2018-B, Compact

Authors: Chenxi Shan (Shanghai Jiao Tong University (SJTU))

Abstract: With the development of new radio telescopes reaching the fainter radio sky, star-forming galaxies and radio-quiet AGNs (Active Galactic Nuclei) have an expected, surprising emergence at the radio domain. The main players of the radio sky have a changing landscape. It has realized that there is a continuum of galaxy properties in radio bands, from pure star-forming galaxies with radio power dominated by star-forming processes, to the radio-loud objects powered with the central AGN, and a composite of the prior two kinds in between. We proposed to use a sample of well-studied nearby low-luminosity Quasi-Stellar Objects (QSOs) with spatially resolved mapping via various instruments across many wavelength bands to probe their radio properties with the MWA. We performed a positional cross-match of a nearby QSO sample with the GaLactic and Extragalactic All-sky MWA Survey (GLEAM) extragalactic catalog searching for their low-frequency radio counterparts. Three targets, a radio-loud AGN, a radio-quiet AGN, and a star-forming galaxy, were selected for a pilot study of the effect of AGN feedback and the interplay between star formation and nucleus activity with the nearby QSOs.

Authors: Dan Hu (Shanghai Jiao Tong University (SJTU)), Melanie Johnston-Hollitt (Curtin University),Haiguang Xu (SJTU), Weitian Li (SJTU), Stefan Duchesne (Curtin University)

Abstract: Diffuse radio structures (radio halos, mini-halos, and radio relics), which have been detected in > 100 galaxy clusters, are seldom reported in galaxy groups, tending to be found in higher mass cluster systems. However, recently diffuse emission has been reported in both low mass clusters using the MWA (e.g., Dwarakanath et al. 2018; Johnston-Hollitt et al. 2018), demonstrating the feasibility of less massive cluster systems to support diffuse emission. Consequently, understanding the distribution of diffuse radio emission as a function of mass is an important outstanding issue in cluster physics, and will provide valuable information to constrain cosmological models, and study the associated cluster physics (e.g., merger process, AGN feedback, magnetic fields). Additionally, understanding the true number counts for such sources will be vital to model and remove this component of the contaminating foreground important for detecting the EoR signal. We propose to carry out deep pointed observations of six galaxy groups across full MWA Phase II band 72-231 MHz, observed a 1 hour per frequency band, per source for a total of 24 hours. We will use the acquired high-quality radio images and spectral index maps derived across the band to characterize the spatial distributions of the diffuse radio emission components. Together with the existing high-quality Chandra, XMM-Newton, and SDSS data available, we will be able to describe the origin and evolution of diffuse radio structures in galaxy groups and distinguish between the roles of merger and AGN activity.

Authors: Torrance Hodgson (Curtin University), Melanie Johnston-Hollitt (Curtin University)

Abstract: We propose to re-observe an ultrasteep radio source (α = −3.4) provisionally labelled Abell 2877 HT. This source was previously imaged in GLEAM but due to the poor resolution of MWA Phase I, we have not been able to discern the morphology of this source. Abell 2877 HT has no obvious optical counterpart, and both cross referencing with other radio survey data, as well as a follow up observation with the Australia Telescope Compact Array in 2018, have failed to detect the source. We attribute this absence in other radio data due to observing frequencies that are too high and/or poor sampling and suppression of short baselines. We therefore propose to re-observe this source with MWA phase II which we expect will greatly improve the resolution, and allow us to discern between a number of competing explanations for this emission.

Authors: Jaiverdhan Chauhan (ICRAR-Curtin), Dr. Gemma Anderson (ICRAR-Curtin), A/Prof. James Miller-Jones (ICRAR-Curtin), Dr. Paul Hancock (ICRAR-Curtin) Prof. David Kaplan (UWM), Dr. Marcin Sokolowski (ICRAR-Curtin),

Abstract: We propose pointed observations with the MWA of any nearby bright (& 50 mJy) outbursting X-ray binary (XRB) during the 2018-B observing semester. The low-frequency behavior of radio jets in XRBs is still poorly understood, especially at frequencies < 1 GHz. XRBs can produce two different types of radio jets, optically thick, flat-spectrum, compact steady jets and steep-spectrum, relativistically-moving transient jets, over the course of a single outburst. Both types of jets can be bright in the low-frequency regime. We aim to study both types of radio jets using MWA observations to constrain the radio spectrum in the low-frequency band. Previous LOFAR observations have shown that the standard van der Laan model of expanding spheres of plasma does not provide a good description of the low-frequency behaviour of X-ray binary jets, so we seek additional observations to ascertain their low-frequency behaviour and thereby constrain jet models. To the end, we aim to provide high-quality low-frequency radio light curves of XRBs covering a few epochs in the hard state, and denser sampling over the hard-to-soft state transition.

