Section 1: Introduction

[plasky]

Add issues about the introduction here

[nikhil-sarin]

From a brief skim so apologies if this is already in there.

• [x] The introduction should mention briefly that given what we think we already know about the EOS, i.e Mtov \lesssim 2.3 Msun e.g., Shibata et al. 2019 [1]. We expect a large fraction of BNS mergers to produce NS remnants that OzHF is targeting. Margalit and Metzger 2019 [2] using their measurement of Mtov (2.17Msun) estimate that up to ~79% of BNS mergers will result in a hypermassive NS while a not so negligible fraction of the rest will result in a supramassive NS, both of which are relevant to OzHF. Note these percentages assume a galactic BNS mass distribution so GW190425 changes things if it is a BNS. The calculation including GW190425 is not hard to perform, but it will just make things messy.

[1] https://ui.adsabs.harvard.edu/abs/2019PhRvD.100b3015S/abstract - There are plenty of other papers one can cite here. Although, have to to be careful about whether the measurement comes from the local distribution of BNS or from GW170817 alone. The former is messed up in light of GW190425. [2] https://ui.adsabs.harvard.edu/abs/2019ApJ...880L..15M/abstract

[ddobie]

• [x] also cite Hotokezaka et al. (2019) (https://ui.adsabs.harvard.edu/abs/2019NatAs...3..940H/abstract) in measurement of H0
• [x] "The technologies that will enable an EMO are key components for third-generation observatories such as Cosmic Explorer." -> "The technologies that will enable an EMO are key components for third-generation observatories." since third generation observatories are already mentioned in a preceeding paragraph

[jade-powell]

• [x] Line 16 - has a unnecessary space before a comma

• [x] and also this part needs an A+ reference and the aLIGO paper reference. Having the aLIGO paper referenced is one of the P&P requirements.

[A-Graham]

• [x] I like the second sentence's effort to show the importance of GW research. Can you give it even more punch (especially for non-experts in GW research but who may be funding-decision-makers) by noting something like it provides a fundamental test/confirmation(?) of Einstein's theory of the fabric of spacetime.

• [x] Line 16: as with the Abstract, your semi-colon needs to be a colon. but... perhaps it would flow better without this punctuation. How about: "... have financed an upgrade to Advanced LIGO (aLIGO), known as A+, which will increase..."

• [x] line 21: semi-colons could be your Achilles heel. How about: "... observatories such as the Einstein Telescope and Cosmic Explorer, which are broadband..."

• [ ] line 23: At the end of the first paragraph, I found myself thinking that you should have already mentioned why EMO is needed.

• [x] line 27, second paragraph: the term "prudent" comes across as somewhat weak. How about: "... it is necessary to explore smaller-scale facilities that will not only produce ... but will simultaneously drive..."

• [x] I'm not a fan of the acronym EMO, given that the term emo is popularly used to describe goths, people who dress in Gothic style with black makeup. You wouldn't want to call the experiment bogan, and I suggest you don't call it EMO. An ill-chosen name could put off a politician spending tax-payers dollars.

• [x] line 40, end of the second paragraph: Should it / can it be better clarified what EMO is? You've suggested that it consists of at least two A+ interferometers, but noted in the previous paragraph that several governments are already funding two such interferometers (LIGO Hanford and LIGO Livingston). I'm missing something, and so may future readers.

[A-Graham]

• [x] line 42: Black holes, not neutron stars, are the densest objects in the Universe.

• [ ] line 51: It may be nice if you add the wavelength range, which more readily conveys the size of the orbit/phenomenon. For example, given that neutron stars are ~10 km across - which you may like to remind readers of - the wavelength of the gravitational radiation (~300 km) will, I presume, better inform readers as to the evolutionary stage that the binary neutron stars are in, and thus the tidal forces they are experiencing at these orbital radii. Or, if I'm mistaken as to what is going on, is it possible/appropriate to quickly explain it here in the text?

AG: Having slept on this issue, I realised that I was mistaken because the orbit is of course not moving at the speed of light; I am now thinking that you are more likely dealing with the acceleration of a non-symmetrical merger remnant as it rapidly rotates with the frequency already mentioned. Do you feel it would be apt to mention this?

• [x] line 55: "... dependent on THE details... "

• [x] line 56: Do you want to put "equation of state" in parenthesis. I'm trying to expand the number of readers who can follow what you are describing.

• [ ] line 58: I did not feel that the "therefore" was justified. I need more prior explanation. Sorry to be a pain, but I'm hoping this results in a document that is more clear for a greater number of readers.

• [x] 63: "... such as THE Cosmic Explorer."

• [ ] 64: It may (may not) be appropriate to explain what the jargon "squeezing" refers to, depending on who you want your audience to be...

