Demonstration of Ultrawideband Polarimetry Using VLBI Exploration of Radio Astrometry (VERA)
, Kazuhiro Hada 3,4, Mieko Takamura 3,5, Tomoaki Oyama 3, Aya Yamauchi 3 and Syunsaku Suzuki 6Round 1
Reviewer 1 Report
This paper describes the recent technical developments performed at the antennas of the VLBI Exploration of Radio Astronomy (VERA) array, which made possible to conduct wide-band polarisation observations at 22 GHz and 43 GHz. The authors briefly describes these technical developments and present results from the first commissioning observation, focusing on three calibrator sources.
These technical developments of the array are of certainly interest to its current user base, but also for the wider (radio) astronomical community as it can allow to study new scientific fields with the instrument and thus can widen the user base as well. In this regard, it is important to demonstrate the new capabilities of the system which is done in this manuscript by presenting results from the commissioning observations.
This is an important work and it should be published after some minor corrections of the text. I give my suggestions below in order of their appearance in the text.
1. To make the paper useful to an audience not (yet) familiar with the VERA array, I suggest to include in the Introduction a map of the VERA array, so it is clear where the four antennas located with respect to each other.
2. I suggest to decide whether to use RHCP or RCP for the abbreviation of right circular polarization (and similarly for left circular polarization), and stick to this one abbreviation in the whole text.
3. Also if an abbreviation is getting introduced, than use the abbreviation in the subsequent text. E.g., LNA for low-noise amplifier is introduced in line 31 and again in line 50.
4. I suggest to avoid using the notation of K band and Q band and stick to the 22 GHz band and 43 GHz band description so as to make the content clearer for a reader not familiar with band naming conventions.
5. In section 3 Observations, where D-terms first mentioned (line 84), I suggest to very briefly introduce what D-term is (mixing of polarization signals, or leakage of polarised signals between polarization channels). E.g. write "polarization leakage terms (D-terms)". Then in subsequent text, it can be referred to as D-terms.
6. In the observation section, or in Table 2, I would indicate which sources were calibrators and which are target sources. In this particular, case calibrator sources are more relevant, so there is no need to include the list of targets in the text.
7. For the AIPS software package (line 89), I suggest to include the following reference: https://ui.adsabs.harvard.edu/abs/1990apaa.conf..125G/abstract
8. For the Difmap package (line 95), I suggest to include this reference: https://ui.adsabs.harvard.edu/abs/1997ASPC..125...77S/abstract
9. Section 4 Data reduction: Although, it is not strictly relevant to the topic of this work, I think it would be still useful to state whether phase and/or amplitude self-calibrations were performed for the total intensity mapping of the calibrators in Difmap.
10. In table 3, the authors can include the three letter abbreviations of the different stations, which are currently used in Figure 3.
11. In the caption of Figure 3, open and filled symbols are mentioned however, there are only filled symbols in the plots (I suspect the caption of a previous plot version remained there by accident). This has to be corrected.
12. Section 5.2 D-terms: I wonder if it is possible to include some reference to D-term values obtained in similar bands for other arrays, e.g. VLBA, so the VERA ones can be compared to other ones.
13. Line 130: use either "show" or "present".
14. Figure 5 images of calibrators: I suggest to set the contour levels of the total intensity maps in a way, that the rms noise level of the images can be easily seen, e.g., include one negative contour. Also indicate in the caption (or in a separate table) the details of the images, peak intensity, beam size, value of the lowest contour. I also feel that the color scale can be somewhat adjusted as there are no pixels with yellow colors (the maximum polarised intensity), thus the maximum value can be lowered.
15. Section 5.3 (or possibly mention this in data reduction part): I would prefer to read a bit more details on how the polarization (color) images were created, e.g. at what noise levels were the polarization signal disregarded in the images.
16. In Section 5.3, line 139 and so, the authors give the fractional polarization values, it would be useful to give the total intensity flux densities with errors, together how they were obtained, e.g. fitting the visibilities or the images, or summing up clean components etc.
17. In line 143 the reference is missing for the unpolarization of 3C84.
Finally, I wonder whether there is any plan to monitor the polarization at 22 and 43 GHz of possible calibrator sources to facilitate EVPA calibration in the future. If there is, it can be mentioned in section 6.
Author Response
A reply to the Referee Report
Revised manuscript for
“Ultra-wide band polarimetry using VLBI Exploration of Radio Astrometry”
(Hagiwara et al.)
Comments and suggestions in the Referee Report are all considered and answers are given below by indicating “=>”.
The revisions were indicated in bold types.
We thank you very much for considerable comments that certainly improved our manuscript.
Referee 1:
==============
(x) I don't feel qualified to judge about the English language and style
=> The language editor went through the revived manuscript.
1. To make the paper useful to an audience not (yet) familiar with the VERA array, I suggest to include in the Introduction a map of the VERA array, so it is clear where the four antennas located with respect to each other.
