arXiv subjects

W. Armour

Publications and source records attributed to W. Armour.

14 recordsLinked to original sources

arXiv2025

FIP-TOI: Fast Imaging Pipeline for Pulsar Localisation with a Transient-Oriented Radio Astronomical Imager

Rapid localisation of radio transients requires imaging pipelines that combine low latency, high sensitivity, and accurate transient positioning. Fast Imaging Pipeline (FIP) defines a (quasi)-real-time image-based transient detection pipeline for next-generation radio telescopes such as the Square Kilometre Array (SKA). However, the current FIP within the SKA Science Data Processor (SDP) remains at an early stage, leaving substantial scope to improve its performance. To address this need, we develop FIP-TOI, which combines a novel Transient-Oriented Imager (TOI) with the transient detector FITrig. FIP-TOI is highly parallelised and GPU accelerated. In experiments, TOI improves signal-to-noise ratio (SNR) by at least 15 compared with WSClean and SKA-SDP imagers, while providing higher positional precision than WSClean snapshot imaging. On a 396 GB MeerKAT Measurement Set containing 1500 snapshots, FIP-TOI processes the data in 170-190 s on a single NVIDIA H100, corresponding to approximately 120 ms per snapshot, while using 714 MB of RAM and about two CPU cores. Testing on diverse datasets --- including fields with multiple faint transients, an on-and-off pulsar, and a pulsar exhibiting intensity changes --- FIP-TOI demonstrates robust performance across all scenarios and achieves lower localisation errors than SKA-SDP-FIP.

astro-ph.IM↗

arXiv2025

FITrig: A High-Performance Detection Technique for Efficient Ultra-Long-Period Pulsars

Ultra-long-period (ULP) pulsars, a newly identified class of celestial transients, offer unique insights into astrophysics, though very few have been detected to date. In radio astronomy, most time-domain detection methods cannot find these pulsars, and current image-based detection approaches still face challenges, including low sensitivity, high false positive rate, and low computational efficiency. In this article, we develop Fast Imaging Trigger (FITrig), a GPU-accelerated, statistics-based method for ULP pulsar detection and localisation. FITrig includes two complementary approaches -- an image domain and an image-frequency domain strategy. FITrig offers advantages by increasing sensitivity to faint pulsars, suppressing false positives (from noise, processing artefacts, or steady sources), and improving search efficiency in large-scale wide-field images. Compared to the state-of-the-art source finder SOFIA 2, FITrig increases the detection speed by 4.3 times for large images ($50\mathrm{K} \times 50\mathrm{K}$ pixels) and reduces false positives by up to 858.8 times (at 6$\sigma$ significance) for the image domain branch, while the image-frequency domain branch suppresses false positives even further. FITrig maintains the capability to detect pulsars that are 20 times fainter than surrounding steady features, even under critical Nyquist sampling conditions. In this article, the performance of FITrig is demonstrated using both real-world data (MeerKAT observations of PSR J0901-4046) and simulated datasets based on MeerKAT and SKA Array Assembly (AA) 2 telescope configurations. With its real-time processing capabilities and scalability, FITrig is a promising tool for next-generation telescopes, such as the SKA, with the potential to uncover hidden ULP pulsars.

astro-ph.IM↗

arXiv2025

GPU Accelerated Image Quality Assessment-Based Software for Transient Detection

Fast imaging localises celestial transients using source finders in the image domain. The need for high computational throughput in this process is driven by next-generation telescopes such as Square Kilometre Array (SKA), which, upon completion, will be the world's largest aperture synthesis radio telescope. It will collect data at unprecedented velocity and volume. Due to the vast amounts of data the SKA will produce, current source finders based on source extraction may be inefficient in a wide-field search. In this paper, we focus on the software development of GPU-accelerated transient finders based on Image Quality Assessment (IQA) methods -- Low-Information Similarity Index (LISI) and augmented LISI (augLISI). We accelerate the algorithms using GPUs, achieving kernel time of approximately 0.1 milliseconds for transient finding in 2048X2048 images.

astro-ph.IM↗

arXiv2024

Intensity-sensitive quality assessment of extended sources in astronomical images

Radio astronomy studies the Universe by observing the radio emissions of celestial bodies. Different methods can be used to recover the sky brightness distribution (SBD), which describes the distribution of celestial sources from recorded data, with the output dependent on the method used. Image quality assessment (IQA) indexes can be used to compare the differences between restored SBDs produced by different image reconstruction techniques to evaluate the effectiveness of different techniques. However, reconstructed images (for the same SBD) can appear to be very similar, especially when observed by the human visual system (HVS). Hence current structural similarity methods, inspired by the HVS, are not effective. In the past, we have proposed two methods to assess point source images, where low amounts of concentrated information are present in larger regions of noise-like data. But for images that include extended source(s), the increase in complexity of the structure makes the IQA methods for point sources over-sensitive since the important objects cannot be described by isolated point sources. Therefore, in this article we propose augmented Low-Information Similarity Index (augLISI), an improved version of LISI, to assess images including extended source(s). Experiments have been carried out to illustrate how this new IQA method can help with the development and study of astronomical imaging techniques. Note that although we focus on radio astronomical images herein, these IQA methods are also applicable to other astronomical images, and imaging techniques.

