arXiv subjects

Marcin Sokolowski

Publications and source records attributed to Marcin Sokolowski.

At least 19 recordsLinked to original sources

arXiv2026

50-250 MHz Pulsar Census with an SKA-Low prototype station: Spectra and Polarization

Low-frequency pulsar observations are crucial for understanding pulsar emission spectra and population physics, as well as for probing the interstellar medium (ISM) and Earth's ionosphere. We report the largest low-frequency pulsar census conducted in the southern hemisphere, covering 50-250 MHz, using the EDA2, an SKA-Low prototype station. In this survey, we detected 120 pulsars, including 23 first-time detections below 150 MHz and 5 below 100 MHz. For each source, we provide integrated pulse profiles and flux-density measurements across five sub-bands spanning 50-250 MHz. We also obtained improved dispersion measure (DM) values for 110 pulsars, with a median absolute DM correction of about 0.1 pc cm^-3. We measured significant Faraday rotation for 40 pulsars with improved rotation measure (RM) values for 4 pulsars, as well as phase-resolved RM variation in J1453-6413. Full-polarimetric pulse profiles are provided for all these pulsars, with multi-frequency polarimetric data for 20 of them. These results will enhance future SKA-Low science: refining pulsar population models, informing survey strategies, and advancing characterization of both the ISM and the ionosphere through low-frequency pulsar monitoring.

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arXiv2026

A signal dedispersion algorithm for imaging-based transient searches

Dedispersion is the computational process of correcting for the frequency-dependent time delay affecting a radio signal that propagates through the interstellar and intergalactic media. It is a crucial component of transient search pipelines that maximises the signal-to-noise ratio, especially when targeting highly dispersed signals: for instance, pulsar emissions making their way through a dense cloud of ionised gas, and fast radio bursts travelling cosmological distances. This paper introduces Streaming high Time-Resolution Imaging DEdispersion (STRIDE), a novel dedispersion algorithm to generate per-pixel dedispersed time series from high time and frequency resolution interferometric images. Unlike straightforward approaches to image dedispersion, STRIDE does not involve expensive manipulation of the input data layout, such as explicitly building dynamic spectra or shifting images. Furthermore, it is the first dedispersion algorithm to partition a dispersive sweep over the time dimension, in addition to frequency. As a consequence, images corresponding to the entire time span of the target dispersive delay are not required all at once. Instead, the algorithm works with an arbitrarily-sized subset of images at a time, adopting an incremental, streaming-based approach to dedispersion. In evaluating STRIDE on the presented test case, it is shown that the minimum memory requirement is reduced by 97.9%, going from 684.5 GB to 14.4 GB. As current and future generations of widefield interferometers increasingly turn to imaging techniques for detection and localisation of radio transients, STRIDE positions itself as a strong alternative to traditional dedispersion methodologies. It arguably is the only viable option for imaging-based searches with low-frequency instruments such as the Murchison Widefield Array (MWA) and low-frequency Square Kilometre Array (SKA-Low).

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arXiv2025

Intrinsic Cross Polarization Ratio maps from all-sky observations with the SKA-Low prototype station Aperture Array Verification System 2

The low-frequency radio telescope of the Square Kilometre Array (SKA-Low), currently under construction in the remote Murchison shire in the Western Australia's outback, will observe the sky between 50 MHz and 350 MHz with unprecedented sensitivity and stringent requirements for polarization accuracy. In this work, we investigate the instrumental polarization purity of a SKA-Low prototype station by means of the Intrinsic Cross-Polarization Ratio (IXR) figure of merit. We derive all-sky experimental IXR maps using data from the Aperture Array Verification System 2 (AAVS2). The results are presented at three frequencies within the SKA-Low bandwidth (110, 160, and 230 MHz) with a quantitative comparison between observed and simulated all-sky IXR maps. Our findings show good agreement in IXR map distributions and promising consistency in their radial profiles, meeting SKA-Low's IXR specification overall. This study offers an empirical approach to verifying SKA-Low's polarization performance using all-sky observations from individual stations and will potentially support the telescope's early science commissioning phase.

