TITLE: GCN GRB OBSERVATION REPORT NUMBER: 40 SUBJECT: GRB980329 VLA observations DATE: 98/04/03 07:10:15 GMT FROM: Greg Taylor at NRAO G.B. Taylor, D.A. Frail (NRAO), S.R. Kulkarni (Caltech), and the BeppoSAX GRB team report: We have observed the field containing the proposed x-ray counterpart 1SAX J0702.6+3850 of GRB 980329 (IAUC 6854) with the VLA at 8.4 GHz on UT 1998 Mar 30.2, April 1.1, and April 2.1. Observations on April 1.1 detected a radio source VLA J0702+3850 within the 1 arcminute error circle of 1SAX J0702.6+3850. The coordinates of VLA J0702+3850 are: ra = 07h02m38.02170s dec = 38d50'44.0170" (equinox J2000) with an uncertainty of 0.05 arcsec in each coordinate. The size of this radio source is less than 0.25 arcsec. The density of sources on the sky stronger than 250 microJy at this frequency is 0.0145 arcmin**-2. The flux density measurements of VLA J0702+3850 are as follows: Date(UT) 8.4 GHz Flux Density -------- ---------------------- Mar 30.2 166 +/- 50 microJy Apr 1.1 248 +/- 16 " Apr 2.1 65 +/- 25 " where the uncertainty in the measurement reflects the 1 sigma rms noise in the image. These measurements clearly demonstrate that the radio source is variable on timescales of less than 1 day. This rapid variability is similar to that observed in the radio afterglow from GRB 970508. We propose VLA J0702+3850 is the radio afterglow from GRB 980329. Additional radio observations are in progress. This note is citable in publications.