Constraining the rate and luminosity function of Swift gammaray bursts
Abstract
We compute the intrinsic isotropic peak luminosity function (LF) and formation rate of long gammaray bursts (LGRBs) using a novel approach. We complement a standard log Nlog P brightness distribution and V_{max} estimations with two observationtime relations: a redshiftobservationtime relation (log zlog T) and a new luminosityobservationtime relation (log Llog T). We show that this approach reduces degeneracies that exist between the rate and LF of a brightness distribution. To account for the complex triggering algorithm employed by Swift, we use recent results of Lien et al. (2014) to produce a suite of efficiency functions. Using these functions with the above methods, we show that a log Llog T method can provide good constraints on the form of the LF, particularly the high end. Using a sample of 175 peak luminosities determined from redshifts with welldefined selection criteria, our results suggest that LGRBs occur at a local rate (without beaming corrections) of [0.7 < ρ_{0} < 0.8] Gpc^{3} yr^{1}. Within this range, assuming a broken powerlaw LF, we find best estimates for the low and highenergy indices of 0.95 ± 0.09 and 2.59 ± 0.93, respectively, separated by a break luminosity 0.80 ± 0.43 × 10^{52} erg s^{1}.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 October 2014
 DOI:
 10.1093/mnras/stu1403
 arXiv:
 arXiv:1407.2333
 Bibcode:
 2014MNRAS.444...15H
 Keywords:

 methods: data analysis;
 gammaray burst: general;
 supernovae: general;
 cosmology: miscellaneous;
 Astrophysics  High Energy Astrophysical Phenomena
 EPrint:
 Accepted for publication in MNRAS