What fraction of observed GRBs may be galactic?

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Abstract
We analyze the burst fluxes and directions reported in the Second BATSE Burst Catalog in the context of two‐component standard‐candle models that attribute a fraction, f, of observable bursts to a local population in a Bahcall‐Soneira dark matter halo, and the remainder to a cosmological population. Our analysis uses a Bayesian method that fits the joint differential distribution of fluxes and directions, and accounts for measurement uncertainties and selection effects. Models with nonzero f are strongly preferred over purely cosmological models, with the best‐fit value and allowed range of f depending on the luminosity of the halo sources. For bright sources (visible to ≊70 kpc), f≊0.2, with values up to 0.4 within the 95% credible region. For dim sources (visible to ≲1 kpc), f≊0.5±0.13. Most of the improvement arising from inclusion of the local component is due to superior fitting of the flux distribution and not to anisotropy, although the anisotropy of these models does improve their quality of fit.

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