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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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arXiv2025

BLINK: an End-To-End GPU High Time Resolution Imaging Pipeline for Fast Radio Burst Searches with the Murchison Widefield Array

Petabytes of archival high time resolution observations have been captured with the Murchison Widefield Array. The search for Fast Radio Bursts within these using established software has been limited by its inability to scale on supercomputing infrastructure, necessary to meet the associated computational and memory requirements. Hence, past searches used a coarse integration time, in the scale of seconds, or analysed an insufficient number of hours of observations. This paper introduces BLINK, a novel radio interferometry imaging software for low-frequency FRB searches to be run on modern supercomputers. It is implemented as a suite of software libraries executing all computations on GPU, supporting both AMD and NVIDIA hardware vendors. These libraries are designed to interface with each other and to define the BLINK imaging pipeline as a single executable program. Expensive I/O operations between imaging stages are not necessary because the stages now share the same memory space and data representation. BLINK is the first imaging pipeline implementation able to fully run on GPUs as a single process, further supporting AMD hardware and enabling Australian researchers to take advantage of Pawsey's Setonix supercomputer. In the millisecond-scale time resolution imaging test case illustrated in this paper, representative of what is required for FRB searches, the BLINK imaging pipeline achieves a 3687x speedup compared to a traditional MWA imaging pipeline employing WSClean.

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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

Calibration of an SKA-Low Prototype Station Using Holographic Techniques

Performance of digitally beamformed phased arrays relies on accurate calibration of the array by obtaining gains of each antenna in the array. The stations of the Square Kilometer Array-Low (SKA-Low) are such digital arrays, where the station calibration is currently performed using conventional interferometric techniques. An alternative calibration technique similar to holography of dish based telescopes has been suggested in the past. In this paper, we develop a novel mathematical framework for holography employing tensors, which are multi-way data structures. Self-holography using a reference beam formed with the station under test itself and cross-holography using a different station to obtain the reference beam are unified under the same formalism. Besides, the relation between the two apparently distinct holographic approaches in the literature for phased arrays is shown, and we show that under certain conditions the two methods yield the same results. We test the various holographic techniques on an SKA-Low prototype station Aperture Array Verification System 2 (AAVS2) with the Sun as the calibrator. We perform self-holography of AAVS2 and cross-holography with simultaneous observations carried out with another station Engineering Development Array 2. We find the results from the holographic techniques to be consistent among themselves as well as with a more conventional calibration technique.

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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

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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arXiv2022

Trajectory, recovery, and orbital history of the Madura Cave meteorite

On the 19th June 2020 at 20:05:07 UTC, a fireball lasting 5.5 s was observed above Western Australia by three Desert Fireball Network observatories. The meteoroid entered the atmosphere with a speed of $14.00 \pm 0.17$ km s$^{-1}$ and followed a $58^{\circ}$ slope trajectory from a height of 75 km down to 18.6 km. Despite the poor angle of triangulated planes between observatories (29$^{\circ}$) and the large distance from the observatories, a well constrained kilo-size main mass was predicted to have fallen just South of Madura in Western Australia. However, the search area was predicted to be large due to the trajectory uncertainties. Fortunately, the rock was rapidly recovered along the access track during a reconnaissance trip. The 1.072 kg meteorite called Madura Cave was classified as an L5 ordinary chondrite. The calculated orbit is of Aten type (mostly contained within the Earth's orbit), the second time only a meteorite is observed on such an orbit after Bunburra Rockhole. Dynamical modelling shows that Madura Cave has been in near-Earth space for a very long time. The NEO dynamical lifetime for the progenitor meteoroid is predicted to be $\sim87$ Myr. This peculiar orbit also points to a delivery from the main asteroid belt via the $\nu6$ resonance, and therefore an origin in the inner belt. This result contributes to drawing a picture for the existence of a present-day L chondrite parent body in the inner belt.

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arXiv2021

The Engineering Development Array 2: design, performance and lessons from an SKA-Low prototype station

We present the Engineering Development Array 2, which is one of two instruments built as a second generation prototype station for the future Square Kilometre Array Low Frequency Array. The array is comprised of 256 dual-polarization dipole antennas that can work as a phased array or as a standalone interferometer. We describe the design of the array and the details of design changes from previous generation instruments, as well as the motivation for the changes. Using the array as an imaging interferometer, we measure the sensitivity of the array at five frequencies ranging from 70 to 320 MHz.

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arXiv2021

Characterization of the SKA1-Low prototype station Aperture Array Verification System 2

The low frequency component of the Square Kilometre Array (SKA1-Low) will be an aperture phased array located at the Murchison Radio-astronomy Observatory (MRO) site in Western Australia. It will be composed of 512 stations, each of them consisting of 256 log-periodic dual polarized antennas, and will operate in the low frequency range (50 MHz - 350 MHz) of the SKA bandwidth. The Aperture Array Verification System 2 (AAVS2), operational since late 2019, is the last full-size engineering prototype station deployed at the MRO site before the start of the SKA1-Low construction phase. The aim of this paper is to characterize the station performance through commissioning observations at six different frequencies (55, 70, 110, 160, 230 and 320 MHz) collected during its first year of activities. We describe the calibration procedure, present the resulting all-sky images and their analysis, and discuss the station calibratability and system stability. Using the difference imaging method, we also derive estimates of the SKA1-Low sensitivity for the same frequencies, and compare them to those obtained through electromagnetic simulations across the entire telescope bandwidth, finding good agreement (within $\leq 13%$). Moreover, our estimates exceed the SKA1-Low requirements at all the considered frequencies, by up to a factor of $\sim$2.3. Our results are very promising and allow an initial validation of the AAVS2 prototype station performance, which is an important step towards the upcoming SKA-Low telescope construction and science.

