Superluminal Motion and Jet Parameters in the Gamma-ray-Emitting Narrow-Line Seyfert 1 Galaxy TXS 1206+549

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The authors present analysis of the VLBA monitoring data on the jet in the active galactic nucleus of the narrow-line Sy1 galaxy TXS 1206+549. Between 2011 and 2019 a superluminal jet clump motion is detected at 8 GHz. The intrinsic parameters of the jet are calculated, including the jet inclination to our line of sight. It has appeared to be around 24 deg that is too large to classify TXS 1206+549 as a blazar (or as a future blazar). It is a very interesting result. If being supported later by studies of similar NLS1 radio-loud objects, this result can exclude possible evolutionary relation between NLS1 and blazars that is extremely important for exploring the evolution of AGN.

Comments on the Quality of English Language

I have found only one misprint - at the 103rd line, a word 'calibratated'.

Author Response

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Reviewer 2 Report

Comments and Suggestions for Authors

The paper investigates the mas structure of the gamma-ray emitting NLS1 galaxy TXS 1206+549 (also classified as a FSRQ blazar in the literature), as mapped by 8 GHz VLBI multi-epoch data, with the goal of evaluating the transverse motion of the jet components and estimate its proper motion speed, the Doppler factor, the bulk Lorentz factor and the jet viewing angle.

From the innermost ~ 1 mas structure motion the authors estimate an apparent transverse speed of 3.5 c, and from the brightness temperature they estimate a Doppler factor of 2.2, leading to an estimated bulk Lorentz factor of 4.1 and a jet viewing angle of 23.5 degrees.

These values challenge the source classification as a FSRQ blazar, but the authors suggest that the jet is likely to bend at larger scales with respect to the mas scale investigated by VLBI data, leading to the larger bulk Lorentz factors and smaller jet viewing angles reported in the literature that are suggestive of its blazar classification.

The paper is interesting and straightforward, I only have some very minor comments for the authors before the paper can be considered for publication on Galaxies.

Detailed comments follow: --------------

1) Sect. 1, line 39. I suggest the authors to mention that most radio-loud jetted AGNs are gamma-ray emitters.

2) Sect. 4, line 223. “our characteristic brightness temperature determined”  -> “the characteristic brightness temperature that we determined”

 

Author Response

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Reviewer 3 Report

Comments and Suggestions for Authors

In the current work, the authors present an analytical study of NLS1 galaxy TXS 1206+549 regarding the issue of superluminal motion and jet properties.

In recent years, more and more people have found it interesting that the NLS1 exhibit unique observation characters and challenges the conventional AGN unification.

The authors have analyzed archival high-resolution VLBI data at 8 GHz in six epochs between 1994 and 2018, found an apparent superluminal jet component with speed of ~3.5c and further constrained the Doppler factor, Lorentz factor, and viewing angle. This is a regular observation study paper, the paper is well structured and the results are properly presented and discussed.

I recommend this manuscript be accepted for publication after a minor reversion. Moreover, this topic deserves to be explored more, I will be glad if the authors are willing to address such a study on more NLS1 in the future.

Minor：

1. Line 168, ‘seems to coincide with a major outburst indicated by the high core flux density in 2017’. I think this statement is improperly stressed, because the brightness temperature is calculated through flux, thus a higher brightness result from a higher flux density is evident not a coincidence, unless you can calculate brightness temperature independently.

2. I would suggest the authors provide a lower and an upper for the Doppler factor through the corresponding lowest and highest brightness temperature, this would help the authors to make a comparison between the Doppler factor from this work and those from previous works. Note that for the highest brightness temperature (also the highest flux density), you may have to use the intrinsic brightness temperature from Readhead et al. (1994) (5 * 10^10 K).

3. As the authors know, the Doppler factor is estimated by many methods. In this work, a median brightness temperature was employed during the calculation of \delta and consequently determined the viewing angle. You may need to mention that if you employ the highest brightness temperature and obtain a larger Doppler factor, and thus a smaller viewing angle, this source could possibly show a blazar-like viewing angle. 

4. Can you provide insights on possible evolution among Radio-loud AGNs, RL-NLS1s, and Radio-quiet AGNs?

 

Author Response

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