Intensity Distribution and Luminosity Function of the Swift Gamma-Ray Bursts

Abstract

Using the sample of long Gamma-ray bursts (GRBs) detected by Swift-BAT before June 2007, we measure the cumulative distribution of the peak photon fluxes (log N - log P) of the Swift bursts. Compared with the BATSE sample, we find that the two distributions are consistent after correcting the band pass difference, suggesting that the two instruments are sampling the same population of bursts. We also compare the log N - log P distributions for sub-samples of the Swift bursts, and find evidence for a deficit (99.75% confident) of dark bursts without optical counterparts at high peak flux levels, suggesting different redshift or Gamma-ray luminosity distributions for these bursts. The consistency between the log N - log P distributions for the optically detected bursts with and without redshift measurements indicates that the current sample of the Swift bursts with redshift measurements, although selected heterogeneously, represents a fair sample of the non-dark bursts. We calculate the luminosity functions of this sample in two redshift bins (z<1 and z>1), and find a broken power-law is needed to fit the low redshift bin, where dN/dL \propto L^{-1.27\pm0.06} for high luminosities (L_{peak} > 5e48 erg/s) and dN/dL \propto L^{-2.3\pm0.3} at for low luminosities, confirming the results of several studies for a population of low luminosity GRBs.

13 pages, 3 figures, Accepted by ApJ Letters

References in corpus (14)

• On the normalisation of the cosmic star formation history
• An optical supernova associated with the X-ray flash XRF 060218
• Relativistic ejecta from XRF 060218 and the rate of cosmic explosions
• Low Luminosity Gamma-Ray Bursts as a Unique Population: Luminosity Function, Local Rate, and Beaming Factor
• On the Rates of Gamma Ray Bursts and Type Ib/c Supernovae
• Swift Identification of Dark Gamma-Ray Bursts
• The First Swift BAT Gamma-Ray Burst Catalog
• SN 2006aj and the nature of low-luminosity gamma-ray bursts
• An Unexpectedly Swift Rise in the Gamma-ray Burst Rate
• Low-Luminosity Gamma-Ray Bursts as a Distinct GRB Population:A Firmer Case from Multiple Criteria Constraints
• Post-Launch Analysis of Swift's Gamma-Ray Burst Detection Sensitivity
• The Gamma Ray Burst Luminosity Function in the Light of the Swift 2-year Data
• Evidence for Luminosity Evolution of Long Gamma-ray Bursts in Swift Data
• Gamma-Ray Bursts are Produced Predominately in the Early Universe

Cited by in corpus (14)

• Discerning the physical origins of cosmological Gamma-ray bursts based on multiple observational criteria: the cases of z=6.7 GRB 080913, z=8.3 GRB 090423, and some short/hard GRBs
• The Afterglows of Swift-era Gamma-Ray Bursts. I. Comparing pre-Swift and Swift era Long/Soft (Type II) GRB Optical Afterglows
• Connecting the Gamma Ray Burst Rate and the Cosmic Star Formation History: Implications for Reionization and Galaxy Evolution
• Gamma-ray burst rate: high-redshift excess and its possible origins
• Diffuse PeV neutrinos from gamma-ray bursts
• Redshift distribution and luminosity function of long gamma-ray bursts from cosmological simulations
• Nearby low-luminosity GRBs as the sources of ultra-high energy cosmic rays revisited
• Counts of high-redshift GRBs as probe of primordial non-Gaussianities
• High-energy gamma-ray afterglows from low-luminosity gamma-ray bursts
• GRB Probes of the High-z Universe with EXIST
• Modeling gamma-ray burst observations by Fermi and MAGIC including attenuation due to diffuse background light
• SRG/eROSITA prospects for detection of GRB afterglows
• The Optical Luminosity Function of Gamma-ray Bursts deduced from ROTSE-III Observations
• Study of shock wave dynamics produced by interaction of a fireball with the surrounding medium to it, to explain the x-ray afterglow of Gamma Ray Burst-GRBs