C. J. Riseley
A5043929951- Radio Astronomy Observations and Technology
- Galaxies: Formation, Evolution, Phenomena
- Astrophysics and Cosmic Phenomena
- Astronomy and Astrophysical Research
- Astronomical Observations and Instrumentation
- Gamma-ray bursts and supernovae
- Astrophysical Phenomena and Observations
- Pulsars and Gravitational Waves Research
- Scientific Research and Discoveries
- Stellar, planetary, and galactic studies
- Astrophysics and Star Formation Studies
- Computational Physics and Python Applications
- Particle Accelerators and Free-Electron Lasers
- Geomagnetism and Paleomagnetism Studies
- Solar and Space Plasma Dynamics
- Geophysics and Gravity Measurements
- Superconducting and THz Device Technology
- Calibration and Measurement Techniques
- Scientific Measurement and Uncertainty Evaluation
- Fusion materials and technologies
- Magnetic and Electromagnetic Effects
- Science, Research, and Medicine
- Statistical and numerical algorithms
- Dark Matter and Cosmic Phenomena
- Adaptive optics and wavefront sensing
University of Bologna
2019-2024
Istituto di Radioastronomia di Bologna
2019-2024
Astronomy and Space
2016-2024
Commonwealth Scientific and Industrial Research Organisation
2016-2024
Australia Telescope National Facility
2018-2024
Zambon (Italy)
2021
ARC Centre of Excellence for All-sky Astrophysics
2021
ASTRO-3D
2021
National Institute for Astrophysics
2019
University of Manchester
2016-2017
In this data release from the LOFAR Two-metre Sky Survey (LoTSS) we present 120-168MHz images covering 27% of northern sky. Our coverage is split into two regions centred at approximately 12h45m +44$^\circ$30' and 1h00m +28$^\circ$00' spanning 4178 1457 square degrees respectively. The were derived 3,451hrs (7.6PB) High Band Antenna which corrected for direction-independent instrumental properties as well direction-dependent ionospheric distortions during extensive, but fully automated,...
Aims. This work provides an update to existing reconstructions of the Galactic Faraday rotation sky by processing almost all data sets available at end year 2020. Observations extra-Galactic sources in recent years have further illuminated previously underconstrained southern celestial sky, as well parts inner disc Milky Way, along with other regions. has culminated all-sky set 55 190 points, thereby comprising a significant expansion on 41 330 used previous works. At same time, this novelty...
We present the Multifrequency Snapshot Sky Survey (MSSS), first northern-sky LOFAR imaging survey. In this introductory paper, we describe in detail motivation and design of Compared to previous radio surveys, MSSS is exceptional due its intrinsic multifrequency nature providing information about spectral properties detected sources over more than two octaves (from 30 160 MHz). The broadband frequency coverage, together with fast survey speed generated by LOFAR's multibeaming capabilities,...
Abstract We present the data and initial results from first pilot survey of Evolutionary Map Universe (EMU), observed at 944 MHz with Australian Square Kilometre Array Pathfinder (ASKAP) telescope. The covers $270 \,\mathrm{deg}^2$ an area covered by Dark Energy Survey, reaching a depth 25–30 $\mu\mathrm{Jy\ beam}^{-1}$ rms spatial resolution $\sim$ 11–18 arcsec, resulting in catalogue 220 000 sources, which 180 are single-component sources. Here we together (where available) optical...
Abstract We present LOw Frequency ARray observations of the Coma Cluster field at 144 MHz. The cluster hosts one most famous radio halos, a relic, and low surface brightness bridge. detect new features that allow us to make step forward in understanding particle acceleration clusters. halo extends for more than 2 Mpc, which is largest extent ever reported. To northeast cluster, beyond virial radius, we discover an arc-like source could trace particles accelerated by accretion shock. west...
The Square Kilometre Array (SKA) will answer fundamental questions about the origin, evolution, properties, and influence of magnetic fields throughout Universe. Magnetic can illuminate phenomena as diverse star formation, galactic dynamics, fast radio bursts, active nuclei, large-scale structure, dark matter annihilation. Preparations for SKA are swiftly continuing worldwide, community is making tremendous observational progress in field cosmic magnetism using data from a powerful...
We present the first deep low frequency radio observations of massive and highly disturbed galaxy cluster Abell 2744 using upgraded Giant Metrewave Radio Telescope (uGMRT). The is experiencing a very complex multiple merger hosts giant halo four relics. uGMRT observations, together with existing VLA Chandra allow us to study complexity physical mechanisms active in this system. Our new images reveal that central emission more extended toward frequencies. find integrated spectrum follows...
Abstract We describe a new low-frequency wideband radio survey of the southern sky. Observations covering 72–231 MHz and Declinations south $+30^\circ$ have been performed with Murchison Widefield Array “extended” Phase II configuration over 2018–2020 will be processed to form data products including continuum polarisation images mosaics, multi-frequency catalogues, transient search data, ionospheric measurements. From pilot field described in this work, we publish an initial release 1,447...
Abstract Clusters of galaxies have been found to host Mpc-scale diffuse, non-thermal radio emission in the form central halos and peripheral relics. Turbulence shock-related processes intra-cluster medium are generally considered responsible for emission, though details these still not clear. The low surface brightness makes detection a challenge, but with recent surveys high-sensitivity telescopes we beginning build large samples sources. Evolutionary Map Universe (EMU) is Southern Sky...