=> Added a figure 1, for an introduction of VERA array for readers who are not familiar with the VERA
2. I suggest to decide whether to use RHCP or RCP for the abbreviation of right circular polarization (and similarly for left circular polarization), and stick to this one abbreviation in the whole text.
=> Yes, we agree. We take only RCP or LPC throughout this article. RHCP and LHCP have be taken out form the text.
3. Also if an abbreviation is getting introduced, than use the abbreviation in the subsequent text. E.g., LNA for low-noise amplifier is introduced in line 31 and again in line 50.
=> Again, we agree that the abbreviation should be used once after it is defined in the text. Please take a look into the revised text.
4. I suggest to avoid using the notation of K band and Q band and stick to the 22 GHz band and 43 GHz band description so as to make the content clearer for a reader not familiar with band naming conventions.
=> Also, we agree that K/Q-band should be replaced with 22/43 GHz band. Please see the revised text.
5. In section 3 Observations, where D-terms first mentioned (line 84), I suggest to very briefly introduce what D-term is (mixing of polarization signals, or leakage of polarised signals between polarization channels). E.g. write "polarization leakage terms (D-terms)". Then in subsequent text, it can be referred to as D-terms.
=> We re-wrote as polarization leakage terms (D-terms) as suggested above.
6. In the observation section, or in Table 2, I would indicate which sources were calibrators and which are target sources. In this particular, case calibrator sources are more relevant, so there is no need to include the list of targets in the text.
=> In a revised Table 2, target sources and calibrators were separately accommodated. Please see Table 2.
7. For the AIPS software package (line 89), I suggest to include the following reference: https://ui.adsabs.harvard.edu/abs/1990apaa.conf..125G/abstract
8. For the Difmap package (line 95), I suggest to include this reference: https://ui.adsabs.harvard.edu/abs/1997ASPC..125...77S/abstract
=> The references for AIPS and DIFMAP above have been included.
9. Section 4 Data reduction: Although, it is not strictly relevant to the topic of this work, I think it would be still useful to state whether phase and/or amplitude self-calibrations were performed for the total intensity mapping of the calibrators in Difmap.
=> Right. The sentences below that explain how phase calibrations were performed are added.
“CLEAN imaging of Stokes I, Q and U were performed in DIFMAP. To correct antenna gains, self-calibration of both phase and amplitude was performed using the Stokes I data set. “
10. In table 3, the authors can include the three letter abbreviations of the different stations, which are currently used in Figure 3.
=> The three letter abbreviations are newly added to the table. Please see a revised Table 3.
11. In the caption of Figure 3, open and filled symbols are mentioned however, there are only filled symbols in the plots (I suspect the caption of a previous plot version remained there by accident). This has to be corrected.
=> Figure 5 ,6 (former Figure 3) using larger symbols have been revised along with a figure caption. Please see them.
12. Section 5.2 D-terms: I wonder if it is possible to include some reference to D-term values obtained in similar bands for other arrays, e.g. VLBA, so the VERA ones can be compared to other ones.
=> We added references of D-terms for VLBA (Gomez+ 2002) and KVN (Park+ 2018) , with a sentence commenting on the different D-term values from ours.
13. Line 130: use either "show" or "present".
=> Right! We take “show”.
14. Figure 5 images of calibrators: I suggest to set the contour levels of the total intensity maps in a way, that the rms noise level of the images can be easily seen, e.g., include one negative contour. Also indicate in the caption (or in a separate table) the details of the images, peak intensity, beam size, value of the lowest contour. I also feel that the color scale can be somewhat adjusted as there are no pixels with yellow colors (the maximum polarised intensity), thus the maximum value can be lowered.
=> The contour levels are plotted from 3 sigma to show the quality of the imaged instead of a negative contour. Additionally, some details of the images ( ms or peak flux values) are newly added to each panel.
15. Section 5.3 (or possibly mention this in data reduction part): I would prefer to read a bit more details on how the polarization (color) images were created, e.g. at what noise levels were the polarization signal disregarded in the images.
16. In Section 5.3, line 139 and so, the authors give the fractional polarization values, it would be useful to give the total intensity flux densities with errors, together how they were obtained, e.g. fitting the visibilities or the images, or summing up clean components etc.
Comments on 15 and 16 are somehow related, so we reply together.
=> To explain how we estimated flux errors etc, we added equations (1-2), and sentences in Sec 5.3.
=> We newly made Table 4 to show total intensity flux densities, linear polarization densities, fractional polarization, and their errors. Please take a look into the new table.
17. In line 143 the reference is missing for the unpolarization of 3C84.
=>Added a reference for Taylor et al. 2006, along with a sentence below.
“On the other hand, the nucleus of radio galaxy 3C84 is well known as a very weakly polarized source at these frequencies.”
Finally, I wonder whether there is any plan to monitor the polarization at 22 and 43 GHz of possible calibrator sources to facilitate EVPA calibration in the future. If there is, it can be mentioned in section 6.
