From: Greg Aldering (aldering@panisse.lbl.gov)
Date: Sat Mar 15 2003 - 12:37:38 PST
Hi all,
Before the discussion of the late-time fitting gets out of hand, let
me try to introduce some new information into the debate.
1) First some history:
In P99 we cut points after +60 restframe days post-max. According
to my inspection of the fitting files and the text of P99, we did
not deweight!
In Goldhaber 2001 we cut points after 40 restframe days post-max
and seem to have put in an error floor of 0.007 (The only place
I could find where this error floor is mentioned is in the footnote
to Table 7 of that paper!).
These are published procedures (although the deweighting is not
clearly presented) that we can adopt and cite without further
justification, if desired.
2) Since P99, in particular in AKN00, we generally agreed that stretch
begins to fail and our knowledge of SN lightcurve variety is poor
starting 25-40 days after max. This argues for the concept of an
uncertainty on the TEMPLATE (as Saul has suggested).
3) We know that if we cut at (1+z)*40 days, following G01, we will lose
some HST lightcurve points. However, if we cut at (1+z)*60 days,
following P99, we should be OK.
4) In the case of the nearby SNe, we know that final reference
images were not always used to obtain the galaxy contamination
level. We do not know for which SNe references were or were not
used, and we don't know the uncertainty to associate with galaxy
missubtraction. For that reason, there is additional justification for
cutting or deweighting the nearby late-time points despite the quoted
uncertainties.
5) Note that at 50 days the B-band template is a f/fmax = 0.054, so
even this late the error floor of 0.007 would affect points with
claimed S/N > 8.
Putting this altogether, I suggest that we cut points after 60
rest-frame days (but not final refs of course) as in P99, and add in an
error floor, with the error floor to be interpreted as accounting BOTH
for uncertainty in the template shape and stretchability at late epochs
and for some uncertainty in the final-reference subtraction for nearby
SNe. We can cite this a combining the treatments presented in P99 and G01.
- Greg
This archive was generated by hypermail 2.1.4 : Sat Mar 15 2003 - 12:37:58 PST