2016-A, 128T

Authors: N. D. R. Bhat (Curtin), S. M. Ord (Curtin), S. E. Tremblay (Curtin), R. M. Shannon (Curtin/CASS), W. van Straten (Swinburne), D. Kaplan (UWM), J.-P. Macquart (Curtin), F. Kirsten (Curtin)

Abstract: Pulsar timing array (PTA) experiments exploit the clock-like stability of fast-spinning millisecond pulsars for direct detection of low-frequency (nano-Hertz) gravitational waves (GWs). Detection of GWs is an eagerly pursued goal of modern astronomy and a key objective of the Square Kilometre Array (SKA). There is now increasing realisation that interstellar propagation effects on pulsar sig- nals may ultimately limit the detection sensitivity of PTAs unless they are accurately measured and corrected for in timing measurements. The influence of the interstellar medium is much higher at low radio frequencies; therefore the MWA presents an exciting and unique opportunity to calibrate interstellar propagation delays and thereby significantly enhance the sensitivity and scientific impact of the Parkes pulsar timing array (PPTA) project.

Significant improvements have been made to enhance pulsar observing capabilities of the MWA. Our development of a tied-array beam processing pipeline for VCS-recorded data yields an order of magnitude improvement in sensitivity for pulsar observations with the MWA, opening up new science avenues, as well demonstrated through our recent work on high-resolution dynamic spectral studies of the timing-array millisecond pulsar PSR J0437−4715. The full processing pipeline including stan- dard pulsar software packages are now successfully tested on the Galaxy cluster of Pawsey.

We will take advantage of these improved capabilities to build on our pilot project and propose to make regular observations of the four best PTA pulsars in the semester 2016A. Our main scientific goals are characterising the nature of the turbulent ISM through high-quality scintillation studies as well as making high-precision DM measurements which we will compare with Parkes measurements to look for any evidence of chromatic (frequency-dependent) DMs. Success of this project will define the breadth and scope of a much more ambitious program in the future, bringing in a new science niche for the MWA and SKA-low.

Authors: Dr. S.E. Tremblay (Curtin), Dr. C.M. Trott (Curtin), Prof. S.J. Tingay (Curtin), Dr. N.D.R. That (Curtin), Dr. S.M. Ord (Curtin), Dr. J.-P. Macquart (Curtin)

Abstract: Fast Radio Bursts (FRBs) are millisecond-duration events whose dispersion measures exceed the con- tribution of the Milky Way’s ISM by factors of > 5, placing them prima facie at cosmological distances. The origin of FRBs is presently a topic of intense speculation and poorly constrained by observational facts. The localisation of such an event would provide a breakthrough in this field. The MWA has the potential to make a decisive contribution by furnishing the first interferometric localisation of an event, and the first detection outside the 1.2-1.5 GHz band. This is facilitated by the uniquely large field of view presented to each MWA tile, in conjunction with its ability to combine tiles for sub-arcminute localisation.

In this proposal we seek commensal observing time to detect and, for the first time, localise FRBs, thereby confirming their cosmological origins and opening a new field of astrophysics and cosmology. While most FRBs to date have been discovered well off the Galactic plane, we would be remiss not to search these data for FRBs. All these observations will be analysed similar to our previously approved program (G0024). A continued MWA observing campaign searching for FRBs will compliment LOFARs similar Northern Hemisphere search for these events at low radio frequencies. Low frequency detections, or or more stringent limits, from either of these telescopes will provide spectral constraints on these events which have only been detected at 1.4 GHz so far. Additionally, since our analysis pipeline improvements have removed the lower limit on our DM search, we are now automatically performing a search for Rotating Radio Transients (RRATs) as well.

Authors: Dr. Nick Seymour (ICRAR/Curtin), Dr. Randall Wayth (ICRAR/Curtin), Dr. Thomas Franzen (ICRAR/Curtin), Dr. Minh Huynh (ICRAR/UWA)

Abstract: Searching for and detecting HI absorption is a powerful technique to measure the neutral HI gas abundance within powerful radio sources or in intervening sources along the line of site. The sensitivity of this technique is independent of redshift as a given optical depth causes a fractional decrease in the spectrum. Hence only a bright radio source is required at the appropriate redshift. Traditionally this technique is limited to low redshifts (below z=1) due to the frequency coverage of the most sensitive radio telescopes (0.7-1.4GHz). However, the MWA presents the opportunity to conduct such an experiment in the early Universe (z>3.5) at frequencies below 315MHz. For technical and scientific considerations our best candidate, which we propose here, is the very bright quasar 7C 1023+2558 at z=5.28. We request a 4hour pilot observation of this unique galaxy in the early Universe to search for internal and intervening HI absorption

Authors: Dr. Paul Hancock (Curtin), Dr. Randall Wayth (Curtin), Ms. Xiang Zhang (Curtin/Purple Mountain Observatory), Prof. David Kaplan (UWM), Prof. Steven Tingay (Curtin)

Abstract: We propose to use the MWA to search for radio emission from bright meteors (fireballs). Radio emission coincident with fireballs has been observed and studied for some time, however it has always been under- stood that the radio emission is a result of reflected terrestrial radio sources. Recently the Long Wavelength Array (LWA), reported a detection of radio emission from fireballs (Obenberger et al., 2014) using the Pro- totype All-Sky Imager (PASI). The remarkable aspect of this detection is that the authors claim that the observed emission cannot be simply reflected RFI, and that there must be intrinsic emission associated with these fireball events. Five of the radio transients detected by PASI were coincident with known fireball events, thanks to an overlap between the field of view of the PASI and nearby fireball monitoring cameras. The PASI actually detected some 44 bright radio transients, however the overlap with the optical cameras meant that only 5 could be positively identified with optical events.

