Gamma Ray Bursts

1. 1 Gamma Ray Bursts Ashley S. Pagnotta Texas A&M University November 25, 2003 All sources cited at end.

2. What is a Gamma Ray Burst? Gamma Ray Bursts (GRBs) are very short bursts of gamma rays from a distant point in space. They are believed to be associated with a certain type of supernova called a hypernova and with the formation of black holes. 2 NASA graphic of the initial stage of a GRB.

3. What are Gamma Rays? Gamma (γ) rays are a type of electromagnetic radiation. As such, they travel at the speed of light, and exhibit the same wave-particle duality as the rest of the spectrum. They are the highest energy photons that have ever been detected. This means that they also have the shortest wavelength, approximately 0.0001 nm. 3

4. How were Gamma Ray Bursts discovered? In the late 1960’s, the American government launched satellites to watch the Soviet Union and ensure they were holding to the provisions of the nuclear test ban treaty. They sent up satellites to detect gamma rays, since these are released in large quantities during nuclear explosions. The satellites, however, detected gamma rays coming from distant sources in outer space. At first it was unclear as to whether the sources were within the boundaries of the Milky Way or extragalactic. This discovery excited astronomers and led them to study these mysterious bursts much more closely. 4

5. Two Types of Gamma Ray Bursts There are two main types of Gamma Ray Bursts: short and long duration. Short duration bursts last from a few milliseconds to 2 seconds (with 0.3 seconds being the average duration). Long duration bursts last longer than 2 seconds, and can last up to several minutes, however the average duration is approximately 30 seconds. Much more is known about long duration bursts and this presentation will focus on them. 5 Duration curves for three GRBs. As you can see, no two GRBs are alike.

6. What causes Gamma Ray Bursts? 6 Typical massive star (“Wolf-Rayet” Star) Astronomers are fairly certain that Gamma Ray Bursts happen during the “abrupt and violent transition between the death of a massive star and the resulting birth of a black hole” (1). A dying star collapses into a hypernova explosion, which is an especially energetic supernova, causing the inner core to collapse into a black hole while jets of extremely energetic radiation are shot outward along the black hole’s polar axis. Hypernovae are approximately 100 times more energetic than typical supernovae, and the bursts they produce are thought to rival the Big Bang on an energy scale. This is called the Collapsar/Hypernova model of Gamma Ray Burst Formation, sometimes known as the Fireball model. Hypernova 7 8 Gamma Ray Burst 9 Black Hole (Chandra Image)

7. How are Gamma Ray Bursts detected? 10 The detection and observation of Gamma Ray Bursts is a finely coordinated combination of different satellites and detection systems. The first afterglow observation was made in 1997 with the help of the Italian-Dutch satellite Beppo-SAX. The Compton Gamma Ray Observatory (1991-2000) could detect GRBs, but was not able to pinpoint their location. Beppo-SAX proved that it could on February 28, 1997 (with the observation of GRB970228). After its detection and calculation of the source, powerful ground-based optical telescopes and most importantly the Hubble Space Telescope were trained on the site of the source and got the first glimpses of the optical source of the gamma rays. Beppo-SAX’s original observations of GRB970228 11 GRB970228 Host Galaxy HST’s follow-up observation of GRB970228

8. Why do Gamma Ray Bursts matter? Gamma Ray Bursts are an important process in our universe. They are an extremely violent and detectable transition from an overabundance of matter (hypernova explosion) to a complete lack thereof (black hole) and they possibly explain some of the mysteries of our universe. Researchers have even suggested that “a nearby gamma ray burst long-ago might have seeded our solar system, providing the needed influx of energy to urge a vast disk of sun-circling dust to begin forming into small chunks, which eventually became the asteroids and planets” (2). This is an exciting possibility and just another reason to continue studying the fascinating and enigmatic events we call Gamma Ray Bursts. 12 The Swift GRB Detector, set to launch in 2005.

9. Sources, page 1 Graphic Sources: 1: http://space.com/imageoftheday/image_of_day_030813.html 2: http://imagine.gsfc.nasa.gov/docs/science/know_l1/grbs_explosion.html 3: http://www.astro.virginia.edu/class/skrutskie/images/light_em_spectrum.jpg 4: http://www.mitrecaasd.org/proj/satnav/gps_modernzation.cfm 5: http://imagine.gsfc.nasa.gov/docs/science/know_l1/grbs_duration.html 6: http://www.astro.uiuc.edu/~kaler/sow/sowlist.html 7: http://www.astro.uio.no/ita/arrangementer/norgerom.html 8: http://www.harvard-magazine.com/on-line/1102183.html 9: http://exn.ca/Stories/2000/09/12/53.asp 10: http://imagine.gsfc.nasa.gov/docs/science/how_l1/how_bursts.html 11: http://imagine.gsfc.nasa.gov/docs/science/how_l1/how_bursts.html 12: http://imagine.gsfc.nasa.gov/docs/science/know_l1/grbs_mysteries.html

10. Sources, page 2 Information Sources: http://www.space.com/scienceastronomy/astronomy/grb_supernova_991021.html http://www.space.com/scienceastronomy/astronomy/gamma_990930.html http://www.space.com/scienceastronomy/astronomy/gammaray_burst_991022.html http://imagine.gsfc.nasa.gov/docs/science/know_l1/grbs.html (and all subsequent pages) http://imagine.gsfc.nasa.gov/docs/science/how_l1/how_bursts.html http://imagine.gsfc.nasa.gov/docs/science/know_l1/why_hyper.html Quote Sources: 1: http://www.space.com/scienceastronomy/astronomy/gamma_990930.html 2: http://www.space.com/scienceastronomy/astronomy/grb_supernova_991021.html

11. Ashley S. Pagnotta Physics 314 H Extra Credit Presentation November 25, 2003