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Minutes for MWA Transient meeting on the theme: Proposal deadline 18 Feb

Attendees: Gemma Anderson, Natasha Hurley-Walker, Tara Murphy, Sam McSweeney, Clancy James, Xiang Zhang, John Morgan, Joe Callingham, Zhijun Xu, Laura Driessen, Steve Croft

Declined due to timezone or other commitments: James Miller-Jones

Proposed Agenda (see email sent on 9 Feb 2022):

  • New proposal discussions
    • Sam McSweeny – detecting lightning with the MWA (~10 mins including discussions)
    • Natasha Hurley-Walker – searching for ultra-long period transients (~10 mins including discussions)
  • Round table discussion from each member on proposals they plan to (re)submit.
  • Clancy: Authorship on ANTARES follow-up paper
  • March meeting - Suggest a meeting on MWA Transients Scheduling.
  • Any other business


New proposal discussion:

Sam McSweeny - MWA Lightnight

  • Open for people to participate: talk slides and overleaf link can be found here
  • LOFAR published paper so decided to look into how MWA could do it. 
  • Very active sphere of research, many open questions on how it starts, propagates in the atmosphere and how plasma channels are maintained, how does a lightning strike know where to go?
  • Expensive equipment - can we stop lightning striking it? This is a problem for ASKAP. 
  • Naturally extends to other industries, etc
  • Research by New Mexico Tech - 2 or 3 element interferometer 16km apart and able to map lightning in 3D with super-fast time resolution and trace the progress of the lightning strike in 3D as it happened. They were able to measure how fast the "leader" propagated through the atmosphere and showed that it slowed down as it got closer to the ground.
  • LOFAR tracked lightning at <80 MHz - they were able to track the "seed" event that starts high up in the clouds - the electric fields that cause this are not well understood. They were able to track in microseconds the progress of "streamers", which are tracked in the nearfield. It increased in power exponentially with time.
  • LWA - studied how the lightning signals bounce off the underside of the ionosphere.
  • MWA
    • The plan is to do something similar to tracking the progress of lightning in 3D (first example). 
    • Ideal specs for this work include
      • Sampling rate >200 MHz
      • Baselines >10km as lightning strikes over >15 km
      • Freq < 300 MHz
    • MWA can recover sampling rates > 70 MHz and reconstructed waveform
    • MWA is in a regime where we can do this. 
  • This is a pilot survey for proof-of-concept.
  • Nearfield imaging - Vanessa Moss has software to do this. Plane ~300m above the ground. 
  • Use the VCS and correlate the voltages up to 2ms to create images. Potential for imaging on 100 microsec - Marcin Sokolowski's work 
  • Following this we can push for full 3D interferometry
  • The trick is how to know when to observe. There is nothing set up on-site to allow for an automated study. Initially, the data recording of lightning will need to involve Sam watching the weather and looking for storms within 25 km of the MWA site. 
  • Plan to request up to 5 hr of VCS data spread out over many storms. 
  • Q John: What is the likely brightness, dynamic range, and does it need attenuation?
    • Sam - turn off all but one dipole per tile. Potentially for a proof of concept, it may be okay if it is saturated?
    • Clancy - If it saturates at the analog level then you would lose channel information. 
    • John - The most sensitive bit is the coarse channel bays and we can put attenuation in here. 
    • John - Has contacts that can tell us how bright this emission will be.
    • Sam - First few sessions may be to test exactly this.
    • John - Look at the statistics in the archive. PTD data
  • Q Gemma: Talking to Andrew about different MWA array modes and configurations that are possible?
    • Sam - Yes
  • Q Gemma: There are archival triggers on Fermi TGF events from before we improved the GRB trigger filtering. Could these be useful?
    • Clancy - Fermi could be detecting lightning from everywhere on the Earth's surface so it is unlikely that any of these storms could have been above the MWA. 
  • Q Joe : LOFAR starting grant to study lightning. They already have information on saturation - Joe to put Sam in contact
  • Q Xiang: Mentioned images with terrible RFI that were thrown away that might actually be lightning storms. 
    • Sam: Lightning is astronomer FRI - could use this information to try and mitigate it to make data useful? 
    • Gemma: Is it useful for Xiang to send obsIDs even if correlated data?
      • Sam: It May not be useful from studying lightning but useful for practicing techniques. 
    • Natasha - there is an app that tells you when its raining at a location, which could be used as a proxy for thunderstorms?

