J. Greiner, A. Rau (both MPE Garching) and S. Klose
(Thueringer Landessternwarte Tautenburg) report for the GRACE collaboration:
We have observed the original, 2 arcmin radius error box of GRB 030528
(=H2724) (Atteia et al, GCN 2256) with the near-infrared camera SOFI
at the NTT (La Silla, ESO) on three epochs as given below:
Date (Start UT) Filters Exposure time Seeing
2003-05-29 04:58 JHKs 15 min each 0.6"
2003-05-30 04:54 JHKs 20 min each 1.0"
2003-06-01 04:07 Ks 60 min 0.7"
The Chandra sources #1 and #10 (Butler et al., GCN 2269) are within
our field of view, the other two Chandra sources from within the
shifted GRB location (Villasenor et al, GCN 2261) are outside our
images. Comparing the Ks band images of the first and third epoch
reveals a counterpart for each of the two Chandra sources. One of
these two sources, i.e. #1 = CXOU J170400.3-223710 shows a fading
by about 0.9 mag. The other of these two Chandra sources,
#10 = CXOU J170354.0-223654 is about 4 magnitudes brighter in Ks, and
constant to within 0.1 mag (provisional photometric calibration was
done against the 2MASS catalog, taken from the NASA/ IPAC Infrared
We therefore propose Chandra source #1 = CXOU J170400.3-223710 and
its near-infrared counterpart as the tentative afterglow of GRB 030528.
K band images of two epochs for this source will be displayed at
Since we are missing two of the Chandra sources due to the shift of the
GRB location, only a second Chandra observation can (dis)prove this
tentative counterpart. We note, that the proposed counterpart is
the brightest X-ray source in the previous Chandra image, so a second
Chandra observation of the same exposure time can already be decisive.