2020-A, Extended
Approved Proposals
PI | Title | Abstract | Science Theme | Triggered? | Visibility Time Requested (Hours) | VCS Time Requested (Hours) |
|---|---|---|---|---|---|---|
| Anderson (1) | Catching the low frequency radio component of stellar X-ray superflares | 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 2020A 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. | Transients | Yes | 4.5 | 0.0 |
Anderson (2) | Negative-latency triggering on gravitational wave events with the Murchison Widefield Array | We request the use of the Murchison Widefield Array (MWA) rapid-response mode to perform VCS triggered observations of negative latency gravitational wave alerts of binary neutron star (BNS) and neutron star (NS) - black hole (BH) mergers detected by Advanced LIGO/Virgo (LV). While the prompt and early-time radio emission associated with BNS mergers is an unexplored regime, leading theories suggest that fast radio bursts (FRBs; extreme radio transients of unknown origin) are related to these events (Totani, 2013; Falcke & Rezzolla, 2014; Zhang, 2014). The best chance to detect a prompt FRB-like event associated with a BNS merger requires that LV rapidly disseminate alerts of GW events. However, the estimated delay between merger and alert generation for the current LV O3 run, combined with the response times of most radio telescopes, is too slow to catch a simultaneous FRB. However, by sending negative latency GW triggers to the MWA (response times <14s; Hancock et al. 2019), it is possible to be on-target before an associated FRB arrives. The current O3 LV run has been detecting GW mergers involving at least one NS at a rate of ~1 per month. Using the high-time resolution capabilities of the MWA VCS, we therefore request to trigger on up to 2 events during the remainder of the O3 LV run (April and May 2020), of which we estimate up to 1 will be an MWA-detectable GW-FRB event. | Transients | Yes | 0.0 | 0.3 |
| Bhat (1) | Tracking Interstellar Space Weather Toward Timing-array Millisecond Pulsars | Searching for nanohertz gravitational waves (GWs) using a celestial array of extremely stable millisecond pulsars (MSPs) is amongst the high-profile science goals of the SKA and its pathfinders. The success of these Pulsar Timing Array (PTA) experiments will extend the spectrum of gravitational-wave astronomy that has been opened by the LIGO/VIRGO detections of kilohertz-frequency gravitational waves produced by black-hole and neutron-star mergers. PTAs exploit the clock-like stability of MSPs to make a direct detection of ultra-low frequency (nano-Hertz) gravitational waves, and the science is highly complementary to that possible with LIGO-like detectors. PTAs are most sensitive to GW signals produced by supermassive black-hole mergers. Interstellar propagation effects on pulsar signals are a major contributor to timing noise, which, if not accurately measured and corrected for in timing measurements, may ultimately limit the detection sensitivity of PTAs. The interstellar medium (ISM) effects are much stronger at low frequencies, and hence the MWA presents an exciting and unique opportunity to calibrate interstellar propagation delays. Here we propose continued regular observations of three promising PTA pulsars that we have already demonstrated to be most suitable for detailed studies using the MWA. The primary goals include characterising the nature of the turbulent ISM through high-quality scintillation and dispersion studies, including the investigation of chromatic (frequency-dependent) dispersion measures (DMs) and high-precision DM determinations that are now possible with the MWA. Our success and accomplishments in this area will also help define the scope of a more ambitious program in the future, as upgrade plans move forward for the MWA and with the prospects of a pulsar monitoring capability in the horizon in the era of Phase 3 MWA. This will also prove to be an excellent scientific niche for the MWA, and eventually for the SKA-low. | Pulsars and Fast Transients | No | 0.0 | 15.5 |
