Low-Energy Cosmic Rays and Associated MeV Gamma-Ray Emissions in the Protoplanetary System

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

 

Report on manuscript universe-3112690

“Low-energy Cosmic Rays and Associated MeV Gamma-ray Emissions in the Protoplanetary System”

This review aims to study the low energy cosmic rays as an important component in understanding the mechanism of our planetary system. The authors propose a study to use gamma-ray emissions to infer LECR properties. The paper is interesting and well written. It has the potential to be published but after revision. I would like the authors to address the following issues:

Main Comments:

-        L.5: the sentence is not really clear. “these gamma ray emissions” it is the first time to mention gamma ray emission. Please revise.

-        L.20: “1 GeV per nucleon” I believe the entire GeV range is considered as low energy cosmic rays.

-        In this first paragraph in the introduction, the authors defined cosmic rays as high energy particles and then jumped directly to talk about low energy cosmic rays. It would be beneficial to add some discussion about the high energy cosmic rays first, and then move on to discuss low energy and its importance for the study. Here are some examples from high energy cosmic ray measurements:

o   https://doi.org/10.1016/j.astropartphys.2012.11.003

o   https://doi.org/10.1016/j.astropartphys.2013.01.016

o   https://doi.org/10.1088/0004-637X/765/1/55

o   https://doi.org/10.1088/0004-637X/746/1/33

-        L62: “which may shed light”: How? please elaborate more here because this is the motivation of the study.  

-        Equation 1: I am not sure the equation is correct. What is this 1/3 factor? Please check the reference of the Parker equation!

-        L80: LHS? This abbreviation is mentioned one time in the article. Better to write the full name and add it to the abbreviation table at the end.

-        Figure 1: the behaviour of flux is different at 0.33 AU! Please elaborate on potential reasons.

-        L210-216: this belongs to the outlook section!

-        L206: You need to expand the discussion of Figure 3

 

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Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This paper deals with the results of interactions between incoming low energy galactic cosmic rays and a protoplanetary system.  The galactic environment is taken to have properties like those found outside our own heliosphere, although this clearly varies considerably through our galaxy.  With a simple system model, the penetration of cosmic rays into the system is studied, as are their subsequent interactions to produce gamma-rays which could be observed as indicators of the physical state of the system.  The work is a simplified version of propagation calculations which have been familiar for many years.  However, its study of gamma-ray lines is particularly interesting.  This work is not definitive, it uses many assumptions (the authors recognise this), so it is a pilot study which, one hopes, the authors will continue to develop.

Major simplifications in this work are in the diffusion coefficient, which does not represent the many spatial variations in density and magnetic field to be found in a protoplanetary system, the protoplanetary system model (sometimes described as a disk but is modelled as a sphere), and the detailed effect of the change in the cosmic ray spectrum with distance (depth) travelled into the system.  It is assumed that the system itself does not accelerate particles (CMEs are mentioned but the system rotates and other acceleration is possible).  Calculations which attempt to include these issues have been performed over the years for the heliosphere in terms of the solar rotation and the solar cycle and, more recently, for pulsar wind nebulae.

The work has produced results which look to be reasonable, so there are no obvious problems with the approach, although the use of the Parker equation may prove challenging as the work further extends to more complex scenarios.  In equation (4) the diffusion coefficient is expressed in terms of energy density (units unclear) to the power of (1-gamma), we are then told that gamma=1 so the index is zero.  Is this intentional?  The composition of the cosmic ray beam is unclear and some results depend on this such as in figure 1 (the relationship of this to the data in table 1 wasn't clear to me - does the composition change within the system?).  In page 5, there is mention of broad and narrow gamma-ray lines.  This is important in the paper and the origin of these two effects should be expanded on.  In page 6, we have mention of the continuous gamma-ray component, we should have some discussion of how this is calculated.

Many of these future issues are usefully identified at the end of the discussion section and one hopes to see more realistic results in future work.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf