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GCN Circular 23

1970-01-01T00:00:00Z (55 years ago)
Dave Balam additionally reports:

  A precise optical position of Object 3 in our previous report has been 
  determined as follows:

              12h 57m 04s.93 +59o 24' 39".1 (J2000)

  The astrometric solution was obtained using 17 USNO catalog stars, 
  m.e. 0".41 (RA) and 0".32 (Dec)

[The "previous report" referred to above is attached below for reference. SDB]
Howard E. Bond (Space Telescope Science Institute)
David Balam (University of Victoria)
Kailash C. Sahu (Space Telescope Science Institute)

There seems to have been some confusion about possible optical counterparts of 
GRB 971227 in recent GCN e-mails.

We believe that this is because THREE different optical objects have been
mentioned in recent communications, as follows: 

Object            RA    (J2000)    Dec       Remarks

   1              12h57m10.6s   +59o24'43"   proposed as GRB counterpart by 
                                             Castro-Tirado et al., IAUC 6800

   2              12h57m08.6s   +59d24'40"   described as non-variable at 
                                             R=20.4 by Galama et al. (GCN 
                                             notice Dec 31) based on KPNO and 
                                             APO data

   3              12h57m04.8s   +59d24'42"   reference star with R=19.0 used 
                                             by Galama et al.

We note that objects 1 and 2 ARE NOT IDENTICAL.  Object 2 is in fact faintly
visible on direct examination of POSS-II films, in accordance with the above
report of non-variability.  Object 1 is NOT visible on POSS-I prints nor the 
POSS-II films.

A 630-sec CCD R-band exposure on the field was obtained on 1997 Dec 31.44
by D. Balam under poor observing conditions with the 1.8-m Plaskett reflector
of the Dominion Astrophysical Observatory; the limiting magnitude (S/N=3) is
R=20.5 (assuming Object 3 to have R=19.0). Object 2 is faintly visible, in
accordance with the above. 

Object 1, visible at R=19.5 in a Calar Alto image of Dec 27.91 posted on the
WWW by Castro-Tirado et al. (see IAUC 6800), and reported as NOT seen above
R=20.5 on Dec 30.16 by Bartolini et al. (GCN notice, Dec 30), is likewise NOT
visible above R=20.5 in Balam's image of Dec 31.44. 

This observation would appear to strengthen the reported variability of Object
1 and its identification with the GRB afterglow. 

Deeper images should urgently be obtained and monitoring should continue.
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