| Bhat (2) | Triggering on ASKAP FRB Detections | The Fast Radio Bursts (FRB) research is a rapidly emerging frontier of radio astronomy. Since their early discoveries by Lorimer et al. (2007) and Thornton et al. (2013), there have been a number of significant developments, including an explosion in their tally with the CHIME/FRB project coming online. Measurements of their scattering, scintillation, polarisation and Faraday rotation properties are becoming routine, and theoretical efforts to understand their origin continues unabated. As observational evidence continues to mount in support of their extragalactic origin, the world-wide competitive race is on, with a suite of new generation instruments geared up to find them in large numbers, and efforts are in earnest to localise them. With its large field of view of _30 deg2 and interferometric advantages, ASKAP has proven to be a uniquely capable instrument for detecting them, as well as localising them on sky with arcsecond (or better) precision. TheMWA’s co-location at the MRO site enables unique opportunities for undertaking efficient co-observing and triggering obseravtions. Our shadowing campaign in 2018-2019 has placed the most stringent constraints on low-frequency emission of FRBs and their spectral indices. For the 2020A semester, we intend to shift the focus to further development and testing of VCS triggering strategies and optimising them for improved efficiency. Simultaneous ASKAP+MWA detection of even a single FRB would mean a huge science payoff and will yield the first unambiguous constraints on the spectral and scattering properties of FRBs, besides putting an end to the long-unresolved puzzle relating to the lack of FRB emission at low frequencies. A detection within the MWA band (<300 MHz) will also help exclude certain classes of progenitor models that involve dense plasma surrounding FRB hosts, and confirm their cosmological distances. | Pulsars and Fast Transients | Yes | 0.0 | 15 |
| Chauhan* | Monitoring of X-ray binary transient outbursts with the MWA | We propose pointed observations with the MWA of any nearby bright (&50 mJy) outbursting X-ray binary (XRB) during the 2020{A observing semester. The low-frequency regime of radio jets in XRBs is still not fully explored, especially at frequencies < 500 MHz. XRBs can produce two different types of radio jets over the course of a single outburst. Optically thick, at-spectrum, compact steady jets are observed during the hard state whereas steep-spectrum, relativistically-moving transient jets are detected near the peak of the outburst, when the source undergoes a transition from the hard to the soft X-ray spectral state. Both types of jets can be observed 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. The prime aim of this proposal is to detect the possible low-frequency turn-over in the compact jets. The turn-over frequency along with the spectral slope below the turn-over frequency will put observational constraints on the electron energy distribution and magnetic field strength. Simultaneous high-cadence monitoring of transient jets at low and high frequencies will provide observational measurements essential for constraining the low-frequency emission geometry and thereby constrain various theoretical 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. | Transients | Yes | 30 | 0.0 |
| Croft | MWA Follow-up of Neutrino Transient Candidates | We request MWA follow-up of neutrino transient candidates detected by the ANTARES/KM3NeT and IceCube telescopes during 2020-A. These observations would be disruptive target of opportunity observations. Around 30% of ANTARES/KM3NeT triggers are expected to be visible immediately from the MWA site (Adrian-Martinez et al. 2015). IceCube alerts favouring high-energy events are also more likely to originate from the Southern Hemisphere (https://icecube.wisc.edu/science/data/TXS0506_alerts), and approximately 30% are likely to be visible to the MWA. We expect to follow up three or four triggers during the semester. We request 30 min of prompt follow-up of each trigger, followed by a second epoch 1 – 2 weeks later (matched in LST range) 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. We expect ANTARES to be decommissioned part-way through the semester, and to implement parsing software to accept IceCube alerts prior to the beginning of the semester. | Transients | Yes | 4.0 | 0.0 |
| Hurley-Walker | GaLactic and Extragalactic All-Sky MWA-eXtended (GLEAM-X) survey | We propose the second half of observations of an extension to the highly successful GaLactic and Extragalactic MWA (GLEAM) survey. The aim is to create a legacy data set for innovative low-frequency science which will serve many astronomers overcoming years. This proposal covers an RA range of 20 to 06h, concluding the observation program initiated in 2018-A. The optimal time for our observations is a month between mid-September and mid-November, which straddles 2020-A and B, so we are submitting this proposal now for ease of scheduling. A deeper all-sky survey at higher resolution will enable a legion of science capabilities, whilst maintaining advantages over LOFAR including larger field-of-view (and survey speed), wider frequency coverage, and better sensitivity to extended emission. We propose to cover the GLEAM frequency range of 72—231 MHz and use repeated drift scans to observe 8,000 deg2, which in combination with the 20,000 deg2 observed in2018-A, will cover the entire southern sky. We will continue the successful snapshot imaging and image-plane combination strategy of GLEAM. We will utilise calibration strategies we have developed over the last year of research. The GLEAM extragalactic sky catalogue improves the prospects for good ionospheric calibration in this new regime, as well as trivialising absolute flux density calibration. Extrapolating from GLEAM, GLEAM-X will have lower noise, higher surface brightness sensitivity, and considerably wider bandwidth than TGSS. These properties will enable a wide range of science, such as:
In addition, the proposal is designed to be commensally used for transients science. | GEG | No | 280 | 0.0 |
| Janagal† | Investigation of sub-pulse drifting properties for three pulsars | A significant population of pulsars exhibits the extremely intriguing drifting subpulse phenomenon. When individual pulses are stacked vertically to form a two-dimensional pulse stack, the individual components of pulses, termed subpulses, are observed to undergo a regular modulation pattern in both amplitude and phase, which visually resemble a set of discrete diagonally-oriented burst regions called drift bands. The study of this phenomenon is essential for unlocking the mystery of radio pulsar emission mechanisms. A systematic single pulse study with enhanced sensitivities of a sample of pulsars exhibiting subpulse drifting can provide a better understanding of this phenomenon. We selected a sample of three pulsars, PSR J1543+0929, PSR J1820-0427, and PSR J1834-0426, for investigation of subpulse drifting properties with the MWA. A separate proposal to observe these targets (among others) at higher frequencies has been recently submitted in Cycle-38 of uGMRT. These pulsars have high flux at both uGMRT (Band-3 and 4) and MWA frequencies. There is evidence that each of these pulsars exhibit subpulse drifting (Weltevrede et al., 2006,2007), but no studies have yet been conducted using single pulse data. These sources lie in the field of view of MWA and are nightly targets for the 2020A semester, hence providing low RFI conditions. Also, the new MWA beamformer equips the instrument to study the listed sources, some of which are at high DM, with better sensitivity. The sample of pulsars selected has previously indicated the presence of subpulse drifting at different frequencies (Weltevrede et al., 2006, 2007) and requires further detailed multi-frequency investigation. Since the target pulsars have different profile shapes with multi-component profiles generated from varied emission geometry, our study will probe the connection between subpulse drift properties of various emission components. The lower frequency and high sensitivity of our targets at MWA frequencies will provide a useful platform to study the subpulse behaviour, mode switching and fluctuation spectra. In addition, MWA has also demonstrated the capability for high-quality single pulse work through multiple recent publications (McSweeney et al. 2017, 2019). | Pulsars and Fast Transients | No | 0.0 | 6.7 |
| Kaplan | Searching for Prompt Emission from Binary Neutron Star Mergers | We propose a triggered search for prompt emission from up to three binary neutron stars 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. | Transients | Yes | 1 | 0.0 |
| Morgan | An Interplanetary Scintillation Survey with the extended Phase II MWA | We propose to conduct daily observations of Interplanetary Scintillation (IPS). We can use these observations for both space weather monitoring, and for determining the arcsecond-scale structure of the detected sources. With 8⨉10 minute observations per day we can cover all solar elongations where we can make optimum IPS measurements, broadly following the survey methodology used in 2019A. In the first part of the 2020A we will be re-observing the same sky areas from 2019A. However, these will be independent observations from a space weather point of view; and this is also useful for improving our astrophysical modelling, since multiple independent observations reduce uncertainty introduced by space weather variations. Observing later in the year than was possible in 2019A will allow us to access parts of the sky for which we have no prior data. The parts of the sky opened up are particularly interesting as they cover high Galactic latitude fields well studied by other radio surveys such as FIRST. In contrast to most other projects using the long-baseline MWA, IPS is not strongly affected by bandwidth smearing and we can accept 40kHz frequency resolution, reducing the archive volume of our observations by a factor of 4. | SHI | No | 240 | 0.0 |
