Detection of Solar Neutrons and Solar Neutron Decay Protons

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The paper claims that energetic protons, origination from solar neutrons were detected in association with a huge flare. This was the 4^th  observation of such an event, among them  the second measurement carried out on the ground. The subject is interesting and may contribute to the understanding of the energization processes at impulsive flares. The paper is interesting and suitable for publication in the Universe , but I have some questions and suggestion for minor changes, before publication, as follows.

 

The paper is very long and contains 33 figures. It is quite hard to go through all of the information given in the paper. I wonder, weather some of the figure can be neglected. For instance, fig 13 gives the spectrum of the neutrons, based on the travel time from the Sun to Earth, assuming that the production was instant. Figure 14 is the same but correction was made for the energy dependence of the detector’s efficiency. I think that the correction is quit necessary, the information in fig 13 is not really interesting, i.e., the figure can be omitted (or at least, the two figure can be combined in one frame). 

 

In fig 19 the detector efficiency is given (as a function of zenith angle). I wonder why the efficiency goes up to 120% at zero zenith angle for gamma rays (triangles)?

 

Line 355 tells “This speed (speed of CME, calculated from the travel time Sun to Earth) is classified as the high-speed solar wind”. I am not sure about that, behind a travelling interplanetary shock, the speed of the plasma used to be higher than that of the shock.

 

Line 414: “front edge of the Earth’s magnetosphere (magnetopause), which is approximately 8 times the radius of the Earth (8 RE)”. Magetosphere or magnetopause? The 8 RE standoff distance for the magnetopause is unusual. Anyway, the precise value of the size of the magnetopause/magnetosphare is available from Earth orbiting satellite data for the time period in question.

 

I have problems with the Oulu neutron monitor experiment. Fig 16 does not include the geographical position of Oulu (although it must). Taking the geographical coordinates of Oulu on the map, it is clear that the it is far from the ideal position, as far as the atmospheric depth is concerned. In addition, the neutron monitor in Finland is not located at high altitude (15 m from sea level). Therefore, the attenuation of particle fluxes through the atmosphere is a concern. Another issue is that 6.5 sigma confidence level for the increase of flux (line 462) is probably an overestimation. The 1 minute bins on fig 27 were averaged over 4 bins to obtain a histogram with 4 minute time resolution. The phase of the averaging period was adjusted to start with 15:59 UT time, however, there is no a priory reason to do so. This calculation require a more precise statistical treatment.

 

A general question is about the attenuation of the protons passing through the magnetopause. The problem was investigated numerically by emitting antiprotons 20 km above the detectors. The trajectory calculation must assume scatter-free propagation (otherwise this time-reversed technique is not applicable). In such a case, the Liouville theorem must be true, giving the conservation of the phase-space density of particles. I wonder if the attenuation effect can not be calculated more precisely, taking into account the change of the velocity vector of particles (i.e., not only from the area they spread over).    

 

Author Response

Reviewer 1

 

The paper is interesting and suitable for publication in the Universe , but I have some questions and suggestion for minor changes, before publication, as follows.

The paper is very long and contains 33 figures. It is quite hard to go through all of the information given in the paper. I wonder, weather some of the figure can be neglected. For instance, fig 13 gives the spectrum of the neutrons, based on the travel time from the Sun to Earth, assuming that the production was instant. Figure 14 is the same but correction was made for the energy dependence of the detector’s efficiency. I think that the correction is quit necessary, the information in fig 13 is not really interesting, i.e., the figure can be omitted (or at least, the two figure can be combined in one frame).

• Thank you very much for reading our manuscript and providing several useful comments. According to your suggestion, we deleted Figure 13, instead describing the process by the sentence.

 

In fig 19 the detector efficiency is given (as a function of zenith angle). I wonder why the efficiency goes up to 120% at zero zenith angle for gamma rays (triangles)?

• To avoid miss-leading, we added a word “multiplicity”. This means when we deduce the incident flux of gamma-rays, we must correct the observed value by the “multiplicity” of gamma-rays produced (amplified or reduced) in the atmosphere.

 

Line 355 tells “This speed (speed of CME, calculated from the travel time Sun to Earth) is classified as the high-speed solar wind”. I am not sure about that, behind a travelling interplanetary shock, the speed of the plasma used to be higher than that of the shock.

• We have deleted miss leading sentence from the original draft.

 

Line 414: “front edge of the Earth’s magnetosphere (magnetopause), which is approximately 8 times the radius of the Earth (8 RE)”. Magetosphere or magnetopause? The 8 RE standoff distance for the magnetopause is unusual. Anyway, the precise value of the size of the magnetopause/magnetosphare is available from Earth orbiting satellite data for the time period in question.

• We have referred a paper for correct definition of it (reference 40). According to a text book by Kokubun (who has the charge of the magnetometer of the GEOTAIL satellite), the GEOTAIL satellite measured the magnetopause at 9 R_E and Magneto-sheath at 15 R_E. However the first measurement was made by Explorer-12. They measured the magnetopause at 8.2 Re on September 13, 1961.  So we used this value.  But, we have continued and traced the anti-proton trajectory beyond 8Re, to 15 Re, 100 Re until 0.1 au.  Some of the behavior of the trajectory may be found in an open source of PoS ( ICRC2023)1256.  If you have interest, please see it.

