GeV Proton Detection in the 8 November 2000 Solar Event

Round 1

Reviewer 1 Report

The article reports an amazing fact - the detection of protons with energies above 40 GeV of solar origin in the event of November 8, 2000, the flux being ~9.2×10 ⁻³  cm^-2 s^-1 sr^-1. At present, solar protons of such energy can only be detected by muon detectors, so the result of this work is unique. The detailed description of the L3 spectrometer muon detector and careful analysis of data convincingly proves the validity of the results obtained.

However, the ground-level neutron monitors, sensitive to solar protons above 1 GeV, did not detect any effect during November 8, 2000. Moreover, the energy spectrum of solar protons, measured at the maximum time profile of the event, as obtained by spacecraft and balloons, when extended to energies of 40 GeV, gives an expected flux ~within 1.8×10 ⁻¹⁵  cm^-2 s^-1 sr^-1 and 3.4×10 ⁻⁹ cm^-2 s^-1 sr^-1, i.e. by 6-13 orders of magnitude lower than the authors of the article report.

The authors' discussion about the reasons for the lack of registration of the November 8, 2000 event by neutron monitors (lines 266-271) is not convincing. If we assume that the proton flux recorded by L3 lies on the continuation of the spectrum from the fluxes at E>500 and E>700 MeV recorded by GOES, then the expected proton fluxes at energies of ~1 GeV, measured by NM, would be of the order of 0.02 cm^-2 s^-1 sr^-1. Such fluxes would most certainly be recorded by a network of neutron monitors, which covers a wide range of asymptotic directions of particle arrival. In the event of January 6, 2014, mentioned by the authors on line 271 the proton flux was I(>1 GeV)»0.01 cm^-2 s^-1 sr^-1.

The L3 collaboration has already published a similar result related to the July 14, 2000 solar event, when an upper flux limit of  I(Ep≥40GeV) ≤2.8×10 ⁻³cm⁻² s^-1 sr^-1 was reported [L3 collaboration, A&A 456, 351–357 (2006)]. The results were supported by the theoretical upper limit fluxes [Miroshnichenko, 2002] and the observation of ~500 GeV protons by Baksan installation [Karpov et al., 1998]. The Baksan results were neither confirmed nor discarded by the recent works. The upper limit as defined by Miroshnichenko, is sufficiently higher than the solar proton fluxes observed by neutron monitors in the solar event of July 14, 2000 [Mishev and Usoskin, 2016, https://doi.org/10.1007/s11207-016-0877-2]. 

The results of solar proton observation for the both events can be found in http://www.wdcb.ru/stp/data/SPE/Catalog_SPE_23_cycle_SA.pdf.

Thus, the solar protons (E~40 GeV) fluxes discussed in the given paper cannot be reconciled with the commonly accepted paradigm of the solar proton generation. This discrepancy indicates different mechanisms of acceleration, or conditions in the field of acceleration. The presence of such possible circumstances is evidenced by data on high-energy gamma radiation of solar origin (for example, Pesce-Rollins, 2018, PoS(IFS2017)173), which does not correlate with flare X-ray radiation accompanying ordinary solar events in energetic particles.

I believe the article should be published. However, the existence of sufficiently large fluxes of solar protons with an energy of tens of GeV does not fit into the modern paradigm of particle acceleration on the Sun. This should be explicitly stated. The source of such particles must be special processes on the Sun.

Minor comments

The PDF version used in the article does not allow copying individual phrases, which creates inconvenience when writing a review. Therefore, I use only line numbers for comments.

Lines 18-20. This definition of SPE is used only by the NOAA SPE list. Actually, the solar proton flux may be much lower.

Line 25. Now 74 GLEs were recorded.

There are many spelling errors in the manuscript. It must be edited by a native English-speaking person.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

   This paper includes a very important scientific result, so this paper should be published.  However, still some fine modifications are necessary.  Because the contents include an essential fact on solar cosmic ray physics, so the paper should be presented under better way.

(1) First point: I found a problem in the data themselves provided in the line 174-184.

Figure 3a shows that the background counting rate is estimated as to be 400/bin. One bin corresponds to 8.39 minute.  On the other hand, the horizontal axis of Figure 4 is presented as the number of muons in 8.39 seconds.  However the average number is 535/bin.  Then, the duration of one bin of Figure 3a should be 60 times (one minute) higher than 8.39 seconds.  Why the numbers 500 are as close as 400 ?   In figure 4, the authors gave the RMS as 20.85.  So 20.88×20.88=423.  This value is close to value of the background presented in Figure 3a.  Please fix this difference between 400 and 535.

  According to the value of Figure 3a, the statistical significance is estimated as to be 4.1 σ by the Li-Ma method, i.e., (490-400)/ √400+90=4.1.  Then, the chance probability is ~0.1% and your estimation is correct.

(2) Second point on the line 220-222.

  The authors have written as follows: about 90% of recorded muons are produced by primary protons with the energy range from 40 GeV to 200 GeV and the most probable energy is around 74 GeV.

   I think that this estimation maybe either in-correctly given or incomplete. 

Suppose a very simple interaction process; protons with energy 400 GeV enter into the atmosphere.

