Abstract:A hundred hours of observing time for solar observations is requested during the 2019-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.

Abstract:We have examined the data taken for the GaLactic and Extragalactic All-sky MWA eXtended (GLEAM-X) survey and determined which nights cannot be processed due to highly active ionospheric weather. This proposal requests re-observations of these nights in order to complete our sky coverage. The aim of GLEAM-X is to create a legacy dataset for innovative low-frequency science which will serve many astronomers over coming years. This proposal covers an RA range of ~4 to 21h, with the expectation of observing the other half of the sky in 2020. 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 over 20,000 deg2 this semester, and a further overlapping 20,000 deg2 in 2019-B. We will continue the successful snapshot imaging and image-plane combination strategy of GLEAM, and ionospheric triage methods we have developed for GLEAM-X. 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 possess the critical wide bandwidth that sets it apart from complementary surveys such as TGSS. These properties will enable a wide range of science, such as:

• Detecting and characterising cluster relics and haloes beyond z = 0.45;
• Measuring the low-frequency luminosity function to z~0.5 (particularly the bright end);
• Characterising the low-frequency polarised sky;
• Investigating the spectral energy distributions (SEDs) of selected AGN to characterise jet activity;
• Providing broad-band radio SEDs of up to 1 million radio sources (especially in combination with upcoming ASKAP surveys);
• Better constraining the typical ionospheric diffractive scale at the MRO, feeding into SKA_Low calibration strategies.

Abstract:This proposal is a request to re-observe G0015 with a modified strategy using the improved MWA Phase II. After a number of unsuccessful attempts to detect radio recombination lines (RRLs) in G0015 data we’ve concluded that most of the data can not be used due to incorrect gains setup for most of the tiles during observing (See Part C for details). Successful detection of molecular lines and some recombination lines by Tremblay, C. et al. (2017, 2018a, 2018b) motivates us to re-observe Galactic Centre and observe NGC6334. We would also like take advantage of better capabilities of MWA Phase II and re-observe Galactic Centre and NGC6334 at the central frequency of 154.24 MHz, and observe both sources at 215.68 MHz, where the lines have been previously detected in greater optical depths. These observations can be taken and simultaneously processed for the search of molecular lines, although the processing requirements between molecules and recombination lines are somewhat different. See the proposal submitted by Chenoa Tremblay. As by-product, continuum images will have to be created. Deep integrated continuum images of the Galactic Centre and NGC6334 can also be developed to explore other scientific goals.

Abstract:This proposal is a follow-up to our previous project which found two molecules in four objects around the Galactic Plane (Tremblay et. al., 2017) and molecules and recombination lines observed around the Orion Molecular Cloud Complex (Tremblay et al., 2018a, 2018b). By re-observing the Galactic Centre with the extended array we hope to confirm the results through associated transitions and search a greater frequency range than previous observations. Previous successful observations of the Galactic Centre were at 99--129MHz. Observing at 70-100MHz and 140-170MHz and using the wide field-of-view of the MWA we can continue to survey the Galactic Plane. By utilising the extended array, we will decrease the beam size which subsequently reduce the effects of beam dilution by 53% when the ratio of solid angles is calculated. This makes us increasingly sensitive to emission from more distant fields, like the Galactic Centre. These observations can be taken and simultaneously processed for the search of carbon recombination lines, although the processing requirements between molecules and recombination lines may be unique. See the proposal submitted by Slava Kitaeff for a separate recombination line project. Even though the search for spectral signatures requires the removal of the continuum, full continuum images are created a part of the developed spectral line pipeline. The long integration continuum image can provide better detail than other surveys around the Galactic Centre and so other science goals can be explored as well. For this data we will be utilising and modifying the already developed pipeline for calibrating, imaging, image combination and continuum subtraction strategies with the new long baselines.

Abstract:The LIGO detection of milli-Hertz gravitational wave (GW) signals from black-hole merger events, and its due recognition by the award of 2017 Nobel Prize, has further reinforced the important role of Pulsar Timing Array (PTA) experiments in extending the spectrum of GW astronomy. PTAs ex- ploit the clock-like stability of fast-spinning millisecond pulsars (MSPs) to make a direct detection of ultra-low frequency (nano-Hertz) gravitational waves, and this is a key science driver for the SKA and its pathfinders. The science enabled by PTAs is highly complementary to that possible with LIGO/VIRGO detectors, as PTAs are most sensitive to GW signals from supermassive black-hole mergers. PTA efforts over the past few years suggest that interstellar propagation effects on pulsar signals, if not accurately measured and corrected for in timing measurements, may ultimately limit the detection sensitivity of PTAs. Interstellar medium (ISM) effects are much stronger at lower radio frequencies and therefore the MWA presents an exciting and unique opportunity to calibrate interstel- lar propagation delays. Here we propose further observations of three promising PTA pulsars that are proven suitable for detailed studies using the MWA, and exploratory observations of two additional ones. The main goal is to characterise the nature of the turbulent ISM through high-quality scintilla- tion and dispersion studies including the investigation of chromatic (frequency-dependent) dispersion measures (DMs). Success of these efforts will define the breadth and scope of a more ambitious pro- gram in the future, and will bring a new science niche for the MWA and SKA-low.

