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Minutes for MWA-VAST Transients Synergy meeting

23 Feb 2023, 00:00 UT

Attendees: (~38 participants) Gemma Anderson, Yuanming Wang, Tara Murphy, Natasha Hurley-Walker, Tao An, Laura Driessen, Josh Pritchard, Andy Wang, John Morgan, Sam McSweeney, Steve Prabu, Zhijun Xu, Gary Strain, Roberto Soria, Greg Sivakoff, Kovi Rose, Susmita Sett, Ben Pope, Aillin, Andy Wang, Daniele D'Antonio, Manesha Caleb, Hannah Dykaar, Miguel Perez-Torres, Mark Edwards, Xiang Zhang, George Heald, Dougal Dobie, Andrew O'Brien, Jai Chauhan, James Leung, Ashna Gulati, Chenoa Tremley, Harry Qiu, Yang, Andrew Zic

Proposed Agenda (see email sent on 22 Feb 2022):

  • Natasha Hurley-Walker: Long-period transient searches with the MWA and potential links with VAST (10 mins)
  • Tao An: ASKAP and MWA combined searches for giant M dwarf flares and star-exoplanet interactions (10 mins)
  • Laura Driessen and Josh Pritchard: ASKAP/VAST stellar searches (10 mins)
  • Yuanming Wang and Andy Wang: Searching for unknowns in the Galactic Centre and LMC (10 mins)
  • John Morgan: The first MWA IPS data release and IPS with ASKAP (10 mins)
  • Open discussion (10 mins)


Zoom meeting: saved chat

Natasha Hurley-Walker

  • 18 min transient, bright in low freq radio, highly polarised
  • Timescales and frequency not probed by other surveys
  • Possible magnetar
  • Based on simulated pulsar population: DM smearing not a problem at 200 MHz (recover all sources over the Galaxy) - optimised survey could easily search at 154 MHz and find a large sample. 
  • The realistic dwell time for the survey - 10 pointings at 30 mins. 130 hr for 6 months in 2022A. Could increase cadence once developed the processing strategy.
  • Cadences it is useful for
    • 4s - 5m: 50 mJy/b
    • 5-30m: 5mJy/b
    • Weeks to months
    • Years
  • VAST database - MWA ADACS proposal to turn MWA PSR database code into a transient database
  • Greg: If we could get monitoring approved with VAST, what sort of coordination would we need.  
    • Natasha: GP time with VAST then could use coordinated schedular designed by Vanessa Moss. 
    • Advanced scheduling is necessary for both instruments could allow for simultaneous scheduling
    • April lead time
    • Dynamic schedular
    • Talk to the MWA ops team
  • Tara: Unlikley ASKAP schedule of surveys will be available in April
    • Potential early time GC monitoring at before then.
    • Quarter 3?
    • If near-real-time pipeline up and running then can delete data on the fly
  • George: Real full survey operations Q3
    • Constraints around Pawsey update
    • Targes of opportunity for ASKAP still valid even before the full survey

Tao An

  • Ideas for coordinated multiwavelength observations of flare stars and exoplanets
  • Multi-wavelength campaign
  • FK Aqr - MWA detection in GLEAM-X
  • AU Mic - active M dwarf and at least one Neptune sized planet
    • Southern hemisphere candidate for MWA, ASKAP, LBA
  • Laura: FK Aqr - undetected in RACS at the time. 
    • Difficult to "target" sources with ASKAP but can check
    • Tao An: Good targets could do coordinated
    • Gemma: Good target within a few days - ASKAP can do this. Trigger MWA ToOs/automated triggering
    • Tara: Can do ToO but best if its for widefield strength with ASKAP. ATCA would be better for flare star follow-up. 
  • Natasha: GP monitoring will pick up flare stars - do want to do polarisation searches too.
    • George: Flare stars (unresolved) should stay polarised. 
    • Josh: Depends on luminosity distribution. 
    • Gemma: pc (kpc very optimistic)
    • Josh: Must be close and luminous
  • Ben: Optical exoplanets expert: 
    • 10's of pc
    • Sensitivity of LOFAR dont know how achievable with MWA
    • AU Mic exceptional candidate that we MUST get time on as 10 pc, very bright, multiple transiting so lots of radio emission
    • Optical support: Simultaneous with radio - we know the TESS schedule so devoting some time to co-observing test fields. 
    • Optical support for simultaneous SKA surveys of stars to nail the astrophysics.

