TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  645
SUBJECT: GRB000418, near-infrared observations
DATE:    00/04/25 18:04:17 GMT
FROM:    Sylvio Klose at TLS Tautenburg  <klose@tls-tautenburg.de>

S. Klose, B. Stecklum (Thueringer Landessternwarte Tautenburg),
O. Fischer (Universitaets-Sternwarte Jena), 
J. Gorosabel (DSRI, Copenhagen),  
C. Sanchez-Fernandez (LAEFF-INTA, Madrid),
A. Castro-Tirado (LAEFF-INTA, Madrid, and IAA-CSIC, Granada), 
D. Butler (Max-Planck-Institut fuer Extraterrestrische Physik, Garching),
S. Hippler, Th. Ott, M. Kasper, R. Weiss
   (Max-Planck-Institut fuer Astronomie, Heidelberg),
L. Montoya, A. Aguirre (Max-Planck-Institut fuer Astronomie, Heidelberg, 
   and Calar Alto observatory),
F. J. Vrba, A. A. Henden, C. B. Luginbuhl, B. Canzian, S. E. Levine, 
   H. H. Guetter, J. A. Munn (U.S. Naval Observatory, Flagstaff),
D. H. Hartmann (Clemson University, Clemson), and
J. Greiner (AIP Potsdam)

report:


The central part of the error box of GRB 000418 (Hurley et al., GCN
#642) was imaged with the Calar Alto 3.5-m telescope on April 20,
20:55 UT - 21:54 UT, using the near-infrared camera Omega Cass. The
limiting magnitude of the K'-band image is about K'=17 after adding
all images taken at different position angles of a wire-grid
polarizer. A second observing run was performed on  April 22, 02:22 UT
- 03:23 UT, using the same telescope and the same instrumentation.

The same region of the error box was also covered by K'-band (April
20, 22:06 UT - 22:46 UT and April 24, 21:36 UT - 22:30 UT) and
J-band images (April 21, 22:23 UT - 22:48 UT) taken with the Calar
Alto 1.23-m telescope using the near-infrared camera MAGIC.
Additional frames covering the whole error box (Hurley et al. GCN
#642) are being processed and the results will be reported soon.

A comparison between the April 20 and April 22 images and a
cross-check with the 1.23-m images has revealed a potentially fading
source within the central GRB error box at RA, DEC (J2000) =
12:25:19.3, 20:06:12 (+/- 1 arcsec). This source (K' ~ 16) is visible
on the 3.5-m and 1.23-m frames obtained during the first night. It has
no counterpart on the corresponding DSS2-red image. Since standard
stars are not available at the moment we can only  provide a rough
estimate of the brightness of the source. Further data reduction 
is in progress.

The K'-band image from April 22 will be posted on the Tautenburg Web page at
http://www.tls-tautenburg.de/research/grb000418.html.


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