LBNL-2020: Transients: Science Pipelines Data

Connection Details

https://lbnl.zoom.us/j/177357834

Please post slides!

Scribe: Cail Daley, google doc for notes

Charge

To bring together science, technical, and data management requirements for transient science, for example, sensitivity, cadence, and data structure

Agenda

--Science Overview (Gil Holder) Slides

--Lessons from stage 2/3 (Nathan Whitehorn) Slides

--Restrictions on scan strategy & cadence (Reijo Keskitalo) File:Modulated high cadence scans.pdf

--Data management ideas (Don Petravick) https://docs.google.com/presentation/d/1lK125xlBPJk-cug1eD08EcK3Q2i-f2_X2Mro3n4j1Bw/edit?usp=sharing

--Open Discussion

Notes

Science Overview (Holder)

• Fewer transients for CMB-S4 than LSST: <= O(1000) for any given source type
  • Lower depth, not sensitive to stars, etc.
• Multimessenger:
  • Neutrino events may be associated with Blazars?
  • Gamma ray multimessenger prospects aren’t great, cm/mm may be the most promising place to look
  • Possibility for (first) follow-up of LIGO events
• Timescales: huge range (hours to years, depending on source type)
  • e.g. supernovae: may not be seen until shell slams into ISM, months later
  • “Hierarchy of timescales” that we need to track simultaneously
• GRBs
  • Some long, on-axis GRBs show up in the mm, O(1) mJy
  • Baseline goal: nail down mm GRB rate as a function of flux
  • We could possibly see “orphan” (off-axis, high-z) population missed by gamma ray observations
  • Afterglows can peak in the mm!
  • Reverse shocks: early (< 1 day), we should catch a few within hours of burst
  • Uncertainty in GRB event rate means big science potential!
• Requirements:
  • ~ mJy sensitivity, 2’ resolution
  • Transient pipeline:
    • Daily difference maps
    • Protocol for issuing and responding to alerts.
    • Lightcurve querying (as a function of ra, dec)
• Discussion:
  • Joaquin: didn’t we decide not to look at external triggers?
    • We already scan the sky quickly…
    • ALMA probably better for follow-up, except for very large localization regions?
    • Gil: no need to box ourselves out of things preemptively, stay flexible

Lessons from stages 2 & 3 (Whitehorn)

• SPTpol pathfinder analysis found one GRB afterglow candidate (Whitehorn et al. 2016)
• Technique
  • Measure map change relative to some reference template
  • Template can be constructed from small amount of data
  • Sensitive to glitches, pointing offsets that would usually average down in CMB products
• Current SPT3G analysis:
  • just commenced
  • “strongly analogous” to S4 effort, high potential for code reuse if we don’t box ourselves in
• Multi-messenger & Multi-wavelength:
  • Three Astronomer’s Telegrams from SPT and ACT in 2019.
  • Millimeter flares of interest for cross-correlation with high-energy datasets
• Key Requirements:
  • Real-time calibration information
  • Low latency mapmaking, on-site if at Pole
  • Automated pipeline needs babysitting
  • Outreach to broader astronomical community (currently bad)
• Difficulties: gaps in light curves, field switching, post-calibration, insufficient computing
• Discussion:
  • Chile vs. Pole: generally easier from Chile, with two caveats:
  1. Calibration may be less reliable?
  2. No on-site dedicated computing infrastructure in Chile, data analysis happens on shared cluster in US. This may cause latency issues, unless we make a dedicated queue.
     • MOU for real-time queue at NERSC?
     • Argument for diversity in computing infrastructure

Restrictions on scan strategy & cadence (Keskitalo)

• Scan strategy presented in San Diego had high (50-70%) daily sky coverage, but unevenness in hit maps hurts statistical analyses.
• New strategy modulates scan rate by observing azimuth to make hit map more uniform, maintains high daily sky coverage:
• -
• Higher scan rate as you approach turnaround (there is still a slowdown just before turnaround).
  • Diminishing returns in sky coverage as you increase scan rate near turnarounds.
• While changing scan rate in order to even the hit map simplifies statistical map analysis, it also complicates filtering.
• Evidence from current telescopes indicate that they can (mechancialy) handle such high scan rates.
• Discussion:
  • Conventional scan strategy is constant velocity, or sinusoidal to avoid sharp changes at turnaround. This strategy is the opposite of both, Joaquin’s brain is broken.
  • This means spatially varying transfer function? How does a more complicated analysis pipeline weigh against uniform sky coverage?

Data management ideas (Petravick & Vieira)

• Each object has its own long-term, short-term, and special requirement.
• Needed infrastructure: map sims, low-latency processing, alerts/triggers, lightcurves, thumbnails, polarization
• Different releases for transient analysis vs. CMB analysis? Transient products would presumably be point-source filtered.
• Both offline and online (daily) processing pipelines.
• Probably don’t need to worry about doing alert distribution ourselves, can hook up existing multi-messenger infrastructure (can also dump real-time variability information here)
• Data management responsible for transient products?
  • Where do we draw the line between data management (project) and transient (working group) responsibilities?
  • transient working group may end up having their own catalogue anyway.
  • Galaxy cluster people and transient people shouldn’t need to talk to each other