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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.

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arXiv2020

Noise Temperature of Phased Array Radio Telescope: The Murchison Widefield Array and the Engineering Development Array

This paper presents a framework to compute the receiver noise temperature (Trcv) of two low-frequency radio telescopes, the Murchison Widefield Array (MWA) and the Engineering Development Array (EDA). The MWA was selected because it is the only operational low-frequency Square Kilometre Array (SKA) precursor at the Murchison Radio-astronomy Observatory, while the EDA was selected because it mimics the proposed SKA-Low station size and configuration. It will demonstrated that the use of an existing power wave based framework for noise characterization of multiport amplifiers is sufficiently general to evaluate Trcv of phased arrays. The calculation of Trcv was done using a combination of measured noise parameters of the low-noise amplifier (LNA) and simulated S-parameters of the arrays. The calculated values were compared to measured results obtained via astronomical observation and both results are found to be in agreement. Such verification is lacking in current literature. It was shown that the receiver noise temperatures of both arrays are lower when compared to a single isolated element. This is caused by the increase in mutual coupling within the array which is discussed in depth in this paper.

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arXiv2017

The Engineering Development Array: A low frequency radio telescope utilising SKA precursor technology

We describe the design and performance of the Engineering Development Array (EDA), which is a low frequency radio telescope comprising 256 dual-polarisation dipole antennas working as a phased-array. The EDA was conceived of, developed, and deployed in just 18 months via re-use of Square Kilometre Array (SKA) precursor technology and expertise, specifically from the Murchison Widefield Array (MWA) radio telescope. Using drift scans and a model for the sky brightness temperature at low frequencies, we have derived the EDA's receiver temperature as a function of frequency. The EDA is shown to be sky-noise limited over most of the frequency range measured between 60 and 240 MHz. By using the EDA in interferometric mode with the MWA, we used calibrated visibilities to measure the absolute sensitivity of the array. The measured array sensitivity matches very well with a model based on the array layout and measured receiver temperature. The results demonstrate the practicality and feasibility of using MWA-style precursor technology for SKA-scale stations. The modular architecture of the EDA allows upgrades to the array to be rolled out in a staged approach. Future improvements to the EDA include replacing the second stage beamformer with a fully digital system, and to transition to using RF-over-fibre for the signal output from first stage beamformers.

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arXiv2017

The statistics of radio frequency interference propagating from long distances to the Murchison Radio-astronomy Observatory

BIGHORNS is a total power radiometer developed to identify the signal from the Epoch of Reionisation in the all-sky averaged radio spectrum at low frequencies (70-300 MHz). In October 2014, the system with a conical log spiral antenna was deployed at the Murchison Radio-astronomy Observatory (MRO) and has been collecting data since then. The system has been monitoring the radio frequency interference (RFI) environment at the future site of the low-frequency component of the Square Kilometre Array. We have analyzed almost two years of data (October 2014 - August 2016 inclusive) in search for events of long distance propagation of the RFI in FM and digital TV bands due to tropospheric ducting and reflections (of the meteor trails or aircraft). We present statistics of tropospheric ducting events observed in the digital TV band over nearly two years, which shows seasonal changes. We also present a system using upper atmosphere data (temperature, humidity and pressure as a function of altitude) from all stations in Western Australia to calculate the modified refractive index and make predictions of tropospheric ducting events. Preliminary tests indicate that the system can be very useful in predicting tropospheric ducting events (even with limited amount of available upper atmosphere data).

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arXiv2016

The statistics of low frequency radio interference at the Murchison Radio-astronomy Observatory

We characterize the low frequency radio-frequency interference (RFI) environment at the Murchison Radio-astronomy Observatory (MRO), the location selected for the low-frequency component of the Square Kilometre Array. Data were collected from the BIGHORNS instrument, located at the MRO, which records a contiguous bandwidth between 70 and 300 MHz, between November 2014 to March 2015 inclusive. The data were processed to identify RFI, and we describe a series of statistics in both the time and frequency domain, including modeling of the RFI occupancy and signal power as a series of distribution functions, with the goal of aiding future scientists and operation staff in observation planning.

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