=> in Section 6, added a sentence below with a reference on the KVN EVPA monitoring of Kang et al. 2015 and
“With the KVN, both single-dish and VLBI monitoring 188 observations of the polarization of blazars at 22 and 43 GHz are being conducted, which 189 will enable to facilitate EVPA calibration for polarimetric observations using VERA or a 190 combined array observation with KVN and VERA (KaVA) in future.”
Reviewer 2 Report
Reviewer Report for Manuscript Entitled:
Ultra-wide band polarimetry using VLBI Exploration of Radio Astrometry
The authors reported on the conducted technical developments of front- and back-end for four 20-m radio telescopes of VLBI Exploration of Radio Astrometry (VERA). The topic and results are interesting but the presentation and literature review need improvement. Below, please find my comments.
Line 2. Please define acronym VLBI and add sentence at the beginning of the manuscript to highlight why this research is important and give motivation to readers.
Lines 12 and 13. The definition of VLBI should come first. One full paragraph is needed here to discuss VLBI and applications. Its different types and applications need to be generally discussed in the first paragraph. Please include the following four articles when describing this:
https://doi.org/10.1088/1538-3873/abcc4e
https://doi.org/10.1007/s00190-016-0950-5
https://doi.org/10.1016/j.jog.2012.07.007
https://doi.org/10.1117/12.390461
Lines 68-87. Please elaborate on the type and source of noise in the observations. Please refer to the first article that I mentioned above for VLBI. I suggest also to show an time series example of the VERA measurements with their error bars.
Figures 3 and 4. Please enlarge the numbers and texts in these figures. Your Figure 5 has good font size, and it is appreciated.
Lines 147,148. Please join this sentence to the next paragraph. Please note that a paragraph should at least have two sentences. Please check the entire manuscript and check and correct this issue.
Line 173. Please insert a comma after “was designed”.
Please mention the limitations/assumptions of the study in the Conclusions.
Please follow the MDPI guideline for format and style of references.
Thank you!
Author Response
A reply to the Referee Report
Revised manuscript for
“Ultra-wide band polarimetry using VLBI Exploration of Radio Astrometry”
(Hagiwara et al.)
Comments and suggestions in the Referee Report are all considered and answers are given below by indicating “=>”.
The revisions were indicated in bold types.
We thank you very much for considerable comments that certainly improved our manuscript.
Referee 2:
==============
(x) Moderate English changes required
=> The language editor went through the revived manuscript. Please check texts in the manuscript.
Line 2. Please define acronym VLBI and add sentence at the beginning of the manuscript to highlight why this research is important and give motivation to readers.
=> Revived the acronym in abstract. Also, a sentence is added (see below) for justifying our technical development.
The wider band 5 VLBI observations not only improve the sensitivity of VLBI observations for both continuum and 6 spectral line emission, but also enable to study the magnetic fields of relativistic jets ejected from 7 super massive back holes in active galactic nuclei and in sites of star-formation and evolved stars 8 at unprecedented sensitivity.
Lines 12 and 13. The definition of VLBI should come first. One full paragraph is needed here to discuss VLBI and applications. Its different types and applications need to be generally discussed in the first paragraph. Please include the following four articles when describing this:
https://doi.org/10.1088/1538-3873/abcc4e
https://doi.org/10.1007/s00190-016-0950-5
https://doi.org/10.1016/j.jog.2012.07.007
https://doi.org/10.1117/12.390461
=> At the beginning of Sec 1., added a VLBI introductory paragraph including the references above. Please take a look.
Lines 68-87. Please elaborate on the type and source of noise in the observations. Please refer to the first article that I mentioned above for VLBI. I suggest also to show a time series example of the VERA measurements with their error bars.
=> Added about the descriptions of the sources of errors in Sec 3.
=> In Figure 4, plots of delay solutions, are newly included for showing
“time series example of the VERA data”.
Figures 3 and 4. Please enlarge the numbers and texts in these figures. Your Figure 5 has good font size, and it is appreciated.
=> Figures 5 and 6 (former figures 3 and 4) are re-created using larger symbols and numbers.
Lines 147,148. Please join this sentence to the next paragraph. Please note that a paragraph should at least have two sentences. Please check the entire manuscript and check and correct this issue.
=> Done.
Line 173. Please insert a comma after “was designed”.
=> Done.
Please mention the limitations/assumptions of the study in the Conclusions.
=> Included a entence on the “limitation” in Summary, like below.
“With the current front-end configuration, the recording rate can be extended up to 32 201 Giga bit s−1 . The ultra-wide band observation needs the recording rate expansion of 202 other VLBI stations or arrays, such as KVN. “
Please follow the MDPI guideline for format and style of references.
=> You are right. References are revised, following the format of the MDPI.
Thank you!
=> We appreciate you for many useful suggestions and comments !
