2007/02/27 by E. Berger · 2 citations
Physics and Astronomy · #Astro and Planetary Science #Gamma-ray bursts and supernovae #Pulsars and Gravitational Waves Research #astro-ph
paper · pdf · doi:10.1086/522195
Submitted to ApJ; 9 pages, 2 figures, 1 table
arxiv created 2007/02/27 · openalex publication_date 2007/12/01 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/31
I present an analysis of the γ-ray and afterglow energies of a complete sample of 16 short-duration GRBs with prompt X-ray follow-up. I find that 80% of the bursts exhibit a linear correlation between their γ-ray fluence and the afterglow X-ray flux normalized to t = 1 day, a proxy for the kinetic energy of the blast wave ( F X,1 ∝ F ). An even tighter correlation is evident between the isotropic γ-ray energy, E γ,iso , and the X-ray luminosity at t = 1 day, L X,1 , for the subset of 12 bursts with measured or constrained redshifts. The remaining 20% of the bursts have values of F X,1 / F γ that are suppressed by about 3 orders of magnitude, likely as a result of low circumburst densities; this has been noted based on a smaller sample by Nakar (2007). These results have several important implications: (1) the X-ray luminosity is generally a robust proxy for the blast wave kinetic energy, indicating ν X > ν c , and hence a circumburst density n ≳ 0.05 cm -3 ; (2) most short GRBs have a narrow range of γ-ray efficiency, with ⟨ γ ⟩ ≈ 0.1 and a spread of 0.3 dex; and (3) the isotropic-equivalent energies span 10 48 -10 53 erg. Furthermore, I find tentative evidence for jet collimation (opening angle, θ j ≈ 6 ° ) in GRB 061006 leading to E γ ≈ 4 × 10 48 erg, similar to other short bursts with jet breaks. I find no clear evidence for a relation between the overall energy release and host galaxy type, but a positive correlation with duration may be present, albeit with a large scatter. Finally, I note that the low-density hypothesis for the outliers can be explained in the context of neutron star-neutron star (NS-NS) mergers in globular clusters (as opposed to large kick velocities), but present short GRB rate estimates may be an order of magnitude too large for this scenario to work.