New instrument CASATTTA - Radio All-sky monitor

[strocode]

At ATNF we are researching a new radio aperture-array telescope concept called CASATTTA (Coherent all-sky all-the-time array).

In it's final form (64k elements) it has the sensitivity of Parkes / Murraying 10k square degree field of view (1/4 of the sky) and a frequency range around 500-1000 MHz. The system would include outriggers out to > 10km to enable sub-arcsecond localisation accuracy.

Such telescope can be implemented in the second half of this decade. Engineering and science demonstrations and investigations can be done in the first half of the decade.

This instrument represents an excellent niche for Australia to exploit. SKA and it's precursors, and other proposed telescopes (SKA, CHORD, DSA-2000 etc.) occupy very different locations in the parameter space of sensitivity, field of view, observing frequency.

No similar instrument is being proposed elsewhere to my knowledge.

Science case includes:

• 1 million FRBs out to z < 3. This is 1 million sightlines through the universe to investigate gas / feedback / cosmology
• All-sky - will detect to detect nearest FRBs - help solve the FRB progenitor /emission mechanism problem. Measure the maximum luminosity of FRBs (Emax)
• All-sky - contemporaneous measurements of radio emission from multiwavelength transients - e.g. binary neutron star mergers, supernovae, gamma-ray bursts, neutrinos
• Galactic science: radio stars, pulsars, magnetars, ultra-long period transients, solar-energetic particle (SEP) events.
• Unknown: Huge chunk of unexplored phase space (all-sky, all the time at 700 MHz)- to date the best all-sky experiments above 700 MHz have been single elements.
• SETI / technosignatures
• DIffuse polarisation of the milky way on the largest scales
• HI intensity mapping

[strocode]

@ethrane - sorry I don't think I have permissions to add the right label

[adamdeller]

One thing that might be worth doing (or perhaps should be avoided like the plague, I don't know!) is to connect this to development work for SKA phase 2. One of the SKA concepts was a mid frequency aperture array - this proposal shares some key elements with that. (If the SKA was being designed right now, rather than 10+ years ago, I doubt the split between dishes and aperture arrays would be put at 350 MHz, for instance). This could be pitched as the logical extension of developments in antenna + DSP technology that could carve out the best bang-for-buck phase space expansion as part of any next-step SKA. The SKA is supposed to be finishing construction before the midway point of this decadal plan, so what comes next?

[mlower]

At 500-1000 MHz, you'll be missing radio emission from most Galactic magnetars due to pulse scatter broadening.

[gemmaanderson]

As a science case, make sure to say multi-messenger rather than multi-wavelength. If a radio telescope is on sky all the time we are contemporaneous with LIGO-Virgo-KAGRA detections AND the Cherenkov Telescope Array (CTA).

[strocode]

@adamdeller re SKA - there are definitely pros and cons. I think it's definitely an option we should look into. I don't know how much detail is required for the decadal plan. Do we need to describe that as an option do you think?

[ethrane]

The thing that appeals to me about @adamdeller's suggestion, "to connect this to development work for SKA phase 2," is that there does not seem to be much of an established paper trail for CASATTA. (I gather that the acronym is like a week old or something. :P) Attaching it to a well-established community priority might be a good way to establish the proper provenance. Thoughts?

[strocode]

CASATTA (as an acronym and feasible idea) been under discussion in the CRAFT collaboration since January. Technical disucssions started at ATNF in 2023.

But the concept has been around since the 1990s.

You're right there isn't much of an established paper trail for CASATTA for the reason we've only started talking about it recently.

But: Isn't talking about it at the decadal plan the way to establish the proper provenance and attach it to a community priority? Is there another avenue?

[ethrane]

@strocode, my take is that the decadal plan is meant to highlight emerging and established community priorities. It's probably not the right place to pitch something perceived as new. It sounds like CASATTA is a complicated case because the basic idea has been around for a long time, but––from what I understand––people in the community are still debating what an actual radio all-sky monitor should look like in practice.

I should add: I think the science case is extremely compelling. I'm not suggesting we should not support this. I'm just asking whether it would make sense to propose this (as Adam has suggested) as a potential development for SKA phase 2. Feedback from other radio astronomers would be helpful. . .

