2015-A, 128T

Authors: Dr. Benjamin McKinley (U. Melbourne), Dr. Randall Wayth (Curtin), Prof. Rachel Webster (U. Melbourne), Prof. Frank Briggs (ANU), Prof. Judd Bowman (ASU), Dr. Gianni Bernardi (SKA SA), Dr. Natasha Hurley-Walker (Curtin), Dr. Emil Lenc (U. Sydney), Mr. Jack Line (U. Melbourne), Dr. Andre Offringa (Astron), Dr. Bart Pindor (U. Melbourne), Dr. Pietro Procopio (U. Melbourne), Prof. Steven Tingay (Curtin), Dr. Cathryn Trott (Curtin)

Abstract: We propose to measure the global redshifted 21-cm signal from the epoch of reionisation using the MWA and a novel technique involving observations of the Moon. The global signal and how it evolves as a function of redshift, can provide information on when reionisation of the Universe occurred, how long it took, and what types of ionising sources were responsible. Currently, only loose limits on the reionisation history exist from single dipole experiments, which face challenging systematic errors, such as frequency-dependent receiver noise contamination. The use of an interferometer would overcome many of the problems associated with the singe dipole experiments, however, interferometers are insensitive to a spatially-invariant global average, such as the global EoR signal. Lunar occultation imprints a spatial structure on the global signal, which allows it to be detected with an interferometer such as the MWA, using the brightness temperature of the Moon as a reference. The fact that the Moon moves relative to the background sky can also be exploited to reduce the effects of side lobe confusion and imaging artefacts through uv differencing of identical observations on different days. With 160 hours of observing time (including ‘on Moon’ and ‘off Moon’ observations, as well as calibration scans) we can expect sub-Kelvin sensitivity to the occulted Moon signal, which contains the global EoR signal, across the frequency range of 80-200 MHz. This will allow us to place the best limits yet on the global signal at certain frequencies. It will also enable us to measure the Galactic global signal and learn more about the thermal properties of the Moon. Perhaps most importantly, it will allow us to develop the techniques and tools required to make a robust detection in the future with more observing time and possibly an enhanced MWA.

Authors: Chenoa D. Tremblay, Andrew J.Walsh, Slava Kitaeff, Steven Tremblay, Natasha Hurley-Walker

Abstract: Sprectal line data has been used to explore our Galaxy since the 1800s, when scientists first classified stars. However, the chemistry within our Galaxy is virtually unexplored in the region of 100-300MHz. Instruments like the Robert C. Byrd Green Bank Telescope has been used to publish data on recombination lines at 80-100MHz, but no one has published to date any data on complex molecules in this frequency range. The MWA offers a chance to explore the constant chemical reactions that happen each second within our Galaxy and discover what information may be hiding in this frequency range. The current 10kHz spectral resolution may be well-suited for discovery of broad molecular lines. In this proposal we would like to map the Orion region in January or February over the full frequency range of the MWA in order hunt for molecular lines. Additionally we would like an hour of VCS time, also in Orion, to process through a polyphase filter bank (PFB) to assess the MWA's performance at higher spectral resolution.

Authors: Colin Lonsdale, Leo Benkevitch, Roger Cappallo, Phil Erickson, Lynn Matthews, Divya Oberoi, John Morgan, Steven Tremblay

Abstract: We request Voltage Capture System (VCS) data on the Sun in order to explore the parameter space of digital Van Vleck corrections along two axes. These two axes are (1) the effective number of bits being toggled in the post fine PFB data streams entering the cross multipliers, and (2) the strength of the correlation on a given baseline. The primary goal is to develop a quantitative understanding of the magnitude of the necessary Van Vleck corrections across the typical range of MWA operational conditions, and thereby devise methods of applying the corrections. Such corrections are a necessary but perhaps not sufficient step toward achieving the full potential of the MWA in high dynamic range imaging of strong sources. The necessary data can be gathered within 1 hour, but to insure against unanticipated problems, we request a second hour, to be gathered after the first set of data has been thoroughly inspected.