Abstract:Fast Radio Bursts (FRBs) is a rapidly emerging frontier of radio astronomy. Since their discovery by Lorimer et al. (2007) and Thornton et al. (2013), there has been a six-fold increase in the number of FRB detections, and measurements have been made of their scattering, scintillation, polarisation and Faraday rotation properties, thereby firmly establishing their astrophysical nature. As observational evidence continues to mount in support of their extragalactic origin, the world-wide competitive race is also ramping up, with a suite of new and existing instruments gearing up to find them in large num- bers, and efforts are in earnest to localise them. With its large field of view of ∼30 deg2 , ASKAP has proven to be a uniquely capable instrument for detecting FRBs in large numbers, as vividly demon- strated by the > 26 FRB detections by the CRAFT project in the past couple of years. The MWA’s co-location at the MRO site enables unique opportunities for undertaking efficient co-observing and triggering. Our shadowing campaign has already placed stringent constraints on low-frequency emis- sion of FRBs and their spectral indices. 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.

Abstract:The long baselines of MWA Phase 2 present an exciting opportunity to probe deeper than has been possible in GLEAM and a factor of 4 deeper than is planned in GLEAM-X (the long baseline all-sky successor to GLEAM). MIDAS targets six well-studied extra-galactic fields and integrates down close to the natural confusion limit. These deeper surveys, covering a total of 3,000deg2 at higher resolution, will enable a legion of science covering galaxy evolution, clusters and the cosmic web, whilst maintaining the advantages the MWA has over LOFAR (including larger field- of-view, wider frequency coverage and better sensitivity to extended emission). In this proposal we will target the remaining two extra-galactic fields visible: GAMA15 and SPT/XXL fields. The other four fields were observed in 2018A, three at night and one, GAMA23, during the day. Our day time observations were very successful; hence we propose that our final two fields also be observed during the day in 2019A. As before these observations will cover the original GLEAM frequency range of 72-231 MHz. The GAMA15 field, ~60deg2, is a wide area multi-frequency survey with photometry across the UV to far-IR regime, providing estimates of star formation rate, stellar mass and environment. The SPT/XXL survey field, ~50deg2, has a complementary swath of multi-wavelength data. We will utilise calibration, imaging, and image combination strategies developed using pilot observations to be obtained in 2017B with the new long baselines and boot strap off GLEAM in a similar fashion to GLEAM-X. MIDAS will enable a wide range of science, such as:

• Accurately determining radio source counts at multiple frequencies;
• Measuring the low-frequency luminosity function to z~1;
• Characterising the deep low-frequency polarised sky;
• Providing broad-band radio SEDs across 0.07 to 1.8 GHz (inconjunction with continuum surveys with ASKAP);
• Commensal coverage for transient science.

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 come to the realisation 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 propose to use a nearby low-luminosity Quasi-Stellar Objects (LLQSOs) sample with the extended configuration of the MWA phase II to probe the changing landscape. The sample, which is well-studied via spatially resolved mapping by various instruments across many wavelength bands, is an ideal playground for probing the various radio populations, as the sample contains radio-loud AGNs, radio-quiet AGNs, star-forming galaxies, and composite galaxies. The observing targets are selected by performing a positional cross-match of the nearby LLQSO sample with the GaLactic and Extragalactic All-sky MWA Survey (GLEAM) extragalactic catalogue searching for their low-frequency radio counterparts. As a follow up of our 2018-B pilot observations, we propose to observe another 6 targets for our sample in 2019-A.

Abstract:We propose pointed observations with the MWA of any nearby, bright (at GHz frequencies) out- bursting X-ray binary (XRB) during the 2019–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, flat-spectrum, compact steady jets are observed during the hard X-ray spectral 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 obser- vations to constrain the radio spectrum in the low-frequency band. The main aim for the compact jets is to detect the possible low-frequency turn-over. The turn-over frequency, along with the spec- tral slope below the turn-over frequency will put observational constraints on the electron energy distribution and the 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 this 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.

