Redshift and blueshift are what we observe when the electromagnetic radiation (light at various energies) appears shifted to the left or toward the right due to motion (the light source moving toward or away from us, or us moving toward or away from the light source). Cosmological redshift is the redshift caused by the expansion of the universe. The larger the redshift, the greater the distance the light source is from us, and the farther back in time we are observing.

Gamma-ray burst measurements, from what I understand, are obtained from the observations of the burst host galaxies. If a GRB is associated with a galaxy, the redshift of the GRB should be the same as the redshift of the galaxy. (I am ignoring, for the moment, that an assumed galaxy association is merely coincidence and that the galaxy is actually at a different distance than the GRB.) By measuring the redshift, we can get an idea of how far from us the GRB occurred (and how far back in time). The closest GRB observed (I think) had a redshift of 0.01, and the farthest GRB observed (I think) had a redshift of around 6.3. The measurements and interpretations are always in debate, but I think that's the current consensus.

I've been going through the GRBs in my timing study and gathering reported redshift measurements and upper limits. Nearly half of them have a reported value. I don't really know what I'm looking for yet. Perhaps all the close ones have some property I never noticed before, or the farther ones have some other correlation which makes them interesting. I'm really not sure.

I'm at the point where I'm gathering information and facts and looking to see if there are any puzzle pieces which might go together in a way that creates a different picture than the one on the box sold to the masses. Since childhood, I've loved puzzles. :)