| Oberoi | MWA Observations of the Sun | Two hundred hours of observing time for solar observations is requested during the 2020-A observing semester. These data will be used to address science objectives for solar burst science (Goal A); studies of weak non-thermal radiation (Goal B); quiet sun science (Goal C), imaging of CME plasma (Goal D); observations coordinated with the trajectory of the Parker Solar Probe (Goal E); and measuring CME magnetic fields (Goal F). Goal A will focus on detailed investigations of individual events seen in the MWA data, using the unsurpassed spectroscopic imaging ability of the MWA to address some key solar physics questions. Detailed observations of type II bursts, of which MWA has observed two, and type III bursts will be one focus. Goal B will address studies of the numerous short lived and narrow band emission features, significantly weaker than those seen by most other instruments revealed by the MWA. These emission features do not resemble any known types of solar bursts, but are possible radio signatures of the “nanoflares' which have long been suspected to play a role in coronal heating. A large database of these events is needed to be able explore this possibility and to reliably estimate their contribution to coronal heating. These observations will contribute to this database. Goal C will focus on characterizing the Sun’s background thermal emissions, their short and long term variability and look for evidence of a scattering disc around the Sun. Goal D makes use of our high dynamic range capability to directly image the gyrosynchrotron emission from the CME plasma. Goal E proposes opportunistic observations during the perihelion of PSP. Finally, Goal F will explore the use of Faraday rotation of linearly polarised light from background radio source due CME plasma to build a 3D model for the CME magnetic field. | SHI | No | 200 | 0.0 |
| Ross* | Low-Frequency Variability Monitoring of Peaked Spectrum Sources | Gigahertz-peaked spectrum (GPS) radio sources are a unique subset of active galactic nuclei (AGN) which can display compact, double-lobe morphology. GPS sources are identified by a spectral peak in their radio spectral energy distributions (SED) in the gigahertz regime, typically have sizes of 1-20 kpc, and show little to no polarisation or variability. As compact radio galaxies can also peak at MHz frequencies (often referred to as Megahertz-peaked spectrum (MPS) sources) we refer collectively to all sources displaying a peak in their SED as peaked spectrum sources (PSS), regardless of peak frequency. PSS have played a pivotal role in shaping our understanding evolutionary paths of radio galaxies as they are hypothesised to be the progenitors to massive, radio-loud AGN (O'Dea, 1998). We have performed a comparison of ˞500 peaked spectrum sources identified from the GaLactic and Extragalactic All-sky MWA Survey (GLEAM; Hurley-Walker et al., 2017; Wayth et al., 2015), by Callingham et al. (2017) with the second year of GLEAM observations (Franzen et al. in prep). We find ˞ 25 sources (˞ 30% of the variable population and ˞ 5% of the PSS population) which show significant variability across the two years of observation but, unexpectedly, maintain their peaked spectrum classification. Furthermore, we have discovered extreme variability in the SEDs of 10 peaked-spectrum sources (˞ 12% of the variable population) that maintained their curved or peaked spectral classification over both epochs. Year-long variability, much shorter than the expected evolution variation of these sources, suggests a fundamental misunderstanding of the physical mechanisms causing the spectral peak and/or a departure from the stereotypical structure of peaked-spectrum sources. We aim to conduct year-long monitoring of 15 of these sources with both the MWA and ATCA in order to detect and classify any observed variability across the entire SED. Our ATCA proposal was 100% awarded in the OCT19 semester for which we obtained matching DDT MWA observations. We have a follow-up APR20 ATCA proposal under review to continue these observations for a further five epochs of 2.1GHz, 5GHz and 9GHz imaging spread across the semester. We request simultaneous (subject to availability, otherwise within 2 days) MWA time with the APR20 ATCA observations. | GEG | No | 62.5 | 0.0 |
| Seymour | Observing HI in Absorption Against a Luminous z ∼ 10 Radio Galaxy | We have been conducting a search for high redshift (z>5:5) radio galaxies in order to investigate the formation and evolution of super-massive black holes in the early Universe. In addition to studying super-massive black holes, we can use these sources to study the formation of massive host galaxies and their environments. Of particular interest is how the host galaxy interacts with its environment. The HI/ 1420.4 MHz hyperfine transition is a tracer of the cold neutral hydrogen, but this line is too weak to detect in emission at this redshift. However, it should in theory be detectable in absorption with a bright enough background source. We propose a long observation to obtain a spectrum of a newly confirmed powerful radio galaxy at z=10.154. At the HI observed frame frequency, 127 MHz, this galaxy has a flux density of ~600 mJy. We estimate that a 100-hour observation would detect HI with an optical depth of tau= 0:1 with a SNR of ˞~6 over one 10 kHz channel. We estimate the HI to be 7-10 channels wide boosting our SNR. Such an observation naturally pushes the capability of the MWA regarding systematics, but we argue that this is a great example of a high-risk/high-reward project. At minimum we would obtain an upper limit for the HI optical depth in this galaxy. We may see intervening absorption from neutral HI along the line sight within the Epoch of Reionisation. | GEG | No | 100 | 0.0 |
| Sobey | Targeted MWA pulsar search towards promising candidates identified in radio surveys | We propose a pilot targeted pulsar search towards five promising pulsar candidates. These were identified as polarised sources in POGS (POlarised GLEAM Survey; MWA imaging data), or steep spectrum sources in TGSS, and have properties consistent with those of the pulsar polulation. This is a proof-of-concept study that presents the opportunity to efficiently discover more pulsars, which are powerful probes of a range of physics. We request 5 h of observing time using the MWA in the extended configuration, mostly utilising the high-time and -frequency resolution VCS mode. | Pulsars and Fast Transients | No | 0.8 | 4.2 |
| Tian* | Rapid-response MWA observations of Swift and Fermi gamma-ray bursts | We request the use of the MWA rapid-response mode to perform triggered standard correlator and VCS observations of Swift and Fermi gamma-ray bursts (GRBs) during the 2020A 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 a hot topic in astronomy as they are linked with the compact binary coalescence of binary neutron stars (BNS), or a neutron star (NS) -black hole (BH) binary. BNS 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 burst alerts at MWA frequencies. Given that the MWA rapid-response mode can automatically repoint the telescope within 20seconds 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 (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. | Transients | Yes | 8 | 1 |
| Williamson* | Detecting cosmic-ray extensive air showers | Following the request for DDT last year, the purpose of this proposal is to use the improved methods developed through the DDT to detect the first radio emission from cosmic ray air showers at the MWA. The aims for this observation proposal are: • To detect the first cosmic ray event using the MWA • To further investigate the RFI at nanosecond timescales • To monitor the cosmic ray detector on site in conjunction with MWA data for any concurrent cosmic ray detections • To limit the impact of these observations on the limited space available on the archive. (See Part C for more details). The detection of the first cosmic ray event at the MWA would open up opportunities in the development of cosmic ray reconstruction and analysis techniques and would benefit transient science at nano second timescales. There have been two ARC grants (ARC Discovery Project DP200102643, Detecting cosmic rays using precision radio imaging; and ARC LIEF grant LE200100078, A particle detector array for the Murchison Widefield Array) awarded towards cosmic ray science at the MWA with the specific purpose of detecting and analysing many cosmic ray events, where this work will allow for a better understanding of the view that the MWA has of cosmic ray air showers. Using the DDT data we achieved: • The inverse Polyphase Filter Bank software was further optimized and benchmarked • The inversion was validated through an experiment conducted on site with a gas lighter (see Part Cand Figures 2 and 3). | Transients | No | 0 | 24 |
| Totals: | 930.8 | 66.7 |
*Student PI; †Open Access proposal