Abstract:This proposal seeks to use the new capabilities of the Murchison Widefield Array (MWA) phase II to augment the existing phase I data in the search for evidence of the synchrotron cosmic web. Previous searches using just phase I or phase II data in isolation have not been successful in detecting the cosmic web. The phase I configuration had a plenitude of short baselines that made it well suited to detect extended emission like the cosmic web, but deep observations were confusion limited after just a few hours of integration (Vernstrom et al. 2017). The phase II extended configuration increased the resolution and greatly reduced the confusion limit, but at the expense of the shorter baselines. We propose to combine phase I and II deep field data and jointly image, in an attempt to maximise the strengths of each array. To do this, we propose to make use of existing deep observations by the Epoch of Reionisation (EoR) group, and augment this data with new phase II observations. 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.

Abstract:We request the use of the new MWA rapid-response mode to perform triggered correlated and VCS observations of Swift and Fermi gamma-ray bursts (GRBs) during the 2019A 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 16 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 (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.

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 2019A 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.

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.

Abstract:We request MWA followup of neutrino transient candidates detected by the ANTARES/KM3NeT and IceCube telescopes during 2019A. 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.

Abstract:Astrophysical observations of galaxies and galaxy clusters, and cosmological observations of the temperature fluctuations of the cosmic microwave background provide strong evidence for the existence of dark matter (DM) in the Universe. One of the oldest and theoretically best motivated DM candidates are QCD axions, ultralight particle that solves the strong CP problem of the Standard Model of particle physics. For masses in the μeV range, these particles also naturally explain the observed amount of cold DM. Substantial experimental efforts are underway to search for these particles in laboratory experiments. Here, we propose to leverage on the fact that DM axions can resonantly convert into photons when traversing the strong magnetic field in the magnetosphere of neutron stars (NS). The observable signal is a narrow spectral line, with frequency that depends on the (unknown) axion mass. Detailed calculations show that slowly-spinning NSs lead to the most efficient conversion. An optimal target for axion searches is hence the large population of dead NSs, which can be inferred from population synthesis arguments. We propose here to use the unique capabilities of the Murchison Widefield Array to search for narrow spectral lines from the Galactic center (GC) region in the 80 – 300 MHz frequency range. The proposed searches are complementary to similar proposed work with the Green Bank, Effelsberg, and Sardinia radio telescopes. A discovery of an axion line would be a major breakthrough, but even null results will provide the strongest limits on the axion photon coupling and will significantly deepen our understanding of DM in the Universe.

Abstract:Stellar flares and coronal mass ejections (CMEs) play an important role in the habitability of their planetary companions. M-dwarf stars are particularly interesting in this regard, as they are known to flare more frequently and powerfully than the Sun. At the same time, a large number of these stars are likely to host planets within their habitable zones. While stellar flares have been observed ubiquitously across the electromagnetic spectrum, observational identification and characterisation of space weather events such as CMEs around other stars is lacking. These space weather events are expected to cause effects such as magnetospheric compression and atmospheric stripping of planetary companions, degrading their habitability. One promising method to detect and characterise stellar CMEs is to detect low-frequency Type II bursts, associated with radio emission from the CME shock front. Analysis of these bursts from the Sun have enabled characterisation of the CME shock-front propagation speed, the density profile of the corona and interplanetary medium, and the mass and energy of the ejected material. Therefore, the detection and characterisation of Type II bursts from other stars may lead to rich insights into the activity of these stars, and its impact on the habitability of their planetary companions. We propose 54 hours of observations targeting the closest star to the Sun, Proxima Centauri. This star is a well-known active flare star, but its low-frequency emission remains observationally unconstrained. This program will enable us to understand the low-frequency emission of this star, and may allow us to make the first detection of a Type II burst from another star beyond the Sun. This will permit a more detailed characterisation of the impact of Proxima Centauri’s activity on various stellar parameters, as well as the habitability of any planetary companions such as Proxima Centauri b.

Abstract:Detecting radio emission from gas bridges in between galaxy clusters before major mergers has the potential of unveiling so far underlooked pre-processing of gas matter and magnetic fields in large scale structures. We propose here to use the MWA observe the gas bridge in the A3391—A3395 interacting pair of galaxy clusters, whose emission has already been detected in the X-ray band and through the Sunyaev-Zeldovich effect. Through simulations, we predict that the radio emission from the bridge will be at the 10-20 mJy level, on scales of 10-20’ in ~150-200 MHz frequency range - mostly powered by weak shocks in the interaction regions of the two structures - in presence of ~0.1-0.2 μG magnetic fields. Such expectations are within the capabilities of a 4 hour long MWA observation. The proposed observations will shed light into acceleration mechanism in the outer regions of galaxy clusters which are important in the pre-processing of gas matter and magnetic fields well before more classic major mergers takes place.