[adamdeller]

I think that maybe the thread here has started a bit backwards - the actual instrument (and the means to get there - SKA development or otherwise) is secondary to the science case and the capability needed to achieve it. I understand why Keith would come at it from that angle though - CSIRO builds stuff! :)

Anyway, doing that flip: the science case for a (close to) all sky radio transient monitor with ASKAP or better sensitivity is really strong (and we could flesh it out much more thoroughly here, or perhaps better in a new, alternate github thread). We've been developing along this pathway with from instruments that have very narrow FoVs (e.g. Parkes) through ASKAP FoVs and we now know what we could expect to see with 10,000+ sq deg FoV and what we could do with that. There's a number of what I would call pathfinder type telescopes working towards that at the moment with lower sensitivity or not really all sky FoV (e.g. BURSTT) but no-one is yet aiming to build a full on all sky radio transient monitor with serious sensitivity. But the science case for that capability is very strong, and I for one would want to have access to such a capability when it eventuates! So I'd suggest re-framing it this way: an all sky radio transient monitor should become feasible over the course of the next decade, here's all the awesome things it could do (and Australia has led the world in developing those science cases on instruments like Parkes and ASKAP) so while the narrow-field transient case is more or less sewn up by SKA phase 1 and DSA-2000, there is a really compelling case to be involved with the development of an all-sky(ish) radio transient monitor. Specific names or possible pathways to implementation are secondary to that aspiration.

[mlower]

The science case currently written for Galactic science is quite weak. If you're looking for buy in from pulsar astronomers, this bit will need to be fleshed out in more detail.

For instance, what is the intended goal of observing/detecting "radio stars, pulsars, magnetars, ultra-long period transients"? If the answer is "To find more of them", then what does an all-sky monitor bring that couldn't be done with a targeted survey of the Galactic plane with the Parkes CryoPAF? Or ASKAP? Or thinking further ahead: DSA-2000?

Another missing detail: how is this instrument going to observe these sources? Will it just pick up pulsars/ULPs as they drift through beams at fixed positions on the sky? Will it have the capability to put tracking beams on the Galactic plane/specific sources? If the latter, then that opens up a huge opportunity to observe hundreds of pulsars a day (possibly up to 1000 if you have enough tracking beams + compute). This then ties in with several key questions posed by this working group (e.g. #3 #5 #6 #7 #11 #19), and those with a focus on Stars and the ISM.

Also, have you considered that by building and supporting this instrument, one of the existing ATNF facilities would likely need to be shut down?

[strocode]

Hi Marcus,

Re galactic science: The important aspect is "All-sky, all the time". The aim is not to find more of the same, but to explore different types. This falls under the umbrella of "unknown" or "pushing into new parameter space".

For example: Rare and episodic transients cannot be detected with narrow field instruments no matter how sensitive or how much observing time they have. e.g imagine there's 1 magic unicorn object in the Milky Way and gives a 1ms, 100 Jy burst once per year. You'll have a 1/4100 chance of finding such a transient with DSA2000 (10 square degree FOV) but you'll have a 1/4 chance with an "all-sky" monitor (10k square degree FoV).

You make some great contributions to the potential science case for an all-sky, all-the time capability. We should say we want a capability that can do all sky monitoring and 1000 tracking beams, then we can indeed address your key questions you reference.

I think it was a mistake(mine!) to propose a particular instrument in this forum. How it would be funded and built, and how it would observe are details we haven't really worked out. As far as I can tell, the purpose of this science working group is to describe the important science questions, and map that into what capabilities we need. How we fund, build and operate facilities that deliver those capabilities is the next step. It may be that it falls neatly under an SKA2 system, but I wouldn't want to restrict our attention necessarily to just that avenue. In the same vein, it's not clear whether such an instrument would take funding off any ATNF facilities (e.g. if it was part of SKA2), so I haven't considered that question.

On Fri, 3 May 2024 at 13:22, Marcus Lower @.***> wrote:

The science case currently written for Galactic science is quite weak. If you're looking for buy in from pulsar astronomers, this bit will need to be fleshed out in more detail.

