1ES 1011+496, EBL with flare 2014: 3rd Referee report

[david.paneque]

Posted on behalf of Adiv Gonzalez

Hi all

The referee has sent his reply. He basically insist that we should change "measurement" to "constraint" or "upper limit" in the title and the text. Please see his reply in the following lines

Referee Report

I feel rather strongly that the results of this manuscript should not
be described as a "measurement" or "detection" of the EBL, as I
discussed in my previous report. If the authors insist on
characterizing their results this way, I think at this point it will
save everybody time if they ask the scientific editor to overrule my
objection, or ask for another referee. Otherwise, I think we will
just go around in circles. Rather than the standard format of quoting
the authors followed by my response, I give a summary of both the
authors' position and my position. I hope the authors will think the
summary is fair to them. I think this summary will be more useful to
the editor and/or future referee.

I would like to say once again that, aside from this disagreement, the
authors present an interesting, well-written paper that should be
published in A&A.

The authors' position:

1) The authors put an upper limit on the EBL based on MAGIC
observations of the source 1ES 1011+496 and the primarily assumption
that its gamma-ray spectrum is concave. This upper limit is reliable
and robust.

2) Their lower limit on the EBL depends strongly on the assumed form
for the intrinsic gamma-ray spectrum of 1ES 1011+496, and so the
lower-limit is not particularly robust. It their response to my first
report, the authors modified the manuscript in several places to say
this.

3) Despite the fact that it is not robust, the authors think the lower
limit is still meaningful. This is because the intrinsic spectrum is
"describable by one of the simple concave function" they use (listed
in Table 1 of the manuscript, and described in a previous paper by the
HESS Collaboration).

4) The authors put the word "detection" in quotation marks in several
places as an indication that it is "not a formal detection". In at
least one instance they replaced the word "detection" with
"constraint" in response to my last report.

5) Previous papers have used similar techniques and referred to the
result as a "detection". It is not completely clear which papers the
authors are referring to in their last response, but I assume they
mean the paper by the HESS Collaboration (2013, A&A, 550, A4).
Keeping the phrase "measurement" in the title and other places will
allow readers to compare this result with the previous results by the
HESS Collaboration.

6) All of the assumptions are clearly spelled out in the manuscript.
The readers can read the details of the technique for themselves and
determine for themselves whether or not the phrases "measurement of
the EBL" or "detection of the EBL" are justified.

7) The lower limit on the EBL is not particularly interesting. The
authors' exact words: "the goal is not to detect the EBL, since there
is no doubt that some level of EBL must exist at least from the
resolved galaxies. In this sense the lower constraint is of no big
interest as long as it does not go significantly above the lower
limits from galaxy counts (and it doesn't)."

The referee's position/response:

1) The authors put an upper limit on the EBL based on MAGIC
observations of the source 1ES 1011+496 and the primarily assumption
that its gamma-ray spectrum is concave. This upper limit is reliable
and robust. I completely agree with the authors about the upper
limit.

2) The lower limit on the EBL depends strongly on the assumed form for
the intrinsic gamma-ray spectrum of 1ES 1011+496, and so the
lower-limit is not particularly robust. The authors and I seem to be
in agreement about this also, at least to a certain extent.

3) I do not think the lower limit is meaningful because of this lack
of robustness. Unlike the upper limit, the lower limit does not
depend only on the assumption that the intrinsic spectrum is concave,
but depends on the particular choice of function to model the
intrinsic spectrum. I think there are many possibilities for the
intrinsic spectrum that are not adequately described by one of their
simple functions. The intrinsic spectrum could have peculiarities due
to the (poorly understood) particle acceleration process, or cutoffs
from internal absorption, or cutoffs in the electron distribution, or
turnover in the Klein-Nishina cross-section at high energies (the
latter two assume the gamma-rays are produced by Compton scattering).
If the gamma-rays are produced by a hadronic process, the shape of the
gamma-ray spectrum is even less well-understood.

4) Because the lower limit is not meaningful, I do not think the
result should be characterized as a "detection of the EBL" or a
"measurement of the EBL". Instead phrases like "constraint" or "upper
limit" should be used. I do not think putting "detection" in
quotation marks is an adequate substitute for using the phrase
"constraint". Also I note their are many instances of the phrase
"measurement of the EBL" without quotation marks. This includes in
the title of the paper, the abstract, the last paragraph of Section 1,
the title of Section 4, etc. I disagree with all of these uses.

