(Submitted September 12, 2009)
How can we confirm the redshift of a Gamma-ray brust?
The redshift of gamma-ray bursts can be measured in several different
ways. For relatively nearby ones, we can wait for the gamma-ray bursts
themselves to fade, and obtain long-exposure spectra of the host
galaxies. There are now so many gamma-ray bursts with known host
galaxies, so this method is as solid as it gets in cosmology.
For more distant gamma-ray bursts, for which the host galaxy is too
faint for the current generation of instruments, things are a bit
trickier. In such a case, astronomers often are able to detect
absorption features in the gamma-ray afterglows themselves (which,
in the optical, persist for hours to days). Such absorption may
occur in the host galaxies, or in the intergalactic space between
us and the host galaxies. Therefore, the measured redshift of the
absorbers is the minimum redshift for the gamma-ray bursts themselves.
Hope this helps,
Koji & Barb
for "Ask an Astrophysicist"