Authors: Torrance Hodgson (Curtin University), Melanie Johnston-Hollitt (Curtin University), and Ben McKinley (Curtin University)

Abstract: This proposal seeks to use the new capabilities of the Murchison Widefield Array (MWA) phase II to search for evidence of the synchrotron cosmic web. In particular, the extended baselines reduce the confusion limit that was encountered in previous searches using the MWA (Vernstrom et al. 2017), allowing us to probe for fainter diffuse emission. This, in addition to the other features of the MWA such as its wide field of view and sensitivity to extended angular features on the sky, make it an ideal apparatus for this search. We propose three deep field observations: two observations that trace out the expected filamentary structure of the Horologium Reticulum supercluster; and one of a cluster pair previously identified in X-ray ob- servations as being linked by a filament (Planck Collaboration et al. 2013). Detection of the synchrotron web would provide definitive support for our current models of cosmic evolution, as well as providing indirect evidence for magnetic fields on the very largest of cosmic scales. A null result, on the other hand, allows us to place even stronger constraints on these unknown parameters.

Authors: Dr. A. P. Beardsley (ASU), Prof. J. D. Bowman (ASU), Prof. D. C. Jacobs (ASU), Prof. C. M. Trott (Curtin), Prof. R. B. Wayth (Curtin), M. Kriele (Curtin), Dr. J. L. B. Line (Curtin), Dr. C. R. Lynch (Curtin)

Abstract: We propose to conduct pilot observations to deploy the m-mode analysis strategy on MWA data with the intent of filling a gap in the Global Sky Model, which is commonly used as a diffuse foreground model for Epoch of Reionization measurements. Current EoR power spectrum experiments are limited by the large dynamic range required to overcome foregrounds to reach the faint redshifted 21cm signal. Understanding how these instruments couple with the large scale diffuse structure residing in the Milky Way and other nearby radio sources is crucial to make an EoR detection. We will utilize the flexibility of MWA tiles by only using a single dipole per tile in two 25 hour drift scans, and leverage the surface brightness sensitivity of the compact Phase-II configuration. These features of the MWA will help us to simplify the m-mode analysis technique and capture the large scale structure in the low frequency southern sky.

Authors: Dr Gemma Anderson (ICRAR-Curtin), Dr Paul Hancock (ICRAR-Curtin), Dr Antonia Rowlinson (U. Amsterdam/ASTRON), Dr Andrew Williams (ICRAR-Curtin), A/Prof David Kaplan (U. Wisconsin, Milwaukee), A/Prof Tara Murphy (U. Sydney), Prof. Steven Tingay (ICRAR-Curtin), Dr Keith Bannister (CSIRO), Dr Martin Bell (UTS), and A/Prof. James Miller-Jones (ICRAR-Curtin)

Abstract: "We request the use of the new MWA rapid-response mode to perform triggered observations of Swift and Fermi gamma-ray bursts (GRBs) during the 2018B observing semester. The prompt and early-time radio emission associated with GRBs is still a poorly explored regime, particularly at MHz frequencies. Short-duration GRBs (SGRBs), one of the two main classes of GRBs, are currently a hot topic in astronomy as they are linked with the compact binary coalescence of binary neutron stars (BNSs), or a neutron star (NS) - black hole (BH) binary. BNSs mergers are the main classes of gravitational wave events known to have electromagnetic counterparts (Abbott et al. 2017). Several theories predict such mergers should produce prompt, coherent emission (such as fast radio bursts, FRBs; Totani, 2013; Falcke & Rezzolla, 2014; Zhang, 2014) the detection of which would allow us to distinguish between different binary merger models and scenarios. It is also possible that low-frequency pulsed radio emission could be generated by long-duration GRBs (LGRB; the other main GRB class resulting from stellar collapse; Usov & Katz, 2000).

