From apj@phy.ohiou.edu Tue Aug  6 11:16:20 2002
Date: Sun, 4 Aug 2002 15:47:38 -0500
From: apj@phy.ohiou.edu
To: yaqoob@pha.jhu.edu
Cc: ApJ-MS56330@mss.uchicago.edu, apj@phy.ohiou.edu
Subject: Your ApJ Submission MS# 56330

Dr. Tahir Yaqoob
Department of Physics and Astronomy
Johns Hopkins University
3400 North Charles Street
Baltimore, MD 21218 USA

Dear Dr. Yaqoob:

Appended below is the referee's report on your submission to the ApJ entitled
"The Kinematics and Physical Conditions of the Ionized Gas in Markarian 509. I.
Chandra High-Energy Grating Spectroscopy"  ( MS# 56330).  

The referee has indicated that the results of this paper merit publication, but
has noted a number of substantive matters that should be dealt with before the
paper is accepted.  I would be happy to consider for publication a revised
version that addresses these points.  When you resubmit the paper through the
ApJ ftp site, please include a detailed cover letter containing the (mandatory)
listing of the changes you have made to the text and your responses to the
report.

Processing of your revised manuscript will be expedited if you make your
revisions to the manuscript latex file available for downloading from the ApJ
Web Peer Review System (http://mss.uchicago.edu/ApJ/).	This version includes
your previous submission plus any modifications to latex commands necessary for
smooth processing by the ApJ electronic system.

If you have any questions, feel free to contact me.

Best regards,

Joseph Shields, Scientific Editor
The Astrophysical Journal
Phone:740 593-0336
Fax:740 593-0433
apj@phy.ohiou.edu

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The Yaqoob et al. paper "The Kinematics and Physical Conditions of the 
Ionized Gas in Markarian 509. I. Chandra High-Energy Grationg Spectroscopy" 
presents new data about the warm absorber in this well-studied Seyfert
1 Galaxy. I will highly recommend it for publication after the following
comments are addressed.

First some general comments. (1) The authors did a very thorough job of 
considering the many factors which may affect their modeling efforts,
including X-ray continuum shape, multiwavelength SED, and velocity profile.
I have some concern about the measurement of a Doppler b value, which 
I discuss below (See comments (13) and (16)).

(2) Even though it is likely that a multi-zone or continuous range of 
ionization states is present, a single zone is apparently adequate to 
describe the observed X-ray lines. For example, the high-ionization
species Si XIV is not present. But what about ionization states between
those observed in the UV and those observed in X-ray? In particular,
it would be interesting to measure or put constraints on inner-shell
transitions from O I-VI, Si I-XII, etc.. which have been seen in other
Seyferts in the X-ray band.

**(3) What are the more general implications of this study? I come
to the conclusion that warm absorbers contain clouds with a wide range
of ionization states, and that the UV and X-ray absorbers are associated
but not identical. What is implied for the mass flux in the ionized outflow?
Are the absorbers associated with the BLR or NLR, or is this not yet clear?
The high densities implied by the Pounds et al. result suggest BLR.
I am skeptical of this, since the emission lines and associated absn
lines are narrow. Kraemer et al. 2002 (your Paper II) suggest an origin in the 
NLR for a similar reason.

Next some specific comments:

(4)Intro, para 3, sentence 1:
"..models span a wide range in distance...out to the putative (parsec-scale)
molecular torus" AND the extended NLR. C.f. Seyferts such as Mrk 3, NGC 4151,
NGC 1068, with extended X-ray emitting NLRs. 

(5) Section 2, sentence 1: "..duration of ~59 ks" In a few places, you
   give: ~59ks, 57.950 ks, and ~60 ks. Make sure these are consistent.

(6) Section 2. Impressively detailed Observations section. Kudos.

(7) Section 3. para 3: "The origin of the soft excess is unclear...."
    I would also add here the possibility that a relativistic O VIII 
    Ly-alpha line contributes at least part of the soft excess.
    This is important, because the assumed continuum shape may affect your
    warm absorber column density measurements. (See 21 below.)