 

I have problems with the Oulu neutron monitor experiment. Fig 16 does not include the geographical position of Oulu (although it must). Taking the geographical coordinates of Oulu on the map, it is clear that the it is far from the ideal position, as far as the atmospheric depth is concerned. In addition, the neutron monitor in Finland is not located at high altitude (15 m from sea level). Therefore, the attenuation of particle fluxes through the atmosphere is a concern.

à We have added the atmospheric depth of Oulu station in the figure caption of Figure 15, and added the number of the deep atmospheric depth of the station toward the Sun at 15:50 UT up to 100 hecto pascal.  We also added the location of Oulu station in Figure 15 by the white circle.

 

 Another issue is that 6.5 sigma confidence level for the increase of flux (line 462) is probably an overestimation. The 1 minute bins on fig 27 were averaged over 4 bins to obtain a histogram with 4 minute time resolution. The phase of the averaging period was adjusted to start with 15:59 UT time, however, there is no a priory reason to do so. This calculation require a more precise statistical treatment.

• Following your question, we have tested one minute data by changing the combining duration from 2 minutes to 10 minutes and taking the running average of the data set. We have only show in the paper the 4-minute running average plot in Figure 27.  However we have checked the excess changing the duration from 2 minutes to 10 minutes.

 

A general question is about the attenuation of the protons passing through the magnetopause. The problem was investigated numerically by emitting antiprotons 20 km above the detectors. The trajectory calculation must assume scatter-free propagation (otherwise this time-reversed technique is not applicable).  In such a case, the Liouville theorem must be true, giving the conservation of the phase-space density of particles. I wonder if the attenuation effect can not be calculated more precisely, taking into account the change of the velocity vector of particles (i.e., not only from the area they spread over).

• At the moment, we do not have an elegant software to pursue the anti-proton trajectory by the Hamiltonian formalism. Therefore, we have used RKG equation to pursue the anti-proton trajectory inside the magnetosphere and magneto-sheath; the “test particle method”. In relation with your general concern on the methodology, we have added a new paragraph in between line 448 and 462 with figures26 a and b (yellow belt region).  Since near the rigidity region, anti-protons are mostly reflected toward the sun-shadow area by the geomagnetic force and the number of particle toward the Sun may be not conserved (∂n/∂t =not 0) from actual use of point (x>0), therefore we used the test particle method.

 

Reviewer 2 Report

Comments and Suggestions for Authors

This paper reports multiple observations and interpretations of a large flare that occurred on the surface of the Sun on November 7, 2004. This reviewer enjoyed reading the paper, including the openness of the authors to clearly state the uncertainties of the interpretations of the data they offer. The authors are also to be complimented on the high quality of the diagrams included in the paper. This reviewer was a little disappointed with the brevity of the 'Summary and Conclusions'. He would have liked to see more material highlighted there, including the range of types of detectors referred to in the paper, and the concommitant range of data-types discussed in the paper. This reviewer also requests that a number of English errors be corrected to enhance the readability of the paper, as follows:-

Line 19, change districting to differing

Line 20, insert to after clarified

Line 23, remove are

Line 31, insert and before Somov

Line 44, remove causes the and insert s after effect

Line 100, change impressive to interesting

Line 134, change had been to were

Line 140, change possible to able

Line 197, change It to it

Figure 10, change corresponds to correspond

Line 341, explain what is meant by the word "rope"

Line 496, remove was

Line 540, change you to One

Line 542, change Also, you may to One may also      

Comments on the Quality of English Language

The English requires multiple corrections as stated above

Author Response

Reviewer 2

 

This paper reports multiple observations and interpretations of a large flare that occurred on the surface of the Sun on November 7, 2004. This reviewer enjoyed reading the paper, including the openness of the authors to clearly state the uncertainties of the interpretations of the data they offer. The authors are also to be complimented on the high quality of the diagrams included in the paper.

 

This reviewer was a little disappointed with the brevity of the 'Summary and Conclusions'. He would have liked to see more material highlighted there, including the range of types of detectors referred to in the paper, and the concommitant range of data-types discussed in the paper.

• Following your suggestions, we have re-written the last chapter on Conclusion. Please check them.
• Thank you for pointing out several mistakes of English. We have corrected all of them with appreciation.

This reviewer also requests that a number of English errors be corrected to enhance the readability of the paper, as follows:-

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors answered all of my questions and they have performed minor changes considering my suggestions. The paper is ready for publication.

Reviewer 2 Report

Comments and Suggestions for Authors

My comments from the first review have been adequately taken care of.

Comments on the Quality of English Language

Yellow highlighted sections on pages 12, 16, 19, 25 and 26 require minor clarification by the authors which this reviewer does not need to check.

Yellow highlighted sections on pages 32 and 35 do not require clarification by the authors.