2001/01/25 by Bradley E. Schaefer, Ming Deng, D. L. Band +1 · 5 citations
Mathematics · Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysics #Galaxy #Gamma-ray burst #Gamma-ray bursts and supernovae #Lag #Light curve #Logarithm #Luminosity #Luminosity function #Mathematics #Physics #Power law #Redshift #Statistics #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/338651
13 pages, 4 figures, submitted to ApJLett
arxiv created 2001/01/25 · openalex publication_date 2001/12/20 · arxiv updated 2009/12/01 · openalex created_date 2020/11/23 · openalex updated_date 2026/08/05
Two different luminosity indicators have recently been proposed for gamma-ray bursts that use gamma-ray observations alone. They relate the burst luminosity ( L ) with the time lag between peaks in hard and soft energies (τ lag ) and the spikiness or variability of the burst's light curve ( V ). These relations are currently justified and calibrated with only six or seven bursts with known redshifts. We have examined BATSE data for τ lag and V for 112 bursts. (1) A strong correlation between τ lag and V exists, and it is exactly as predicted from the two proposed relations. This is proof that both luminosity indicators are reliable. (2) GRB 830801 is the all-time brightest burst, yet with a small V and a large τ lag , and hence it is likely the closest known event, being perhaps as close as 3.2 Mpc. (3) We have combined the luminosities as derived from both indicators as a means to improve the statistical and systematic accuracy when compared with the accuracy from either method alone. The result is a list of 112 bursts with good luminosities and hence redshifts. (4) The burst-averaged hardness ratio rises strongly with the luminosity of the burst. (5) The burst luminosity function is a broken power law, with the break at L = 2 × 10 52 ergs. The numbers in logarithmic bins scale as L -2.8±0.2 above the break and as L -1.7±0.1 below the break. (6) The comoving number density of GRBs varies with redshift roughly as (1 + z ) 3.5±0.3 between 0.2 < z < 5. This demonstrates that the burst rate follows the star formation rate at low redshifts, as expected since long bursts are generated by very massive stars. Excitingly, this result also provides a measure of the star formation rate out to z ~ 5 with no effects from reddening, and the rate is rising uniformly for redshifts above 2.