From: Lifan Wang (lifan@panisse.lbl.gov)
Date: Fri Mar 14 2003 - 13:48:35 PST
Isn't it true that we plan observations in terms of S/N ratio ? I will be
very surprised if anyone is observing the same SN with constant exposure
time. Check observing logs of published light curves, and you can see that
it changes. Then why is the errors on flux more relavent than errors on
magnitude (or S/N ratio) ?
Lifan
> From owner-deepnews@listserv.lbl.gov Fri Mar 14 13:10:29 2003
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> To: "Robert A. Knop Jr." <robert.a.knop@vanderbilt.edu>
> cc: Lifan Wang <lifan@panisse.lbl.gov>, <saul@lbl.gov>, <deepnews@lbl.gov>,
> <hstpaper@panisse.lbl.gov>
> Subject: Re: "Error floor"
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>
> I'll go with Rob on this one. Magnitude is a concept not without its
> charms, but when we're thinking about errors and statistics and stuff, we
> stick with intensities.
That may be true, but when we talk about observations when always talk
about S/N ratios, or magnitude errors, first.
>
> D
>
> On Fri, 14 Mar 2003, Robert A. Knop Jr. wrote:
>
> > On Fri, Mar 14, 2003 at 11:15:15AM -0800, Lifan Wang wrote:
> > > Would not this error floor introduce unreasonably large errors at the
> > > late time light curves ? At day 40, the supernova is about 3 magnitude
> > > fainter, i.e. the flux is about 0.063 times that of the peak. The error
> > > floor then implies late time errors are around above 0.1 mag and increases
> > > at later epoch. I don't think this is the correct way of treating the
> > > data, as the measurement can definitely be better than the error floor.
> >
> > I disagree.
> >
> > Unless you integrate a WHOLE Lot longer, the late time data *is* going
> > to have larger *magnitude* error bars than the early time data!
> > Measurements are really flux, and comparable *flux* error bars is what
> > I'd expect... unless you really do integrate an awful lot longer for the
> > late time points.
I don't believe those guys cannot scale their S/N ratio calculation with
exposure time, but then may be they cannot. In terms of photon statistics,
there is NO floor in the errors of flux. You can only justify the use of
error floor if you think they cannot reach their flux calibration to
0.007 times that of the peak magnitude of an SN, which is what I don't believe.
> >
> > -Rob
> >
> > --
> > --Prof. Robert Knop
> > Department of Physics & Astronomy, Vanderbilt University
> > robert.a.knop@vanderbilt.edu
> >
>
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