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Chapter 13: Gamma Ray Burst, Neutron Stars, and Black Holes

Chapter 13: Gamma Ray Burst, Neutron Stars, and Black Holes. An early gamma ray-burst. Vela satellite. A Gamma Ray Burst Sampler. Great debate: 1967-1997. Bepposax Satellite. GRBM: 40-600 keV WFC: 2-30 keV NFI: 2-10 keV. X-Ray Afterglow from GRB 971214. t=6.5 hrs. t=12.5 hrs.

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Chapter 13: Gamma Ray Burst, Neutron Stars, and Black Holes

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  1. Chapter 13: Gamma Ray Burst, Neutron Stars, and Black Holes

  2. An early gamma ray-burst Vela satellite

  3. A Gamma Ray Burst Sampler

  4. Great debate: 1967-1997

  5. Bepposax Satellite GRBM: 40-600 keV WFC: 2-30 keV NFI: 2-10 keV

  6. X-Ray Afterglow from GRB 971214 t=6.5 hrs t=12.5 hrs t=54 hrs

  7. Optical Afterglow from GRB 971214 Keck Images 2 days 2 months Host HST Image

  8. Uh-oh

  9. GRBs are a type of Supernova“Hypernova” Peak toward low end of gamma-ray, complex gamma-ray light curves Often have bright afterglows Evidence for a relativistic explosion Energy required of ~ 1053 ergs (isotropic) Associated with regions of star formation in distant galaxies (out to edge of observable universe) Sometimes obscured by dust Plus …

  10. Example Hypernova: 1998bw

  11. Long GRBs clearly connected to Supernovae Hjorth et al 2003

  12. WR104 - Looking Down the Barrelof a GRB system 8000 lt-years from us

  13. Clicker Question: All of the following atoms have a total of 4 nucleons (protons or neutrons).Which of the following has the smallest mass? A: 4 hydrogen atoms B: 2 deuterium atoms C: 1 tritium atom and 1 hydrogen atom D: 1 Helium atom E: None of the above, they all have the same total mass

  14. Final States of a Star 1. White Dwarf If initial star mass < 8 MSun or so. (and remember: Maximum WD mass is 1.4 MSun , radius is about that of the Earth) 2. Neutron Star If initial mass > 8 MSun and < 25 MSun . 3. Black Hole If initial mass > 25 MSun .

  15. Pulsars Discovery of LGM1 by Jocelyn Bell and Tony Hewish (Cambridge) in 1967. Nobel Prize to Hewish in 1974. Pulse periods observed from 0.001 sec to 10 seconds - DEMO Explanation: "beamed" radiation from rapidly spinning neutron star. Usually neutron stars are pulsars for 107 years after supernova.

  16. The Crab Pulsar

  17. The Crab Pulsar Chandra X-ray image On Off

  18. Neutron Stars Leftover core from Type II supernova - a tightly packed ball of neutrons. Diameter: 20 km only! Mass: 1.4 - 3(?) MSun Density: 1014 g / cm3 ! 1 teaspoon = 1000 great pyramids Surface gravity: 1012 higher Escape velocity: 0.5c Rotation rate: few to many times per second!!! Magnetic field: 1012 x Earth's! A neutron star over the Sandias?

  19. General Relativistic deflection of light More than half the surface is visible at any one time! Each square is 30 degrees x 30 degrees

  20. An Isolated Neutron Star T ~ 2 million K Size ~ 30 km

  21. The Lighthouse model of a pulsar

  22. Pulsars are incredibly accurate clocks! Example: period of the first discovered "millisecond pulsar" is: P = 0.00155780644887275 sec It is slowing down at a rate of 1.051054 x 10 -19 sec/sec The slowing-down rate is slowing down at a rate of: 0.98 x 10 -31 /sec

  23. Multi-wavelength observations of Pulsars

  24. Pulsar Exotica Binary pulsars: two pulsars in orbit around each other. Einstein predicted that binary orbits should "decay", i.e. the masses would spiral in towards each other, losing energy through "gravitational radiation". Confirmed by binary pulsar. Curve: prediction of decaying orbit. Points: measurements. year Planets around pulsars: A pulsar was found in 1992 to have three planets! Masses about 3 MEarth, 1 MEarth, and 1 MMoon ! Millisecond pulsars: periods of 1 to a few msec. Probably accreted matter from a binary companion that made it spin faster. Gamma-ray Bursts: some pulsars produce bursts of gamma-rays, called Soft Gamma-Ray Repeaters or SGRs

  25. Time history of the 4 confirmed SGRs: Woods & Thompson 2004

  26. Soft Gamma-Ray Repeaters • Eiso ~ a few1044 erg in gamma-rays Where does this energy come from? X-ray image - Accretion? No sign of a disk - Rotation? Not enough energy available - Magnetic fields? Yes

  27. What is our basic model for a pulsar? A: a rotating white dwarf B: a rotating neutron star C: a rotating black hole D: an oscillating star Clicker Question:

  28. NS Merger Model for short GRBs Mean redshift ~ 0.25 for short hard bursts (SHB) No supernova association expected SHBs often found at outskirts of galaxy (implies large peculiar velocities) SHBs found in - Elliptical galaxies - galaxies with low star formation rates

  29. Black Holes 29 A stellar mass black hole accreting material from a companion star

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