Ronald D. Ekers

In this pilot study, we use data from the First Large Absorption Survey in H I (FLASH) to search for redshifted H I 21 cm absorption at 0.4 < z < 1 towards 157 bright radio sources with Interplanetary Scintillation (IPS) measurements at 820 MHz in a single field observed with the Australian Square Kilometre Array Pathfinder (ASKAP) radio telescope. The ASKAP IPS measurements, which use only 2.5 minutes of observing time in total, allow us to estimate the compactness of these radio sources on sub-arcsecond scales at a frequency within the 712–1000 MHz FLASH band. In particular, the Normalised Scintillation Index (NSI) for each source reflects the fraction of the flux density arising from compact components less than 0.1 arcsec in diameter. We find that 18 ± 5% of ASKAP sources with flux densities above 150 mJy are highly compact with NSI ≥ 0.8 – implying that at least 80% of their radio emission arises from a single region smaller than about 800 pc in size. The compactness of these sources makes them ideal probes for an H I absorption search, since the covering factor for any H I gas clouds along the line of sight is likely to be high. About half of the sources with NSI ≥ 0.8 also have peaked radio spectral energy distributions (SEDs), consistent with previous IPS studies at lower frequencies. These pilot results imply that IPS measurements with ASKAP can provide a simple and powerful tool for identifying uniform samples of compact radio sources at frequencies of a few hundred MHz across large areas of sky. With FLASH, we detect two new H I absorption lines against compact sources in the ∼ 30 deg ² region of sky covered by the IPS data; an associated H I line at redshift z = 0.9540 (with a matching optical redshift) in MRC 2125-237 (NSI = 0.98), and a likely intervening line at z = 0.4632 towards MRC 2131-241 (NSI = 0.84). The radio sources with these two detections are both bright and compact, with peaked radio SEDs.

We have conducted a comprehensive comparison of interplanetary scintillation (IPS) observations taken by the Murchison Widefield Array (MWA) with several heliospheric transient event catalogs, over a time period of 7 months during solar minimum. From this analysis we have found that of the 84% of cataloged events that have MWA IPS data available, 68% of them appear in MWA observations. Of the enhancements first identified in IPS observations, only 58% have a potential match with a cataloged event. The majority of enhancements that were identified in the IPS observations were situated greater than 10 from the ecliptic plane. Two such features were selected for detailed analysis, connecting their solar origins to their propagation through the heliosphere. The first of these features was created by a coronal mass ejection (CME), captured over two successive MWA observations and recorded in several catalogs. The second feature has the potential of being a stream interaction region (SIR) traveling out of the ecliptic plane. This particular SIR was not recorded in any catalog. Thus the MWA shows promise in detecting heliospheric transients that other commonly‐used techniques may overlook. These results show the strength of the MWA in having unbridled access to the heliosphere, able to make remote observations of events far out of the ecliptic as it is not restrained to the orbits of spacecraft. We demonstrate how the inclusion of MWA IPS data can potentially boost the number of CME and SIR events that are characterized.

We present a study of the solar wind over different periods of the solar cycle, specifically focusing on the minimum between solar cycles 24 and 25, and the active, ascending phase of solar cycle 25. With the use of interplanetary scintillation (IPS) data taken by the Murchison Widefield Array (MWA) from mid‐2019 and early 2023, we have sampled over a wide range of solar latitudes and elongations, probing a large section of the surrounding heliosphere from 90 to . The MWA observations provide the highest density of sampled IPS radio sources to date, allowing for an investigation into the latitudinal dependence of the scattering effect caused by the solar wind on a radio source as observed throughout the solar cycle. We find our measurements during periods of heightened solar activity are consistent with a spherically symmetric solar wind. On the other hand, with a reduction in solar activity we find the solar wind density inherits a latitudinal dependence. As is consistent with prior studies, an elliptical function better represents the transition from poles to equator, although we find a more exaggerated sigmoid shaped curve is required to represent the low‐to mid‐latitude transition region during the minimum of solar cycle 24. We find for a heliospheric distance range of 108– the reduction ratio between the equator and the southern pole is 1.62 0.02.

We report the detection of a burst of emission over a 695.5–1031.5 MHz bandwidth by the Australian Square Kilometre Array Pathfinder. The burst was localized through analysis of near-field time delays to the long-decommissioned Relay 2 satellite and exhibited a dispersion measure of 2.26 × 10⁻⁵ pc cm⁻³—69.7 total electron content units, consistent with expectations for a single pass through the ionosphere. After coherent dedispersion, the burst was determined to be less than 30 ns in width, with an average flux density of at least 300 kJy. We consider an electrostatic discharge (ESD) or plasma discharge following a micrometeoroid impact to be plausible explanations for the burst. ESDs have previously been observed with the Arecibo radio telescope, but on 1000 times longer timescales. Our observation opens new possibilities for the remote sensing of ESD, which poses a serious threat to spacecraft, and reveals a new source of false events for observations of astrophysical transients.

Fast radio bursts (FRBs) are highly energetic events of short-duration intense radio emission, the origin of which remains elusive. Polarization of the FRB signals carries information about the emission source as well as the magnetoionic media the signal passes through before reaching terrestrial radio telescopes. Currently known FRBs show a diverse range of polarization, sometimes with complex features, making it challenging to describe them in a unified model. FRB 20230708A and FRB 20210912A are two bright and highly polarized (apparently) one-off FRBs detected in the Commensal Real-time ASKAP Fast Transients survey with the Australian Square Kilometre Array Pathfinder (ASKAP) that exhibit time-dependent conversion between linear and circular polarizations as well as intraburst (apparent) variation of the Faraday rotation measure. We investigate the intraburst temporal evolution of the polarization state of radio emission in these two events using the Poincaré sphere representation and find that the trajectories of the polarization state are well described by great circles on the Poincaré sphere. These polarization features may be signatures of a transition between two partially coherent orthogonal polarization modes or propagation through a birefringent medium. We find that the observed variations of the polarization states of these two FRBs are qualitatively consistent with a magnetospheric origin of the bursts and the effects of propagation through a birefringent medium with linearly polarized modes located close to the emission source—likely in the outer magnetosphere or near-wind region of a neutron star.

There is no denying that we are living in a state of climate emergency, and yet across both astronomy and globally, the shift away from “business as usual” towards more sustainable practices seems too slow to realise meaningful change on the required timescale. One of the key challenges in the current situation is knowing exactly what we can do to improve things, or what actions can be taken at different scales ranging from individuals to institutions. As has been previously discussed by Stevens et al. 2020, carbon emissions associated with travel are a large fraction of the total emissions produced by astronomers in our professional capacity, and still we are yet to see a significant change in physical travel for meetings, conferences or collaboration (e.g. Figure 1). Our work as part of “The Future of Meetings” (TFOM) community of practice (consisting of people working in the field of astronomy, professional scientists in other disciplines such as climate science, computational chemistry and archaeology, and broader academic and industry contacts) has focused especially on the gains that can be made by the widespread adoption of effective online and hybrid meeting practices. The benefits of embracing online interaction are huge when considering sustainability and the climate, as the successful enacting of online meetings can significantly reduce the need to travel physically, whether that travel be locally to a workplace, nationally for collaborations and meetings or internationally for large-scale conferences. These benefits carry through to other important aspects of improving astronomy, such as increasing accessibility where barriers exist for in-person travel and enhancing inclusivity for groups that have been historically excluded from traditional meeting practices. It is clear when we measure attendance at meetings and conferences (Figure 2) that the attendee population, and their associated carbon emissions, are dominated by the most wealthy and privileged countries.Astronomy especially can provide a unique voice in the global conversation about the future of meetings, interaction and distributed work, considering additionally the significant carbon demands of our field in terms of travel, observatory operations and computing. Our work by default focuses on looking outwards into the Universe, and in placing our experience on Earth in the bigger picture of what is happening beyond our planet. We are a field with a long history of innovative global collaboration, with tendencies towards early adoption of new technologies as well as collaborative teams that are distributed by their nature either across countries or continents. As a field, we have also taken significant steps already towards tangibly increasing the diversity of contributions to advancing research in astronomy, moving beyond the concept of acknowledging the challenges and focusing on measurable solutions.The recent publication of “Climate Change for Astronomers” (Figure 3), edited by Travis Rector, focuses on addressing the climate crisis specifically from the astronomy perspective. The final chapter in this book was contributed by our group, with a focus on practical advice and examples that are intended to give people a sense of what can be done to measurably improve the sustainability of our meetings and interactions, from the individual through to institutional and international practices.In this presentation, we will give an overview of the contents of the chapter and provide additional context to it for those interested to make use of our advice. We will cover: 1) introduction to TFOM and context around our general work, 2) the history and evolution of meetings in astronomy, 3) motivations for meetings and interactions in astronomy, 4) the benefits of online interaction in improving our “business as usual” practices in astronomy, 5) the role of technology in facilitating these improvements, 6) suggestions for next steps, 7) examples of common concerns about online and hybrid meetings and how to address them, 8) example case studies of online and hybrid meetings, and 9) looking to the future. We especially hope to engage with the EPSC community about their experiences in this area and the unique challenges facing this segment of the global astronomy community, and form connections with those in attendance with a look towards the potential for future collaboration in the context of TFOM and ways of tangibly addressing the climate emergency. We firmly believe that online interaction offers immense opportunities for improving both our practices and our experiences in astronomy, and that by embracing these possibilities and the benefits they provide, we can truly go “beyond being there” in a way that also helps preserve our unique place in the Universe for future generations. FiguresFigure 1: Indicative conference formats in astronomy as a function of time, based on meetings recorded by the Canadian Astronomy Data Centre. The format of a meeting was determined based on referring to the location provided for each meeting (where "online" aims to capture both online-only and hybrid meetings), and thus is likely to be incomplete in terms of meetings which provide hybrid access (if not indicated by the location text). Similarly, the measurement of cancelled meetings is a lower limit since it is likely many cancelled meetings do not feed back into the CADC listing. 2024 is incomplete given it is a year still in progress. While we saw a significant increase in meetings providing online access around the COVID-19 pandemic, this trend has reversed almost completely as of 2024. Credit: Vanessa Moss, for this Figure 2: Number of conference attendees at astronomy conferences, normalised by country population, in 2019 as a function of Human Development Index (HDI) for a given country. The colour scale and size of the markers show the total amount of travel...