As prompt radio emission becomes delayed with decreasing frequency due to dispersion, such signals associated with GRBs may not arrive for seconds up to several minutes following the initial alerts at MWA frequencies. Given that the MWA rapid-response mode can automatically repoint the telescope within 10 seconds of receiving an alert, MWA is uniquely capable of being on-target in time to observe the earliest prompt emission. An additional advantage of the MWA is its large field-of-view, making it possible to follow-up Fermi detected GRB events, which have poor position constraints on the order of ~10 deg. Such rapid-response MWA observations have the sensitivities necessary to rule out some GRB models, which will in-turn constrain different neutron star equation-of-state models. These experiments also directly test transient strategies for SKA-Low.

Authors: ​Dr. Gemma Anderson (Curtin), Dr. Christene Lynch (Curtin/ASTRO3D), Dr. Paul Hancock (Curtin), Mr. Andrew Zic (U. Sydney), Dr. Tara Murphy (U. Sydney), Dr. David Kaplan (UW-Milwaukee), Dr. Emil Lenc (CSIRO), and A/Prof. James Miller-Jones (ICRAR-Curtin)

Abstract: We request the use of the new MWA rapid-response mode to perform triggered observations of X-ray/gamma-ray flaring magnetically active stars detected with the Swift Burst Alert Telescope and the Monitor of All-sky X-ray Image (MAXI) instrument during the 2018B observing semester. Flare stars, such as rapidly rotating M dwarfs (dMe) and tidally-locked RS Canum Venaticorum binaries (RS CVn), are known to produce coherent, highly-circularly polarised flares at low radio frequencies (<5 GHz), particularly in the MHz range (Spangler et al. 1974a). These low frequency flares are indicative of unusual emission mechanisms such as electron-cyclotron masers or plasma radiation (Dulk 1985). The MWA has already proven to be a sensitive instrument for low frequency flare star studies through the detection of flares at 154 MHz from UV Ceti in Stokes V maps, which are thermal noise (rather than confusion noise) limited. These flares were likely generated via the electron-cyclotron maser mechanism (Lynch et al. 2017). dMe and RS CVn also experience extreme flaring events via incoherent emission mechanisms, producing synchrotron X-ray/gamma-ray “superflares” that are bright enough to trigger high-energy satellites such as Swift. Rapid-response radio observations performed with the Arcminute Microkelvin Imager (AMI) at high (15 GHz) radio frequencies have demonstrated that such superflares are accompanied by giant radio gyrosynchrotron flares peaking within a few minutes of the high-energy trigger (Fender et al. 2015). However, it is unknown whether X-ray/gamma-ray superflares can also be temporally coincident with low-frequency (coherent) radio bursts. By using the MWA rapid-response mode to trigger on Swift and MAXI detected high-energy superflares, we can investigate whether the same magnetic event that produces these bright, incoherent X-ray/gamma-ray superflares could also trigger the emission mechanisms responsible for bright, coherent low-frequency radio flares, providing a more unified understanding of the plasma physics in these stellar systems.

Authors: N. D. R. Bhat (Curtin; PI), N. A. Swainston (Curtin), S. E. Tremblay (Curtin), J. W. T. Hessels (ASTRON), G. Hobbs (CASS), W. van Straten (AUT), D. Kaplan (UWM), S. M. Ord (CASS), R. M. Shannon (Swinburne)

Abstract: Over the past decades, pulsars have firmly established themselves as nature's premier laboratories for uncovering new vistas in extreme physics. With applications ranging from probing the state of ultra-dense matter to testing gravity in the strong-field regime, and from probing complex plasma physics in the relativistic regime to the search for ultra-low frequency gravitational waves, they enable us to push the frontiers of physics and astrophysics. This enviable accomplishment is the direct result of multiple large sky surveys of the past five decades, which not only led to a steady increase in the known pulsar population, but also proven invariably rewarding by facilitating discoveries of exotic objects such as millisecond pulsars and those in relativistic binary orbits. Every major leap in radio astronomy instrumentation or technology tends to trigger a large pulsar survey; the advent of Phase 2 MWA and the well-matured voltage-capture capability now brings another unique opportunity. We propose to conduct an all-sky survey, the {\bf S}outhern-sky {\bf M}W{\bf A} {\bf R}apid {\bf T}wo-metre (SMART) pulsar survey, which will surpass all previous and ongoing surveys in survey speed, owing to the development of novel strategies and survey methodologies. Our goal is to survey the entire sky visible to the MWA in a uniform systematic manner. With a survey speed of $\sim$600 \sqdeghr, the entire sky can be completed in less than 100 hours, to reach a limiting sensitivity (10$\sigma$) of $\sim$3 mJy in pulsar flux density (at 150 MHz). Based on our initial pulsar census and simulation studies, we expect to discover more than 100 pulsars. Alongside its numerous scientific benefits, this SMART survey will also serve as an important demonstrator survey for SKA-Low, which is expected to be the most efficient pulsar finding machine in the coming decades.