(8) Section 3, para 4: "The measured edge energies are in excellent 
    agreement with  the expected values" I note that the O VII edge 
    energy is marginally inconsistent at the >90% conf level. It concerns
    me that the O VII edge is contaminated by absorption from Fe M-shell
    UTAs in some objects, and may also be here. You discuss this later
    but should also note it here. This can affect your fit ionization 
    parameter if you overestimate the O VII column density. A similar
    problem with other Fe transitions  may cause an overestimate
    of the O VIII edge depth. You do address the Ne IX, but not the Fe here.
    This is a crucial point to address. 

(9) Section 4.1, para2, Figs 4, 5, 6, 7 seem a bit redundant. I would
    kill figures 4 and 5 and combine figures 6 and 7. One can see the
    S/N from your errorbars and it is not necessary to include the counts
    spectra. I will not be adamant about this, since it is a matter of
    taste.

(10) Section 4.2, para 1, Last sentence: "..there may be emission filling
    in the trough.." OR contamination from other absn lines, OR a truly 
    different absn profile.

(11) Section 5, 2nd sentence: "Table 2 gives the abundances we used..."
     How did you decide on these particular abundances? Reference?

(12) Section 5.2, para 1, "...we fixed n_e at 10^8" and "..data were 
     indistinguishable for densities in the range ne=10^5-10^11."
     The high densities you consider seem to betray a prejudice toward
     an origin in the BLR. Why not "n_e=10^2-10^11", to include the 
     possibility that the absn is coming from the NLR?

**(13) Section 5.2, para 2, 1st sentence:
    "...all models assumed a velocity turbulence of 1 km/s, and  since
     XSTAR broadens lines by the greater of the turbulent velocity and
     the thermal velocity, it is the latter which is relevant for these
     models." 
     
     This sentence leads me to believe that you are using purely the 
     thermal velocity width for the fit, which is much less than 100 km/s.
     But then in the next sentence, you correctly recognize that the
     choice of b is vital for getting the proper equivalent widths and
     fitting for the column density. I hope this is just a misstatement,
     since it appears that you _did_ fit with b=100 km/s (Section 5.4)?
     Please clarify.

14) Section 5.3, para 2: "We had to apply an additional (but non-physical)
    correction of -270 km/s... XSTAR v2.1.d contains wavelengths of SOME
    atomic transitions which disagree with wavelengths published elsewhere."

    I have to say that this does not inspire great confidence in your fits!!!
    Are you confident that your correction does a decent job of matching
    the wavelengths of _ALL_ the important observed lines?

    "It is the published values which we used to construct the velocity 
     spectra in Fig. 8 and Fig. 9". Why don't you use these values for
     your model fits? Accurate wavelengths are really important for fitting
     the line strengths.

15) Section 5.4, 1st para: "the strongest absorption line features are NVII...
    ..and Mg XI 1s2.." I don't see the Mg XI line in Fig 3.
    It would be good to include it there.

**16) Section 5.4, 1st para (curves of growth):

    Clever idea to use lines from multiple ions to constrain a Doppler b-value.
    However, you need to state that this depends on the assumption of
    a particular set of abundances (eg solar). Also, you use a somewhat 
    circular argument: points in Fig 10 use the "predicted column densities".
    Predicted from where? From the model which you fit with b=100 km/s?
    
    A more correct argument might go: All Ly-alpha transitions from H-like
    and He-like ions have the same equivalent width (to within uncertainty).
    This suggests that all of these lines are on the saturated part of the COG.
    The measured equivalent width of ~1 milliAngstrom is consistent with
    b=100 km/s, assuming solar abundances.

    The best way to determine an independent b-value is doing a 
    curve-of-growth analysis on at least 2 lines from the same ion. 
    Can you do this for O VII 1s-2p through 1s-5p??  