5) I also disagree with the HESS Collaboration's characterization of
their result as a "measurement". I stated this in my first report.

6) Let's face it, most readers are not going to dig into the details
of this paper. If they read the title of the paper, where a
"measurement" is claimed, they are going to think there is a robust,
meaningful, upper AND lower limit on the EBL. Words matter, and I
think the title of the manuscript gives a misleading impression.

7) In none of my reports have I given an opinion on how interesting
the lower limit is relative to the upper limit.

Final thoughts from the referee: The fact that the authors "partially
agree" with me about the lower limit, and that they do not think the
lower limit is particularly interesting, indicates that this is mostly
a semantics argument. But, I do feel that the semantics are important
in this case. Consider if MAGIC put only an upper limit on the
gamma-ray flux from a particular source. This would not be
characterized as a "detection" or "measurement". If an upper limit on
gamma-ray flux was described as a measurement in the title and
abstract of a paper, a referee would certainly object.

[adiv.gonzalezmunoz]

As agreed in the e-mail exchange, I have changed the title and the text substituting all the parts where instead of measurement it should say (according to the referee) constraint.

Please find in the attachment the updated version of the draft where all the substitutions are highlighted with bold face text.

As for the replies to the editor and the referee these are my proposals



Dear Sergio Campana, A&A Editor

We have reviewed all the comments issued by the referee and we have agreed on changing the title of our paper and also the parts in the text where instead of "measurement" or "detection" the referee requested to be changed for "constraint". The changes are in boldface.

Best regards

The corresponding authors.

-------------------------------------------------------------------------------------

Dear referee,

Thanks again for a comprehensive review of our work and the subsequent changes that has been made through this exchange of replies. As you aptly remark, there is no point in going in circles with the question whether this work could be presented as a measurement or a constraint of the EBL, and we also think is unnecessary to go back to square one with another referee. Therefore the corresponding authors have agreed to make the modifications to the title and the text changing the interpretation of our work from "measurement" to "constraint" of the EBL.
We appreciate that despite our disagreements in the previous replies you still insist that our paper should be published.

-------------------------------------------------------------------------------------

Please let me know for any change that should be made in the manuscript and fell free to make changes in the replies to the editor and the referee

[abelardo.moralejo]

Hi,

some suggestions:

Thanks again for a comprehensive review of our work and the subsequent changes that has been made through this exchange of replies.

==> "Thanks again for a comprehensive review of our work and for the suggestions you have made to improve the paper."

As you aptly remark, there is no point in going in circles with the question whether this work could be presented as a measurement or a constraint of the EBL, and we also think is unnecessary to go

=> "...we also think it is unnecessary"

back to square one with another referee.

Sounds a bit too colloquial to me, but fine.

Therefore the corresponding authors have agreed to make the modifications to the title and the text changing the interpretation of our work from "measurement" to "constraint" of the EBL.
We appreciate that despite our disagreements in the previous replies you still insist that our paper should be published.

As for the new paper draft:

- "an average spectrum from which the EBL imprint could be constrained with a significance of 4.6 sigma"

This seems a bit like pulling the referee's leg… Actually the last part of the abstract has to be significantly re-written:

Now it reads:

from which the EBL imprint could be constrained with a significance of 4.6 sigma, corresponding to an opacity normalization factor 0 = 1.07 (-0.20,+0.24)stat+sys with respect to the nominal one in the assumed EBL template (Domínguez et al. 2011). This delimitation on the EBL flux density is the most constraining one obtained with VHE data from a single source on the wavelength range [0.24 um, 4.25 um], with a peak value at 1.4 um of F = 12.27 +2.75 -2.29 nW m^-2 sr^-1, including systematics.

I propose:
"...from which the EBL imprint could be constrained. The likelihood ratio test shows that the model with an EBL density 1.07 (-0.20,+0.24)stat+sys, relative to the one in the tested EBL template (Domínguez et al. 2011), is preferred at the 4.6 sigma level to the no-EBL hypothesis, with a log-parabola as the model for the intrinsic spectral shape. Under the {\it assumption} that the intrinsic source spectrum is indeed log-parabolic, this would translate in a constraint of the EBL density in the wavelength range [0.24 um, 4.25 um] of F = 12.27 +2.75 -2.29 nW m^-2 sr^-1, including systematics."


