Gravitational Radiation, Vorticity And Super–Energy: A Conspicuous Threesome
Round 1
Reviewer 1 Report
This paper introduces how the gravitational radiation produces vorticity and super-Poynting vector, and it suggests a possibility for detection of the gravitational waves through the induced vorticity. Although the topic is very interesting, in my opinion the Author only summarize his and his co-authors’ previous results. The first part of subsection 2.1 summarizes the main results of Ref. [2]. The equation (2.2) shows the relation of the vorticity to the news function and $M_{\theta}$ leading to the interpretation that the gravitational wave and the tail of the wave create vorticity. This formula also can be found in Ref. [2] where this conclusion was also made. In the second part of subsection 2.2 the Author presents such formulae which are the special cases of those derived in Ref. [8]. Equations (17) and (18) shows that the super-Poynting vector is related to the function $c$ and its derivatives. From the presentation it is unclear why only the meridional component of the super-Poynting vector is related to the vorticity. Finally, subsection 2.2 summarize the results of Ref. [22]. In addition in my opinion the detection of gravitational waves through the associated vorticity is not worked out in more detail than it was in the previous articles. Therefore I do not suggest this paper to publish in the Universe periodical.
Author Response
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Author Response File: 
Author Response.pdf
Reviewer 2 Report
This is an interesting work on the study of gravitational radiation and its relation with vorticity. Also some interesting proposals on relation with obsrrvations are made.
I only have minor question. It looks that author strictly believes to GR. However, it is clear that in modified gravity (see Physics Reports reviews on this) it may qualitatively change. Some short discussion along this point may benefit the reader.
Author Response
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Author Response File: Author Response.pdf
Reviewer 3 Report
In this paper the asymptotic behavour of axially and reflection symmetric spacetimes is studied.
The super Poynting vector, defined from the Bel-Robinson tensor, and the vorticity of a comoving observer is determined and from these the effects of, e.g. graviational waves can be seen. An alternative way of detecting gravitational waves by measuring the induced vorticity using gyroscopes is also suggested.
The results are quite interesting and the paper is well written, so I recommend publication.
Author Response
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Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The Author improved the discussion and now I understand the novelty of this paper better. I suggest this Manuscript for publication in the periodical Universe.
Reviewer 2 Report
Maybe accepted.
