2016-B, Compact

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

Abstract: Recent LIGO detection of milli-Hertz gravitational wave (GW) signals from a black-hole merger event has further reinforced the important role of Pulsar timing array (PTA) experiments in the GW astronomy. PTAs exploit the clock-like stability of fast-spinning millisecond pulsars (MSPs) to make a direct detection of ultra-low frequency (nano-Hertz) gravitational waves. The science enabled by PTAs is thus highly complementary to that possible by LIGO-like detectors. PTAs are also a key science objective for the SKA. PTA efforts over the past few years suggest that interstellar propaga- tion effects on pulsar signals may ultimately limit the detection sensitivity of PTAs unless they are accurately measured and corrected for in timing measurements. Interstellar medium (ISM) effects are much stronger at lower radio frequencies and therefore the MWA presents an exciting and unique opportunity to calibrate interstellar propagation delays. This will potentially lead to enhanced sensi- tivity and scientific impact of PTA projects.

Since our first demonstration of ability to form a coherent (tied-array) beam by reprocessing the recorded VCS data (Bhat et al. 2016), we have successfully ported the full processing chain to the Galaxy cluster of Pawsey and demonstrated the value of high-sensitivity multi-band pulsar obser- vations that are now possible with the MWA. Here we propose further observations of two most promising PTA pulsars that will be nightly objects in the 2016B period. Our main science driver is to characterise the nature of the turbulent ISM through high-quality scintillation and dispersion studies including the investigation of chromatic (frequency-dependent) DMs. Success of these efforts will define the breadth and scope of a more ambitious program in the future, bringing in a new science niche for the MWA and SKA-low.

Authors: Mengyao Xue (Curtin), Ramesh Bhat (Curtin), Steven Tremblay (Curtin), Stephen Ord (Curtin/CSIRO), Charlotte Sobey (Curtin/CASS), Franz Kirsten (Curtin)

Abstract: The MWA VCS pipeline is now reliably generating high time resolution observations of radio pulsars in all four Stokes parameters. Here, we are proposing to test the polarimetric response of and our ability to calibrate the new Hex array currently under construction. These ob- servation will provide data that will be used to study the pulsars themselves (including their emission mechanism and beam geometry), the interstellar medium and towards understanding the Galactic magnetic field. We are proposing a set of observations of three pulsars (J0034-0534, J0437-4715, and J2145-0750) at a wide range of hour angles to characterise the fidelity and sta- bility of the polarimetric solutions with the hexes. The observation would be performed between 170-200 MHz and 140-170 MHz respectively. This project will form part of the PhD program of Mengyao Xue.

Authors: B. Meyers (Curtin), S. Tremblay (Curtin), R. Bhat (Curtin), R. Shannon (Curtin/CASS)

Abstract: Rotating radio transients (RRATs) are neutron stars whose radio emission is typically detectable as sporadic emission (as opposed to periodic emission). This RRAT study will observe two RRATs (J0614-03, J0545-03) which have low to moderate dispersion measures and should be detectable with the MWA. Nominally, both RRATs should be within a single pointing, due to the increased field-of-view provided by the compact hex-tile core. Given our first concrete detec- tion of the RRAT J2325-0530 with the recently implemented coherent beamformer, we expect that these sources will also be detectable. Observations below 300MHz of these RRATs have not been reported, thus the MWA provides an opportunity to perform the first low-frequency, high time resolution studies of these objects.

Authors: S.J. McSweeney (Curtin, PI), N.D.R. Bhat (Curtin), S.E. Tremblay (Curtin), S. M. Ord (CASS)

Abstract: Globular clusters are breeding grounds of binary millisecond pulsars, which provide perfect tools for a wide range of astrophysics. 47 Tuc, located in the far southern hemisphere has proven to be a real gold mine, with 24 pulsars already known. Its extreme southern latitude (at a declination of -72deg) makes it inaccessible to almost all telescopes except Parkes, which operate only at frequencies >700 MHz. In this proposal we seek 1.5 hr time to confirm our tantalising detections of two of 47 Tuc pulsars in MWA VCS data recorded last year. If confirmed, this will constitute the first low-frequency detection of 47 Tuc pulsar(s), and the very first detection of a pulsar in a globular cluster with the MWA. This will have important implications for targeted searches with the expanded MWA and SKA-low, besides the prospects of probing the cluster ISM via low-frequency MWA observations.

Authors: Sourabh Paul, Akash Kumar Patwa, Shiv Sethi, K.S. Dwarakanath (RRI)

Abstract: The detection of redshifted HI from the Epoch of Reionization (EoR) is one of the outstanding aims of modern day observational cosmology. Like many other radio in- terferometers, EoR research is one of the major science goals of MWA. We, at RRI have been involved in EoR research from past few years. We have successfully developed an independent pipeline to extract the delay power spectra from MWA tracking observation. We, simultane- ously have been progressing towards the set up of another pipeline to obtain the power spectra from drift scan observation. We seek, based on our existing endeavors, 30 hours of drift scan data from MWA observing time 2016B. Our aims are to attain both 2d & 1d power spectra, also to study various foreground removal and noise reduction strategies. The new ‘hex configuration’ of MWA would be a favorable feature for this effort, owing to many short spacing & redundant baselines, which are essential requirements for EoR science.

