From: Serena Nobili (serena@lpnhep.in2p3.fr)
Date: Thu Aug 26 2004 - 07:53:04 PDT
Hi Alex,
thanks for your comments. I try to answers below to some of your
questions. Please, let me know if something is still unclear
Ciao
Serena
On Mon, 23 Aug 2004, Alex Kim wrote:
> 2
> You say "Implicitly, we have thus assumed that the rising part of the
> lightcurve in the I-band is the same as in B-band". Technically, this
> is true only if on average if s_I=1, which isn't quite true when I look
> at Fig 6. The assumption is that the relative rise and decline are the
> same.
>
I think this is a delicate point. I believe we have never claimed the
stretch method to work in the I-band before. It is, therefore, not obvious
to me that the rise and decline are the same, nor that the s_I=1 has any
meaning at this moment of the paper (in fact the relation between s_I and
s_B is not well defined). The template used for fitting the I-band is a
double B-band template (i.e. s_B=1), thus, I would assume this could
correspond to a s_I=1. However, as I show later in the paper (e.g. fig6)
the relation is not obvious at all. My intention with that sentence is to
warn the reader that we are trying to describe the rise of I-band
lightcurve with a B-band template, and that this could be not optimal, as
in fact happens to be (see end of section 2.2).
> 2.2
>
> Wondering why you didn't plot a histogram for t_Imax-t_sec. This may
> give a tighter dispersion that t_Bmax
>
Unfortunately, it does not.
> 2.3
> SNe 97br and 98ab have the most plateau-like light curves. This may
> have to do with why some Monte Carlo realizations the don't give good
> chi-squared. Is there something obvious going on with the light curves
> in these cases?
>
What it looks like from the MonteCarlo is that the first peak is not well
constrained (there is only one point). Sometimes the fitting procedure
tries to put the first peak to a too earlier epoch, and screw it up.
Although this could be worsen by the "plateau-like light curves", the real
problem is in the sampling of the lightcurve, I believe.
>
> 5.
>
> In Table 9, do the delta chi-squares convey any meaning in terms of
> precision of the determination of Omega_M? The large delta chi-squares
> makes it look like, contrary to your sentence, that the high-redshift
> sample is sufficient to make strong conclusions on cosmological
> parameters.
>
I am not sure what you mean by delta chi-squares.
The reduced chisq in Table 9 are all very different from 1. The reason for
that is mainly 1999Q which is quite far from any of the models considered.
This, while making the chisq larger than the degrees of freedom, does
push toward the concordance model, because is the model closer to 1999Q.
My conclusion is simply that trying to make a statistical analysis based
on three data points is extremely dangerous.
> I am curious whether, in your sample of three supernovae, if there is
> any correlation between the magnitude residuals from the concordance
> cosmology of the high-z SNe and their corresponding low-z template.
>
I have tried to check for correlations in this sense. There is a
correspondence only if the magnitudes are stretch corrected. In any case,
I would not trust any conclusions on this, given the large systematic
uncertainty on the fit of the high-z SNe.
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