# Improved Fermi-GBM GRB localizations using BALROG

## TL;DR

This paper improves the localization accuracy of Fermi-GBM gamma-ray bursts by using the BALROG method, reducing systematic errors from several degrees to about 1-2 degrees through simultaneous spectral and positional fitting.

## Contribution

The study demonstrates that systematic localization errors in Fermi-GBM GRBs can be significantly reduced by applying the BALROG method, which accounts for spectral mismatches.

## Key findings

- Systematic errors reduced to 1-2 degrees.
- Validated method on 105 bright GRBs with Swift localizations.
- Improved localization accuracy enhances follow-up observations.

## Abstract

The localizations of gamma-ray bursts (GRBs) detected with the Gamma-ray Burst Monitor (GBM) onboard the Fermi satellite are known to be affected by significant systematic errors of 3-15 degrees. This is primarily due to mismatch of the employed Band function templates and the actual GRB spectrum. This problem can be avoided by simultaneously fitting for the location and the spectrum of a GRB, as demonstrated with an advanced localization code, BALROG (arXiv:1610.07385). Here, we analyze in a systematic way a sample of 105 bright GBM-detected GRBs for which accurate reference localizations are available from the Swift observatory. We show that the remaining systematic error can be reduced to $\sim$1-2 degrees.