The Error Distribution of BATSE GRB Locations

Abstract

Empirical probability models for BATSE GRB location errors are developed via a Bayesian analysis of the separations between BATSE GRB locations and locations obtained with the InterPlanetary Network (IPN). Models are compared and their parameters estimated using 392 GRBs with single IPN annuli and 19 GRBs with intersecting IPN annuli. Most of the analysis is for the 4Br BATSE catalog; earlier catalogs are also analyzed. The simplest model that provides a good representation of the error distribution has 78% of the probability in a `core' term with a systematic error of 1.85 degrees and the remainder in an extended tail with a systematic error of 5.1 degrees, implying a 68% confidence radius for bursts with negligible statistical uncertainties of 2.2 degrees. There is evidence for a more complicated model in which the error distribution depends on the BATSE datatype that was used to obtain the location. Bright bursts are typically located using the CONT datatype, and according to the more complicated model, the 68% confidence radius for CONT-located bursts with negligible statistical uncertainties is 2.0 degrees.