Subject: Re: GRB990123, Probability of gravitational lensing (fwd)

From: elt@astro.Princeton.EDU

Submitted: Sun, 31 Jan 1999 17:43:19 -0500 (EST)

Message number: 32 (previous: 31, next: 33 up: Index)

Hi all,

For whatever it is worth, I think most of Brad's technical statements
(GCNC-241) where correct, but I did not find the conclusion (no lensing) very

The only serious indication of lensing, in my opinion, is/was the alignment
of a foreground galaxy at z=0.28 (a good redshift for lens cross section)
with a z>1.61 source to within 1.8 +/- 0.4 arc sec.  If those numbers are
correct, we either have significant lensing or only missed it by a narrow
margin...completely independent of energetics worries, a posteriori
statistics, Kulkarni's motivations, etc.  On that basis alone, I would consider
a bit of continued monitoring worthwhile...far from a sure bet, but worth
trying (given the rather minimal observing time cost).

However, 1) there seems to be some confusion about these redshift and
alignment "facts" based on second hand reports from Keck, etc. and 2) I have
heard support for APO monitoring from only a couple of people (Alan and
Karen) and silence from all orhters on the grb distribution list.  So, I am
confused about the alignment situation and am inclined to view the silence
as absence of enthusiasm for an APO monitoring program.  Thus, I have not
scheduled any DD02 program so far.  If you have some view about whether we
should or should not give it a try, please let me know.

Finally, I can report one fact:  HST has scheduled a 3 orbit unfiltered
STIS CCD image of the system for 8-9 Feb UT.  It will be made with STScI DDT
and released to the public immediately, following the day or two it takes it
to filter back to the Institute via TDRS, GSFC etc.  These images should be
plenty deep enough to show distorted and perhaps multiple images of the
host galaxy if there is strong (macro) lensing, and thus pretty well settle 
the issue.  Between now and then, there is relatively little opportunity for
APO monitoring.  Tonight is full moon (but feel free to give it a try with
UW08, if you are so inclined, Alan...either using GRIM2 or DIS before the 
swap following Paula's program), and then we have a long Echelle commissioning
run.  We should decide what we want to do by its end, I guess.



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