Constraining the Location of γ-Ray Flares in the Flat Spectrum Radio Quasar B2 1633+382 at GeV Energies

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This paper presents a detailed analysis of several major flaring epochs of the FSRQ 4C 38.41. The paper shows 7-day bin and 1-day bin light curves, variability analysis, spectral analysis of the Fermi data, and some theoretical considerations of the gamma-ray emission region and mechanisms.

Overall, the paper clearly shows some hard work by the authors and is nicely presented. However, it lacks scientific merit, as Fermi Light Curve Repository (LCR) has effectively half of the main content of the paper already reported. Since the paper also uses the standard Fermi tools for the analysis, the difference from the LCR is minimal. 1-day bin light curve has too bad statistics to show anything new or important.

Section 3.1 presents the light curves, which is nearly identical to the LCR data. Worse, Figure 1 caption is wrong, as the light curve here only extends to 2019/2020, not to 2022. Section 3.2-3.4 analyzes the variability properties, which are indeed not present in LCR. But these analyses are very simplified, and do not provide considerable physical insights. Section 4 shows the spectral analyses, including both log-parabola and power-law fittings. But LCR has power-law index for every data point, not just the average of the four major flaring epochs. Section 5 presents very basic theoretical estimates, which have limited scientific impact either.

Therefore, I do not recommend this paper for publication at this stage. The authors should try additional analyses and/or modeling. While the paper clearly does not suffer from plagiarism, it does not offer much more than LCR.

Author Response

We sincerely thank you for carefully reading our manuscript and providing the valuable suggestions that help us improve the manuscript. Based on the referee's suggestions, we have revised our manuscript, including the language and language logic of the whole paper. We also added the discussion of the results from broadband SEDs modeling (Please see Section 5 and Section 6.1, and see Figure 1\&2). Based on some useful discussions from Fan Wu, Nan Ding, we added them as an author of the paper. We have carefully checked both spelling and grammar errors of the whole paper following your suggestions. Please find the attachment. 

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Minor:

1. Abstract: in lines 2 and 3 you mention the gamma-ray light curve.  Is there any information about how many outburst periods there are in the optical?
2. Line 4, reword “observed hours scale variability”. This is confusing written this way.
3. Line 10, “maybe” should be rewritten as “may be”
4. Line 23, eliminate “which”
5. Line 211, instead of “cann’t” write “cannot”
6. Line 308, should read, “The study of both …”
7. Line 312, replace “don’t” with “does not”
8. Line 316, begin with “In this work, …”
9. Line 340, “maybe attribute” should be rewritten as “may be attributable”
10. Line 341, “ruled” should be changed to “rule”
11. Line 342, “suggest” should be changed to “suggests”
12. Line 343, “maybe” should be rewritten as “may be”

Major:

1. Abstract (line 14) and elsewhere, you should consider what optical variability may say here. Perhaps it, too, would be due to reconnection, or perhaps by another mechanism, but this needs mentioning especially when considering various models for gamma-ray outbursts.
2. Line 35, here you mention the possible binary supermassive black hole of 1633+382, but fail to mention a much more investigated and confirmed binary black hole of OJ 287. You need to mention this with a reference.  (I would suggest any articles by Mauri Valtonen.)
3. Line 47. This would be a good place to describe reverberation mapping, the technique of cross correlating light curves of different frequencies to see how an outburst propagates along the jet, if indeed it does that.
4. Equations 1 and 2. Both are useful and viable models.  You need to write a sentence or two for each to motivate as to why that model might be used.

Comments on the Quality of English Language

Editing for grammar and style is recommended.

Author Response

We sincerely thank you for carefully reading our manuscript and providing the valuable suggestions that help us improve the manuscript. Based on the referee's suggestions, we have revised our manuscript, including the language and language logic of the whole paper. We also added the discussion of the results from broadband SEDs modeling (Please see Section 5 and Section 6.1, and see Figure 1\&2). Based on some useful discussions from Fan Wu, Nan Ding, we added them as an author of the paper. We have carefully checked both spelling and grammar errors of the whole paper following your suggestions. Please find the attachment. 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

This paper has very limited scientific merit, and even after adding the SED fitting, it is not much improved. Same issues remain although with some small improvements:

1. LCR has exactly the 7-day binned data and spectral data, which is nearly one third of the main results of this paper.
2. The 1-day binned data presented here has too large error bars to constrain any physics.
3. The variability analyses, based on the 1-day binned data, have, as expected, very large error bars. If the error bars in many cases as large as the data point, as shown in Table 2, they are not reliable.
4. The newly added SED fitting is useful, but it is also flawed in two parts. First, the ~GHz emission is most likely strongly synchrotron self absorbed, and it should originate from the large-scale jet instead of the blazar zone. By closely fitting the data points, the paper effectively overestimates the blazar zone contribution, even if their code includes SSA. This is because the blazar zone contribution plus a large-scale jet contribution will then overshoot the data. Second, the fitting quality in the optical and X-ray bands are questionable. MCMC does not guarantee a good fitting, given that the radio points are not supposed to be fit and the optical and X-ray data points include many asynchronous data points.
5. But the addition of the SED fitting does help to provide slightly better insights on physical parameters than the previous version. Given that the paper insists on very simplified theoretical estimates and discussions, it is fine to proceed with that.

While I agree that the paper appears to have put considerable efforts, the scientific merit is quite limited. I would suggest the authors to consider more detailed data collection and analyses, for instance but not limited to: 1. multi-wavelength data; 2. variability correlation; 3. multi-wavelength spectral evolution trends such as harder-when-brighter; 4. polarization; 5. more detailed spectral modeling. The 1-day binned data, though clearly extra work on top of the LCR, has too bad quality to constrain physics. And the main goal of the paper, which is in the title, constraining the location of gamma-ray flares, is far from achieved with the present paper.

 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf