Radio Transients in the Era of Multi-Messenger Astrophysics

AbstractRadio emission from astrophysical transients allows us to derive calorimetry of kinetic feedback and detailed imaging in ways that are not possible at other wavelengths, and as such it forms an important part of the multi-messenger follow-ups of these events. The field is burgeoning, with a renaissance of interest in accretion, stellar explosions and jetted supernovæ, alongside newer classes of phenomena such as fast radio bursts and tidal disruption events. The purpose of this workshop was to discuss the infrastructure and techniques for detecting, identifying and probing radio transients, with a particular focus on how best to exploit transient alerts from multi-messenger facilities. We examined the type of transient alerts those facilities will broadcast, and methods for following them up, such as rapid-response triggering and shadowing. In break-out groups, participants chose a science question related to a particular radio transient type or class and discussed whether the planned transient strategies and observing techniques on the Square Kilometre Array will be adequate to address the particular question. The classes they chose included fast radio bursts, supernovæ, cataclysmic variable and unknown transients. Any proposed adaptation or suggestion was relayed to a panel of experts for further discussion. The second part of the workshop concentrated on the application of long baseline interferometry for detecting and measuring radio transients.

Download Full-text

A search for fast-radio-burst-like emission from Fermi gamma-ray bursts

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1889 ◽

2020 ◽

Vol 497 (1) ◽

pp. 125-129 ◽

Cited By ~ 1

Author(s):

Mieke Bouwhuis ◽

Keith W Bannister ◽

Jean-Pierre Macquart ◽

R M Shannon ◽

David L Kaplan ◽

...

Keyword(s):

Radio Emission ◽

Radio Burst ◽

Gamma Ray ◽

Gamma Ray Bursts ◽

Dispersion Measure ◽

Radio Bursts ◽

Square Kilometre Array ◽

Fast Radio Burst ◽

Short Grbs

ABSTRACT We report the results of the rapid follow-up observations of gamma-ray bursts (GRBs) detected by the Fermi satellite to search for associated fast radio bursts. The observations were conducted with the Australian Square Kilometre Array Pathfinder at frequencies from 1.2 to 1.4 GHz. A set of 20 bursts, of which four were short GRBs, were followed up with a typical latency of about 1 min, for a duration of up to 11 h after the burst. The data were searched using 4096 dispersion measure trials up to a maximum dispersion measure of 3763 pc cm−3, and for pulse widths w over a range of duration from 1.256 to 40.48 ms. No associated pulsed radio emission was observed above $26 \, {\rm Jy\, ms}\, (w/1\, {\rm ms})^{-1/2}$ for any of the 20 GRBs.

Download Full-text

The capability of the Australian Square Kilometre Array Pathfinder to detect prompt radio bursts from neutron star mergers

Publications of the Astronomical Society of Australia ◽

10.1017/pasa.2020.42 ◽

2020 ◽

Vol 37 ◽

Author(s):

Ziteng Wang ◽

Tara Murphy ◽

David L. Kaplan ◽

Keith W. Bannister ◽

Dougal Dobie

Keyword(s):

Neutron Star ◽

Radio Emission ◽

Theoretical Models ◽

Field Of View ◽

Radio Bursts ◽

Square Kilometre Array ◽

Physical Conditions ◽

Credible Region ◽

Fast Radio Burst ◽

Prompt Emission

Abstract We discuss observational strategies to detect prompt bursts associated with gravitational wave (GW) events using the Australian Square Kilometre Array Pathfinder (ASKAP). Many theoretical models of binary neutron stars mergers predict that bright, prompt radio emission would accompany the merger. The detection of such prompt emission would greatly improve our knowledge of the physical conditions, environment, and location of the merger. However, searches for prompt emission are complicated by the relatively poor localisation for GW events, with the 90% credible region reaching hundreds or even thousands of square degrees. Operating in fly’s eye mode, the ASKAP field of view can reach $\sim1\,000$ deg $^2$ at $\sim$ $888\,{\rm MHz}$ . This potentially allows observers to cover most of the 90% credible region quickly enough to detect prompt emission. We use skymaps for GW170817 and GW190814 from LIGO/Virgo’s third observing run to simulate the probability of detecting prompt emission for GW events in the upcoming fourth observing run. With only alerts released after merger, we find it difficult to slew the telescope sufficiently quickly as to capture any prompt emission. However, with the addition of alerts released before merger by negative-latency pipelines, we find that it should be possible to search for nearby, bright prompt fast radio burst-like emission from GW events. Nonetheless, the rates are low: we would expect to observe $\sim$ 0.012 events during the fourth observing run, assuming that the prompt emission is emitted microseconds around the merger.