Authors: Prof Rachel Webster (Melbourne); Dr Jack Line (Melbourne), Dr Ben McKinley (Curtin), A/Prof Randall Wayth (Curtin)

Abstract: "In order to measure the signal from the spatial fluctuation in the 21cm EoR signal, the shape of the beam needs to be understood to better than 1dB over the entire visible sky. Currently, a ‘full embedded element’ (FFE) model is used for in the EoR pipelines. However the pilot experiment (Line+ 2018, submitted) established that there are individual differences in the tile beams at a level that may be an issue for EoR experiments. Therefore we plan to conduct a second experiment to obtain more data, collected commensally during EoR observing, to achieve the following scientific goals:

• Measure the beam shape for multiple pointings, with greatly increased S/N
• Use XX and YY to estimate leakage, and compare to estimates using recorded visibilities
• Check the stability of the beam as a function oftime
• Compare our findings to the FEE
• Determine whether we need to measure the beams on all tiles to optimize the measurement of the EoR. Results from these measurements will be ultimately incorporated in the EoR pipelines, and made available to the wider MWA collaboration as appropriate.

Authors: David Kaplan (UWM); Gemma Anderson (Curtin); Keith Bannister (CSIRO); Ian Brown (UWM); Dougal Dobie (Sydney); Bryan Gaensler (Toronto); Paul Hancock (Curtin); Emil Lenc (CSIRO); Christene Lynch (Curtin); Tara Murphy (University of Sydney); Andrew Williams (Curtin)

Abstract: We propose a triggered search for prompt emission from a binary neutron star discovered through gravitational waves with the LIGO/Virgo detectors. A detection of such emission would immediately yield enormous insight into the physics of the explosion, the cosmic baryon distribution, and other topics, and would open up a new avenue for multi-messenger exploitation of these amazing events.

Authors: C. Sobey (Curtin University, CSIRO), C. Riseley (CSIRO), N. D. R. Bhat (Curtin University,CAASTRO), D. Kaur (Curtin University (CAASTRO), S. J. McSweeney(Curtin University, CAASTRO), B. W. Meyers (Curtin University,CSIRO,CAASTRO), S. M. Ord (CSIRO), S. E. Tremblay (Curtin University, CAASTRO), M. Xue(Curtin University, CAASTRO)

Abstract: We propose to conduct a pulsar search towards GLEAM J134038–340234 – the first pulsar candidate identified using POGS (POlarization from the GLEAM Survey; MWA imaging data). The source has properties consistent with that of a pulsar, including a steep spectral index and a high degree of linear polarisation. Only a handful of pulsars have been discovered using imaging data, including the first isolated millisecond pulsar and the first pulsar located in a globular cluster. Using existing sky survey images to identify pulsar candidates presents an efficient method for discovering new, and potentially unusual, pulsars, especially using low-frequency instruments like the MWA.

Authors: Steve Croft (UC Berkeley); David Kaplan (UWM); Clancy James (Curtin); Damien Dornic (Marseille); Marcos Santander (Alabama); Tara Murphy (University of Sydney); Andrew Williams (Curtin); and the MWA Transients collaboration

Abstract: We request MWA followup of neutrino transient candidates detected by the ANTARES/KM3NeT and IceCube telescopes during 2018B. These observations would be disruptive target of opportunity observations. Around 30% of triggers are expected to be visible immediately from the MWA site (Adrian-Martinez et al. 2015). We expect to follow up three or four triggers during the semester. We request 30 min of prompt followup of each trigger, followed by a second epoch 1 – 2 weeks later for comparison. These will allow the strongest limits to date on prompt radio emission from neutrino transients and may aid in localization of these new astrophysical probes.