2003ApJ...590..192C

We present 1.4 GHz VLA observations of the variability of radio sources in the Lockman Hole region at the level of ≥100 µJy on timescales of 17 months and 19 days. These data indicate that the areal density of highly variable sources at this level is <5x10^–3 arcmin^–2. We set an upper limit of 2% to the fraction of 50 to 100 µJy sources that are highly variable (ΔS≥50%). These results imply a lower limit to the beaming angle for gamma-ray bursts (GRBs) of 1° and give a lower limit of 200 arcmin² to the area that can be safely searched for GRB radio afterglows before confusion might become an issue.