Download Full-text

A circular polarization survey for radio stars with the Australian SKA Pathfinder

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab299 ◽

2021 ◽

Vol 502 (4) ◽

pp. 5438-5454

Author(s):

Joshua Pritchard ◽

Tara Murphy ◽

Andrew Zic ◽

Christene Lynch ◽

George Heald ◽

...

Keyword(s):

Radio Emission ◽

Brightness Temperature ◽

Circular Polarization ◽

Flux Density ◽

Wide Band ◽

M Dwarfs ◽

Square Kilometre Array ◽

Population Statistics ◽

Chemically Peculiar ◽

Radio Stars

ABSTRACT We present results from a circular polarization survey for radio stars in the Rapid ASKAP Continuum Survey (RACS). RACS is a survey of the entire sky south of δ = +41○ being conducted with the Australian Square Kilometre Array Pathfinder telescope (ASKAP) over a 288 MHz wide band centred on 887.5 MHz. The data we analyse include Stokes I and V polarization products to an RMS sensitivity of 250 μJy PSF−1. We searched RACS for sources with fractional circular polarization above 6 per cent, and after excluding imaging artefacts, polarization leakage, and known pulsars we identified radio emission coincident with 33 known stars. These range from M-dwarfs through to magnetic, chemically peculiar A- and B-type stars. Some of these are well-known radio stars such as YZ CMi and CU Vir, but 23 have no previous radio detections. We report the flux density and derived brightness temperature of these detections and discuss the nature of the radio emission. We also discuss the implications of our results for the population statistics of radio stars in the context of future ASKAP and Square Kilometre Array surveys.

Download Full-text

Tidal disruption events seen in the XMM-Newton slew survey

Proceedings of the International Astronomical Union ◽

10.1017/s1743921317001776 ◽

2016 ◽

Vol 12 (S324) ◽

pp. 123-126

Author(s):

Richard Saxton ◽

S. Komossa ◽

Andrew Read ◽

Paulina Lira ◽

Kate D. Alexander ◽

...

Keyword(s):

Radio Emission ◽

Real Time ◽

Power Law ◽

Early Phase ◽

Classical Model ◽

Thermal Processes ◽

Tidal Disruption ◽

X Ray ◽

Hard Power ◽

Sky Survey

AbstractXMM-Newton performs a survey of the sky in the 0.2-12 keV X-ray band while slewing between observation targets. The sensitivity in the soft X-ray band is comparable with that of the ROSAT all-sky survey, allowing bright transients to be identified in near real-time by a comparison of the flux in both surveys. Several of the soft X-ray flares are coincident with galaxy nuclei and five of these have been interpreted as candidate tidal disruption events (TDE). The first three discovered had a soft X-ray spectrum, consistent with the classical model of TDE, where radiation is released during the accretion phase by thermal processes. The remaining two have an additional hard, power-law component, which in only one case was accompanied by radio emission. Overall the flares decay with the classical index of t−5/3 but vary greatly in the early phase.

Download Full-text

Exploring the bulk of the BL Lacertae object population

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833540 ◽

2018 ◽

Vol 618 ◽

pp. A175

Author(s):

F. D’Ammando ◽

M. Giroletti ◽

S. Rainó

Keyword(s):

Radio Emission ◽

Test Statistic ◽

Large Area ◽

Bl Lacertae ◽

The Third ◽

Long Baseline ◽

Photon Index ◽

Multi Wavelength ◽

Doppler Factor ◽

Bl Lacs

Aims. We are studying an unbiased sample of 42 nearby (z < 0.2) BL Lacertae objects with a multi-wavelength approach. The results of Very Long Baseline Interferometry observations were presented in the first paper of this series. In this paper, we study the γ-ray properties of the sample. Methods. We analyse data collected by the Fermi-Large Area Telescope (LAT) during its first 8.5 yr of operation in the energy range 0.1−300 GeV. Results. We reveal 23 sources with a test statistic greater than 25 (corresponding to ~4.6-σ) out of 42, with 3 sources not detected in the third LAT active galactic nucleus (AGN) catalogue, and fluxes between 3.5 × 10−10 and 7.4 × 10−8 ph cm−2 s−1. The majority of the sources have hard spectra (Γ ≤ 2), with only four having values in the range 2.1–2.4. The three newly detected sources have fluxes in the range between 0.54 × 10−9 and 1.35 × 10−9 ph cm−2 s−1 and photon index 1.7–1.9. Among the 23 LAT-detected sources, 19 are included in the third catalogue of hard Fermi-LAT sources, with a spectrum that connects relatively smoothly from 0.1 GeV to 2 TeV. LAT-detected BL Lacs are more luminous on parsec scales with respect to non-LAT-detected sources and have larger core dominance according to the unified models. Conclusions. The LAT-detected BL Lacs seem to be composed of a bulk of “classical” sources dominated by Doppler boosting and characterised by compact and bright radio emission as well as hard γ-ray spectra. Moreover, we have identified a possible population of low-luminosity BL Lacs not detected by LAT, lacking a VLBI core, and with a small Doppler factor. Furthermore, three LAT-detected sources show non-classical properties for γ-ray emitting BL Lacs (no evidence of relativistic jet, low Doppler factor in radio images, relatively low core dominance) and three other sources, while showing radio emission on parsec scales, are not detected in γ rays so far.

Download Full-text

The square kilometre array and the transient universe

Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rsta.2012.0284 ◽

2013 ◽

Vol 371 (1992) ◽

pp. 20120284 ◽

Cited By ~ 3

Author(s):

B. W. Stappers

Keyword(s):

Radio Emission ◽

Large Range ◽

Great Sensitivity ◽

Wide Field ◽

Power Mean ◽

Computing Power ◽

Square Kilometre Array ◽

Wide Field Of View ◽

Two Phases ◽

Aperture Arrays

The square kilometre array (SKA) is a next generation radio telescope that will be built in southern Africa and Australasia. It will be built in two phases and will use a range of detectors, from aperture arrays to dishes, to span the frequency range from a few tens of megahertz to a few gigahertz. The combination of great sensitivity, wide field of view and unprecedented computing power mean that the SKA will be an excellent instrument for studying the transient radio universe. Transient radio emission is generated in extremes of: gravitational and magnetic fields, velocity, temperature, pressure and density. While we know about plenty of source classes for this type of short duration radio emission, there is still a large range of transient parameter space that has not yet been sampled owing to the limitations of current generation radio telescopes.

Download Full-text

Comparative analysis of solar radio bursts before and during CME propagation

Astronomy and Astrophysics ◽

10.1051/0004-6361/201629489 ◽

2019 ◽

Vol 625 ◽

pp. A63 ◽

Cited By ~ 1

Author(s):

G. Dididze ◽

B. M. Shergelashvili ◽

V. N. Melnik ◽

V. V. Dorovskyy ◽

A. I. Brazhenko ◽

...

