Preflight 6

Reading:

Pick at least one of the following hot-off-the-presses discussions of the current high-redshift recordholding object, the gamma-ray burst GRB 090423. The Zhang article is less technical. while the two other articles show the real data and analysis, but are accessbile.

Bing Zhang, "Most distant cosmic blast seen"

Nature 461, 1221-1223 (2009) or arXiv:0911.0202

N.R. Tanvir et al, "A gamma-ray burst at a redshift of z~8.2"

Nature 461, 1254-1257 (2009) or arXiv:0906.1577

R. Salvaterra et al, "GRB 090423 at a redshift of z ~ 8.1"

Nature 461, 1258-1260 (2009) or arXiv:0906.1578

Questions

The questions are really meant to help guide your thinking as you read. You may find it helpful to look at the questions first and bear them in mind as you read.

1. Gamma-Ray Bursts: The Basics
   1. What are the main observed properties of gamma-ray bursts as seen in the gamma-ray band?
   2. What evidence did BATSE give that GRBs are cosmological? How strong is this evidence?
   3. Prior to BATSE, few theorists believed GRBs had a cosmological orign. What was the main objection? Where does this issue stand in light of our current understanding of GRBs?
   4. In the BATSE era, a strong argument against cosmological GRBs came from the GRB fluence distribution. What is a fluence? Why is the fluence distribution most simply explained in a Galactic GRB model? Finally, given that GRBs are definitely cosmological, what might account for the observed behavior of the fluence distribution?

2. Gamma-Ray Burst 090423.
   Read at least one of the nature articles above.
   1. What data lead to the redshift estimate for this burst? What was the age of the universe at this redshift; how does this compare to the current age?
   2. How does GRB 090423 compare to other bursts? What is known about its host, and how does it compare with other GRB hosts? What does this suggest about the nature of GRBs?
   3. What do we learn qualitatively from the fact that there was an observable GRB at this redshift? What can we learn quantitatively?
   4. Given current technology, what is the higest redshift at which a burst could be detected? How might high-redshift bursts be used as probes of astrophysics and cosmology?

3. What material did you find difficult, confusing, or unclear? What material would you like to know more about?

4. Other questions or comments?