Access to Australian facilities and instrumentation to meet the needs for transient discovery and follow up

[jeffcooke]

Looming on the horizon, and one of the most significant facilities for this decade, is the Rubin Observatory. It is expected to detect ~10 million transients per night and Australia leads a transient broker to filter these events. As it is located in Chile, and as the Earth turns, Australian facilities are first, and for some events, the only to follow up these transients ~10 hours later after a long stretch of Pacific Ocean. The world will watch to see how Australia handles these events, as much of Rubin science will result from early detections, evolution measurements and classifications, early line emission and nucleosynthesis and from fast-evolving transients and other yet unknown phenomena. Some of these data will be the only data on the transients before they fade forever. Other data are needed to direct other follow up observations elsewhere in Australia, in South Africa, on large telescopes, with radio telescopes and with high-energy facilities in which Australia is involved (e.g., SVOM, CTA, etc). An effective (and funded) Siding Spring Observatory Transient Factory is needed using the multiple small optical and infrared (0.5-1.5m) wide-field imaging telescopes to confirm the two 15-second exposure Rubin detections as bona-fide transients for the brighter events and those that are rising; the ANU 2m robotic telescope to obtain a select fraction of redshifts, classifications and host galaxy information; and the AAT to obtain these same data for fainter events, among other strategies. Such a versatile Australian Transient Factory would accommodate gravitational wave electromagnetic follow up and other time domain science.Importantly, there are many other needs for facilities to discover and follow up radio and high-energy transients (e.g., fast radio bursts, radio transients, gamma-ray bursts, kilonovae, etc).

[clidman]

A comment on the AAT. The AAT is not well placed for rapid ToO follow-up, as instruments are scheduled for fixed periods, meaning that the instrument that is needed for the follow-up might not be available. The 2.3m is far better. WiFES is always available, the telescope is robotic and can be used by all Australian-based astronomers. The AAT is only available to astronomers affiliated with one of the AAT Consortium member universities.

WiFES is very efficient. To get the same SNR, integration times are only a factor of two longer.

The AAT is more efficient if run in the mode that was used for OzDES or the DWF program, i.e. set observing times on preselected fields.

[jeffcooke]

Hi Chris,

Thanks for the input. This clarification is important and I agree that this is currently the case for the AAT. And I agree (of course) that the 2.3m is well suited for this purpose. If things are left 'as is', the imaging/discovery telescopes (optical, IR, radio) are needed to as described, as well as the ANU 2.3m, which should be quite effective for brighter event follow up. But these will be in the minority for Rubin (and other) detections.

I may have not been sufficiently clear in my infrastructure question. What I was suggesting is for the decadal plan to include the much-needed AAT capability for an instrument (high-throughput spectrograph with single and/or multi-object capability) that can be used for programs and ToO follow up when on the telescope. Here, follow up the same night and not rapid minutes later follow up (or it would be used on later nights if other sites around the world are weathered out, for example). This capability is already needed for the large number of events too faint for the 2.3m, but will be highly in demand for Rubin and for other existing and upcoming MW, high-energy particle, and GW programs. Importantly, it will help maintain the AAT as a key facility throughout the decade to serve Australia.

As you're well aware (but others may not be), this transient factory approach spectroscopic capability was done for the Palomar Observatory (i.e., PTF, iPTF, ZTF), with great success and they have a very similar set of telescopes and capability. for this next decade, a SSO transient factory is very much needed and will be powerful.

From my understanding, the decadal plan is to identify and describe what is needed for the next decade. Given the imminent Rubin, GW, radio, and high-energy programs and facilities (SKA, CTA, KM3Net, SWGO, Roman, etc.), this is an identified need for Australia.

• Jeff

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From: clidman @.> Sent: Monday, 11 March 2024 5:38 PM To: ethrane/transients @.> Cc: jeffcooke @.>; Author @.> Subject: Re: [ethrane/transients] Access to Australian facilities and instrumentation to meet the needs for transient discovery and follow up (Issue #10)

A comment on the AAT. The AAT is not well placed for rapid ToO follow-up, as instruments are scheduled for fixed periods, meaning that the instrument that is needed for the follow-up might not be available. The 2.3m is far better. WiFES is always available, the telescope is robotic and can be used by all Australian-based astronomers. The AAT is only available to astronomers affiliated with one of the AAT Consortium member universities.

WiFES is very efficient. To get the same SNR, integration times are only a factor of two longer.

The AAT is more efficient if run in the mode that was used for OzDES or the DWF program, i.e. set observing times on preselected fields.

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[clidman]

Hi Jeff, I agree, there is a need for a high-throughput spectrograph for rapid follow-up of targets on the AAT. Something like WiFES with three arms (two in the optical) and one in the near-IR (up to 1.7 microns) would be ideal and possibly unique.

The current plan is to operate the AAT until at least 2031 (if funding can be secured) with Veloce, Hector, 2dF+AAOmega, 2dF+HERMES, and KOALA. This is the time required to complete the major surveys using Veloce and Hector that have just started. Instruments like 2dF and KOALA may be decommissioned before 2031.

That's only 7 years away, which is not much time to fund, design, build and install a new instrument on the AAT. Veloce and Hector were conceived over a decade ago and have been operating for less than a year. However, I do not think any of us want to wait 7 years for this instrument. I'll certainly be retired by then.

Top-end changes take between 1 and 2 days and can only occur on certain days due to the number of staff needed to change the top-end.

The AAT is now one of only two 4-m class equatorial telescopes built in the 1970s that has multiple instruments and top-end changes. The CFHT 3.6m is the only other one that I can think of. Most of the 4-metre class telescopes built at the same time as the AAT (Mayall, Blanco, and ESO 3.6m) now have a single instrument or no top-end changes.

Will there be a time when the AAT has a single instrument? The answer to this question depends on funding. The current operating cost of the AAT is $3.5m per year (CFHT's budget is three times larger). With just a single instrument, this could come down slightly, but not by much. Would there be enough interest from the community to fund the AAT with just a single instrument? If it is the universities that are the only source of funds, then the answer is no. The universities currently cover 80% of the operating cost (the rest comes from selling time on the telescope) and that percentage is dropping every year. Outside funding is needed. Indeed, outside funding will be needed if the AAT is to continue operations beyond June next year, as the universities will only cover 60% of the cost of operations beyond 2025. Where that funding will come from is a very open question and June 2025 is just over one year away.

Chris

[cwjames1983]

@jeffcooke I've created a new proposal that's specifically radio, since I see this one as being optically based. However, in principle, we could merge them, since they're both under the banner of National facilities

[jeffcooke]

@cwjames1983 If these infrastructure priorities are merged to a few very general priorities, yes, that would be a good idea. However, different from the key questions, if we are to present distinct infrastructure priorities, these two would be better served being separate. Previous decadal plans put forth radio and optical infrastructure needs separately. If this approach continues with this decadal plan (and all things look like we're mimicking the form of the last few), perhaps we present these separately(?) Merging them would make sense, in a way, for transients, but much of the science, and mode for science, is different. One main point of the optical infrastructure priority is that there are aspects that require strong linking of the facilities for coordinated observations, urgent and rapid-response ToOs, feeding from brokers, roboticised facilities, etc. If the decision-makers in the position to fund things can see these differences clearly, that's great. But that's not been the practice in the past.