Review Reports - Swift/UVOT: 18 Years of Long GRB Discoveries and Advances

Round 1

Reviewer 1 Report

The paper “Swift/UVOT: 18 years of long GRB discoveries and advances” is a review of the best results obtained by Neil Gehrels Swift Observatory (Swift) that has been collecting data for 18 years. In my personal opinion this paper is clear, well written and deserves to be published in the present form. I would suggest only few minor corrections:

- Chap. 4. Swift/UVOT long GRB discoveries. I would suggest to add a deeper comment on the long GRB discoveries, stressing the scientific framework before the data collected by Swift and nowadays.

- line 366: … can be constructed in a similar way…

Pag. 12, Figure 5: I think the content and the problems treated by this figure needs more comments and analysis in the text too.

Par. 4.4.4 Jet Breaks. Is it possible to deep the discussion about the jet breaks, stressing what could be inferred from Swift observation?

Par 4.4.5 After Glow luminosity: I think Swift observations represents an unique opportunity to contribute clarifying many questions about after glows. Could you add some comments and make a wider analysis with respect to the GRB Hubble diagram?

5. Conclusions. Conclusions, for such a long paper, are a bit poor! I would suggest in this paragraph to stress again the success of Swift campaign, which are the still open problems and what, according to the author, could be the future developments.

Author Response

- Chap. 4. Swift/UVOT long GRB discoveries. I would suggest to add a deeper comment on the long GRB discoveries, stressing the scientific framework before the data collected by Swift and nowadays.

>>I have expanded the second paragraph in this section to reiterate the scientific framework laid out in Section 2.2 and how Swift/UVOT observations have expanded this picture.

- line 366: … can be constructed in a similar way…
>> Corrected

Pag. 12, Figure 5: I think the content and the problems treated by this figure needs more comments and analysis in the text too.

>> I have expanded this section further, explaining what the different segments represent and giving the fraction of GRBs that fit into each category. I have also provided the results of the X-ray analysis for comparison. I have also discussed what this implies for the different emission processes producing the optical/UV and X-ray light curves.

Par. 4.4.4 Jet Breaks. Is it possible to deep the discussion about the jet breaks, stressing what could be inferred from Swift observation?

>> I have expanded the discussion on what can be inferred about GRBs from the jet break and opening angle of the GRB, including discussing the geometric corrected prompt emission energy and kinetic energy, implications for the rates of GRBs and the use of the geometric corrected prompt emission energy in the Ghirlanda relation.

>> I should have been clearer in this section that most of the work on utilising GRB afterglow correlations for cosmology has been done so far using the X-ray variants. Since the focus of this review is on discoveries using optical/UV observations and using these optical correlations is not well established as yet, I don't feel this section can be expanded further. Instead, I have clarified in the text that the work to use GRB correlations for cosmology mainly stems from the X-ray variants of these correlations and added further references.

>>I have expanded the conclusions section, I have discussed the success of swift, summarised the discoveries that have been made with swift and given some examples of open questions.

Reviewer 2 Report

Swift is an important space observatory for studying GRBs to monitor the afterglow in X-ray, and UV/Visible light at the location of a burst. It had made many important discoveries. In this paper, the author gave a comprehensive review of the 18 years of long GRB discoveries and advances by Swift/UVOT telescope. First, the discussion of the discovery and status of long GRBs before the launch of Swift is presented. Then, an overview of long GRBs observed with Swift/UVOT is shown. Last, the mechanism of the optical/UV emission is discussed. The paper is important and well written. A few places will need to be resolved for the paper to be considered for the Universe.

1. Section “Optical Flares”

In this subsection, the author discussed the detected optical flares by Swift/UVOT. However, no physical mechanism for flares is discussed. The possible mechanism of optical flares can be given, as shown in literature. Some statistical similarities between X-ray and optical flares have been found, which indicates a similar origin of them.

2. Section “Afterglow Luminosity and Correlations”

In this subsection, the afterglow correlations and possible cosmological applications are shown. I have two suggestions. First, for the origin of the restframe time at the end of

the plateau phase with the luminosity at the same time, a theoretical interpretation of this correlation is that it may be explained within the context of the standard fireball model through evolution of the microphysical parameters. Other physical models have been proposed, for example, the energy injection from a newborn neutron star (https://ui.adsabs.harvard.edu/abs/1998A%26A...333L..87D/abstract, https://ui.adsabs.harvard.edu/abs/2001ApJ...552L..35Z/abstract, https://ui.adsabs.harvard.edu/abs/2011MNRAS.413.2031M/abstract), and the jet core viewed off-axis model (https://ui.adsabs.harvard.edu/abs/2020MNRAS.492.2847B/abstract). For the first model, the plateau luminosity is inversely proportional to the timescale of energy injection, supporting the fact that the energy reservoir is almost a constant (https://ui.adsabs.harvard.edu/abs/2022ApJ...924...97W/abstract). This nearly constant energy of newly born magnetars supports the fact that they can be treated as a standard candle, which is similar to SNe Ia.

Second, some correlations in the prompt and afterglow emission are reviewed, please see https://ui.adsabs.harvard.edu/abs/2015NewAR..67....1W/abstract.

Author Response

1. Section “Optical Flares”

>> I thank the referee for pointing this out. Unfortunately, I had previously missed the Yi et al 2017 paper, which I hope was the paper that the referee was referring to. I have now updated the text to discuss also this, which points to similar behaviour in X-ray and optical flares and the potential common origin of internal emission process as a result of central engine activity.

2. Section “Afterglow Luminosity and Correlations”

In this subsection, the afterglow correlations and possible cosmological applications are shown. I have two suggestions. First, for the origin of the restframe time at the end of

the plateau phase with the luminosity at the same time, a theoretical interpretation of this correlation is that it may be explained within the context of the standard fireball model through evolution of the microphysical parameters. Other physical models have been proposed, for example, the energy injection from a newborn neutron star (https://ui.adsabs.harvard.edu/abs/1998A%26A...333L..87D/abstract, https://ui.adsabs.harvard.edu/abs/2001ApJ...552L..35Z/abstract, https://ui.adsabs.harvard.edu/abs/2011MNRAS.413.2031M/abstract), And the jet core viewed off-axis model (https://ui.adsabs.harvard.edu/abs/2020MNRAS.492.2847B/abstract). For the first model, The plateau luminosity is inversely proportional to the timescale of energy injection, supporting the fact that the energy reservoir is almost a constant (https://ui.adsabs.harvard.edu/abs/2022ApJ...924...97W/abstract). This nearly constant energy of newly born magnetars supports the fact that they can be treated as a standard candle, which is similar to SNe Ia.

>>I thank the referee for providing further references for explanations of the luminosity-plateau correlation. I have added them all to the text.

Second, some correlations in the prompt and afterglow emission are reviewed, please see https://ui.adsabs.harvard.edu/abs/2015NewAR..67....1W/abstract.

>> I have added further references and discussion on GRB prompt emission-afterglow correlations in the second paragraph of Section 4.4.5. I have also added the reference stated above in the jet break section and in the 'Afterglow Luminosity and Correlations' section.