Fast radio bursts (FRBs) are brilliant short-duration flashes of radio emission originating at cosmological distances. The vast diversity in the properties of currently known FRBs and the fleeting nature of these events make it difficult to understand their progenitors and emission mechanism(s). Here we report high time resolution polarization properties of FRB 20210912A, a highly energetic event detected by the Australian Square Kilometre Array Pathfinder (ASKAP) in the Commensal Real-time ASKAP Fast Transients survey, which show intraburst position angle (PA) variation similar to Galactic pulsars and unusual variation of Faraday rotation measure (RM) across its two sub-bursts. The observed intraburst PA variation and apparent RM variation pattern in FRB 20210912A may be explained by a rapidly spinning neutron star origin, with rest-frame spin periods of ∼1.1 ms. This rotation timescale is comparable to the shortest known rotation period of a pulsar and close to the shortest possible rotation period of a neutron star. Curiously, FRB 20210912A exhibits a remarkable resemblance to the previously reported FRB 20181112A, including similar rest-frame emission timescales and polarization profiles. These observations suggest that these two FRBs may have similar origins.

Fast radio bursts (FRBs) are millisecond-duration pulses of radio emission originating from extragalactic distances. Radio dispersion is imparted on each burst by intervening plasma, mostly located in the intergalactic medium. In this work, we observe the burst FRB 20220610A and localize it to a morphologically complex host galaxy system at redshift 1.016 ± 0.002. The burst redshift and dispersion measure are consistent with passage through a substantial column of plasma in the intergalactic medium and extend the relationship between those quantities measured at lower redshift. The burst shows evidence for passage through additional turbulent magnetized plasma, potentially associated with the host galaxy. We use the burst energy of 2 × 10 ⁴² erg to revise the empirical maximum energy of an FRB.

We have conducted a blind search in 49 consecutive days of interplanetary scintillation observations made by the Murchison Widefield Array from mid‐2019, with overlapping daily observations approximately East and South‐East of the Sun at an elongation of ∼30° and a field of view of 30°. These observations detect an unprecedented density of sources. In spite of these observations being taken at sunspot minimum, this search has revealed several interesting transitory features characterized by elevated scintillation levels. One solar wind enhancement is captured in two observations several hours apart, allowing its radial movement away from the Sun to be measured. We present here a methodology for measuring the plane‐of‐sky velocity for the moving heliospheric structure. The plane‐of‐sky velocity was inferred as 0.66 ± 0.147 hr⁻¹, or 480 ± 106 kms⁻¹ assuming a distance of 1AU. After cross‐referencing our observed structure with multiple catalogs of heliospheric events, we propose that the likely source of our observed structure is a stream‐interaction region originating from a low‐latitude coronal hole. This work demonstrates the power of widefield interplanetary scintillation observations to capture detailed features in the heliosphere which are otherwise unresolvable and go undetected.

We have shown previously that the Murchison Widefield Array (MWA), can detect 100s of Interplanetary Scintillation (IPS) sources simultaneously across a field of view (FoV) ∼30° in extent. To test if we can use this capability to track heliospheric structures, we undertook a search of 88 hr of MWA IPS data, and identified an observation likely to have a significant Coronal Mass Ejection (CME) in the FoV. We demonstrate that in a single 5‐min MWA observation we are able to localize and image a CME ∼33 hr after launch at an elongation of ∼37° from the Sun. We use IPS observables to constrain the kinematics of the CME, and describe how MWA IPS observations can be used in the future to make a unique contribution to heliospheric modeling efforts.