TITLE: GCN GRB OBSERVATION REPORT NUMBER: 55 SUBJECT: GRB980329, Fading IR counterpart to radio source DATE: 98/04/12 14:10:51 GMT FROM: Mark R. Metzger at CIT M.R. Metzger (Caltech) reports: Near-infrared K-band images of the area surrounding the variable radio source detected by Taylor et al. (GCNC #40), possibly associated with GRB 980329 (IAUC 6853, 6854), were obtained on Apr 6.27 and Apr 8.28 with the Keck-I 10m telescope. The source reported by Larkin et al. (GCNC #51, coincident with the galaxy reported by Djorgovski et al., GCNC #41) was detected on both nights, at K=21.4 +/- 0.2 mag (6.27) and K = 21.9 +- 0.4 mag (8.28). Comparison with the magnitudes reported by Larkin et al. indicates that the source has faded by about 1 mag between Apr 2.3 and Apr 8.28. This suggests that part of the K flux may be IR afterglow of GRB 980329. It is consistent with fading, detections, and upper limits reported previously (GCNC #41, #46, #48, IAUC 6864, 6866, 6868). Further measurements are suggested to estimate the IR brightness of any underlying host. ------------ Mark R. Metzger, mrm@astro.caltech.edu Caltech 105-24 Pasadena, CA 91125 [GCN Operator's Note: If you received 1 copy (this copy) of this circular, you have not completed the 6 pieces of information needed to be converted from this old manual method of distributing the circulars to the new automated method. Not only does this delay the distribution of the circulars to you, but it also means that you are not enabled for submitting to the automated system. If you received two copes of this circular, it means that you are signed up for the automatic list (you need do nothing further) and that I have not deleted you from the old manual list yet.]