For instance, what is the intended goal of observing/detecting "radio stars, pulsars, magnetars, ultra-long period transients"? If the answer is "To find more of them", then what does an all-sky monitor bring that couldn't be done with a targeted survey of the Galactic plane with the Parkes CryoPAF? Or ASKAP? Or thinking further ahead: DSA-2000?

Another missing detail: how is this instrument going to observe these sources? Will it just pick up pulsars/ULPs as they drift through beams at fixed positions on the sky? Will it have the capability to put tracking beams on the Galactic plane/specific sources? If the latter, then that opens up a huge opportunity to observe hundreds of pulsars a day (possibly up to 1000 if you have enough tracking beams + compute). This then ties in with several key questions posed by this working group (e.g. #3 https://github.com/ethrane/transients/issues/3 #5 https://github.com/ethrane/transients/issues/5 #6 https://github.com/ethrane/transients/issues/6 #7 https://github.com/ethrane/transients/issues/7 #11 https://github.com/ethrane/transients/issues/11 #19 https://github.com/ethrane/transients/issues/19), and those with a focus on Stars and the ISM.

Also, have you considered that by building and supporting this instrument, one of the existing ATNF facilities would likely need to be shut down?

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-- Keith Bannister

[ethrane]

@strocode writes: As far as I can tell, the purpose of this science working group is to describe the important science questions, and map that into what capabilities we need. How we fund, build and operate facilities that deliver those capabilities is the next step.

I think the decadal plan does all of these things: describes important science questions, maps that onto capabilities, and describes the facilities needed to carry out the science we are advocating. (One of the primary functions of the decadal plan is to advise the government on what facilities to support financially.) Thus we have different options. We could present an all-sky radio monitor as a general capability we would like to pursue without saying how we see that happening. Or we could flag this as something that we would like to prioritise for SKA Phase 2, which would make things more concrete.

I think @mlower's is correct: the decadal plan is to a large degree about prioritisation. The government's unlikely to fund everything we ask for so we should be thinking about the kind of tradeoffs Marcus is highlighting.

[strocode]

@ethrane - I think the former of your options is what I'd advocate: i.e. general capabilities and science questions that would address.

[RonEkers]

@ethrane @adamdeller @strocode First a comment on some history and the relationship to SKA. A major component of the European led SKA Design Studies (SKADS) was a mid-frequency dense aperture array based on the Thousand Element Array (THEA) prototype built by ASTRON in 2001 and followed by EMBRACE. At the time the science case was based on the ability to have multiple beams simultaneously pointing anywhere in the hemisphere, and on the possibility of forming and moving these beams almost instantaneously based on an external multi-messenger trigger. The concept of simultaneous all sky requiring thousands of simultaneous beams was not technically feasible at that time. The cost of elements to provide a large collecting area did not drop fast enough and this option was dropped in the 2011 SKA down select. But that may not have been the decision if it were taken today. This development had very important spinoffs including the SKA precursor, ASKAP, based on the need to combine a dense aperture array (the FPA) with a concentrator (the dishes) which greatly reduces the cost of the collecting area but also greatly reduces the FoV. Keith's proposal and the related much smaller CASPA proposal are derived directly from the success of these focal plane arrays combined with a massive reduction in signal processing cost which now makes all sky feasible for the first time.

[RonEkers]

The science case currently written for Galactic science is quite weak. If you're looking for buy in from pulsar astronomers, this bit will need to be fleshed out in more detail.

The all galactic plane monitor is more than an order of magnitude easier and I think all the science cases you mention could be achieved with a modest version of CASATTTA which could be a prototype for the final system. A separate array operating at higher frequency could be considered. When you have an all sky all the time you should stop thinking about tracking beams which is an unnecessary complication and can be done in post processing. The decadal plan cannot include these design details so should be written generically for the all sky all the time case.

[cwjames1983]

@ethrane @strocode Given the lack of a paper trail, I fully support advertising this via the capability. Then if we can come along with CASATTTA and a $ attached to it, the impetus is already there. But we should also make it clear there are already fleshed-out concepts, and pointing to SKA is likely the right way to motivate this.