17) Section 5.4, 1st para (velocity profiles):
    Fig 8. and Fig. 9.
    I don't understand why you don't simply plot the fit model against the
    data? Why do you go through this complicated excercise of re-calculating
    the model with Gaussians of the appropriate b and EW? It leads me
    to believe that the original model was somehow inadequate, along the
    lines of comments 13 and 14 above.

18) Section 5.4, para 3, 1st sentence: "...the best-fitting XSTAR model is
    moderately good at the O VII edge but should be somewhat lower in flux
    blueward of the O VII edge." I don't follow. Do you mean "good at O VIII",
    but "poor at O VII," or pretty good at "O VII", but not quite deep enough
    at the threshold energy?  Please restructure this sentence.

19) Section 5.4, para 4, "We see that more sophisticated modeling with better
    data now gives a smaller O VIII edge." After giving your new, improved
    edge optical depths, I would add the caveat that they still may be
    overestimated due to the presence of Fe inner shell UTAs. (See comment
    8 above).

20) Section 5.5, para 2, 1st sentence: " C IV Lya" should be "C VI Lya".

21) Section 5.5, last sentence: "..the evidence for relativistically broadened
    O VIII... is not compelling". While it may not be compelling, neither
    is it ruled out. I would be careful here and suggest that further 
    observations are required. Also, how much did your O VII column change
    when you added in the O VIII rel. line? I would guess that it decreased.

22) Section 6, para 2 "...a broad absorption trough, likely to be associated
    with an Fe M-shell UTA" Which ionization state of Fe?

**23) Section 6, para 3 "...the emitting gas did not respond to the continuum
    in ~180 days implies....d>0.15pc". Let me get this straight. The continuum
    increased by a factor of 2.8. The intercombination line EW did not change
    significantly. Therefore the flux of the line could have increased along
    with the continuum, and therefore MAY HAVE responded. This would invalidate
    your size lower limit. If the line flux was constant, the EW should
    have dropped by a factor of 2.8 to EW=0.5 eV; which is also consistent
    with your observation. I would say your observation is insufficient
    to establish whether or not the emission line flux varied!

**24) Section 6, para 3 "We verified the conclusion of Pounds et al.(2001), 
    that the line-emitter must have ne>10^11." You are saying that XSTAR
    model spectra require ne>10^11 in order to explain the line ratios
    observed by Pounds et al. So you haven't actually verified the Pounds
    et al. observation; you just concur that if they measured these lines
    properly, it supports a high density? I would eliminate this statement
    since you aren't actually providing any new data on the line ratios.

    Furthermore, I have looked up the Pounds et al. reference. They find:
    O VII r: EW=0.5+/-0.5 eV
	  i: EW=1.5_/-0.7 eV
	  f: EW=0.6+/-0.4 eV

    So the i line is the only one detected, and at best at 2.1 sigma.
    Are you willing to support such a detection by "verifying" it
    with your own modeling efforts? R=f/i=0.4+/-0.3 (R<1.0 at 2-sigma level)
    is the relevant density sensitive diagnostic. From Porquet and Dubau
    2001, Fig. 8, I read ne>10^11), which is as Pounds and Reeves stated.
    Also see PD01, Fig. 11, it looks like ne=10^12 is necessary to produce
    the observed f/i ratio as well.

    I belabor this point because I think ne>10^11 is rather unlikely,
    but very interesting if true. This density would put the absorber
    in the BLR at 0.1 pc, which seems inconsistent with its narrow width
    (few hundred km/s). I will not be surprised if longer observations of 
    Mrk 509 do not confirm the Pounds et al. result.

25) Section 8, para 3 (point2), line 7: floating period "O VIII  ."

26) Conclusions, point 4: I would eliminate point about emitting material
    being at least 0.15 pc from center (see comment 23 above).

I hope that you find the above comments useful and not overwhelming. Overall,
it is a great paper. Pay special attention to asterisked comments 3, 13, 16, 
23, and 24.

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