Superluminal Motion and Jet Parameters in the High-Redshift Blazar J1429+5406

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

I find this paper to be a very well-written study of the radio jet of a high-redshift quasar. Such studies are important to the cosmological development of black hole systems with jets. I recommend publication after the authors address two minor points:

lines 61-62: It should be specified that the coordinates are in the J2000 system, despite that the name starting with "J" implies this.

lines 199-209: Stationary features are often attributed to standing shocks - "recollimation" shocks or oblique shocks. The latter can cause bends in jets, e.g. where the jet interacts with a cloud, as mentioned in the next paragraph of the paper. I suggest that the  authors mention this possibility.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The authors do a fine job with the analysis of the superluminal motion and jet parameters of J1429+5406.  They present lots of data, taken in five frequencies, over an extended period of time.  Most of the focus is on the particular details of this object, and valid interpretations based on the observations.  This is a high z source, so the investigation is very worthwhile and hard to do.  It is a probe of the early universe.

There are a few questions and considerations I would have to strengthen this paper, however.  I do not insist on any of them.

1. Given that you have observations in five frequencies, would it not be possible for you to measure spectral aging by looking at the changing spectral index of the components along the jet?
2. A very interesting observation is that “the outer jet components … do not show discernible apparent motion.” Perhaps you could show a simple plot apparent velocity versus distance from the proximal end of the jet, with the different jet components shown in this plot.  Other table data may lend themselves to plots as well.
3. Without necessarily presenting any particular conclusions, I think more discussion is in order in trying to explain the change in proper motion along the jet as either a change in the bulk Lorentz factor or a change in the inclination angle with respect to the line of sight. While you mention quite plausibly how a plasmon could slow down, you intriguingly state, without explanation, that it could also speed up.  To what mechanism would you attribute this?  (Lines 223-226.)

 

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

In this work, the authors, the authors investigated the relativistic jet of the source J1429+5406 at redshift z = 3.015 using the VLBI data during the period of 1994 and 2018 at five radio frequencies, found three jet components within the central 10-mas region to exhibit significant proper motions, they calculated the core brightness temperature (3.6 · 10^11 K) implying a Doppler factor  of δ ≳8.8, apparent velocities (β = (17.0 ± 1.9) c,  (7.28 ± 0.04) c, and  (4.7 ± 0.6) c, the δ and the 4.7 c apparent velocity follow a  Lorentz factor of Γ ≳ 5.7 and a inclination angle of the jet to the line of sight (i ≲ 5.4 degree)。 They added the source to the high redshift blazar sample.

I think it is an interesting work and adds one more high redshift superluminal source to the high redshift blazar catalogue.  It is acceptable after  two minor comments are addressed.

Minor comments:

1. Another reason of the jet bending is from a binary black hole at the center (Piner B.G. et al. 2010, ApJ, 723:1150–1167).
2. The source is added to blazar catalogue since the estimated inclination angle (i ≲ 4◦ ) is  well below 10◦ for blazars[Ref. 11] and the Lorentz factor (Γ ≳ 5.7) is near the average value of ~ 6 for blazars [19,25].  Actually, the gamma-ray detection from the source is also an evidence for the source to be a blazar.  I  noticed that there is a work by Fan et al. ( 2012, IAUS 290, 207) who proposed that the gamma-ray emission is an observational property of blazar.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf