Upper Limit on the Diffuse Radio Background from GZK Photon Observation
Round 1
Reviewer 1 Report
Dear authors, I have read your paper with great interest. It is definitely interesting to use GZK photon fluxes in this way.However, I do have several comments on the paper (see the attached file) which, I hope, can lead to improvements on the paper.
Kind regards
Comments for author File: 
Comments.pdf
Author Response
Please see the attachment
Author Response File: Author Response.pdf
Reviewer 2 Report
Recently has been claimed an unexplained excess of radio background in the range 3-90MHz (on top of CMB background). It is unclear whether this excess is of galactic or extragalactic origin. The authors suggest to use UHECRs to constrain the level of Extra Galactic Radio Background (EGRB). In fact, ultra high energy photons produced by scattering of photons on the background can be absorbed by EGRB photons.
The authors upgrade their previous works (refs. [28-30]) to include EGRB photons. In this way upper limits on EGRB photons can be obtained as function of the proton fraction and the UHECRs photons flux that will be measured by the AugerPrime experiment (fig. 3). In my opinion the idea is enough original to warrant publication.
I have just a doubt regarding the contribution of EGRB to UHECRs photons. In fact, in principle EGRB photons should increase the GZK photons due to the scattering of protons. However, EGRB photons contribute to the absorption of the GZK photons. From fig. 2 I argue that the second effect is greater than the first since increasing Frad the photon flux decreases, but from the paper is unclear the net contribution of these two effects. I just suggest to the author to clarify this point. I have found a typo in Eq. (1) (a missed minus sign in the exponential).
Author Response
We thanks both referees for their comments and corrections which have certainly helped us to improve our paper. Since we added two figures, one equation and several explanations to the text, the changes have been large enough that trying to follow the original and final line numbers of all our changes would have become very cumbersome. So we refer to the changes by indicating the present location of the changed paragraphs and reproducing them when pertinent.
We thank Referee 2 for assessment of the main idea of the paper as original enough to warrant publication. The referee expresses doubt about the increase of the level of GZK photons with the radio background due to the interactions of protons with this background. However, the photons of the radio background have too small energy for the interaction of protons on these photons to be above threshold for pion production and finally the GZK photon production. The only effect of the radio background on the level of GZK photons is through their absorption.
We thank the referee also for pointing out a typo in Eq. (2.10) that we have now corrected.
Having addressed all the doubts and questions of the referees, we now hope our paper is now ready for publication.