Authors: Colin Lonsdale, Roger Cappallo, Phil Erickson, Lynn Matthews, Divya Oberoi, John Morgan, Emil Lenc

Abstract: We request imaging observations across a comprehensive range of local times and levels of geomagnetic activity in order to gather information on the nature, severity and duty cycles of different ionospheric conditions and phenomena at the MWA site. The ionospheric information derived from the imagery will take the form of refractive displacements of source positions, and where feasible measurements of ionospheric Faraday rotation (FR), as a function of time and position. This investigation is primarily driven by the short term need to characterize ionospheric FR as the primary contaminant to the weaker FR effects expected from the heliosphere caused by coronal mass ejections (CMEs). Secondary goals of the work are to provide information on ionospheric effects for use in other MWA science investigations for which it is desirable to remove or avoid the worst of those effects, and to study the ionospheric effects themselves, to which the MWA has unique sensitivity due to the inherent precision of interferometric phase measurements in terms of ionospheric electron density gradients.

Authors: N. D. R. Bhat (Curtin), S. M. Ord (Curtin), S. E. Tremblay (Curtin), S. J. Tingay (Curtin), M. Bailes (Swinburne), D. Kaplan (UW), van Straten (Swinburne); R. Shannon (CASS)

Abstract: Pulsar timing array (PTA) experiments exploit the clock-like stability of fast-spinning millisecond pulsars for the prospective direct detection of low-frequency (nano-Hertz) gravitational waves (GWs). Detection of GWs is an eagerly pursued goal of modern astronomy and will mark a major breakthrough. There is now increasing realisation that the interstellar propagation effects on pulsar signals may ultimately limit the detection sensitivity of PTAs unless they are accurately measured and corrected 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.

The MWA’s potential in this arena is vividly demonstrated by our recent work on scintillation and profile studies of the millisecond pulsar (MSP) PSR J0437-4715, using data recorded during the VCS commissioning phase. With the full bandwidth recording now possible with the VCS, and the ability to form coherent (phased-array) beam, it is now possible to exploit the full potential of the MWA forpulsar science.

We propose observations of PPTA pulsars for multiple science goals; we will (i) demonstrate the MWA’s unique capability for high-precision dispersion measure (DM) determinations and profile evolution studies, by exploiting its flexibility to distribute the 30.72 MHz of available bandwidth to span the full 80-300 MHz range; (ii) conduct three-weekly monitoring of PSR J0437-4715 for scintillation and DM variability; and (iii) perform a low-frequency census of millisecond pulsars. The success of this pilot project will define the breadth and scope of a more ambitious, larger-scale program in the future, bringing in a new science niche for the MWA and SKA-low.

Authors: Dr. Ord (Curtin), Dr. Bhat (Curtin), Dr. Tremblay (Curtin), Dr. Hessels(ASTRON), Dr. Kaplan (UWM), Prof. Tingay (Curtin), Mr. McSweeney (Curtin)

Abstract: Discovering new pulsars is one of two main science drivers for SKA Phase 1 because it will enable "Strong Field Tests of Gravity". The MWA provides an opportunity to develop the techniques required to achieve this goal, and it will discover dozens of pulsars along the way. We intend to use the observations taken for the MSP census observations of Bhat et al to begin a survey for pulsars and radio transients with the MWA. We will develop novel processing and analysis pipelines with these data and the presence of known millisecond pulsars in every field will confirm the validity of our survey methods.

As an extension to this commensal program we also intend a targeted search of the globular cluster 47-Tucanae (47-Tuc). 47-Tuc contains 23 known millisecond pulsars, the first 11 of which were discovered at 50 and 70cm (Manchester et al 1990). The cluster is at a declination of -72 degrees, therefore the MWA is the only low frequency instrument able to observe it. This an ideal test observation for the MWA pulsar survey pipeline: it is at a known DM so the number of DM trials is reduced, all the radio pulsars have been found within 1.2 arcmin of the centre, so a single tied array beam will encompass the cluster region of interest. The pulsars are distant, but intrinsically luminous and scintillation increases their measured intensity by a factor of ten. The brightest of the 47-Tuc pulsars (J, C and E) should be easily observable, and even if no new pulsars are discovered these observations will provide details of the observability of the 47-Tuc pulsars at SKA-Low observing frequencies.