Context. Clusters of galaxies are known to be turbulent environments, whether they merging systems where turbulence is injected via the conversion gravitational potential energy into intracluster medium (ICM), or relaxed in which small-scale core sloshing occurring within well. In many such systems, diffuse radio sources associated with ICM found: haloes and mini-haloes. Aims. Abell 2142 a rich cluster undergoing an extreme episode sloshing, has given rise four cold fronts complex...
Context. Radio observations of a few cool-core galaxy clusters have revealed the presence diffuse emission on cluster scales, similar to what was found in merging form radio halos. These sources might suggest that minor merger, while not sufficiently energetic disrupt cool core, could still trigger particle acceleration intracluster medium scales hundreds kiloparsecs. Aims. We aim verify occurrence cluster-scale and test merger scenario. Methods. With LOw Frequency ARray (LOFAR) at 144 MHz,...
Abstract We present techniques developed to calibrate and correct Murchison Widefield Array low-frequency (72–300 MHz) radio observations for polarimetry. The extremely wide field-of-view, excellent instantaneous ( u , v )-coverage sensitivity degree-scale structure that the provides enable instrumental calibration, removal of artefacts, correction ionospheric Faraday rotation through imaging techniques. With demonstrated polarimetric capabilities Array, we discuss future directions science...
We present new LOw-Frequency ARray observations of the massive merging galaxy cluster MACS J0717.5+3745, located at a redshift 0.5458. The hosts most powerful radio halo known to date. These observations, in combination with published uGMRT (300−850 MHz) and VLA (1−6.5 GHz) data, reveal that is more extended than previously thought, largest linear size ∼2.2 Mpc, making it one halos. shows steep spectrum ( α 144 MHz 1.5 GHz ∼ −1.4) steepening 5.5 −1.9) above GHz. find strong scattering...
Abstract We present deep and high-fidelity images of the merging galaxy cluster A2256 at low frequencies using upgraded Giant Metrewave Radio Telescope (uGMRT) LOw-Frequency ARray (LOFAR). This hosts one most prominent known relics with a remarkably spectacular network filamentary substructures. The new uGMRT (300–850 MHz) LOFAR (120–169 observations, combined archival Karl G. Jansky Very Large Array (VLA; 1–4 GHz) data, allowed us to carry out first spatially resolved spectral analysis...
Jets from active galactic nuclei (AGN) are known to recurrently enrich their surrounding medium with mildly relativistic particles and magnetic fields. Here, we present a detailed multi-frequency analysis of the nearby ( z = 0.01646) galaxy group NGC 507. In particular, new high-sensitivity high-spatial-resolution radio images in frequency range 144–675 MHz obtained using Low Frequency Array (LOFAR) upgraded Giant Metrewave Radio Telescope (uGMRT) observations. These reveal presence...
ABSTRACT Abell 3266 is a massive and complex merging galaxy cluster that exhibits significant substructure. We present new, highly sensitive radio continuum observations of performed with the Australian Square Kilometre Array Pathfinder (0.8–1.1 GHz) Australia Telescope Compact (1.1–3.1 GHz). These deep provide new insights into recently reported diffuse non-thermal phenomena associated intracluster medium, including ‘wrong-way’ relic, fossil plasma source, an as-yet unclassified central...
Faraday rotation measures (RMs) have been used for many studies of cosmic magnetism, and in most cases having more RMs is beneficial those studies. This has lead to development RM surveys that produced large catalogs, as well meta-catalogs collecting from different publications. However, it difficult take full advantage all these the individual catalogs published places, formats. In addition, polarization spectra determine are rarely published, limiting ability re-analyze data new methods or...
Pairs of radio relics are believed to form during cluster mergers, and best observed when the merger occurs in plane sky. Mergers can also produce halos, through complex processes likely linked turbulent re-acceleration cosmic-ray electrons. However, only some clusters with double show a halo. Here, we present novel method derive upper limits on halo emission, analyse archival X-ray Chandra data, as well galaxy velocity dispersions lensing order understand key parameter that switches...
Abstract The Murchison Widefield Array (MWA) is an open access telescope dedicated to studying the low-frequency (80–300 MHz) southern sky. Since beginning operations in mid-2013, MWA has opened a new observational window hemisphere enabling many science areas. driving objectives of original design were observe 21 cm radiation from Epoch Reionisation (EoR), explore radio time domain, perform Galactic and extragalactic surveys, monitor solar, heliospheric, ionospheric phenomena. All together...
We present results from LOFAR and GMRT observations of the galaxy cluster MACS$\,$J0717.5$+$3745. The is undergoing a violent merger involving at least four sub-clusters, it known to host radio halo. reveal new sources emission in Intra-Cluster Medium: (i) bridge that connects head-tail located along filament galaxies falling into main cluster, (ii) 1.9 Mpc arc, North West mass component, (iii) X-ray bar, traces gas X-rays South centre. use deep 608 MHz constrain spectral indices these...
ABSTRACT Diffuse radio emission at the centre of galaxy clusters has been observed both in merging on scales Mpc, called giant haloes, and relaxed systems with a cool-core smaller scales, named mini haloes. Giant haloes are thought to be distinct classes sources. However, recent observations have revealed presence diffuse Mpc that do not show strong dynamical activity. RX J1720.1+2638 is cluster, presenting bright central halo fainter diffuse, steep-spectrum extending beyond cluster core...