Peer review of: Measuring the Hubble constant with a sample of kilonovae (2020)


REVIEWER COMMENTS
Reviewer #1 (Remarks to the Author):
Dear Authors,
I am happy to see the improvements in the paper which makes a stronger case for the publication. However there are some partially addressed issues before acceptance for publication. I understand that my scientific bias could cloud my view to see the pathological issues. Please clarify such cases.
“We restrict $0 < \theta_{\rm obs} < 15$ for the sGRB analysis because the viewing angle is much closer to the polar axis than for GW170817\cite{TrRy2018}.”
>> Is this true for all sGRB? Do you expect them to be such for all sGRB that will be observed in the future.
“This means that our analysis is even more general since it indeed holds for all possible parameters, no numerical relativity results enter without our study; we add an additional note to the manuscript stating this fact.”
“This analysis shows that our flat priors cover both of the confirmed events so far, and in this sense, applying flat priors has the significant advantage that a larger range of the parameter space is covered. Further, it reduces systematic uncertainties since no numerical-relativity inferred relations have been applied.”
“This point is related to point 1a and we hope that our answers provided already a better insight. The models from Kasen et al. and Bulla et al. are agnostic to the specific binary systems and properties. That is, they are generic enough to be used to model both BNS and NSBH systems.”
>> I fail to emphasize the point clearly.

Is it possible that by taking all possible combinations of parameters, you are enforcing the standardization?
Since by taking a large number of samples in the unphysical region of parameter space, it is possible to get unrealistically low error. It might happen that if you include only the physically possible combinations, the scatter is too large to be accepted as a standardizable candle. Just a small demonstration would suffice where you take perhaps an equal number of samples but, in the physically possible region of parameter space.
A further question arises whether the standardization for the BNS system would be the same as the BH-NS system due to their different position in parameter space.
“Studying the predictions of two independent models with physical assumptions allows us to estimate the systematic uncertainties of our analysis.”
>> The systematic uncertainties also includes the unmodeled effects, is it possible to get an estimate of that? For example, by choosing a spherically symmetric model or a 2-component model of kilonova light curves, we might get an illusion of several special properties which might not be present in the actual system.
Since the field is still quite young in the literature, just a mention of this point should suffice.
“In addition, the impression that our results are more accurate than Plank or SHOES data is incorrect.”
>> I apologize for this confusion, Authors are correct. Thanks for pointing this out.
“We have added a section (Lightcurves) to the methods discussing the source of the data and remind that the r-band observations are used to standardize the SGRBs due to the sparsity of K-band data, and caveats about GRB060614’s source in particular; exactly as pointed out by the referee.”
>> The original objection was on the use of different bands for Hubble-Lemaitre constant and the derivation of standardization using models. This has not been addressed. In fact, it has become more confusing now because it’s not clear which band is used in Fig. 5. This has to be r-band in order for it to apply to sGRBs for which only r-band observation is of any use.


Reviewer #2 (Remarks to the Author):
The authors address my concerns in the previous report. Therefore, I recommend this article to be accepted.