[plasky]

@A-Graham: Thanks for the comment about EMO. Completely agree (we've had a few comments along this line...). What are your thoughts on ExMO?

To be clear, this would not be the instrument name, but is instead the name of the concept. If we build it in Australia, then I think there is still an appetite to call it OzHF. There is a subtle difference here between the name of a specific instrument and the design concept. We're trying to make this distinction primarily for political reasons.

[kirkmck]

I like the paper.

• [x] Is it important to more clearly describe the timeline of when the EMO detector is useful/viable scientifically*? My understanding is that from a scientific point of view EMO may become redundant once the CE and ET get going.

Something like "EMO extracts some of the most exciting physics that the ET and CE detectors will see, years before they do".

[A-Graham]

@A-Graham : Thanks for the comment about EMO. Completely agree (we've had a few comments along this line...). What are your thoughts on ExMO?

@plasky : ExMO sounds okay to me. It sounds like a cute creature's name, like Gizmo from Gremlins (maybe good. maybe not). Apparently EXMO is an online cryptocurrency exchange platform.

[plasky]

@A-Graham : Thanks for the comment about EMO. Completely agree (we've had a few comments along this line...). What are your thoughts on ExMO?

@plasky : ExMO sounds okay to me. It sounds like a cute creature's name, like Gizmo from Gremlins (maybe good. maybe not). Apparently EXMO is an online cryptocurrency exchange platform.

@A-Graham well, maybe we've found our funding source as well, then :-)

[plasky]

I like the paper.

* [x]  Is it important to more clearly describe the timeline of when the EMO detector is useful/viable scientifically*? My understanding is that from a scientific point of view EMO may become redundant once the CE and ET get going.

Something like "EMO extracts some of the most exciting physics that the ET and CE detectors will see, years before they do".

Thanks @kirkmck. I've added the following sentence to the end of the second paragraph of the introduction.

"To maximise scientific impact, an \EMO{} must exist simultaneously with 2.5-generation observatories, but before full-scale third-generation instruments are realised."

I'll also try to integrate this into the conclusions to make sure the point is clear.

[plasky]

From a brief skim so apologies if this is already in there.

* [ ]  The introduction should mention briefly that given what we think we already know about the EOS, i.e Mtov \lesssim 2.3 Msun e.g., Shibata et al. 2019 [1]. We expect a large fraction of BNS mergers to produce NS remnants that OzHF is targeting. Margalit and Metzger 2019 [2] using their measurement of Mtov (2.17Msun) estimate that up to ~79% of BNS mergers will result in a hypermassive NS while a not so negligible fraction of the rest will result in a supramassive NS, both of which are relevant to OzHF.
  Note these percentages assume a galactic BNS mass distribution so GW190425 changes things if it is a BNS. The calculation including GW190425 is not hard to perform, but it will just make things messy.

[1] https://ui.adsabs.harvard.edu/abs/2019PhRvD.100b3015S/abstract - There are plenty of other papers one can cite here. Although, have to to be careful about whether the measurement comes from the local distribution of BNS or from GW170817 alone. The former is messed up in light of GW190425. [2] https://ui.adsabs.harvard.edu/abs/2019ApJ...880L..15M/abstract

Thanks @nikhil-sarin. I think for the introduction, the mention of Mtov is getting a little lost in the detail for a paper like this. I'll look through section III and see if it has a more natural place there. But your comment about the 79% from Margalit and Metzger is certainly a good point: it quantifies the answer to the question that @A-Graham asked in the abstract...

[kirkmck]

I like the paper.

* [x]  Is it important to more clearly describe the timeline of when the EMO detector is useful/viable scientifically*? My understanding is that from a scientific point of view EMO may become redundant once the CE and ET get going.

Something like "EMO extracts some of the most exciting physics that the ET and CE detectors will see, years before they do".

Thanks @kirkmck. I've added the following sentence to the end of the second paragraph of the introduction.

"To maximise scientific impact, an \EMO{} must exist simultaneously with 2.5-generation observatories, but before full-scale third-generation instruments are realised."

I'll also try to integrate this into the conclusions to make sure the point is clear.

Thanks Paul, that is great.

[PaulEasterMonash]

Hi Paul, some possible suggestions for the intro:

• [x] 28: smaller-scale

• [x] 42-44: They are the densest known objects in the Universe, and are believed to consist of a superfluid, superconducting core of matter at supranuclear densities -> densest known "intrinsically observable" objects..... to distinguish from solar mass BHs.

• [x] 74: example noise-budget ?

[Nangush]

• [ ] Line 66 - 67 but will simultaneously driving technology development should be changed to one of; but will simultaneously drive technology development, or while simultaneously driving technology development.