Authors: ​Steve Croft (UC Berkeley), Dr. Andrew Siemion (UC Berkeley), Prof. David Kaplan (UW­Milwaukee), Dr. Steven Tremblay (Curtin)

Abstract: We propose a pilot study, using the Voltage Capture System, for Breakthrough Listen on the MWA. Breakthrough Listen (BL) is a major new project that aims to dramatically improve the coverage of parameter space in the search for intelligent life beyond Earth. BL has already deployed hardware and software to the Green Bank Telescope, and will bring a similar program with the Parkes Telescope online in the second half of 2016. The low frequency sky is however currently very poorly explored. The superb capabilities of the MWA (large field of view, low frequency of operation, and location in a very radio quiet site) provide a unique opportunity for a pilot study to obtain voltage data for a SETI (Search For Extraterrestrial Intelligence) study of the Galactic Plane.

We propose commensal observations, piggybacking on the proposed pulsar search of Tremblay et al. Using existing VCS software, combined with the pipeline developed for Breakthrough Listen at GBT and Parkes, we will perform a blind search for candidate signals from extraterrestrial intelligence. Although the chances of a detection are not large, particularly for a pilot study such as that proposed here, the Breakthrough Listen team plan to perform extensive testing and analysis on the data obtained which should be useful for other users of the MWA VCS. We will make the secondary SETI data products and associated documentation available as a resource to the community via the Breakthrough Listen online archive.

Authors: ​Steve Tremblay (Curtin, PI), N. D. R. Bhat (Curtin), Nick Swainston (Curtin), Charlotte Sobey (Curtin), David Kaplan (UWM)

Abstract: The voltage capture system (VCS) has been running for roughly a year and a half now. In that time it has generated four publications to date (more in preparation) and detected over three dozen known pulsars. However, due to the combination of a large field of view and a large tile separation of the MWA’s design, we have not been to able to undertake a pulsar survey, as this has been overly computationally expensive. The new, compact configuration changes this and we propose to perform a small pilot survey of a single field that is well populated with pulsars to lay the foundation for a larger future survey.

Authors: Dr. Paul Hancock (Curtin), Dr. Randall Wayth (Curtin), Ms. Xiang Zhang (Curtin/Purple Mountain Observatory), Prof. David Kaplan (UWM), A. Prof Tara Murphy (Sydney University), Dr Emil Lenc (Sydney University), A. Prof Jonathan Pober (Brown University), Dr. John Morgan (Curtin University), Dr. Rajan Chhetri (Curtin University)

Abstract: We propose a pilot study to test the feasibility to use the MWA-Hex configuration to search for radio transients. Projects are already making use of data from the MWA-128T to search for many transient events. Data from G0001 (MWATS) is being used to search for pulsars based on their scintillating behavior (Bell et al., 2016). Project G0026 is searching for intrinsic emission associated with fireballs. Project G0005 has used data from EoR observations to search for fast radio bursts and conduct a blind survey for radio transients (see Rowlinson et al., 2016). These areas of research are still of great interest, and we would like to be able to continue these programs into 2017A, however the feasibility of the MWA-Hex configuration for these projects has not yet been demonstrated. We are asking for 20h of observations to demonstrate the feasibility of the MWA-Hex configuration for fast radio transient detection.

Authors: Rajan Chhetri, Research Associate, (Curtin University), John Morgan, Research Fellow, (Curtin Univer- sity), Steven Tremblay, Postdoctoral Researcher, (Curtin University), Jean-Pierre Macquart, Senior Re- search Fellow, (Curtin University), Jonathan Pober, Asst. Professor, (Brown University), Paul Hancock, Early Career Research Fellow, (Curtin University)

Abstract: A pilot study made with day time observations with the Murchison Widefield Array (MWA) has clearly demonstrated the feasibility using interplanetary scintillation (IPS) to identify compact components (∼ 0.1 arcsec) in MWA data. Subsequently, regular daytime observations have been made with the MWA since December 2015 to obtain an even coverage of the sky with the intention of producing a catalogue of scintil- lating, compact sources using Director’s discretionary time. Analysis of these data is ongoing. Preliminary results from this analysis have affirmed the validity of the IPS technique from the pilot study. These studies made with correlator integration time of 0.5 seconds have suggested that a finer time resolution is necessary to fully resolve and characterise the IPS in very compact sources.

Proof of concept work to image with only short baselines in the pilot data to simulate the MWA config- uration in 2016-B was done by J. Morgan and has shown the possibility of using the MWA configuration in Hexagonal mode to identify IPS. Regular observations in October - December period will allow us to obtain an even sky coverage for our overall project.

Hence, we request time to make 6 minute observations (+ 1 minute calibration scan of the sun) twice weekly in the Voltage Capture System (VCS) mode to identify and characterise IPS due to compact com- ponents in the MWA data.