Review Reports

Round 1

 

Reviewer 1 Report

This article reviews the theoretical motivations and various associated speculations, as well as the current state of observational searches, that surround the subject of gravitational wave echoes. I found some parts to be well-written and interesting, especially the early parts and parts giving a more global view and perspective. There is also some new material not already found in the literature. Some of this and some of the summaries of published work quickly get quite technical and perhaps will seem somewhat obscure to the general reader. The views and work of the authors is emphasized, as is to be expected for a review of this type, but some representation of other work and views is provided. As the authors say, there is quite a bit of confusion and disagreement in the field, both in the various speculations and the searches. Because of this I think the main problem for a review like this is that it could quickly become dated. Nevertheless I still recommend publication.

 

Author Response

Thank you for your positive comments and recommendation for publication. 

 

Reviewer 2 Report

This manuscript reports the main differences between quantum black holes and astrophysical ones, providing observational signatures and phenomenological background on quantum black holes, including gravitational wave signatures. The paper is robustly written and scientifically sound, reviewing global aspects of black holes. English language and style are fine and the paper gives important contributions to this important area. Although surveying most of the seminal references in this field, some refs. are missing, still. Regarding the membrane paradigm, refs. Eur.Phys.J. C78 (2018) no.11, 960 arXiv:1804.03468, Eur.Phys.J. C78 (2018) no.2, 122
arXiv:1708.00407, and Phys.Lett. B763 (2016) 434
arXiv:1610.01572, supply very relevant black hole models, whereas quantum black holes were explored in Refs. Class.Quant.Grav. 35 (2018) no.18, 185001 arXiv:1709.09704, Phys.Rev. D74 (2006) 055006
hep-ph/0607027 and Eur.Phys.J. C76 (2016) no.7, 384
arXiv:1606.07323. These seminal refs. must be included and briefly commented. Once this will be implemented, the paper can be reconsidered for publication. 

 

Author Response

Thank you for your positive feedback and bringing the references to our attention. In the manuscript, we have now properly cited:

[100] Eur.Phys.J. C78 (2018) no.11, 960 arXiv:1804.03468

[99] Eur.Phys.J. C78 (2018) no.2, 122 arXiv:1708.00407

[73] Phys.Lett. B763 (2016) 434, arXiv:1610.01572

However, given that our article mainly focuses on 4-dimensional black holes with modified (or removed) horizons that could lead to novel astrophysical observable consequences, we felt that other three references, while very interesting and important, were outside the direct scope and purview of our review article.  

 

 

Reviewer 3 Report

This work provides an up-to-date comprehensive review of the main results obtained so far regarding quantum aspects of black holes and how the can be distinguished from the classical counterparts. The content is nicely structured, with a good pedagogical introduction to classical and quantum black holes, a discussion of the theoretical foundations and recent observations of gravitational waves echos as a critical smoking gun to probe the properties of space-time around compact objects (with or without horizon), followed by an overview of future prospects, and finally with a summary and discussion of the content.

I find the content of the paper very useful for a very broad range of researchers working on this area or interested in getting in contact with the most relevant recent literature. Thus I strongly recommend this work for publication.

 

Author Response

Thank you very much for your positive review.