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GCN Circular 117

GRB 980613: Optical transient and its host galaxy
1998-06-19T23:23:44Z (25 years ago)
George Djorgovski at Caltech/Palomar <>
[GCN Operator's Note:  This is a redistribution of GCN 117 to correct
a typo in the original distribution.  See full explanation below.]

GRB 980613:  Optical transient and its host galaxy

S. G. Djorgovski, S. R. Kulkarni, and S. C. Odewahn (Caltech), and H. Ebeling
(IfA, Hawaii) report on behalf of the Caltech GRB collaboration:

Further analysis of the Keck images of the field of GRB 980613 (see GCN 114),
calibrated with the Palomar 60-inch images (see GCN 105) gives the following

We resolve the image of the optical transient (OT) found by Hjorth et al.
(GCN 109) from its host galaxy, which extends up to 1.5 - 2 arcsec from
the point source (the OT) in approximate PA ~ 70 deg.

Magnitudes of stars 1-5 from Diercks et al., GCN 108, in the Gunn r band are:

ARC star 1    r = 18.45   RA = 10 17 47.559  DEC = +71 27 00.75
ARC star 2    r = 19.59   RA = 10 17 54.828  DEC = +71 27 39.81
ARC star 3    r = 20.82
ARC star 4    r = 20.07
ARC star 5    r = 19.51   RA = 10 17 41.456  DEC = +71 28 09.11

The positions given are from the USNO A1.0 catalog where available (J2000).
ARC star 2 is identical to star 1 from Hjorth et al. (GCN 109).

In this system, the integrated magnitude of the optical transient (OT) plus
its apparent host galaxy is:  r = 24.15 +- 0.3.  The total flux is divided
approximately equally between the two.  Assuming the mean zero-point offset
<r-R> = 0.4, this implies the magnitude for the OT at this epoch (June 16.30
UT) of R = 24.5 +- 0.5 (and the same for the host galaxy).

Using the measurement of R = 22.9 +- 0.2 on June 13.9 UT from Hjorth et al.,
the implied power-law decay slope is -1.0, which is perfectly normal for
GRB afterglows.

Images are now posted at:

This message can be cited.

[GCN Operator's Note: D. Djorgovski, et al., points out that there was a typo
in their original submission to GCN Circular 117.  The text above is the
corrected version.
The original quoted the "... its apparent host galaxy is:  r = 25.15 +- 0.3",
when it should have said "... its apparent host galaxy is:  r = 24.15 +- 0.3."
This second distribution has been given the same serial number.  The archive
files on the GCN web site have been corrected.]
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