S02-002 may not be too bright for 1.07 redshift...

From: Saul Perlmutter (saul@lbl.gov)
Date: Sat Apr 13 2002 - 19:06:45 PDT

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    Here is an alternative interpretation of S02-002:

    When we compare the zeropoint calibrations of the Japanese group obtained at
    Subaru with the rough APM magnitudes that we are listing on all of our web
    pages, it looks like the candidates that were found on the SS3 field are
    likely to be ~0.5 mag fainter than we listed. This would make S02-002
    closer to I_cousins=24.2 mag, which according to the plot by Ariel on his web
    page is not necessarily too bright for the z=1.07 redshift range.

    Andy Howell wrote:

    > SCPers,
    > I have started running the spectroscopy from the supernovae from this
    > search through my automated matching program. I am posting the results
    > on the SCP spectroscopy web page:
    > http://panisse.lbl.gov/collab/data/spec/
    >
    > My program has 10 template galaxy spectra, and about a hundred template
    > SNe spectra.
    > I simultaneously subtract galaxy light and fit templates until a minimum
    > in residuals is achived. This is done for a range of redshifts. When
    > we have a spectrum of the host galaxy, I use that rather than a template.
    >
    > For S02-002 the results are interesting. I tried redshifts from 0.2 to
    > 1.2. The best fit is to a Type Ia at z=1.08 (SN 1990N at -7d) just as
    > Chris found by eye. While this solution is best, it is far from unique.
    > Several SNe match in the z=0.57 range (esp. Ib/c's), and several match
    > in the z=0.83 range. (See links at the web page for some representative
    > examples).
    >
    > Keep in mind that my program does not cover all of parameter space -- I
    > have no hypernovae spectra for example.
    >
    > So even though the answers run all over the place for this SN,
    > quantitatively, and by eye, the matches at z=1.08 seem to be better than
    > all of the rest. As Chris pointed out, this is problematic because the
    > SN seems too bright to be at that redshift.
    >
    > I think we should consider the possibility that this SN is
    > gravitationally lensed. There are many other possible explanations, but
    > given the data we have I can't be sure what is going on.
    > We really need more spectra. I recommend taking spectra with Keck as
    > soon as possible.
    >
    > -Andy

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