GCN Circular 25

Optical Observations of the GRB971227 field:                            #025

S. G. Djorgovski, S. R. Kulkarni, A. N. Ramaprakash, (Caltech), and 
D. Frail (NRAO) report on behalf of the Caltech GRB collaboration:

"There has been some confusion regarding various objects in the field 
of 1SAX J1257.3+5924, the proposed x-ray counterpart of GRB 971227.
Keck R-band images of the field (obtained on UT 1997 Dec 30.8, limiting
magnitude R ~ 25.5) can be obtained at the following URL:

http://astro.caltech.edu/~george/grb/grb971227.html

There we mark several objects, whose positions (good to 0.4 arcsec,
on the basis of USNO A1.0 catalog) are:

Object   type      RA(J2000)     DEC(J2000)   R mag

   A     star     12 57 13.68   +59 23 36.7   19.1
   B     star     12 57 11.15   +59 24 45.4   22.1
   C     galaxy   12 57 08.74   +59 24 35.7   20.6
   D     star     12 57 04.95   +59 24 39.2   19.4
   E     galaxy   12 57 08.22   +59 24 52.4   21.4
   F     galaxy   12 57 08.30   +59 25 00.5   21.25

The magnitudes have been zero-pointed using a set of APM objects in the 
field; the zero-point is uncertain by at least 0.2 mag.

Star B is the closest object to the detection claimed by Castro-Tirado 
et al. (GCN 30
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 Dec97 [#020], and IAUC 6800), even though it is 4.8 arcsec away 
from their estimated position.  In particular, no object was detected 
within their nominal (3 arcsec radius) error circle down to a magnitude 
of R ~ 24 or even fainter in the Keck images of Dec 30.8 UT.  Star B 
remains constant in brightness over the time span of our data (cf. our earlier
GCN note [#024]), and indeed we detect no significantly variable objects 
in the entire error circle of the x-ray source down to the limits of our 
data.  If the detection claimed by Castro-Tirado et al. was real, it 
would imply a fading with a power-law slope of t^(-2.5) or steeper.

D is the comparison star mentioned by Galama et al. (GCN 31
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 Dec97 [#021]), even 
though it is about 3 arcsec away from their quoted position, and galaxy C 
is almost certainly the object they propose as the possible identification 
of the claimed detection by Castro-Tirado et al.

A is a convenient comparison/offset star.  E and F are random galaxies 
in the same area, also given here as comparisons.

We conclude that there is thus far no evidence for an optical transient
associated with this gamma-ray burst down to significantly faint magnitude
limits, similar to the cases of GRB 970815 and 970828.

This message can be cited."




[GCN Operator's Note:  I have attempted to correct a developing problem of how
to refer to earlier GCN Messages by retroactively adding serial numbers
to the messages contained in the archive files.  I have also added the
appropriate numbers to the three messages referenced in the above message --
that would be the numbers in square brackets [#0nn].  Starting with this
GCN Message, unique serial numbers will be added for reference purposes;
however, it is still wise to refer to the first author as well as the number.]