Inhomogeneous Jets from Neutron Star Mergers: One Jet to Rule Them All

Round 1

Reviewer 1 Report

The paper is well-written and free of typographical or spelling errors. The equations also are correct. The color schemes on several figures makes it difficult to read. For example, in Figure 1 there are supposed to be light grey and dark grey areas. I found it impossible to find these in the plots on the right-hand side. It looks like there is only a single grey shade.

It would advisable for the authors to check whether the color differences are indeed visible in the Figures.

Several Tables and figures bleed over the manuscript margins. This has to be fixed. 

The authors posit that NS-NS merger GRBs have a narrow luminosity range and the observed variation in GRB luminosity is due to a combination of observing angle and variable dusk observation. While neither of these ideas are new, the paper demonstrates the observed luminosity distribution for a narrow progenitor energy range can cover a significant faction of the observed luminosity range, with the rest being picked up by varying the opacity.

However, the paper does not posit a physical mechanism behind the narrow energy range.  The narrow luminosity range of a Type Ia is easily understandable as the object mass is at the edge of nuclear stability as a small amount of accretion mass tips the WD into a runaway process which converts entirety of the mass to energy.  

But NS binary rest mass will vary from combined 2.8 to 4.3 solar masses, which could also provide an additional range of the jet luminosity when these combine.  Differences in magnetic field density in different binary systems may play an additional role in the jet collimation and Lorentz factor. Although this may be outside the scope of the paper, it is something that might be worthy of some comment (and perhaps a future follow-up paper). 

Author Response

Response to Referee 1: --
We thank the referee for their careful reading of our manuscript and the insightful comments they have given. We respond to each comment below:

"The paper is well-written and free of typographical or spelling errors. The equations also are correct."

Thank you for this assessment.

"The color schemes on several figures makes it difficult to read. For example, in Figure 1 there are supposed to be light grey and dark grey areas. I found it impossible to find these in the plots on the right-hand side. It looks like there is only a single grey shade."

We apologise for any confusion with the figure color schemes. We have checked the figures and confirm that we can see all colors and the two grey-shaded regions, although the majority of the grey region is a single shade. However, I did notice that the grey region did not resolve well via a browser viewer for me. This suggests to me that there was some incompatibility with the vectorization of the figures -- I have had this issue before, or a similar issue where the display depended on which monitor I was using!? I have post-processed all the pdf figures to try and remedy this issue but, as the figures all display fine for me, I cannot be 100% certain if this is the case for other systems. My co-authors report no issue with the new figure color or shaded regions.
We can try further remedies if the issue persists, but I believe it is mostly a technical/compatibility issue.

"It would advisable for the authors to check whether the color differences are indeed visible in the Figures."

As noted above, the color differences are clear in our pdf viewers.

"Several Tables and figures bleed over the manuscript margins. This has to be fixed."

We thank the referee for this observation. Figures 1 & 8 and Table 1, which exceed the text width do so intentionally and follow the MPDI Latex Template guidance for large or wide figures and tables. Fitting any of these figures or the table within the text margins would result in a loss of detail/clarity.

"The authors posit that NS-NS merger GRBs have a narrow luminosity range and the observed variation in GRB luminosity is due to a combination of observing angle and variable dusk observation. While neither of these ideas are new, the paper demonstrates the observed luminosity distribution for a narrow progenitor energy range can cover a significant faction of the observed luminosity range, with the rest being picked up by varying the opacity.
However, the paper does not posit a physical mechanism behind the narrow energy range. The narrow luminosity range of a Type Ia is easily understandable as the object mass  is at the edge of nuclear stability as a small amount of accretion mass tips the WD into a runaway process which converts entirety of the mass to energy.
But NS binary rest mass will vary from combined 2.8 to 4.3 solar masses, which could also provide an additional range of the jet luminosity when these combine. Differences in magnetic field density in different binary systems may play an additional role in the jet collimation and Lorentz factor. Although this may be outside the scope of the paper, it is something that might be worthy of some comment (and perhaps a future follow-up paper)."

