X-ray Polarization from Magnetar Sources

Round 1

Reviewer 1 Report

The paper is a review of both theory and observations. As a result it is difficult to read and long. I only became interested at section 5. Still, perhaps the theory has not been assembled elsewhere, but I suspect one finds the essential in the papers that present the results. I would suggest that the author's consider whether this is true and adjust their paper accordingly, but I leave it up to them.

Therea re some minor points:

1. Figure 2 needs a much more explicit caption.

2. In the discussion after figure 5, there is a general statement that the polarization decreases at low energies. However it is 15\% at 2-3 kev and zero at 4-5kev. Some more clarification is needed.

3. A 1 sigma confidence level seems to be a relaxed standard. Is this typical in the field?

4. It would be better to spend more time discussing such results as the anti-correlation between flux and polarization degree in figure 8, than on the theory. The discussion helps a lot, but it would be good to have a most likely conclusion for each source. There are a lot of model parameters to play with. Different spots, atmosphere or not, vacuum birefringence or not.

5. The English is generally fine although wordy. There are obvious typographical errors here and there. `Horothogonal' in 2.2 (no H), `helicity' not `elicity' (need the H) in various places.

6. There is a paper in Frontiers by Alford J and a whole bunch entitled "Magnetars and Other Isolated Neutron Stars' using HeX-P data. It seems that some cross referencing might be possible.

Just minor typos.

Author Response

We thank the referee for his/her useful remarks and comments. The reply to referee 1 is attached as a pdf file.

Author Response File: Author Response.pdf

Reviewer 2 Report

Manuscript ID: galaxies-2839783
Type of manuscript: Review
Title: X-ray polarization from magnetar sources
Authors: Roberto Taverna *, Roberto Turolla

Summary: This is a very nice (and useful) review paper, but missing a few references as noted in the report below.

line 20-21:
"the former exhibit a persistent X-ray 20
luminosity typically in excess of the rotational energy loss rate": this is not a useful statement because it is also true of
conventional X-ray pulsars. Please remove or rewrite to be less confusing (and incorrect).

line 55: you should briefly mention alternate models of magnetars involving quark stars:
2007 Ouyed et al, A&A 473, 357; 2005 Iwazaki, Phys Rev D, 72, 4003


line 91:
this ignores the fundamentally quantum field theory (QFT) nature of the interactions of photons and electrons. You should add some other references (beyond ref 35, and with more details than ref 36) which relate the classical wave description to the more fundamental polarized photon/electron interactions derived using QFT, including quantum propagators and Feynman diagrams. References to add: Semionova & Leahy 1999 Phys Rev D, 60, 073011; Baring et al, 2005 ApJ 630, 430

Fig.4: redo the line colors and types (e.g dot, dot-dash, dash) so that DU 1, DU 2 and DU 3 lines can be seen: right now only DU 3 is clear; if they are all identical please remove the legend and state that.

Please supply higher resolution versions of Figs. 1, 2, 3, 7 if possible, and certainly of Fig. 8 (Fig. 8 is especially hard to read at the current resolution)


minor comments (grammar/spelling):
line 18 "Seventies" change to "1970's"
line 73 "old" change to "older"
line 73 "us to observe" change to "observation of"
line 257 "helicity"
line 309 "see again Fig. 3" change to "Fig. 3")
line 378 "freezed" change to "frozen"
line 405 "can be able" change to "is able"
line 412 "becomes"
line 415 "exists"
line 462 "change continuously direction" change to "change continuously in direction"
line 491 omit "instead"
line 498 sentence is confusing "For what concerns the polarization direction, also in this case the phase-dependent PA behavior turns out to be uncorrelated from the polarization degre": I think you mean "The phase-dependent PA is uncorrelated with the polarization degree"
line 610 "raise" should be"rise"
line 653 "have opened"
line 656 "throughout" should be "in"
line 679 suggest remove "exactly" because there are probably other geometries that can explain the polarization properties.
line 687 "have demonstrated"

see above comments (lower part of the report)

Author Response

We thank the referee for his/her useful remarks and comments. The reply to referee 2 is attached as a pdf file.

Author Response File: Author Response.pdf

Reviewer 3 Report

comments are all minor, mostly slight re-phrasing to make a sentence read more clearly or smoothly

lines where adjective 'star' should be 'stellar' or "star's"
     47  158  174  178  180  217  229  264  405  448  453
   462  575  615  616  


  20: 'both types of sources share':  both types of source share

 119:  'horthogonal'  >> orthogonal
            (the original sounds 'Harry Potter-ish')

 177:  ... change as radiation propagate ... >>
             ... change as the radiation propagates ...
        
 257:  'elicity' should be 'helicity'?

 271:  'emispheres' should be 'hemispheres'?

 279:  'sections becomes' >> 'sections become'

 281:  missing 'is'?  ... in agreement with what IS observed ...
 
 297-299:  at variance with the previous ...
   suggested re-phrase:  The previous instrumentation was based on Bragg  

          diffraction and Compton scattering.  IXPE instead exploits the   photoelectric effect.

 301:  'by' >> 'of'

 378:  'freezed' >> 'frozen'

 387-391: the sentences mention the polarization degree decreases at low
          energies from 15% at 2-3 keV to 0% at 4-5 keV.
     that sentence does not make sense to me:  'reaches at minimum'
     around 4-5 keV is ok, but not as written

 415: ... no numerical model exist as ...:  either 'models' or 'exists'
      (but not both!)

 426: ... pulsars [88] shown an alignment ...:  'shown' >> 'show' or 'showed'

 447: pulsations originates:   originates >> originate

 462:  vectors change continuously direction >>
              vectors continuously change direction

 502: count statistics was increased >> count statistics were increased

 662: Despite the four magnetars share a ...: awkward phrasing:  how
   about:  Despite the similarities in spectral shape shared by the
     four magnetars, ...
    

see above comments - nearly 100% minor fixes

Author Response

We thank the referee for his/her careful reading of the manuscript. We fixed all the minor comments and typos.