GCN Circular 2271

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
Not found
 
 
) 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
Not found
 
 
) are within
our field of view, the other two Chandra sources from within the 
shifted GRB location (Villasenor et al, GCN 2261
Not found
 
 
) 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 
Science Archive).

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
http://www.mpe.mpg.de/~jcg/grb030528.html

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.