We thank the referee for this insightful comment. We agree that the mass range in the observed NS population is reasonably broad and that this may indeed lead to a broader distribution of jet powers than those classically assumed i.e., the narrow single-order of magnitude range given in theoretical studies.
The studies that the narrow range was drawn from are assuming an equal mass NS merger and various EOS. As the energy for the jet is some fraction of the accreted energy, this depends on the accreted mass, the magnetic field strength, and the efficiency of jet production.
A footnote has been added to the introduction to caution this assumption. We similarly agree that this would be worthy of further investigation in a future paper.

We thank the referees for their comments and notes and hope that they are satisfied with our responses and can recommend the paper for publication.
Kind regards,
The authors

Reviewer 2 Report

Congratulations for the nice work. I have one comment and few minor issues to highlight.

General comment

Is the work done applicable also to long GRBs afterglows, and in that case what would be the required changes? This comment might be out of the scope of the present paper, but a small note on the text might be added. 

Minor comments

1. L26. Specify what do you intend by "microphysics". It might be clear for a GRB expert but not for a general reader. 

2. L55. Why do you need to specify what \Gamma is? Are you using it for different purposes? 

3. L78. could you add a note on the "specific enthalpy", and why it's important for the simulation? 

4. I would move note 1 in the text instead that keeping that in the footnote. 

5. L84. What do you mean by "ballistic expansion". I would add a few explaining words. In the same sentence why the "h-1" is relevant? I am not an expert on fluid simulation so I am sorry for the dummy question .. 

6. Table1. could you allign it to the text? 

7. few lines before L120 "mass of the proton" or "proton mass" instead of mass of "a" proton. 

8. L127 I would add also the explanation of "dex" as acronym. I know it's widely used but not in all the fields. 

9. References: please check all of them .. in most references the Journal name is missing 

Author Response

Response to Referee 2 --
We thank the referee for the supportive comments and constructive notes. Our responses to each is copied below:

"Is the work done applicable also to long GRBs afterglows, and in that case what would be the required changes? This comment might be out of the scope of the present paper, but a small note on the text might be added."

We thank the referee for their comment.
The method is indeed applicable for long GRBs, however, we would require dedicated simulations of jets within collapsars.
We would additionally need to consider the differing range of potential jet powers within a collapsar system. This would require a significant effort in terms of simulations.
We have added a note at the end of the discussion within the text to highlight this possibility.

"1. L26. Specify what do you intend by "microphysics". It might be clear for a GRB expert but not for a general reader."

Sentence revised: "environment and microphysics, such as the fraction of energy that contributes to the magnetic field or particle acceleration, ..."

"2. L55. Why do you need to specify what \Gamma is? Are you using it for different purposes?"

This is the first use of \Gamma within the text. Throughout it has the same definition, the bulk Lorentz factor. We've changed "here" to "where" so that it is clear that this is the only use for \Gamma within the text.

"3. L78. could you add a note on the "specific enthalpy", and why it's important for the simulation?"

A note has been added: "...the specific enthalpy which gives a measure of the sum of the system's internal energy and the product of pressure and volume, ..."

"4. I would move note 1 in the text instead that keeping that in the footnote."

Note 1 is now incorporated into the main text.

"5. L84. What do you mean by "ballistic expansion". I would add a few explaining words. In the same sentence why the "h-1" is relevant? I am not an expert on fluid simulation so I am sorry for the dummy question .."

This question is perfectly reasonable and improves the clarity of the paper, thank you. A note has been added i.e., "the system has stopped acceleration and is cold with" (h-1)<1 everywhere on the grid.

"Table1. could you allign it to the text?"

Thanks for this observation. Table 1 is following the MPDI style guide for oversized tables, see MPDI LaTex template guide. I would have to either reduce the text size or split it into two parts to fit within the text margins. I believe that either of these would make the table more difficult to parse.

"7. few lines before L120 "mass of the proton" or "proton mass" instead of mass of "a" proton."

Changed to "proton mass"

"8. L127 I would add also the explanation of "dex" as acronym. I know it's widely used but not in all the fields."

The definition is added. "... where dex is the decimal exponent"

"9. References: please check all of them .. in most references the Journal name is missing"

Thanks, we have added \newcommands to the .txt and now the Journal names appear.

We thank the referees for their comments and notes and hope that they are satisfied with our responses and can recommend the paper for publication.
Kind regards,
The authors