Though the MWA has a snapshot field of view that is only ~1/5th of that of the LWA all-sky camera, the MWA is able to form higher cadence (0.5s vs 5s) images at higher resolution (2” vs 4.4deg), and with a much broader frequency coverage (30MHz vs 75kHz). If the MWA is able to observe a fireball then it will be able to provide unprecedented detail on the nature of the radio emission, and determine if there is an intrinsic, non-thermal, component to these events. Recently two wide-angle optical cameras have been installed near the MWA as part of the Desert Fireball Network (DFN, Bland et al., 2012). The DFN cameras provide an all night, every night, monitoring of the optical sky, with the aim of detecting bright fireballs. In combination with the MWA these cameras will provide a continuous multi-wavelength view of the sky, allowing for the study of both bright and faint fireball events.

This project will: 1) Observe radio emission from fireballs with the MWA, 2) determine whether the radio emission is intrinsic to the fireball or simply reflected RFI, and 3) determine the transient foreground due to atmospheric events such as meteors.

Authors: Mengyao Xue (Curtin), Stephen Ord (Curtin/CSIRO), Ramesh Bhat (Curtin), Steven Tremblay (Curtin), Ryan Shannon (Curtin/CSIRO)

Abstract: The MWA VCS pipeline is now reliably generating high time resolution observations of radio pulsars. We are proposing to expand this capability into the realm of polarimetric, calibrated tied array beam formation. These technologies will enable pointed polarimetric observations of known pulsars to study the pulsars themselves, the interstellar medium and the ionosphere. We are proposing a set of observations of three pulsars at at wide range of hour angles to characterise the fidelity and stability of the polarimetric solutions. This would be performed across the whole MWA band in picket-fence mode, which distributes the 24x1.28 MHz channels of the MWA receiver across the MWA observing band, thereby providing an excellent study of the wide bandwidth evolution of pulsar radio emission. These observations will form part of the PhD program of Menygao Xue.

Authors: Dr. Ryan Shannon (Curtin/CSIRO), Dr. Ramesh Bhat (Curtin), Dr. George Hobbs (CSIRO), Dr. Steve Ord (CSIRO), Dr. Steven Tremblay (Curtin)

Abstract: While pulsars are well known to emit over a wide range of frequencies, the total bandwidth over which the emission is correlated and the pulse-to-pulse variability of this bandwidth are poorly understood. Given this uncertainty, it is unsurprising that the effects of this variability on precision pulsar timing are unknown. We therefore propose to answer three questions about the broadband nature of pulsar emission:

1) Over what bandwidths are individual pulses correlated?

2) Does this bandwidth vary across the pulsar population?

3) How does this bandwidth affect pulsar timing?

To answer these questions, we propose to study 5 bright pulsars that span the neutron star popula- tion, exhibit a diverse range of pulsar phenomenology. We request 5 hours of simultaneous Parkes- Murchinson Widefield Array observations to conduct simultaneous multi-frequency single-pulse obser- vations jointly with the MWA These measurements will be used to construct better empirical models for pulsar emission, test theoretical predictions, and assess the effects of broadband variability on pulsar timing measurements.

Authors: Dr. S.E. Tremblay (Curtin/CAASTRO), Mr. B. Meyers (Curtin), Dr. N.D.R. That (Curtin), Dr. F. Kirsten (Curtin), Dr. S. Ord (Curtin), Dr. R. Shannon (Curtin/CASS), Dr. J.-P. Macquart (Curtin)

Abstract: This pilot study will observe a collection of pulsars which are known to exhibit high pulse-to-pulse vari- ability. The observations of nulling pulsars (B1133+16 and B2045-16), RRATs (J0941-39, J1226-3223, J1653-2330), intermittent pulsars (B1931+24, J1832+0029), and giant pulse emitters (J1824-2452A, J1823-3021A) will guide us in developing a full observing program of these fascinating sources. Up until now observations of these objects were restricted to frequencies above 300 MHz. The MWA opens the door to perform low-frequency studies of these objects which is essential to understand possible similarities and the underlying physical mechanism behind pulse-to-pulse variability.

In this pilot project we aim at first detecting each of the above objects which is greatly supported by the coherent beamforming capabilities developed recently. After first detection and characterisation of each target (e.g. pulse profile, brightness, nulling fraction) we will design a future large-scale program to pinpoint the linkages between these species of pulsars and which will shed light on the fundamentals of the pulsar emission mechanism.