Debrief from recent ASTERICS meeting

[Andy at ROE]

To: IVOA Time Domain Working Group
From: Andy Lawrence 2015-12-04
Re: Discussion at ASTERICS meeting

Dear all

we have just been concluding some discussions about time domain science within WP4 of the ASTERICS project and I thought some of this was worth reporting to the group. For those who don't know, ASTERICS is an EU-funded project meant to plan and implement data-infrastructure for major upcoming European "ESFRI" facilities - SKA, CTA, KM3NET, LIGO/EGO, and ELT. (LSST is not one of these, but its kind of the elephant in the room). WP4 is specifically about the role of VO in the data infrastructure. The heavy-lifting grid-style stuff is elsewhere, in WP3. Much of the discussion of course centred around the precursors and pathfinders - LOFAR, Antares, HESS, LIGO/VIRGO etc. I spoke to the meeting about our experience with PanSTARRS, and the UK plans in LSST (MOA about to be signed!!)

There was lots of interesting discussion, but here are a few key things. Most of the issues will be familiar to people on this list, but still worth saying, especially as ASTERICS-WP4 can be a route to addressing some of these issues.

      andy lawrence

==Existing experience==
The gravy-wave and neutrino folk have already been using VO Event, as well as GCN, and have used them to trigger real follow-up observations. They already appreciate that VO Event gives better automation. In particular the neutrino folk have set up a network of collaborators to share streams of VO Events (AMON : http://amon.gravity.psu.edu/) LOFAR, despite earlier stated intentions, seems not be generating a stream of alerts; they can receive and respond to alerts from others, but they do this "by email". I described our experience with the Belfast-based FGSS system for producing PanSTARRS transients and following them up. This was scientifically very succesful, but could best be described as "semi-automated", relying on both automated junk-filtering, and second-stage grad-student eyeballing - right at the edge of what works. I also described our experience in constructing historial light curves for selected transients by combining data from several archives.

==Astroparticle alerts==
The event rates expected from gravy waves, neutrinos, and gamma-rays are quite modest; but they all want to be able to issue alerts within seconds and potentially have multiple facilities respond in a kind of cascade. This is driven by how fast some likely counterparts (e.g. GRB afterglows) respond. They seem to think so far that VOEvent is fit for purpose, but we encouraged them to write down their experiences and make critical asssessments. The issue of VTP vs XMPP briefly raised its head.

These facilities are generally assuming that they are sharing events with other projects with whom they have MOAs, rather than public broadcasting, but some are considering a kind of mixed economy. There was some discussion about whether or not they needed brokers, whether streams could have auth/auth attached rather than just being hidden by obscurity.

==Optical alerts==
Our experience with PanSTARRS/FGSS shows that full automation of QA is the number one problem. (I have some numbers for those who are interested). However even when you reach the stage of believing all the transients, we were right on the edge of what a research team could cope with; using brokers to filter LSST transients, and handlers of some kind to act on them selectively, will clearly be crucial. This is potentially a volume issue (XML verbosity etc) as well as a CPU issue (parsing, processing, deciding). Although LSST is not an ESFRI project, many other projects will want to consume and act on LSST transients, so the partners are concerned by this issue. So... we are interested in high event rate stress-testing, experiments in compact serialization, and use of brokers. (I suspect we will be able to resource this through the new UK LSST funding, but I will contact Jeff/John/Mario about this separately.)

==Radio alerts and response==
We encouraged the LOFAR rep attending (Roberto Pizzo) to begin some experiments in VOEvent creation/consumption. We stressed that even some simple experiments will help, because we need feedback if VOEVent and VTP don't suit them in some way; reporting experience with brokers such as COMET would also be useful.

==Other VOEvent issues==
I raised other issues that have sometimes come up, such as verification and discoverability, but nobody seemed very exercised about these.

==Light curve use cases==
There was considerable interest in standardising the approach to time series, so that it is easy to mix and match data from various archives. However, it was clear that a collection of use cases was needed if we are to concentrate effort, and not waste effort on unnecessary things. It was pointed out that Enrique Solano and David Ciardi are writing a white paper along these lines, so what we need to do is to collect any use cases and feed to them. 

==Time series standards== 
We discussed "Simple Time Series" and whether to develop that, versus the alternative approach of adapting SSA or upcoming datacube datamodels. There was not a clear conclusion to this debate, but on balance a feeling that a dedicated datamodel and access protocol did make sense, and that it shouldn't be hard. One thing that people clearly wanted was simple discoverability of services with a light curve construction capability. 

One minor specific thing that came up from the CTA people was that a simple timestamp was not enough, because data was accumulated on and off over an extended period. Possibly start-end and live-time would be needed. Another specific issue is how to specify types of flux etc. Possibly this is covered by linking to Photometry DM.

==Time series tools==
There was brief discussion about whether some kind of graphical tool was needed along the lines of Topcat or Aladin or Splat. The mood of the meeting was probably not; astronomers doing this sort of thing would cook their own with Python etc. However, I think this needs a bit more thought.


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Andy Lawrence : Regius Professor of Astronomy, University of Edinburgh
Institute for Astronomy,  Royal Observatory, Blackford Hill, Edinburgh, EH9 3HJ
Email al at roe.ac.uk   /  Phone +44-(0)131-668-8346  / Skype andyxlawrence
Admin contact : Paula Wilkie 0131-668-8403 paw at roe.ac.uk
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