TITLE: GCN GRB OBSERVATION REPORT NUMBER: 887 SUBJECT: Optical/NIR observations of GRB001109 DATE: 00/11/18 16:12:48 GMT FROM: Jochen Greiner at Astrophys.Inst. Potsdam,Germany J. Greiner (AIP, Potsdam), B. Stecklum, S. Klose (both TLS, Tautenburg), A.J. Castro-Tirado (LAEFF-INTA, Madrid and IAA-CSIC, Granada), F.J. Vrba, A.A. Henden (both US Naval Observatory, Flagstaff), M. Feldt (MPIA, Heidelberg), L. Montoya, A. Aguire (both Calar Alto), J. Fliri (LMU, Muenchen), J.M. Castro Ceron (ROA, San Fernando), report: Starting at about 9 hrs after the occurence of GRB 001109 we have observed its 50 arcsec radius error box (GCN #879, #885, IAUC 7519) in the B, R, I and H band with the Calar Alto (CA), and Naval Observatory Flagstaff Station (NOFS) telescopes as detailed below: -------------------------------------------------------------------- Date (UT) Telescope filter exposure seeing limiting (Start) (sec) (arcsec) mag. -------------------------------------------------------------------- Nov. 09.7712 CAHA 1.23 R 7 * 500 1.0 20.9 Nov. 09.7846 CAHA 1.23 B 3 * 600 1.0 19.8 Nov. 10.0980 NOFS 1.0 I 1800 1.9 21.0 Nov. 10.7623 CAHA 1.23 R 9 * 500 1.0 20.9 Nov. 10.8379 CAHA 3.5 H 10 * 300 1.5 20.5 Nov. 13.0664 NOFS 1.0 I 1800 2.6 21.0 -------------------------------------------------------------------- Photometric calibration of the images was done based on USNO magnitudes in the B and R band, and with selected area SA 113 for the I band. A comparison of the two epochs of (summed) R-band and I-band images, respectively, reveals no fading object in the GRB error box down to the limiting magnitudes as given in the table. The summed B band image does not contain any source which is not visible on the blue DSS-2. The H band image, when compared to the H band images of Vreeswijk et al. (GCN #886) also shows no fading object in the GRB error box. The optical source coincident with the radio source mentioned in GCN #880 is detected at R=20.70+/-0.15 (Nov. 9), I=20.07+/-0.1 and R=20.63+/-0.15 (Nov. 10) and I=20.13+/-0.1 (Nov. 13). The constancy of this source as well as the extended shape (GCN #886) make it possible that it could be the host galaxy of GRB 001109. If true, (i) this burst could be similar to GRB 981226 with a radio, but no optical/IR counterpart, and (ii) it would be the brightest host galaxy of any GRB. If, in addition, the GRB occured within that galaxy without substantial offset, the optical afterglow would not have to be particularly faint to be hidden by the light of the galaxy. Under these assumptions, we estimate that we can place a limit of only R > 21.5 mag at 9 hrs and I > 22 mag at 17 hrs after the GRB. We finally note that we don't see very many obvious galaxies in these images. Perhaps there is higher extinction than would normally be expected at this high galactic latitude (bII=+24.96).