astro-ph.IM↗

arXiv2022

Intensity-Sensitive Similarity Indexes for Image Quality Assessment

The importance of Image quality assessment (IQA) is ever increasing due to the fast paced advances in imaging technology and computer vision. Among the numerous IQA methods, Structural SIMilarity (SSIM) index and its variants are better matched to the perceived quality of the human visual system. However, SSIM methods are insufficiently sensitive, when images contain low information, where the important information only occupies a low proportion of the image while most of the image is noise-like, which is common in scientific data. Therefore, we propose two new IQA methods, InTensity Weighted SSIM index and Low-Information Similarity Index, for such low information images. In addition, auxiliary indexes are proposed to assist with the assessment. The application of these new IQA methods to natural images and field-specific images, such as radio astronomical images, medical images, and remote sensing images, are also demonstrated. The results show that our IQA methods perform better than state-of-the-art SSIM methods for differences in high-intensity parts of the input images and have similar performance to that of the original and gradient-based SSIM for differences in low-intensity parts. Different similarity indexes are suitable for different applications, which we demonstrate in our results.

eess.IV↗

arXiv2020

Initial results from a realtime FRB search with the GBT

We present the data analysis pipeline, commissioning observations and initial results from the GREENBURST fast radio burst (FRB) detection system on the Robert C. Byrd Green Bank Telescope (GBT) previously described by Surnis et al. which uses the 21~cm receiver observing commensally with other projects. The pipeline makes use of a state-of-the-art deep learning classifier to winnow down the very large number of false positive single-pulse candidates that mostly result from radio frequency interference. In our observations totalling 156.5 days so far, we have detected individual pulses from 20 known radio pulsars which provide an excellent verification of the system performance. We also demonstrate, through blind injection analyses, that our pipeline is complete down to a signal-to-noise threshold of 12. Depending on the observing mode, this translates to peak flux sensitivities in the range 0.14--0.89~Jy. Although no FRBs have been detected to date, we have used our results to update the analysis of Lawrence et al. to constrain the FRB all-sky rate to be $1140^{+200}_{-180}$ per day above a peak flux density of 1~Jy. We also constrain the source count index $α=0.83\pm0.06$ which indicates that the source count distribution is substantially flatter than expected from a Euclidean distribution of standard candles (where $α=1.5$). We discuss this result in the context of the FRB redshift and luminosity distributions. Finally, we make predictions for detection rates with GREENBURST, as well as other ongoing and planned FRB experiments.

astro-ph.IM↗

arXiv2017

Pulsar Searches with the SKA

The Square Kilometre Array will be an amazing instrument for pulsar astronomy. While the full SKA will be sensitive enough to detect all pulsars in the Galaxy visible from Earth, already with SKA1, pulsar searches will discover enough pulsars to increase the currently known population by a factor of four, no doubt including a range of amazing unknown sources. Real time processing is needed to deal with the 60 PB of pulsar search data collected per day, using a signal processing pipeline required to perform more than 10 POps. Here we present the suggested design of the pulsar search engine for the SKA and discuss challenges and solutions to the pulsar search venture.

astro-ph.IM↗

arXiv2015

Limits on Fast Radio Bursts at 145 MHz with ARTEMIS, a real-time software backend

Fast Radio Bursts (FRBs), are millisecond radio signals that exhibit dispersion larger than what the Galactic electron density can account for. We have conducted a 1446 hour survey for Fast Radio Bursts (FRBs) at 145~MHz, covering a total of 4193 sq. deg on the sky. We used the UK station of the LOFAR radio telescope -- the Rawlings Array -- , accompanied for a majority of the time by the LOFAR station at Nançay, observing the same fields at the same frequency. Our real-time search backend, ARTEMIS, utilizes graphics processing units to search for pulses with dispersion measures up to 320 cm$^{-3}$ pc. Previous derived FRB rates from surveys around 1.4~GHz, and favoured FRB interpretations, motivated this survey, despite all previous detections occurring at higher dispersion measures. We detected no new FRBs above a signal-to-noise threshold of 10, leading to the most stringent upper limit yet on the FRB event rate at these frequencies: 29 sky$^{-1}$ day$^{-1}$ for 5~ms-duration pulses above 62~Jy. The non-detection could be due to scatter-broadening, limitations on the volume and time searched, or the shape of FRB flux density spectra. Assuming the latter and that FRBs are standard candles, the non-detection is compatible with the published FRB sky rate, if their spectra follow a power law with frequency ($\propto ν^α$), with $α\gtrsim+0.1$, demonstrating a marked difference from pulsar spectra. Our results suggest that surveys at higher frequencies, including the low frequency component of the Square Kilometre Array, will have better chances to detect, estimate rates and understand the origin and properties of FRBs.