Natasha Hurley-Walker - Finding more ultra-long-period transients (ULPMs)

  • Natasha's slides can be found here
  • Writing Discovery project for funding to do this work
  • Building on GLEAM-X J162759.5-523504.3 discovery. This may be the brightest case as is traditional in astronomy discoveries.
    • There will be fainter examples
  • Differencing visibilities and making images - limited by ionosphere - working on better techniques
  • Plan to run Quasi real-time data processing to find targets that are "on", which we would follow up with every instrument and observing mode. 
  • Theoretical predictions of ULPMs - there should be lots of them but we shouldn't expect to see them as they won't produce radio emission.
    • Feasible periods between 10 and 10^4 seconds
  • Small amount of DM smearing but not so much at higher frequencies at ~200 MHz for similar durations (20-30s). This means we can get good detection sensitivity without having to do DM trials
  • The compromise between sensitivity and FOV is 154 MHz
  • Survey design - simulated pulsar distribution - used as this GLEAM source is much further off the plane without an SNR, which is unusual for magnetars.
    • 10 pointings - 92% of pulsar population
  • Timestep images - adopt IPS techniques
    • Less processing than IPS as not interested in such short timescales
    • Summer student testing filtering algorithms
  • Working on the sensitivity to determine flux density limit that we are sensitive to
  • Not sure how much time to apply for - Dwell time of 30 mins per pointing. These pointings also overlap.
    • More time means it is less feasible to take observations and reduce these data
    • As sources are visible for a few months we only need to do monitoring on a weekly basis. 
    • Potential for requesting longer dwell times of  60 or 120 mins. 
    • Not much FTE - could bump up dwell times and requests if on top of data analysis and the MWA time is undersubscribed
  • If we actually find a ULP transient then we will drop everything and look at it using all possible observing modes. - Just DDT for VCS and picket fence observations.
  • Q Gemma: Think of this as a pilot survey and get pipelines working so 30 mins is fine and justifiable for the initial request.
  • Q Joe: Scatter broadening in Galaxy? 
    • John: It would have to be enormous to dominate over the intrinsic width of the burst
    • Natasha: If the pulse is smeared to twice the width then the pulse wont be detectable. If faint even a small bit of scattering will be bad.
  • Sensitive to long period transients - sets the dwell time but could pick up medium length timescales (minutes)
    • The images could be searched in other dimensions too. 
    • Many synergies are available for people to work on - contact Natasha!
  • We currently have small resources so will try to set things up so people can use the data for other science cases.
  • Sensitivity for the extragalactic sky should be 1 mJy but GP will be worse. Would not want to do long extragalactic studies on these fields. 

Planned proposal submissions:

  • Natasha: 
    • ULPS survey
    • GLEAM-X reobserving fields
  • Xiang:
    • Still thinking - last year found flaring M dwarf in GLEAM-X data. Not sure if should reobserve that source.
      • Joe - outside of UVCeti, MWA has not seen any other M dwarts. Reobserving at high time resolution with the VCS backend would be interesting.
      • Xiang This source looks more like UVCeti than a normal M dwarf.
      • Joe happy to be involved.
      • Gemma
        • Could request monitoring observations to see if/when it is detectable to target for VCS observations.
        • There is some evidence for periodicity from the flares seen from UVCeti in the MWA observations: Lynch et al. (2017)
        • Christene will have good advice
  • Joe - no proposals but crashing the party. Very interested to contribute expertise. 
  • John -
    • IPS proposal: in principle provide a useful dataset to look for slow and fast transients on various timescales. Following on from 2019 and 2020. Interested in how we could leverage IPS dataset - happy to discuss providing data in forms that are easier to use for transient studies
    • Code for optimising observations when the Sun is up.
    • Rapid, low latency triggering
  • Sam
    • Lightning
    • Still waiting for compact time. Will do some follow-up commissioning observations in the extended configuration to test backends and the beamforming software
    • 3rd pulsar discovered in SMARTS - observations to test the timing. Make sure we can get good timing with the new system and to place constraints on this discovery. 
  • Steve
    • Keen to be involved in continued MWA neutrino triggering work.
  • Clancy
    • Mieke using Robbie to analyse MWA neutrino triggered events. Likely resubmit the neutrino trigger proposal -  need science case updating with help from Steve.
  • Zhijun
    • Meteors in VCS mode? 
    • Achieve studies
    • Xiang - meteor work but looking for intrinsic radio emission. 
    • Steve Prabu is also a good contact.
  • Gemma
    • Gemma to resubmit proposal on MWA VCS triggering on UTMOST-2D FRBs
    • Jun Tian to resubmit proposal on MWA VCS triggering on Swift GRBs
    • James Miller-Jones to resubmit proposal on behalf of Jai Chauhan to perform MWA follow-up of outbursting black hole X-ray binaries

Any other business?

Clancy James - authorship ANTARES paper

  • Overview - includes results from all neutrino observational follow-up of ANTARES triggers. 
  • MWA does trigger on ANTARES events. 
    • Doesn't contain results from the analysis of MWA data but it does say that events are being sent for triggering
    • This paper describes the MWA triggering capability
  • Clancy does not think he is the one to make the decision on the triggering mode authorship contributions.
    • There will already be an extremely long author list (>200)
  • Be inclusive about authorship
  • There is no MWA data used in the paper so it does not trigger a builders list
  • Clancy thinks that people involved with writing the code and implementing the triggering system should be included
    • Gemma said those people are: David Kaplan, Keith Bannister, Andrew Williams, Dougle Dobie, Paul Hancock, Gemma Anderson
    • Gemma mentioned that the updated agenda that was circulated on 9 Feb included this as a discussion so people have had the opportunity to comment.
  • Future paper on the MWA data analysis side. 

Next meeting

  • Gemma proposed the March meeting be on MWA Transient scheduling to maximise the science output, which may also include discussions of data analysis techniques that require certain observational set-ups. 

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