The lag was shorter for the more luminous bursts. The new work was reported at the Fifth Huntsville Gamma-Ray Burst Symposium in Huntsville, Alabama, on October 19, and has been accepted for publication to The Astrophysical Journal. Related findings, derived independently by Dr. Edward Fenimore of Los Alamos National Laboratory and also reported to the Huntsville conference, lend confidence to the new result, astronomers say. Gamma-ray bursts were discovered in the late 1960s, but only recently have most astronomers agreed that a large fraction of the bursts originate in the very distant, early Universe. The bursts fade quickly at gamma-ray energies and are hard to pinpoint, making it difficult to observe a burst's optical afterglow and determine a distance, or redshift.
Redshift is a common measurement of astronomical distances.
The more distant an object is from Earth, the faster it is receding due to the expansion of the Universe, and the greater its light is stretched or redshifted. This is similar to the way a siren on an ambulance appears to drop in pitch as the ambulance speeds away. Objects at high redshifts serve as probes to the early Universe, for their light has taken billions of years to reach Earth. Yet of the thousands of gamma-ray bursts detected, fewer than ten have had an afterglow or host galaxy whose redshift could be determined with optical telescopes. This new finding by Goddard scientists has the potential of gauging the distances of many bursts from gamma-ray data alone.