They make nuclear interactions with the inelasticity 0.5.  Then, half of the primary energy is transferred to the secondary particles.  Pions with energy of almost all secondary energy is very rare (see LHCf experiment for example).  So most pions are produced with the energy of X_F=0.1~0.2, or 20~40 GeV.  The L3 has a nice spectrometer that can select only high energy muons above 40 GeV.  So in principle, 400 GeV protons will be not mainly detected by your muon detector.  This implies what you have found is much more important fact, i.e., the highest solar particles (SEP or SCR).  If you cannot believe this statement, please investigate early works on the treatment of secondary muon production process analytically in the paper of 1972 by Phys. Rev. (Fraser et al.) or the 1981 ICRC paper on MN session by (Jacob et al.).  I recommend that you had better present the CORSIKA results including the various energy spectrum of primary protons by an additional figure.

   Once the highest energy SCR (SEP) events were reported by the Baksan Carpet array group.  But on their events, the time difference were quite long.  But in your event, the evidence is much clear that they were produced by the solar flare, correctly speaking, by the shock acceleration process in the CME.

3) Minor English problem: line 7;   4.7 à 4.1σ

 Line 22; particles cascade à particle cascade

Line 27; incident protons coming from all acceptance at ground level à incident protons at ground level

Line 44 and 46 SPE of non GLEs à SPE without GLEs

Line 202; 4.7σ à 4.1σ excess

Line 205; I can understand 9, but 5, what does 5 mean?

Line 232; What does molasses mean?

Line 250; 450 angle à 45°

Line 277; Remove Up to now.  à until that day?

Author Response

Please see the attachment

Author Response File: Author Response.docx

Reviewer 3 Report

This paper discusses the possibility of proton acceleration above 40 GeV in the M-class flare of November 8, 2000, based on muon observations. This would be quite interesting if this result is true, but to prove that this is the case, I think you would need to either show that there was proton acceleration up to 40 GeV with other information or prove why simulations did not observe any aspect of proton acceleration in other observations (such as GLE).

Also scattered throughout this paper are incorrect English articles or numbers with no units. Units are also written differently in different places. I recommend that you check your manuscript again in detail and submit it for English editing.

Major Comments:

Section 2 (Line 69-83):

It is better to show the time series of each radiation and particle data described in this paragraph here as Figure 1 instead of Figure 3. Since most of the data should be open, it would be easier to show the data in a clear way where it is difficult to understand only by text.

About muon direction (Section 3, Fig.2, Fig.6):

The method of identifying the direction during muon observations is explained in equation in chapter 4.2, but it is not clear from the text how the direction is determined in the instrument. This should be described in detail, e.g., in Chapter 3.

The contour values in Fig. 2 are not shown. It is not clear where the direction of the Sun is in Fig. 2. Also, there is a solid black circle, but there is no explanation for this.

There are 110 cells in Fig. 6, but it is not clear which 59 cells are used for this study.

Section 5:

Even if NM is not sensitive to ~74 GeV accelerated protons, it is hard to understand why relatively low-energy solar protons that are sensitive to NM are not observing. If there are indeed high-energy protons that produce muons, then there should be an order of magnitude greater number of low-energy protons with energies observable with NM. What do you consider the spectral and directional distribution of solar protons on the low energy side? Also, can this be shown by simulation?

The proton beam flux estimated here is sought to be of the same order as the Bastille event, but no reason is given why the GLE should not be observed with such a large proton beam flux.

Minor Comments:

Line 7: 4.7 muon excess -> 4.7 sigma muon excess

Line 10: a Class M -> an M-class

Line 17: (SFs) <- This abbreviation has never been used after this, so there is no need to abbreviate it. It should be deleted.

Line 21-24: Clearly describe that not all SPEs cause GLE.

Line 25: [2] <- Since this site only has data on NM in Oulu, it seems inadequate as a citation.

Line 30: pro-ton -> proton

Line 33: This reference does not present observations of accelerated protons from the Sun above 100 GeV.

Line 38-40: Provide references showing these phenomena.

Line 71: 23:38 UT <- This time is later than the flare peak time of the M7.4 class flare, is this time correct?

Line 165-166: 8.39-min live-time window <- This time is not a multiple of 83.9 seconds, but why are we using these time bins?

Line 250: 450 angle <- The angle is more than 360 degrees, but where is the reference point?

Author Response

Please see the attachment

Author Response File: Author Response.docx

Round 2

Reviewer 3 Report

I understand that it is difficult this paper to prove that GLE and other signals are not observed in NM. I look forward to future research.

There were a few minor errors, so please check the manuscript again.

Line 7: sigma -> σ

Line 42 [21-26] -> [21-26].

Line 71: [230] -> [23]?

Author Response

Dear Reviewer,

Manuscript ID: (universe-1681602) Title: GeV proton detection in the 2000 November 8 solar event.

We greatly appreciate your careful review for the last version. We are pleased with your understanding of this article now. Further study results are expected for this special event.

Thanks!

Ruiguang WANG

There were a few minor errors, so please check the manuscript again.

Reply: ok, thanks!

1. Line 7: sigma -> σ

        Reply: modified

2. Line 42 [21-26] -> [21-26].

       Reply: modified

3. Line 71: [230] -> [23]?

       Reply: modified. [230] -> [23]

Author Response File: Author Response.pdf