- I still see some typos in footnote 1, which sound familiar to me… I think I had already pointed them out. Are we sure the changes have been made w.r.t. thw latest version?? Here they are:
"The fit performed with the Poissonian likelihood approach have therefore one more degree of freedom that…" => have => has and that => than

- Note that "constraint" is just a noun, not a verb. The verb is "constrain". Please fix the several confusions through the paper.


Ok for the rest,

A.

[adiv.gonzalezmunoz]

Hi

Thanks for the corrections. Then, the reply to the referee would go like this


Dear referee,

Thanks again for a comprehensive review of our work and the for the suggestions you have made to improve the paper. As you aptly remark, there is no point in going in circles with the question whether this work could be presented as a measurement or a constraint of the EBL, and we also think it is unnecessary to request for another referee, ruling out all your work. Therefore the corresponding authors have agreed to make the modifications to the title and the text changing the interpretation of our work from "measurement" to "constraint" of the EBL.
We appreciate that despite our disagreements in the previous replies you still insist that our paper should be published.

------------------------------------------------------------------------------------

I have fixed the confusion between "constrain" and "constraint", well, I think I have, that word to me is a little bit confusing in its usage. Please let me know it there is still something wrong. I also have fixed the footnote.

In the abstract I made it a little bit shorter than what Abelardo proposed.

... from which the EBL imprint could be constrained. The likelihood ratio test shows that the model with an EBL density 1.07 (-0.20,+0.24)_{stat+sys}, relative to the one in the tested EBL template (Dominguez et al. 2011), is preferred at the 4.6 \sigma level to the no-EBL hypothesis, with the {\it assumption} that the intrinsic source spectrum can be modeled as a log-parabola. This would translate in a constraint of the EBL density in the wavelength range...

See in the attachment the updated version of the draft.

[abelardo.moralejo]

Hi,

ok with the simplification of the abstract. Just a ninor thing: "translate in" => "translate into"

Other things:

In page 5:

"In our case, the assumption of power-law intrinsic spectrum would result in an EBL constraint at the 13  level."

Sorry, but again, "constraint at a given significance level" is not a standard expression, and not a meaningful concept in my opinion. In that one place of the paper it would be justified to use "measurement" between quotation marks, BUT in order to avoid further problems with the referee let's be just descriptive:

"In our case, the assumption of power-law intrinsic spectrum for 1ES 1011+496 would lead the likelihood ratio test to prefer the best-fit $\alpha$ value to the no-EBL hypothesis by as much as 13 $\sigma$."

Once again, in the conclusions, same problem :

"Under this assumption, the EBL was constrained with a significance of 4.6 sigma in a EBL wavelength range covering most of the COB region,
with a peak of F = 12.27 +2.75 -2.29 nW m^-2 sr^-1 at 1.4 um, systematics included, setting the best constraint to the EBL with VHE data from a single source."

Remove the significance from there, and simplify, i.e.
"Under this assumption, the best-fit EBL density at $\lambda = $1.4 um is F = 12.27 +2.75 -2.29 nW m^-2 sr^-1, which ranks among the strongest EBL density constraints obtained from VHE data of a single source."

(no need to repeat the "systematics included" that can be found in the results section, otherwise the two paragraphs look like clones of each other).

I still am not 100% sure the referee will accept this version, let's see...

Ciao,

A.

[adiv.gonzalezmunoz]

Ok, yes, it make more sense now.
I hope David and the others are following this. Please find in the attachment the latest modifications in the manuscript. If there is no other comments or modifications, I would like to submit it tomorrow morning, MX time.

Cheers


Adiv

[abelardo.moralejo]

Hi Adiv,

fine for me, thanks! Let's hope this is the final submission

Ciao,

A.

[adiv.gonzalezmunoz]

Hi

For bookkeeping purposes I'm attaching the version of the draft (and lets hope the last one that we have to exchange with the referee) that I just submitted.

Cheers

[Brianvaf]

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