david.paneque wrote:Hi Adiv, Priya,
I had a look at the manuscript and I actually already discussed few things with Priya (face to face, at MPI).
I just write here my main evaluation, for bookkeeping.
In general, the paper looks very good, and it is incredibly well written (all very clear). Congrats !!!
Thanks for that!
I only have two remarks on the content:
1) you justify the usage of a single fit for all data with Figure 3, which shows that the PL index is approximately the same for all the nights (regardless of the large change in flux). However, this figure is a bit misleading because you are not showing the quality of the fits for all these nights. You might get a PL index of 2.0, but perhaps the fit quality is very bad, which means that a PL with index 2.0 is not a good representation of the data.
Do you have the Chi2/NDF (or Prob) for all these fits ? How do they look ?
Well, each individual fit had good probabilities, that one thing that we found with 1ES1011, that its intrinsic spectrum seems to be remarkably flat in our energy range. Now, if I force the fits to 2.1, all fits are good (more than 10%) except one day, where the probability is 0.4% (which still is not that bad).
Something that could be more convincing to justify the usage of a single shape would be somethign along these lines.
a) Since you want to test teh EBL, you might want to do the tests in the non-corrected spectra (which are curved)
b) Fit the "all-data" spectrum with a log-parabola ( PL is surely not a good one)
c) Fit each of the spectra for all the single nights with a log-parabola function where the parameters alpha/Beta are fixed to those of the "full data set". That is, only the normalization factor is allowed to change (to absorb the flux variations)
d) Evaluate the goodness of the fit for each of these nights (you can plot Prob vs ObsNight)
What do you think about it ?
Actually, initially that is the approach that we were using, where the normalization was the only parameter allowed to change, and also in that case the worst fit was at the level of 1 or 2% probability. However, we decided to used the de-absorbed spectra since it could be represented with a simpler function, that is, we would be using less parameters.
Regarding the plot Prob vs ObsNight, I would prefer just a table.
2) When computing the systematics, based on the 15% systematic for the energy scale reported in teh performance papers, you are shifting the individual pixel size content by +/-15%. NAturally, the single PMT signals will be related to the overall size of the image, which will also be related to the overall energy estimated for that image. But these quantities are probably not "one-to-one" related, isn't it ?
In other words, a shift in the full energy estimated for an image of 15% might only be attributed with a shift in the PMT signals of 10% (because by increasing individual signals you get more pixels in the image, which were removed before) or by 20% (because besides the Size, there are other parameters that play a role in the estimation of the energy).
I never played with these quantities in MC, and hence I do not have a sense of how they actually relate to each other.
The point is that, while surely these quantities are related, it is not clear that the relation is a one-to-one, and hence our "official" systematic error in energy of 15% may not translate to 15% change in the PMT signals.
Any explanation of why you propagate the systematics using single PMT signals instead of using the reconstructed energy of the events ?
Well, I have to say that also I'm not an expert on analysis but as far as I understood, the energy is directly proportional to the size, and actually, these approach is based in the performance paper. The way they estimated the systematic uncertainties related to the energy scale, was scaling up and down the light in the pixels in the MC. However, and this is a "novelty" in our analysis, we made the scaling on the actual data instead of the MC. In principle the approach is equivalent. Now, as you say, there are another parameters that enter in the calculation, but are stereo parameters and these should remain the same.
cheers,
David
Adiv wrote:
Well, I have to say that also I'm not an expert on analysis but as far as I understood, the energy is directly proportional to the size, and actually, these approach is based in the performance paper. The way they estimated the systematic uncertainties related to the energy scale, was scaling up and down the light in the pixels in the MC. However, and this is a "novelty" in our analysis, we made the scaling on the actual data instead of the MC. In principle the approach is equivalent. Now, as you say, there are another parameters that enter in the calculation, but are stereo parameters and these should remain the same.
david.paneque wrote:Adiv wrote:
Well, I have to say that also I'm not an expert on analysis but as far as I understood, the energy is directly proportional to the size, and actually, these approach is based in the performance paper. The way they estimated the systematic uncertainties related to the energy scale, was scaling up and down the light in the pixels in the MC. However, and this is a "novelty" in our analysis, we made the scaling on the actual data instead of the MC. In principle the approach is equivalent. Now, as you say, there are another parameters that enter in the calculation, but are stereo parameters and these should remain the same.
I do not quite understand your answer.
The systematic that is quoted in the performance paper is 15% in energy scale, not in the "Size" parameter. Surely these two are closely related, but I do not know whether one can directly convert the 15% systematic uncertainty in energy to 15% systematic uncertainty in the parameter "Size". This is not mentioned neither in the performance paper nor in yuour 1011 paper. IF that is the case, then it should be explicitly mentioned in the paper. Otherwise, it is not clear where this "15% shift comes from".
julian.sitarek wrote:Hi David,
Except of some saturation effects, a tail due to high impact events and some logarithmic dependence due to Hmax, there is basically a scaling between the size and energy. Since we are talking about shifts of the order of 15% one can treat the shifts in light scale as shifts in energy scale, especially within the usual accuracy at which the systematic errors are given.
Moreover what we actually did in the upgrade paper (and what we were doing also in the last two performance papers) was to estimate the light scale accuracy, and based on it make a statement on the energy scale. So it is perfectly fine what Adiv et al did.
elisa.prandini wrote:Dear Adiv et al.,
I also went through the new paper version and I have only a couple of minor comments in addition to Julian ones, but let me first congratulate for the paper and in particular for the Introduction section, it is really well written and clear!
Thanks!
My first suggestion is to add the standard reference to Hauser & Dwek paper after the definition of EBL (http://adsabs.harvard.edu/abs/2001ARA%26A..39..249H).
OK, included
The second suggestion is to use the same font size adopted in the axis of Fig.2 (labels and titles) also for the other figures. In figures 4 and 5 you can set the background of the legends white.
OK, done.
There is one point that I asked you in my previous e-mail but you did not address: in the Discussion, you mention that the differences between the two scaling become evident above 200 GeV, but I would rather say at 300 GeV (the 200 GeV points are perfectly compatible). Can you comment on this?
You right, the points at ~200 GeV are compatible (for sure they have the same chi2 contribution). The true is that the way we could chose the energy range is somewhat arbitrary. What HESS did was to take the range in which there was an overlap among the observations of the different AGNs. We think that we are using an conservative approach, since we could use the whole energy range of our observations. Maybe the sentence "evident" is an overstatement. It could say "start to show" instead.
Cheers,
Elisa
david.paneque wrote:julian.sitarek wrote:Hi David,
Except of some saturation effects, a tail due to high impact events and some logarithmic dependence due to Hmax, there is basically a scaling between the size and energy. Since we are talking about shifts of the order of 15% one can treat the shifts in light scale as shifts in energy scale, especially within the usual accuracy at which the systematic errors are given.
Moreover what we actually did in the upgrade paper (and what we were doing also in the last two performance papers) was to estimate the light scale accuracy, and based on it make a statement on the energy scale. So it is perfectly fine what Adiv et al did.
Sounds good. Then I would suggest to write 2-3 sentences about it in the paper (linking the 15% energy shift quoted in the performance paper with the 15% shift in light scale).
Well, I included a sentence linking to the 15% energy shift from the performance paper.
cheers,
David
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