Directional-Sensitive X-ray/Gamma-ray Imager on Board the VZLUSAT-2 CubeSat for Wide Field-of-View Observation of GRBs in Low Earth Orbit

Round 1

Reviewer 1 Report

The article presents a review of a small X-ray and gamma-ray imager deployed in low Earth orbit onboard the 3U CubeSat VZLUSAT-2. As far as I understand from the text, the main aim of the experiment is to verify that a CubeSat-size instrument is able to provide X-ray and gamma-ray observations of both astrophysical and atmospheric origin. The experiment is undoubtedly interesting in view of the modern trends in space-borne studies.

The article is clearly written and well-structured. Illustrations are well-thought and helpful. I think, the article deserves publishing in Universe.

I have a couple of questions I would like to be addressed by the authors:

1. I have failed to figure out from the text how are location and orientation of the device in the LEO are controlled and how accurate is this information.  I believe this is crucial for X-ray and gamma-ray observations. Is this information available or is this beyond the tasks of the presented mission?

2. Another important characteristic of an imaging device is its angular resolution. However, I have failed to find any numbers but only statements about "high-resolution."  Is it possible to provide numbers on the angular resolution of the detector?

Minor comments:

The wording "LEO orbit" might be inaccurate since "LEO" already means "Low Earth Orbit"

Line 284: what is the CPL model? Please, provide a suitable reference.

Page 2: it might be convenient for a reader if references are given in the order they appear in the text.

Finally, a few minor style/language issues:

line 8: $60^0$ -> $60^\circ$
line 128: "2000 um" -> "2000~$\mu$m"
line 128: "configuration in customized" -> "configuration is customized"
line 137: "linux" -> "Linux"
line 216, 220: "120 keV" -> "120 kV"
lines 219-220: extra "(" or missing ")"
line 222: "as part" -> "as a part"

I am looking forward to reviewing a slightly revised version of the manuscript.

Kind regards,

The reviewer

Author Response

All comments accepted and corrected, see in detail in the cover letter.

Author Response File: Author Response.pdf

Reviewer 2 Report

Dear Authors,

I am sorry for the delay with this report. I believe that the manuscript is interesting enough to warrant its publication in Universe. However, I also believe that the crucial Section 3 could be significantly improved.

Indeed, the standard way of characterizing scientific instruments (at least in gamma-ray astronomy) consists in presenting the dependence of the following quantities on the gamma-ray energy: 

1) the effective area

2) the angular resolution

3) the energy resolution

4) the differential sensitivity.

The text of Section 3 is rather descriptive and of limited utility to the reader. I understand that the manuscript was mainly devoted to describe the hardware and laboratory tests of the hardware and not to detailed simulations. 

Indeed, in Figure 7 the authors demonstrate that the response of the instrument depends on the primary X-ray energy. However,  it is not immediately clear how well the primary X-ray energy could be reconstructed. Isn't it possible to add another Figure with the energy resolution vs. the energy (at least some estimates)? Such a Figure would present a more quantitative information about the performance of the instrument.

As well, if the authors could present three more graphs with the above-mentioned quantities: the dependencies of the effective area, the angular resolution, and the differential sensitivity on the primary energy (at least simple estimates), it would greatly help the reader to understand the performance of the instrument. Therefore, I would like to encourage the authors to undertake a major revision of their paper if they agree with me that such estimated are possible to make and advisable to include in the paper.

Minor comments:

1) Figure 8 contains a color palette (signed "Events [cnt]"), but Figures 7 does not. Pleas add a color palette to Figure 7 if possible.

2) Text in Figure 8 reads "X poloha", "Y poloha" I guess that means "X position", "Y position" (from Czech language) just like in Figure 10. Please correct this.

2) In Figure 11 the axes are not signed. The reader could guess that the Y-axis is the number of entries, but it is not so obvious what quantity corresponds to the X- axis. Is it the "measurement channel number"? Please sign the axes if possible.

3) lines 88-90 "Customized optical elements and relatively complex mathematical image deconvolution procedures are used to determine them."  This is rather descriptive. Could you please add more information about the specific "deconvolution procedures" that are used.

4) lines 128-129 "Such configuration in customized for enhanced detection of high energy X rays and gamma rays." Did you mean "is customized"?

5) lines 284-285 "However, the CPL model suggests that most arriving photons are of lower than peak energy." I guess that CPL means power law  with an exponential cutoff. Could you please define the acronym "CPL".

6) I would like to encourage the authors to re-read the text of the manuscript and fix small inconsistencies like 4-5 above if such inconsistencies could be found.

Author Response

All comments and suggestions accepted see cover letter for details

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Dear Authors, I believe that the manuscript could be accepted for publication.

Author Response

Cover letter No 3

for paper universe-1639376

Title: Directional-sensitive X-ray/gamma-ray imager on board the VZLUSAT-2 CubeSat for wide field-of-view observation of GRBs in LEO orbit

Review Run No 2 April 3, 2022

Authors responses are below in italics.

Reviewer 2

Comments and Suggestions for Authors

Dear Authors, I believe that the manuscript could be accepted for publication.

OK, thanks! We have added at the end of the paper: We also acknowledge the valuable comments by the referees and editors which helped to improve the paper.

Submission Date

28 February 2022

Date of this review 01 Apr 2022 18:55:32

Editors Review for Reviewer  1

Dear Authors,

faced with the unresponsiveness of Reviewer 1, I went through his/her comments one by one in unison with your resubmitted manuscript. From what I can see, you adequately adressed most of the suggestions, but apparently missed a few. Therefore, I would like to ask you to clarify and relate to the below:

Line 333: "what is the CPL model? Please, provide a suitable reference."

Please expand and explain the abbreviation CPL and provide a direct reference.

Corrected and explained. Reference added.

<<The wording "LEO orbit" might be inaccurate since "LEO" already means "Low Earth Orbit">>

Indeed, "LEO orbit" = "Low Earth Orbit orbit", which is a pleonasm. Please correct accordingly throughout the text.

And "LEO" should be expanded in the title of the paper.

Corrected

"line 8: $60^0$ -> $60^\circ$"

Corrected

line 231: 'was also performed also' -> 'was also performed'

Corrected

Thank you very much and apologies for the inconvenience.

Best regards,

Mariusz Tarnopolski

Many thanks and regard for authors

Rene Hudec

Author Response File: Author Response.docx