Axion-like Particle Searches with IACTs

Round 1

Reviewer 1 Report

0. General assessment: The paper is a review on the possibility to measure ALP with IACTs. This subject is fundamental in physics, IACTs have an important contribution in studying it and the authors have experience in this analysis. I found sections 1 and 2 a very good review on the theory of ALP. I would have no problem in recommending this paper to publication if the following considerations are taking into account.

1. Figure 1: The colors are badly chosen. The figure is hard to read. I suggest to use transparency as in figure 7 right panel. I find unsatisfactory to cite the program that did the plot. I think the original papers that calculated each exclusion region should be cited.

2. Line 76 and other places: “external magnetic field” - Define external to what ?

3. Line 78 and 79: “strong magnetic field” – Define strong ? Is the galactic magnetic field strong ? Comparing to which field ?

4. Section 3: This is my main concern about this paper. The analysis techniques are not very well explained. The paper is proposed as a review of the detection of ALP with IACTs. However, I found the review on the theory shown in sections 1 and 2 more useful than the review on the measurements shown in section 3. As a review on the detection of ALP by IACTs, I would expect more emphasis on the analysis techniques. I suggest the authors divide section 3 in two sections. In the first one, they explain the analysis techniques. I would expect questions as the following to be answered in this section:

   1. How are the spectrum analyzed ?

   2. How the ALP signal is identified ?

   3. Are there differences between the analysis done for different experiments ?

   4. Are there differences in the detection of the signal related to the telescope type and size ?

   5. How is the ALP signal differentiated from other possible anomalies in the spectrum, for instance, LIV signals ?

   6. The explanation of the “irregularity” estimator is not clear. The estimator itself does not seem to be grounded on fundamental statistics. I would expect a critical review on the estimators.

   7. Fits are mentioned though out this section. What exactly is fitted ?

       

      A second section would be similar to what is shown in section 3 now. A collection of previous results with more critical comments.

       

      In summary, I believe the data analysis is the most trick part of detecting ALP with IACTs. The review is focused on this subject therefore I would expect a more detailed explanation.

    

5. Sections 4 is based on the CTA Consortium paper reference [40]. Do the authors have permission from the CTA consortium to write this section ? Was the paper cleared through an internal review process ? Being a member of large collaborations myself, I know that the journal and the authors might run into troubles if the internal rules were not respected.

Author Response

Dear Reviewer,

Please refer to the attachment for our replies. We have marked the implementations to your comments in blue for the convenience and easier reading. 

Best regards,

Ivana Batković for the co-authors

Author Response File: Author Response.pdf

Reviewer 2 Report

The paper is dedicated to effects of axion-like- particle (ALP) - photon conversion in galactic magnetic fields, which can give interesting features observable by methods of high energy gamma astronomy. The paper is well written and is of definite interest for readers, provided that mentioning of massless ALP, arion

A.A. Anselm, N.G. Uraltsev A second massless axion? Phys.Lett.B 114 (1982) 39-41 • DOI: 10.1016/0370-2693(82)90011-9

effects of arion-photon conversion

A. Anselm, Experimental Test for Arion <---> Photon Oscillations in a Homogeneous Constant Magnetic Field, Phys.Rev.D 37 (1988) 2001; DOI: 10.1103/PhysRevD.37.2001

• ALP, playing simulataneously role of axion, Majoron and familon, - archion

Z.G.Berezhiani, M.Yu.Khlopov
Cosmology of spontaneously broken gauge family symmetry with axion
solution of strong CP-problem. Z.Phys.C- Particles and Fields (1991), V. 49,
PP. 73-78

and primordial large scale correlations in the distribution of ALP field

M.Yu.Khlopov, A.S.Sakharov and D.D.Sokoloff
The nonlinear modulation of the density distribution in standard axionic CDM
and its cosmological impact. Nucl.Phys. B (Proc. Suppl.) (1999) V. 72,
105-109.

is added with proper references. With these additions the paper can be recommended for publication

Author Response

Dear Reviewer,

Please refer to the attachment for our replies. We have marked the implementations to your comments in green for the convenience and easier reading. 

Best regards,

Ivana Batković for the co-authors

Author Response File: Author Response.pdf

Reviewer 3 Report

Postulated in the 70s to solve “the strong CP problem,” axions are a type of pseudoscalar particle beyond the standard model. If they are existing, axions have low mass and can be a possible component of cold dark matter. The generalized axion type is predicted in some extensions of the Standard Model is Axion-like-particles (ALPs), whose two-photon coupling can impact astrophysical observations. Namely, due to the coupling, ALPs can oscillate into photons and back in external cosmic magnetic fields. It leads to the peculiar imprint in the photon spectra of astrophysical objects and, as a result, may allow to put constraints on the parameters of ALPs.

This Review denotes the above ALP problem and lists reconnaissance experiments such as CAST, LSW, OSQAR, ALPS, ADMX, and PVLAS based on different principles. But this manuscript mainly considers the astrophysical searches for axion and ALPs.

It summarizes the constraints of photon-axion coupling and axion mass parameters that are derived from the extragalactic object observation results and their applications to extragalactic background light obtained with Fermi-LAT space telescope, HESS, MAGIC imaging atmospheric telescope experiments as well as related models.

The reviewed manuscript touches on the actual problems of searches for axion and ALPs in astrophysical experiments, but the following points require to be clarified and fixed.

1. All statements in the text should follow consequently, and references should be checked and cited (appear) accurately in the manuscript text.

For example, reference 53 on Aharonian F. et al. “Discovery of very-high-energy γ-rays from the Galactic Centre ridge” does not contain the data about high redshift extragalactic objects and EBL applications.

The results presented in Fig. 5 and its caption contain the mention of HESS observations of SN1987A, but no discussion is given in the paper text.

2. The paragraph “Signatures on the intrinsic gamma-ray spectrum on NGC 1275 - a showcase” should be removed, as the self-sustained consideration of NGC 1275 is presented in paragraph 3. Also, the discussion of the magnetic fields in cosmic space and Bl Lac jets related to ALPs modeling and searces should be detailed and then moved to paragraph 3, where the results of astrophysical searches are presented.
3. As the article type is a review, the description and discussion of the galactic candidates (like pulsars or SNRs) for ALPs searches and corresponding experiment results should be added to the manuscript.

The paper text is inconsequent, which should be corrected.

Author Response

Dear Reviewer,

Please refer to the attachment for our replies. We have marked the implementations to your comments in orange color for the convenience and easier reading. 

Best regards,

Ivana Batković for the co-authors

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The paper improved significantly. The authors have replied to all my concerns. I reccomend the publication of the paper in the present format.

Reviewer 3 Report

The authors revised the manuscript by adding the information about galactic candidates for ALPs and some rearrangements in the text, providing the details about the extraction of axion limits from astrophysical observation data.

 I think the revised manuscript can be recommended for publication