Binary Neutron-Star Mergers with a Crossover Transition to Quark Matter
Round 1
Reviewer 1 Report
Report on the manuscript
“Binary Neutron-star Mergers with a Crossover Transition to Quark-Matter”
by Grant J. Mathews, Atul Kedia, Hee I. Kim, and In-Saeng Suh
Within this manuscript the authors summarize their recent work “Binary neutron star mergers as a probe of quark-hadron crossover equations of state” which was published in PRD. They perform the simulations of binary NS mergers which adopt various parametrizations of the quark-hadron crossover (QHC) equation of state (EOS) and they discuss how power spectral density function may reveal the presence of a crossover transition to quark matter.
As far as the results of binary merger simulations were reported in the mentioned publication, their waveform analysis of the strain in the frequency domain is reported in this manuscript. By plotting the normalized power spectral density, they show that the anticipated gravitational radiation detected in future gravitational wave (GW) detectors from binary neutron star (NS) mergers can probe the high-density equation of state.
Since this manuscript has been prepared for a talk and is a part of a much more complicated problem, I believe their results are sufficient.
Apart from some language editing, I recommend the manuscript for publication.
Comments for author File: 
Comments.pdf
Author Response
We thank the reviewer for a careful reading of the manuscript. The reviewer suggest a need for language editing. We have carefully gone through this version of the manuscript and corrected a number of typographical errors.
Reviewer 2 Report
The manuscript discusses the impact of a possible crossover phase transition to quark-matter in neutron star mergers. The author reports results from numerical relativity simulations performed with the Einstein Toolkit code. One of the main findings is that the crossover phase transition can be revealed from the ratio of two characteristic frequencies in the gravitational wave signal: f_peak and f_max. This is an interesting work and I would recommend it for publication. However, I ask the authors to consider the following suggestions when finalizing their manuscript.
It is not clear how robust is the criterion that the authors suggest to identify crossover transitions, as they also acknowledge. Indeed, one of the hadronic EOSs is located within the same region as the phase transition simulations in Fig. 2. I would suggest the authors to comment on this and potentially (but optionally) to consider including in their analysis data from more hadronic models, for example using publicly available data.
f_max is defined to be "the maximum chirp strain amplitude" f_max = 1/(2 pi) d\phi/dt |_max. It is not really clear what this quantity is: the formula would suggest that this is the maximum frequency of the gravitational wave signal. However, I know from having read the other paper of the authors that f_max is actually the instantaneous gravitational-wave frequency at the time of merger (when the l=2,m=2 mode of the gravitational wave signal is maximum). I would suggest the authors to clarify this point.
Author Response
We thank the reviewer for a careful reading of the manuscript. The reviewer makes 2 suggestions:
1) that we comment on the robustness of figure 2 as an indicator of a crossover transition. We have added a comment in lines 127-131 noting that this is marginally robust and that one hadronc EoS also deviates. We also note the need to consider more hadronic models, but that is left to a future work.
2) that we clarify the meaning of f_max. We have added text in lines 110-113 clarifying the meaning of f_max.
