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The Question

(Submitted September 12, 2009)

How can we confirm the redshift of a Gamma-ray brust?

The Answer

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
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