From: Greg Aldering (aldering@zacharys.lbl.gov)
Date: Sat Nov 30 2002 - 19:37:02 PST
Hi all,
Using Naoki's Suprime-Cam photometry from last night, I have performed
a rough lightcurve fit to SuF02-081. For the redshift of z = 1.478,
established by the probable identification of OII by Chris from the VLT
spectrum, the stretch required of our Leibengut-based U-band template
is s = 0.66. As Lifan has noted, in the restframe UV the lightcurve can
fall quite quickly even relative to restframe U, so the low stretch
might be fine. Indeed, the observation of Nov 30 is 8 days after
B-band max according to my fit, and in that time the SN faded by ~ 1.2
magnitudes. This is almost exactly what Lifan calculated using Peter's
template.
The lightcurve fit gives i'_max ~ 25.15, so we still have the issue of
this SN being brighter than we expect. Has anyone tried to quantify
whether there is an excess of plausible foreground galaxies near the
SN, which might lead to a gravitational lensing explanation?
Regarding the host, it is apparent from the Suprime-Cam image and the
OII emission from the VLT spectrum that the host is morphologically
disturbed. The rest-frame equivalent with of -17A places this host in
Dressler's "e(c)" or "e(a)" class. Among e(c) galaxies, Dressler finds
that only 25% are E/S0 systems. Among e(a) galaxies the fraction that
are E/S0 is much much smaller. Putting all of this together, despite
the possible spectroscopic redness of the host, it is very unlikely to
be an E/S0. Thus, we are not guaranteed that -081 is a Ia, and it is
improbable the host is dust-free.
It is of course possible for the SN to suffer little dust extinction
due to location and selection effects, as seen for the color subset of
the 42 SNe. The fact that it is apparently overluminous also suggests
little dust. Similarly, the VLT spectrum and the good lightcurve fit
are suggestive of a Ia. So, we might have a relatively
unobscured/lensed Type Ia, but will have a hard time proving it with
the data in hand.
One last item for Chris - beware that -017 will be falling much faster
in the restframe UV (covered by i'), than in restframe V (covered by
J). So, the apparent i' faintness of -017 doesn't necessarily preclude its
observation in the NIR at VLT.
Cheers,
Greg
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