We invert directly the redshift-luminosity distribution of observed long Swift gamma-ray bursts (GRBs) to obtain their rate and luminosity function. Our best-fitting rate is described by a broken power law that rises like for 0 < z < 3 and decreases like for z > 3. The local rate is ρ0 ~= 1.3+0.6-0.7 (Gpc-3yr-1). The luminosity function is well described by a broken power law with a break at L* ~= 1052.5+/-0.2 (ergs-1) and with indices α = 0.2+0.2-0.1 and β = 1.4+0.3-0.6. The recently detected GRB090423, with z ~ 8, fits nicely into the model's prediction, verifying that we are allowed to extend our results to high redshifts. While the GRB rate may follow the star formation rate (SFR) for z < 3, the high-redshift slope is shallower than the steep decline in the SFR for 4 < z. However, we cannot rule out a GRB rate that follows one of the recent SFR models.
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- August 2010
- gamma-ray burst: general;
- stars: formation;
- Astrophysics - High Energy Astrophysical Phenomena;
- Astrophysics - Cosmology and Extragalactic Astrophysics
- Significantly revised version, including a comparison of the GRB rate to new results on the SFR, revisions in response to the referee comments and comparison with other works on the GRB rate. 28 pages, 14 figures, 5 tables. MNRAS.