@mlower When you say that scattering kills magnetar emission, I assume you mean the usual magnetar emission you study, i.e. treating the long-period sources as their own thing? Because if they are magnetars, then maybe there are more magnetars to be discovered that way! I guess pulsar timing would inevitably take a hit though?

As far as prioritisation @ethrane : if push came to shove, I'd put CASATTTA ahead of everything else. It does things for FRB, GW and GRB that neither ASKAP nor SKA can do. However, I acknowledge that SKA is being built, so I guess that beats CASATTTA via the "bird in the hand" argument. Then again - if the SKA is being built, do we really need to state it's a priority? (answer: yes, since we still want to do FRB work with it)

[mlower]

@cwjames1983, ULPs aren't magnetars -- none of them X-ray counterparts! Scattering just means that at low frequencies you won't be able to detect the pulses or FRBs from Galactic radio magnetars since the scattering timescale becomes greater than their rotation period (in the case of an FRB, it would be much wider and fainter, and therefore harder to detect).

[taramurphy]

I don't think the Decadal Plan is the right place to pitch for (or even name) an instrument that only seems to have been discussed amongst a very small group of people, and hasn't been evaluated against the other major investments already on the horizon, like SKA, ASKAP upgrades etc.

Making the science case for future can be done (e.g. if SKA doesn't cover this science) but I would definitely not tie it to a specific and completely hypothetical telescope that hasn't been discussed at all in the community.

(I am agreeing with Eric's point above)

[strocode]

OK, so I accidentally through a bomb in but I think the conclusion as far as the decadal plan goes is: There's compelling science we'd like to do with an "all-sky, all the time" capability. SKA will not deliver it, but we'd like it on the roadmap for the future, possibly via SKA2.

If we all agree ... now what happens?

[ethrane]

@strocode, I think my suggestion is to plant a seed in this decadal plan for a radio all-sky monitor. I'm picturing a section where we look forward into the future to discuss things that we are not quite ready to fund now (for example, because they are still being defined), but which the community recognises are promising future goals. There's a mid-term review halfway through the decadal plan period, which provides the community with a chance to amend and update the plan. That might be a good time to propose a more detailed next step for an all-sky radio monitor.

For example, there wasn't much in the last decadal plan about gravitational-wave astronomy, which was drafted before the discovery of gravitational waves. However, we were able to add some specific goals during the mid-term review process.

[RonEkers]

@taramurphy I disagree with your statement that it is inappropriate to include the all-sky monitor as an aspiration in the decadal plan. It is a "decadal" plan and essentially all current prioritisation is based on the next 5 years or less. Surely the decadal plan is also a place for more visionary concepts. The SKA was included in our decadal plan long before it became an established project, but when the government heard about it through Foreign Affairs and the OECD, they cross checked with the decadal plan at that time, and noting it was included, jumped at the opportunity for Australia to be part of this endeavour.

There is also a misconception that it is " a completely hypothetical telescope that hasn't been discussed at all in the community". As noted in my previous comment on the history the dense aperture array concept (which is the same as the all-sky monitor) has been discussed for more than a decade and was a key part of SKA until the 2011 down-select. What @strocode has recognised is that such an instrument is now technically feasible, and that Australia has the almost unique capability to do it, and that the science is now very much stronger. The concept has had plenty of visibility, especially in the FRB community, and Tawain are just completing their implementation (BURSTT). The science case for such an all sky transient monitor was made at ACAMAR at least two years ago and our proposal to put a much smaller dense array on the far side of the moon has been under vigorous discussion with Breakthrough since early 2023. Its terrestrial prototype would also be a prototype for @strocode 's far more ambitious longer-term proposal.

[cwjames1983]

@taramurphy If I read your comment correctly, you would be fine with including the capability in the decadal plan right, just not naming a specific instrument? Seems fine by me, and I don't think @RonEkers that's an issue here.

UPDATE FROM ACAMAR: Apparently NAOC are planning on building essentially this exact instrument. They'll have the downside of being in the North, but will likely move faster than we can.