astro-ph.IM↗

arXiv2011

A GPU-based survey for millisecond radio transients using ARTEMIS

Astrophysical radio transients are excellent probes of extreme physical processes originating from compact sources within our Galaxy and beyond. Radio frequency signals emitted from these objects provide a means to study the intervening medium through which they travel. Next generation radio telescopes are designed to explore the vast unexplored parameter space of high time resolution astronomy, but require High Performance Computing (HPC) solutions to process the enormous volumes of data that are produced by these telescopes. We have developed a combined software /hardware solution (code named ARTEMIS) for real-time searches for millisecond radio transients, which uses GPU technology to remove interstellar dispersion and detect millisecond radio bursts from astronomical sources in real-time. Here we present an introduction to ARTEMIS. We give a brief overview of the software pipeline, then focus specifically on the intricacies of performing incoherent de-dispersion. We present results from two brute-force algorithms. The first is a GPU based algorithm, designed to exploit the L1 cache of the NVIDIA Fermi GPU. Our second algorithm is CPU based and exploits the new AVX units in Intel Sandy Bridge CPUs.

astro-ph.IM↗

arXiv2010

An analysis of the nucleon spectrum from lattice partially-quenched QCD

The chiral extrapolation of the nucleon mass, M_n, is investigated using data coming from 2-flavour partially-quenched lattice simulations. A large sample of lattice results from the CP-PACS Collaboration is analysed using the leading one-loop corrections, with explicit corrections for finite lattice spacing artifacts. The extrapolation is studied using finite range regularised chiral perturbation theory. The analysis also provides a quantitative estimate of the leading finite volume corrections. It is found that the discretisation, finite-volume and partial quenching effects can all be very well described in this framework, producing an extrapolated value of M_n in agreement with experiment. Furthermore, determinations of the low energy constants of the nucleon mass's chiral expansion are in agreement with previous methods, but with significantly reduced errors. This procedure is also compared with extrapolations based on polynomial forms, where the results are less encouraging.

hep-lat↗

arXiv2005

Chiral and Continuum Extrapolation of Partially-Quenched Hadron Masses

Using the finite-range regularisation (FRR) of chiral effective field theory, the chiral extrapolation formula for the vector meson mass is derived for the case of partially-quenched QCD. We re-analyse the dynamical fermion QCD data for the vector meson mass from the CP-PACS collaboration. A global fit, including finite lattice spacing effects, of all 16 of their ensembles is performed. We study the FRR method together with a naive polynomial approach and find excellent agreement ~1% with the experimental value of M_rho from the former approach. These results are extended to the case of the nucleon mass.

hep-lat↗

arXiv2005

Unified chiral analysis of the vector meson spectrum from lattice QCD

The chiral extrapolation of the vector meson mass calculated in partially-quenched lattice simulations is investigated. The leading one-loop corrections to the vector meson mass are derived for partially-quenched QCD. A large sample of lattice results from the CP-PACS Collaboration is analysed, with explicit corrections for finite lattice spacing artifacts. To incorporate the effect of the opening decay channel as the chiral limit is approached, the extrapolation is studied using a necessary phenomenological extension of chiral effective field theory. This chiral analysis also provides a quantitative estimate of the leading finite volume corrections. It is found that the discretisation, finite-volume and partial quenching effects can all be very well described in this framework, producing an extrapolated value of M_ρin excellent agreement with experiment. This procedure is also compared with extrapolations based on polynomial forms, where the results are much less enlightening.

hep-lat↗

arXiv2005

Chiral and Continuum Extrapolation of Partially-Quenched Lattice Results

The vector meson mass is extracted from a large sample of partially quenched, two-flavor lattice QCD simulations. For the first time, discretisation, finite-volume and partial quenching artefacts are treated in a unified framework which is consistent with the low-energy behaviour of QCD. This analysis incorporates the leading infrared behaviour dictated by chiral effective field theory. As the two-pion decay channel cannot be described by a low-energy expansion alone, a highly-constrained model for the decay channel of the rho-meson is introduced. The latter is essential for extrapolating lattice results from the quark-mass regime where the rho is observed to be a physical bound state.

hep-lat↗

arXiv2003

An analysis of the vector meson spectrum from lattice QCD

We re-analyse meson sector data from the CP-PACS collaboration's dynamical simulations. Our analysis uses several different approaches, and compares the standard naive linear fit with the Adelaide Anzatz. We find that setting the scale using the J parameter gives remarkable agreement among data sets. Our predictions for the rho and phi masses have very small statistical errors, ~ 3 MeV, but the discrepancy between the different fitting approaches is ~ 40 MeV.

hep-lat↗