SCUBA sub-millimeter observations of gamma-ray bursters. I. GRB 970508, 971214, 980326, 980329, 980519, 980703, 981220, 981226

We discuss our ongoing program of Target of Opportunity observations of gamma-ray bursts (GRBs) using the SCUBA instrument on the James Clerk Maxwell Telescope. We present observations of GRB 970508, 971214, 980326, 980329, 980519, 980703, 981220, and 981226. Our most important result to date is the detection of a fading counterpart to GRB 980329 at 850 mu m. Although it proved to be difficult to find the infrared counterpart to this burst, the sub-millimeter flux was relatively bright. This indicates that the brightness of this counterpart (corrected for absorption) was very similar to GRB 970508. The radio through sub-millimeter spectrum of GRB 980329 is well fit by a power law with index alpha = +0.9. However, we cannot exclude a nu (1/3) power law attenuated by synchrotron self-absorption. An alpha ~ +1 VLA-SCUBA power law spectrum is definitely ruled out for GRB 980703, and possibly also for GRB 980519. We cannot rule out that part of the sub-millimeter flux from GRB 980329 comes from a dusty star-forming galaxy at high redshift, such as the ones recently discovered by SCUBA. Any quiescent dust contribution will be much larger at sub-millimeter than at radio wavelengths. Both a high redshift and large dust extinction would help explain the reddening of the counterpart to GRB 980329. The large intensity of this burst might then indicate that beaming is important.