Technological Novelties of Ground-Based Very High Energy Gamma-Ray Astrophysics with the Imaging Atmospheric Cherenkov Telescopes

Round 1

Reviewer 1 Report

The paper is substantially an interesting historical review of the ground based very high energy gamma astronomy from the first experiments to the actual arrays. In my opinion it could be useful to have also a short summary of the physical principle of the air showers and Cherenkov emission and the consequences, for example, on the observable energy band and threshold.

Author Response

Thanks to the Reviewer1,

 

Thanks for his/her comments.

In accord with his/her request I added a new paragraph to the text

"2.1.1 Extensive air showers and the Cherenkov light emission" as well as the figures 2.a) and 2.b).

Also, for dwelling a bit more on the threshold issue, I expanded the paragraph 6:

"6. The very low threshold, EBL and solar power plants as gamma-ray telescopes", please find those changes in the revised version of the article.

I hope now the text will look satisfactory for the Reviewer1.

 

Best Regards

Reviewer 2 Report

Referee report universe-1620382
March 1, 2022

This manuscript has reviewed the historical developments of ground-based gamma ray observatories, starting from the earliest measurement of Cerenkov radiation in 1953 to the current newest CTA under construction, focusing mostly on the technological novelties (if any) presented by these 4 generations of experiments. 

Please see my questions/comments below:

1. The first generation of telescopes use the counting method in the ON vs OFF region, is this counting method still in use today?

2. The manuscript mentions many times the efforts to lower the energy threshold, for example one of the early experiments, Chudakov’s telescopes in Crimea has a threshold around TeV scale. And MAGIC has extended the energy threshold down to 20 GeV. Can you add what’s the main science goal that can be achieved from a low energy threshold? I think it’ll be nice to have the scientific motivations which drives the technology development stated in the beginning.

Author Response

Thanks to the Reviewer2,

 

for his/her comments and suggestions.

The first question was:

1. The first generation of telescopes use the counting method in the ON vs OFF region, is this counting method still in use today?

When a telescope or a cluster of telescopes use single PMTs in their foci, they should rely on the ON/OFF counting method. HAGAR telescope in Hanle, India, next to the 21m Mace, could be an example of such a telescope.

The 2nd question was:

2. The manuscript mentions many times the efforts to lower the energy threshold, for example one of the early experiments, Chudakov’s telescopes in Crimea has a threshold around TeV scale. And MAGIC has extended the energy threshold down to 20 GeV. Can you add what’s the main science goal that can be achieved from a low energy threshold? I think it’ll be nice to have the scientific motivations which drives the technology development stated in the beginning.

Thanks to the Reviewer2 for this useful suggestion. The author followed it and expanded the text by adding a new paragraph "

2.1.1 Extensive air showers and the Cherenkov light emission", where also the motivation for the very low threshold issue has been mentioned. But the question of interest is answered in the expanded paragraph 6, please find it attached.

 

Best Regards

Round 2

Reviewer 2 Report

Thanks for addressing my questions and suggestions. I recommend the publication of this revised version.