4270ef9b___The_Gamma_Ray_Bursts_Catalog__Definition
[Geometry] Annulus [Definition] 
The annulus region is described by a center given in RA and Dec, the radius of the annulus (corresponding to the center betewen the inner and outer radii) and by the half-width of the annulus.
GRBCAT - The Gamma-Ray Bursts Catalog
Definition