Authors: Steven Tingay(Curtin), Randall Wayth (Curtin University), Paul Hancock (Curtin University), Christian Wolf (ANU), Fang Yuan(ANU), Brad Tucker (UC Berkeley), Christopher Onken (ANU), Brian Schmidt (ANU), Andre Offringa (ASTRON)

Abstract: We propose MWA observations coordinated with observations by SkyMapper and the Kepler K2 mission, to monitor radio variables and transients and to correlate variability and transient behavior between radio and optical wavelengths. This opportunity is based on Kepler’s schedule, which will continuously observe Fields 4 and 5 of its K2 mission in a broad optical band (420-­‐900 nm), 24hrs/day, from 7 Feb 2015 to 24 April 2015 (Field 4: centred at 03:56:18.2; +18:39:38) and from 26 April 2015 to 11 July 2015 (Field 5: centred at 08:40:37.8; +16:49:47) with a field radius of ~8 degrees and a small pixel filling factor. The Kepler K2 mission provides a unique opportunity for Australia’s premier widefield optical and radio telescopes (SkyMapper and the MWA) to undertake coordinated radio/optical searches for transient and variable phenomena over wide fields. Rapid publication of the MWA results will provide a large-­‐scale database of variability information for thousands of radio sources in each of the Kepler K2 fields, to be utilized by the PIs of dozens of science projects that form the Kepler K2 target list. This will be a unique resource for Kepler K2 science, that can only be produced by the MWA.

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

Abstract: Fast Radio Bursts (FRBs) are a recently discovered new population of highly dispersed radio transients (Thornton et al. 2013). The dispersion of FRBs cannot be accounted for by the ISM within our own Galaxy, with excesses of 15 to 35 times the expected DM_MilkyWay reported. The MWA been predicted to have a unique ability to detect and localise these exciting and still unexplained phenomena (Trott et al. 2013A) due to the large field of view of each tile, and the ability to combine tiles for localization.

In this proposal we seek time for an observational program to detect and, for the first time, localise FRBs, thereby confirming their cosmological origins and opening a new field of astrophysics and cosmology. 12 hours of this proposal are commensal with other proposals for observing known pulsars. While most FRBs to date have been discovered well off the galactic plane, we’d be remiss not to search these data for FRBs. The remaining non-commensal observations will be performed at higher galactic latitudes and analysed similar to our pilot program we’ve performed under Director’s discretionary time. A supported MWA observing campaign searching for FRBs will strongly compliment LOFARs similar Northern Hemisphere search for these events at low radio frequencies. Low frequency detections, or limits, from either of these telescopes will provide spectral constraints on these events which have only been detected at ~1.4 GHz so far.

Authors: Dr. Yogesh Maan (NCRA-TIFR), Dr. N.D. Ramesh Bhat (Curtin)

Abstract: Recently, a pulsar with a period of 785 ms has been discovered at a very low frequency (34 MHz), using the Gauribidanur radio telescope. The dispersion measure of the pulsar is just 1.55 pc cm.3, i.e., lowest among those of the known radio pulsars. Given that the Gauribidanur telescopefs beam is quite wide (0.5. in RA and 35. in Dec.), the declination of the pulsar could be anywhere between ~50deg and ~13deg. Further, this source might be one of those pulsars for which, only their wider, low frequency radio emission beams could be seen from earth. Hence, any effort to re-detect the pulsar as well as to localize its position needs to use a telescope which can facilitate observations in the above mentioned large declination range at a frequency as close to the detection frequency (34 MHz) as possible. The MWA is the only telescope which can be used to observe such a large declination range in the southern sky hemisphere, at frequencies below and around 100 MHz. To make a confirmatory detection of the pulsar and to localize its sky position, we propose to use the MWA in the voltage capture system (VCS) observing mode to carry out tracked observations of the field likely to contain the pulsar. To cover the aforementioned declination range, we will make two pointings of 1 hour each, separated by 15. in declination. A potential detection using these observations would help in revealing a member of the local population of pulsars, as well as enable further study of the pulsar at 100 MHz and other suitable radio frequencies.