined by the proposed method, and the associated radar parameters that would be observed, match those derived from the ephemeris data.

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arXiv2020

High Cadence Optical Transient Searches using Drift Scan Imaging I: Proof of Concept with a Pre-Prototype System

An imaging technique with sensitivity to short duration optical transients is described. The technique is based on the use of wide-field cameras operating in a drift scanning mode, whereby persistent objects produce trails on the sensor and short duration transients occupy localised groups of pixels. A benefit of the technique is that sensitivity to short duration signals is not accompanied by massive data rates, because the exposure time >> transient duration. The technique is demonstrated using a pre-prototype system composed of readily available and inexpensive commercial components, coupled with common coding environments, commercially available software, and free web-based services. The performance of the technique and the pre-prototype system is explored, including aspects of photometric and astrometric calibration, detection sensitivity, characterisation of candidate transients, and the differentiation of astronomical signals from non-astronomical signals (primarily glints from satellites in Earth orbit and cosmic ray hits on sensor pixels). Test observations were made using the pre-prototype system, achieving sensitivity to transients with 21 ms duration, resulting in the detection of five candidate transients. An investigation of these candidates concludes they are most likely due to cosmic ray hits on the sensor and/or satellites. The sensitivity obtained with the pre-prototype system is such that, under some models for the optical emission from FRBs, the detection of a typical FRB, such as FRB181228, to a distance of approximately 100 Mpc is plausible. Several options for improving the system/technique in the future are described.

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arXiv2019

Surveillance of Space using Passive Radar and the Murchison Widefield Array

In this paper we build upon recent work in the radio astronomy community to experimentally demonstrate the viability of passive radar for Space Situational Awareness. Furthermore, we show that the six state parameters of objects in orbit may be measured and used to perform orbit characterisation/estimation.

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arXiv2019

Constraints on dark matter annihilation in dwarf spheroidal galaxies from low frequency radio observations

We present the first observational limits on the predicted synchrotron signals from particle Dark Matter annihilation models in dwarf spheroidal galaxies at radio frequencies below 1 GHz. We use a combination of survey data from the Murchison Widefield Array (MWA) and the Giant Metre-wave Radio Telescope (GMRT) to search for diffuse radio emission from 14 dwarf spheroidal galaxies. For in-situ magnetic fields of 1 $\mu G$ and any plausible value for the diffusion coefficient, our limits do not constrain any Dark Matter models. However, for stronger magnetic fields our data might provide constraints comparable to existing limits from gamma-ray and cosmic ray observations. Predictions for the sensitivity of the upgraded MWA show that models with Dark Matter particle mass up to $\sim$ 1.6 TeV (1 TeV) may be constrained for magnetic field of 2 $\mu G$ (1 $\mu G$). While much deeper limits from the future low frequency Square Kilometre Array (SKA) will challenge the LHC in searches for Dark Matter particles, the MWA provides a valuable first step toward the SKA at low frequencies.

astro-ph.HE↗

arXiv2019

Improved Techniques for the Surveillance of the Near Earth Space Environment with the Murchison Widefield Array

In this paper we demonstrate improved techniques to extend coherent processing intervals for passive radar processing, with the Murchison Widefield Array. Specifically, we apply a two stage linear range and Doppler migration compensation by utilising Keystone Formatting and a recent dechirping method. These methods are used to further demonstrate the potential for the surveillance of space with the Murchison Widefield Array using passive radar, by detecting objects orders of magnitude smaller than previous work. This paper also demonstrates how the linear Doppler migration methods can be extended to higher order compensation to further increase potential processing intervals.

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