Abstract:Galaxy clusters, located at the nodes of cosmic web, are thought to be grown by the infalling mass from surrounding environment. This process are expected to produce virial shocks and deposit a certain fraction of infalling energy into magnetic fields and electrons, latter of which would be accelerated into high relativistic speed. During this process, both γ-ray from inverse Compton emission and synchrotron emission in radio frequency are expected. Recently, Keshet et al. (2017) has found a preliminary evidence of the virial shock outside Coma cluster in γ-ray, but the very existence is still not confirmed, which makes the cluster virial shock remain a theory. With high sensitivity of MWA phase II, it is likely that a clear detection of radio emission from virial shock for the first time can be made by observing Coma cluster. Thus, we propose a deep pointed observation to Coma cluster across full MWA Phase II band 72-231 MHz, for a total observation time of 10 hours to investigate the virial shock. The high-quality radio images and spectral information would help us to confirm the existence of virial shock. Using this signal, we can also give constrains to the magnetic fields of the intergalactic medium (IGM) and trace the possible warm-hot IGM around. Besides, a detailed study of such diffuse structure could also help implement the task of removing the complicated foreground of the 21 cm signal from the era of reionization.

Abstract:We propose timing observations of the relativistic pulsar - white-dwarf binary, PSR J1141−6545. This unique system offers access to a wide range of physics, from relativistic phenomena through pulsar emission mechanism studies, to the structure and distribution of interstellar plasma along our line-of-sight. Our recent analysis of data obtained over almost 2 decades suggests that the pulsar’s 1.4 GHz beam will precess away from our line-of-sight in the next 3-5 years. This provides a unique opportunity to perform regular observations of the pulsar across a wide range of frequencies, which might provide constraints on the latitudinal radius to frequency mapping of the pulsar beam. Our analysis of the 1.4 GHz data also revealed significant phase-resolved, secular Rotation Measure variations. The proposed observations of this pulsar at low frequencies will help resolve if these variations are magnetospheric, due to the intra-binary medium or to interstellar scattering, and result in reliable estimates of the pulsar’s geometry from the Position Angle sweep of its linear polarisation.

Abstract:Pulsars experience a profile broadening when their emissions traverse through turbulent interstellar medium (ISM). This multi-path propagation effect can be quantified by the scattering time scale τ which is strongly dependent on frequency (τ ∝ ν −α ), while the index α represents intrinsic properties of the ISM in depth. In literature, the scattering time scale indices are predicted by models to be α = 4 or 4.4, while showing large discrepancy in observational results. This is mainly caused by the local ISM complications through the pulsar signal transmission, however, could also be biased by observations taken in different frequencies at different time, and with dissimilar telescopes. Recently, using three pulsars, Kirsten et al. (2018) has proved that we are able to estimate τ with single epoch, multi-band MWA observations. Hence we are proposing a single 1.5- hours MWA VCS observation on a line-of-sight toward PSR J1820-0427, distributing the 24×128MHz channels into two different centre frequencies. Using this data set, we will be able to estimate τ at two MWA frequency bands and calculate α for at least six pulsars covered in this field. Results from this project could be used to accurately characterize the turbulence of the ISM and develop the Galactic electron density model. This project will also demonstrate that MWA is capable to measure scattering spectra indices for a large sample of pulsars with high efficiency.

Abstract:During the first half of 2016 we conducted IPS observations for approximately 1 hour daily using Director’s time. Just two of these observations have been used to write a series of papers [1-5], and work is ongoing to reduce a larger fraction these data. Here we propose to conduct a similar number of observations during 2019-A. With one hour of observing per day we can cover all solar elongations where we can make optimum IPS measurements. By using the Phase II extended MWA, we expect to approximately double our sensitivity.

