Abstract

[plasky]

Add issues about the abstract here

[ilyamandel]

• [x] "These signature ... contains" -- grammar

• [x] "an extreme matter observatory; a gravitational-wave interferometer" -> "an extreme matter observatory: a gravitational-wave interferometer"

[jade-powell]

• [x] In the abstract, this line reads funny. "These will provide clues to the extremely hot post-merger environment. These signature of nuclear" I suggest changing it to something like "These remnants will provide clues to the extremely hot post-merger environment. The signature of nuclear"

[A-Graham]

• [x] "Neutron star mergers are expected to often produce rapidly-rotating remnant neutron stars".

1. I thought that neutron stars had masses of ~1.2 to ~2.1 solar masses. Less massive and you have a white dwarf held up by electron degeneracy pressure, and more massive will give you a black hole (or perhaps a quark star). I'm therefore wondering, as may future readers, what I am missing and why/how do we expect NS-NS mergers to often produce a neutron star.

2. The term "expected" seemed worrying/weak. If this behaviour is not merely "expected", but rather is "known", then should we drop the passive voice and go with something like: "Neutron star mergers often produce..." My concern is, if this behaviour doesn't (often) happen, will it undermine this project?

[GavinRowell]

• [x] Thanks for the paper Paul. I'm certainly happy to support the OzHF concept.

My only comment is that I think the abstract could spell out a bit more about the wider range of potential sources in addition to NS star merger ringdowns (e.g. SNe, etc.. even though speculative). Additionally, it'd be nice to see up front the strain sensitivity improvement >1kHz for OzHF compared to A+ and current aLIGO just to reinforce the key message.

all the best

Gavin..

[plasky]

* [ ]  "_Neutron star mergers are expected to often produce rapidly-rotating remnant neutron stars_".

1. I thought that neutron stars had masses of ~1.2 to ~2.1 solar masses.  Less massive and you have a white dwarf held up by electron degeneracy pressure, and more massive will give you a black hole (or perhaps a quark star).  I'm therefore wondering, as may future readers, what I am missing and why/how do we expect NS-NS mergers to often produce a neutron star.

2. The term "_expected_" seemed worrying/weak.  If this behaviour is not merely "expected", but rather is "known", then should we drop the passive voice and go with something like:  "Neutron star mergers often produce..."   My concern is, if this behaviour doesn't (often) happen, will it undermine this project?

Thanks for all the very helpful comments @A-Graham. I'll answer your question here, and see if things need to be changed in the introduction. TL;DR, personally I think that the abstract is okay with the word "expected", but I'm very interested to hear what you think based on my (long) answer below.

To start, we don't know the maximum mass neutron stars can have. It may be ~2.1 Msun, but it may even be more. Regardless, let's assume it's 2.1 Msun for the moment. That's actually the non-rotating maximum mass. You can support more massive NSs if they are rapidly rotating, which we expect these remnants to be. Various works show you can expect NSs up to about 20% more massive to last for many tens to thousands of seconds after the merger (insert blatant self-citation here: https://arxiv.org/abs/1403.6327), and stars up to 50% more massive can produce short-lived remnants (~100s of ms). That means you can have relatively long-lived neutron star remnants up to ~2.5 Msun, and short-lived ones that still emit "detectable" gravitational waves up to more than 3 Msun.

Now, take two 1.35 Msun neutron stars, and merge them. You don't actually get a 2.7 Msun remnant because you have to conserve rest mass, not gravitational mass. It turns out the remnant is approximately 2.45 Msun (although this depends on the equation of state, and doesn't include ejecta mass loss: insert blatant self-cite here: https://arxiv.org/abs/1311.1352). So, when you start taking realistic mass distributions into account for binary neutron star systems, you end up expecting a significant fraction of mergers to produce long-lived neutron stars, and almost all mergers to produce short-lived ones.

Sorry about the long response (I'm passionate about this topic...). We have tentative evidence from x-ray observations of short GRB afterglows that these long-lived stars exist, but it's not definitive (resisting the urge to insert even more blatant self-citations here). I'll try to make sure this is all clear enough in the conclusion, but this is the original motivation for using the word "expected". Let me know your thoughts!

[plasky]

* [ ]  Thanks for the paper Paul. I'm certainly happy to support the OzHF concept.

My only comment is that I think the abstract could spell out a bit more about the wider range of potential sources in addition to NS star merger ringdowns (e.g. SNe, etc.. even though speculative). Additionally, it'd be nice to see up front the strain sensitivity improvement >1kHz for OzHF compared to A+ and current aLIGO just to reinforce the key message.

all the best

Gavin..

Thanks, @GavinRowell. Certainly appreciate the support and the comment. I've added the following to the end of the abstract. Let me know what you think:

"Above one kHz, the proposed strain sensitivity is comparable to full third-generation detectors at a fraction of the cost, potentially allowing for gravitational-wave observations of supernovae, isolated neutron stars, and other exotica."

[A-Graham]

@plasky ... [snip] .... Let me know your thoughts!

It's fascinating stuff when one realises what's going on, and I enjoyed reading your explanations. Of course, use your discretion as to where/if to explain different things in the manuscript.