Connections between the Shadow Radius and the Quasinormal Modes of Kerr-Sen Black Hole
Round 1
Reviewer 1 Report
Please see attached file
Comments for author File: 
Comments.pdf
Author Response
Response to Reviewers:
We highly appreciate the referees for the helpful comments and recommendations. We have carefully read the suggestions and revised our manuscript accordingly. We would like to respond as follows:
1, When using solutions from string theory, like the Kerr-Sen solution discussed here, there is always the issue of frames. This is because the string actions are always expressed in the Jordan frame, while the author most likely have used the metric in the Einstein frame. I believe using the Jordan frame solution would very much alter most of the results derived by the author, due to the behaviour of the conformal factor. A discussion and clear reason for preferring one over the other is necessary.
Thanks to the referee, we were working in the Einstein frame where the metric differs from the Jordan frame by a conformal factor. We add a paragraph below Eq.(2.2) to explain that we are working
2，b) The references should be up to date in the manuscript and include for example arXiv:1910.13329, arXiv:1703.07510, arXiv:1503.04514 etc.
c) There is a minor mistake: the ``radium’’ should be radius in the page 9 above the equation 4.25.
Thanks to the referee. The typos are fixed and references are updated.
Summary of changes:
1, A paragraph is added below Eq.(2.2) to address the referee’s concern.
Sincerely,
Xianglong Wu and Xiangdong Zhang
Reviewer 2 Report
In this paper author elucidates relations between the black hole shadows and quasinormal modes of black holes. As a representative example of these relations authors uses the Kerr-Sen black hole metric. Author calculated the typical shadow radius in dependence of the corresponding parameters of the Kerr-Sen black hole metric. Additionally, author investigated some properties of the massless scalar field perturbations by using the Kerr-Sen black hole metric as background. and demonstrated the separation of variables in the corresponding field equation. All these results are new. This paper, in spite of some formal presentation, may be interesting for a wide scientific community in view of the fundamental importance of the physical properties of the enigmatic black holes. The manuscript is a rather well organized, clearly written and may be published as it is. I recommend to publish this paper in Universe.
Author Response
We would like to thank the referee for his warm recommendations!
Round 2
Reviewer 1 Report
Since the authors implemented my suggestions hence I happily recommend it for publication in the journal universe.