Keyword(s):

Comparative Analysis ◽

Radio Emission ◽

Instantaneous Frequency ◽

Narrow Band ◽

Radio Bursts ◽

Frequency Bandwidth ◽

Plasma Parameters ◽

Type Iii ◽

Type Iv ◽

Band Type

Context. As is well known, coronal mass ejection (CME) propagation often results in the fragmentation of the solar atmosphere on smaller regions of density (magnetic field) enhancement (depletion). It is expected that this type of fragmentation may have radio signatures. Aims. The general aim of the present paper is to perform a comparative analysis of type III solar and narrow-band type-III-like radio burst properties before and during CME events, respectively. The main goal is to analyze radio observational signatures of the dynamical processes in solar corona. In particular, we aim to perform a comparison of local plasma parameters without and with CME propagation, based on the analysis of decameter radio emission data. Methods. In order to examine this intuitive expectation, we performed a comparison of usual type III bursts before the CME with narrow-band type-III-like bursts, which are observationally detectable on top of the background type IV radio bursts associated with CME propagation. We focused on the analysis of in total 429 type III and 129 narrow-band type-III-like bursts. We studied their main characteristic parameters such as frequency drift rate, duration, and instantaneous frequency bandwidth using standard statistical methods. Furthermore, we inferred local plasma parameters (e.g., density scale height, emission source radial sizes) using known definitions of frequency drift, duration, and instantaneous frequency bandwidth. Results. The analysis reveals that the physical parameters of coronal plasma before CMEs considerably differ from those during the propagation of CMEs (the observational periods 2 and 4 with type IV radio bursts associated with CMEs). Local density radial profiles and the characteristic spatial scales of radio emission sources vary with radial distance more drastically during the CME propagation compared to the cases of quasistatic solar atmosphere without CME(s) (observational periods 1 and 3). Conclusions. The results of the work enable us to distinguish different regimes of plasma state in the solar corona. Our results create a solid perspective from which to develop novel tools for coronal plasma studies using radio dynamic spectra.

Download Full-text

Electron acceleration and radio emission following the early interaction of two coronal mass ejections

Astronomy and Astrophysics ◽

10.1051/0004-6361/202038801 ◽

2020 ◽

Vol 642 ◽

pp. A151

Author(s):

D. E. Morosan ◽

E. Palmerio ◽

J. E. Räsänen ◽

E. K. J. Kilpua ◽

J. Magdalenić ◽

...

Keyword(s):

Magnetic Field ◽

Radio Emission ◽

Coronal Mass Ejections ◽

Solar Radio ◽

Electron Beams ◽

Solar Radio Emission ◽

Radio Bursts ◽

Solar Radio Bursts ◽

Dynamic Spectra

Context. Coronal mass ejections (CMEs) are large eruptions of magnetised plasma from the Sun that are often accompanied by solar radio bursts produced by accelerated electrons. Aims. A powerful source for accelerating electron beams are CME-driven shocks, however, there are other mechanisms capable of accelerating electrons during a CME eruption. So far, studies have relied on the traditional classification of solar radio bursts into five groups (Type I–V) based mainly on their shapes and characteristics in dynamic spectra. Here, we aim to determine the origin of moving radio bursts associated with a CME that do not fit into the present classification of the solar radio emission. Methods. By using radio imaging from the Nançay Radioheliograph, combined with observations from the Solar Dynamics Observatory, Solar and Heliospheric Observatory, and Solar Terrestrial Relations Observatory spacecraft, we investigate the moving radio bursts accompanying two subsequent CMEs on 22 May 2013. We use three-dimensional reconstructions of the two associated CME eruptions to show the possible origin of the observed radio emission. Results. We identified three moving radio bursts at unusually high altitudes in the corona that are located at the northern CME flank and move outwards synchronously with the CME. The radio bursts correspond to fine-structured emission in dynamic spectra with durations of ∼1 s, and they may show forward or reverse frequency drifts. Since the CME expands closely following an earlier CME, a low coronal CME–CME interaction is likely responsible for the observed radio emission. Conclusions. For the first time, we report the existence of new types of short duration bursts, which are signatures of electron beams accelerated at the CME flank. Two subsequent CMEs originating from the same region and propagating in similar directions provide a complex configuration of the ambient magnetic field and favourable conditions for the creation of collapsing magnetic traps. These traps are formed if a CME-driven wave, such as a shock wave, is likely to intersect surrounding magnetic field lines twice. Electrons will thus be further accelerated at the mirror points created at these intersections and eventually escape to produce bursts of plasma emission with forward and reverse drifts.

Download Full-text