GRB 980613 follow-up work
S. G. Djorgovski, S. R. Kulkarni, S. C. Odewahn, et al.,
on behalf of the Caltech GRB collaboration:
The text of the
GCN Circ. #114:
GRB 980613: Detection of the probable host galaxy
S. G. Djorgovski, S. R. Kulkarni, S. C. Odewahn (Caltech), and H. Ebeling
(IfA, Univ. of Hawaii), report on behalf of the Caltech GRB collaboration:
Images of the field of GRB 980613 were obtained bu H. Ebeling at the Keck-II
telescope on UT 1998 June 16.3, in the R band. We detect a galaxy coincident
to within 0.5 arcsec with the optical transient (OT) reported by Hjorth et al.
( GCN Circ. #109).
The galaxy may include a faint, unresolved source, which
may be the faded OT. The preliminary total magnitude of the object at the
epoch of our observations, assuming the zero-point given by Hjorth et al.
(R = 19.1 for their star 1, which is identical to star 2 of Diercks et al.,
GCN Circ. #108),
is R ~ 23.3, which is consistent with the conservative
upper limits reported by Hjorth et al. for their June 17 image. We
propose that this is the host galaxy of GRB 980613.
Further analysis of these data is in progress. Images will be posted at:
http://astro.caltech.edu/~george/grb/grb980613.html
This message can be cited.
The text of the
GCN Circ. #117:
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 Circ. #114),
calibrated with the Palomar 60-inch images (see
GCN Circ. #105),
gives the following
results:
We resolve the image of the optical transient (OT) found by Hjorth et al.
( GCN Circ. #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 Circ. #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.
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
= 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:
http://astro.caltech.edu/~george/grb/grb980613.html
This message can be cited.
NB: The images posted here before 5 pm PDST on June 19 had the wrong
object marked -- we apologize for the mistake. These are correct.
CCD image in the R band obtained at the Keck-II telescope by H. Ebeling,
on UT 1998 June 16.30.
The field shown is approximately 170 arcsec square, and the image is
tilted w.r.t. the standard orientation so that the vertical axis is at
a PA of about 23 degrees.
Stars 1 - 5
of Diercks et al. (GCN 108) are marked. The probable host galaxy of
the burst, coincident with the optical transient found by Hjorth et al.
(GCN 109) is indicated.
This image is available in
Postscript ,
and
GIF formats.
A zoom-in on the same image, approximately 32 arcsec square. The point
source, corresponding to the optical transient, and an extension, presumably
its host galaxy, are visible. The total integrated magnitude was about
r = 24.15 at this epoch, with approximately equal shares of the flux in
the point source and in the extended galaxy.
This image is available in
Postscript ,
and
GIF formats.
Hjorth et al. webpage on this burst
Diercks et al. webpage on this burst
Caltech work on other GRBs