Laura Driessen

  • POSSOM pilot 1 fields (8 hrs)
  • Find more radio stars
  • Difficult to match radio and optical as so many extragalactic sources
  • Simbad radio and X-ray stars
  • Match X-ray, GAIA and ASKAP
  • Found 14 sources via matching process in POSSOM 
  • Vedantham - RS CVn fit on Gudel & Benz 1993
  • eROSITA collaboration

Josh Prichard

  • VAST - detecting radio stars: search in Stokes V (filters out AGN)
  • With 12-15m images with ASKAP
  • L_R ~ 10^15 erg/s/Hz
  • Hoping to see more and brighter flares from nearby stars
  • Detections of stars put to 200-300 pc
  • Many of the detections are coherent except for RS CVn
  • 1 star for every 666 deg^2 at 888 MHz, RMS 200 microJy using polarisation method
  • Predict to detect 100s of stars in upcoming ASKAP surveys

Yuanming Wang & Andy Wang

  • Galactic Centre Radio Transients - synergy with MWA transient survey
    • High state ~10mins and other 60 mins low state - period ~77 min
  • ASKAP J1736-3216
    • 100% lin polarised at 1.5 GHz but becomes increasing circular polarised with decreasing freq
  • PSR J0523-7125
    • Highly variable and circ pol so found in continuum images
    • New pulsar in LMC based on DM and most luminous
    • Difficult to identify using traditional PSR search
    • Highlights can find new PSRs found
    • Link to MWA survey - GC and Magellanic clouds
  • MWA & VAST contemporary monitoring required
    • Simultaneous searches
  • Natasha: Agreed we should synchronise our surveys
    • There are some observations of the MCs - pay extra attention
    • MC elevation is quite low 
  • Sam: COordinate with MWAX Smarts
    • Well geared for simultaneous observations

Further discussion - joint monitoring proposal with MWA on AU Mic:

  • AU Mic specific proposal - Xiang & Natasha
  • Ben: Reason to say an extension on a proposal based on a recent paper
    • Even if don't detect planet induced emission, should see normal flares
  • Xiang: Just submitted a proposal
    • Monitoring or deep?
  • Natasha - reasonable part of the sky for observing
    • John - halfway between GP and 3C444, near Zenith
  • Xiang - take the lead and chat with Chris and coordinate with Ben

John Morgan - IPS

  • IPS - variability of compact sources on second timescales due to the solar wind 
    • The primary goal is for solar physics and find more compact sources
  • Phase II first data release - 8000 detections, 31000 upper limits
  • IPS for slower transients and variability monitoring
    • Track Sun around sky within 30 deg so daily monitoring
    • Time-domain Stokes V might be a simple addition to our pipeline
    • About to do data processing so want to add this now. 
    • IPS is a big contaminant but should be able to identify them based on a survey
    • No scintillating sidelobes
    • Should be able to identify transients. 
  • IPS variability also probing ISM
  • Rajan - recently observed an IPS source with ASKAP with help from CRAFT 
    • Working with VAST team to use their real-time calibration hook to get visibilities on 100 ms dump time
    • Hopefully, we can do a similar IPS survey with ASKAP
  • Gemma: What is the difference in IPS observing at 1 GHz rather than 200 MHz.
    • Solar wind is denser as it gets closer to the Sun so at slightly higher frequencies you can reach a sweet spot in minimsing the scatter so you can observe even closer to the Sun
    • Possible to observe on slightly shorter timescales 

Future discussions

Gemma - Suggests we coordinate MWA-VAST meetings for before the MWA proposal deadlines in the future.

Josh - Tend to use ATCA as target follow-up for VAST. Could do this with MWA too

  • Large sample of stars and exploring connection between GHz and MHz
  • Now we have a large ASKAP sample - should just look in existing MWA data

Ben - Build an Australian node to do flare star with the SKA

  • Optical support for SKA synergies

Natasha - check what data already exists 

  • Could be close to EoR field so may have a lot of data

John - Next MWA call for proposals likely for compact config so don't call a meeting on that basis

  • If you have something interesting then lets ask now while we are in the extended config for mJy work
  • Natasha - hoping that we will just add to the array (150T) using new correlator. Potentially we wont have to choose soon. 

Gemma - Could we look at putting in a proposal now for MWA follow-up of AKSAP stars?

  • John - scope out the time you need and have necessary sensitivities and archival data
  • Don't delay on this groundwork
  • Josh - the sensitivity of MWA is the main concern when it comes to observing stars. 
    • Be more proactive in the future

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