In our Guaranteed Time proposal we requested 1 hour per day. This is sufficient to cover all pointings relative to the Sun where we can make ‘optimum IPS measurements’. We have used this time to schedule 6✕10-minute observations per day at approximately 30° elongation from the Sun at Position Angles 60, 90, 120, 240, 270 and 300 (degrees relative to ecliptic North). Position angles further North than this are not accessible at this time of year. However a further 30 minutes per day would allow us to supplement these with Position Angles 150, 180 and 210, giving coverage of the areas of the sky affected by the polar solar wind. This wind is less dense and therefore produces weaker scintillation, however measurements made here will increase our astrophysical survey area and will be just as interesting from a Space Weather point of view. Additionally, the original call for proposals envisaged the semester finishing on 1 Jul. We would like to extend our observation campaign to the end of the semester which will give us considerably more sky coverage. Therefore we request:

• 30 minutes per day 8 Apr - 30 Jun inclusive (41.5 hours);
• 1h30m per day 1 Jul - 18 Aug inclusive (72 hours);
for a total of 113.5 hours (in addition to our 150 hours of Guaranteed time)

Abstract:The Five-hundred metre Aperture Spherical radio Telescope (FAST) in China is fast gearing up for science. With a sensitivity that surpasses all currently operational facilities, this largest single-dish telescope ever built will push the boundaries of parameter space in many areas of science including pulsar searches. Ongoing early science efforts have already led to a number of new pulsar discover- ies, underscoring the exciting scientific promise of this new facility. Here we propose to undertake low-frequency follow-up of a curious pulsar candidate that is potentially detectable with the MWA. The candidate is seemingly bright, with an estimated flux density of ∼4-5 mJy, albeit prominent only within the lower 100 MHz of the 300-800 MHz wide-band system that was used to make the de- tection. The indicated dispersion measure (DM) is highly anomalous for the line of sight and the observed degree of scattering is significantly lower than expected for such a DM. The candidate pul- sar is potentially detectable in a dedicated 1.5 hr observation with the MWA over a 200-230 MHz band. If confirmed, this pulsar will be an extremely interesting object to probe one of the strangely anomalous lines of sight in terms of both the degree of scattering and the dispersion measure. This will also serve as an excellent demonstration of the MWAs potential to undertake fruitful follow-ups of new pulsar discoveries and candidates to come from the FAST, which may open up promising avenues for synergetic science in the areas of pulsars using the two facilities.

Abstract:Despite numerous deep searches over the past 20+ years, the radio pulses from the famous Geminga pulsar (the nearest and brightest gamma-ray pulsar) have remained so far illusive, in the midst of some claims of their detections and many reporting non-detections. The apparent radio-quiet nature of this famous gamma-ray pulsar presents a yet-unsolved puzzle, if not a mystery. The claimed detections, all at the low radio frequencies (~35-110 MHz), are essentially either of low significance (e.g., Malov et al. 2015) or of extremely rare ultra- bright pulses (at 34 MHz; see Maan 2015) with significant spread in the associated dispersion measures. A sensitive search for both periodic and occasional bright pulses done in coordinated manner from at least two distinct locations and simultaneously across a wide range of frequencies appears essential to improve chances of possible conclusive radio detection. With this view, we propose to conduct a coordinated search for radio pulses from the Geminga pulsar using the MWA in its wide-band mode and the Gauribidanur Decametre- wave Radio Telescope (GEETEE) observing in a narrow band around 35 MHz, both recording the data in voltage-capture mode. We request for four 45-min sessions (on 3 separate days) with the MWA to conduct the proposed search using 3 sessions, and one session to observe a control pulsar in the same observing mode. Success of the proposed observations will also pave way for an attractive coordinated mode between the MWA and the GEETEE, offering advantages in both, namely, wider spectral range and finer localization of direction.

Abstract:Removal of dispersive smearing at lower observing frequencies requires phase coherent de-dispersed data. The newly augmented pulsar beamforming pipeline which re-constructs the data at much higher time resolution (∼ 1 μs) enables us to perform high time resolution studies of millisecond pulsars (MSPs). Using this we have made successful detections of a MSP J2241 − 5236 down to 80 MHz. This pulsar is rapidly emerging as a highly promising target for pulsar timing array experiments (PTA). The pulsar is in a 3.5 hour circular orbit with a low mass (0.012 M ) white dwarf companion. The timing studies from MeerKAT observations showed some systematic offset in pulse arrival times (TOAs), related to the binary parameters of this pulsar. These drifts in the TOAs could be due to minute variations in DM introduced by the companion’s stellar winds. The high-quality detections of this MSP with the MWA has enhanced the sensitivity of the telescope, to measure minute DM variations of the order of ∼ 10−4 pc cm−3 in our line of sight. Such subtle DM change is hard to recognize at any other timing frequencies with single observation. Taking advantage of the MWA’s large frequency leverage and the achievable timing precision, we propose the observations of full orbital period of this interesting target to investigate any contribution by the companion in the measured DM.