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Astronomy 305/Frontiers in Astronomy

Astronomy 305/Frontiers in Astronomy

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Astronomy 305/Frontiers in Astronomy

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  1. Astronomy 305/Frontiers in Astronomy Class web site: Office: Darwin 329A and NASA E/PO (707) 664-2655 Best way to reach me: Prof. Lynn Cominsky

  2. Group 8 Congratulations, Group 8! Prof. Lynn Cominsky

  3. Stellar evolution made simple – a review Puff! Bang! BANG! Stars like the Sun go gentle into that good night More massive stars rage, rage against the dying of the light Prof. Lynn Cominsky

  4. Exploding Stars • At the end of a star’s life, if it is large enough, it will end with a bang (and not a whimper!) Supernova 1987A in Large Magellanic Cloud HST/WFPC2 Prof. Lynn Cominsky

  5. Supernova Remnants • Radioactive decay of chemical elements created by the supernova explosion Vela Region CGRO/Comptel Prof. Lynn Cominsky

  6. Neutron Stars: Dense cinders Mass: ~1.4 solar masses Radius: ~10 kilometers Density: 1014-15 g/cm3 Magnetic field: 108-14 gauss Spin rate: from 1000Hz to 0.08 Hz Prof. Lynn Cominsky

  7. Making a Neutron Star Prof. Lynn Cominsky

  8. Black holes Defined: an object where the escape velocity Is greater than the speed of light Ve = (2 G m / r)1/2 Schwarzschild radius = 2 G m/c2 Rs = 3 km for the Sun Mass: > 3 to a few x 109 solar masses Prof. Lynn Cominsky

  9. Accretion • Powered by gravity, heated by friction • Black holes, neutron stars and white dwarfs in binaries • Accretion is 10% efficient 1 marshmallow = atomic bomb (about 10 kilotons) Prof. Lynn Cominsky

  10. Accretion • Matter transfers through inner Lagrange point from normal star onto compact companion • Swirls around in accretion disk movie Prof. Lynn Cominsky Blondin 1998

  11. Accretion movies • Roche lobe overflow • Stellar wind capture 3D Simulations by John Blondin Prof. Lynn Cominsky

  12. Classifying Bursts • In this activity, you will be given twenty cards showing different types of bursts • Pay attention to the lightcurves, optical counterparts and other properties of the bursts given on the reverse of the cards • How many different types of bursts are there? Sort the bursts into different classes • Fill out the accompanying worksheet to explain the reasoningbehind yourclassification scheme Prof. Lynn Cominsky

  13. Aitoff Projection & Galactic Coordinates (1) Prof. Lynn Cominsky

  14. Aitoff Projection & Galactic Coordinates (2) Prof. Lynn Cominsky

  15. X-ray Bursters Soft Gamma-Ray Repeaters Gamma ray bursts 0748-67 0526-66 0501+11 1636-53 1627-41 0656+79 1659-29 1806-20 1156+65 1728-34 1900+14 1338-80 1735-44 1525+44 1820-30 1935-52 1837+05 2232-73 1850-08 2359+08 Answers (1) Prof. Lynn Cominsky

  16. Answers (2) X = Gamma Ray Bursts = Soft Gamma Ray Repeaters = X-ray Bursters Prof. Lynn Cominsky

  17. Distributions • If sources are located randomly in space, the distribution is called isotropic • If the sources are concentrated in a certain region or along the galactic plane, the distribution is anisotropic Prof. Lynn Cominsky

  18. What makes Gamma-ray Bursts? • X-ray Bursts • Properties • Thermonuclear Flash Model • Soft Gamma Repeaters • Properties • Magnetar model • Gamma-ray Bursts • Properties • Models • Afterglows • Future Mission Studies Prof. Lynn Cominsky

  19. X-ray Bursts • Thermonuclear flashes on Neutron Star surface – hydrogen or helium fusion • Accreting material burns in shells, unstable burning leads to thermonuclear runaway • Bursts repeat every few hours to days • Bursts are never seen from black hole binaries (no surface for unstable nuclear burning) or from (almost all) pulsars (magnetic field quenches thermonuclear runaway) Prof. Lynn Cominsky

  20. bursters non-bursters Globular Clusters X-ray Burst Sources • Locations in Galactic Coordinates • Most bursters are • located in globular • clusters or near the • Galactic center • They are therefore relatively older systems Prof. Lynn Cominsky

  21. X-ray Burst Source Properties • Neutron Stars in binary systems • Weaker magnetic dipole: B~108 G • NS spin period seen in bursts ~0.003 sec. • Orbital periods : 0.19 - 398 h from X-ray dips & eclipses and/or optical modulation • > 15 well known bursting systems • Low mass companions • Lx = 1036 - 1038 erg/s Prof. Lynn Cominsky

  22. X-ray Emission • X-ray emission from accretion can be modulated by magnetic fields, unstable burning and spin • Modulation due to spin of neutron star can sometimes be seen within the burst Prof. Lynn Cominsky

  23. Thermonuclear Flash Model movie Prof. Lynn Cominsky

  24. X-ray Burst Sources • Burst spectra are thermal black-body L(t) = 4 p R2s T(t)4 Temperature Radius Expansion c2 Prof. Lynn Cominsky Cominsky PhD 1981

  25. SGR 1627-41 LMC Soft Gamma Repeaters • There are four of these objects known to date • One is in the LMC, the other 3 are in the Milky Way Prof. Lynn Cominsky

  26. Making a magnetar Prof. Lynn Cominsky

  27. SGR Emission movie • Emission from accretion can be modulated by magnetic fields • Modulation due to spin of neutron star can be seen within the burst Prof. Lynn Cominsky

  28. Soft Gamma Repeater Properties • Young Neutron Stars near SNRs • Superstrong magnetic dipole: B~1014-15 G • NS spin period seen in bursts ~5-10 sec, shows evidence of rapid spin down • No orbital periods – not in binaries! • 4 well studied systems + several other candidate systems • Several SGRs are located in or near SNRs • Soft gamma ray bursts are from magnetic reconnection/flaring like giant solar flares • Lx = 1042 - 1043 erg/s at peak of bursts Prof. Lynn Cominsky

  29. SGR 1900+14 • Strong burst showing ~5 sec pulses • Change in 5 s spin rate leads to measure of magnetic field • Source is a magnetar! Prof. Lynn Cominsky

  30. SGR burst affects Earth • On the night of August 27, 1998 Earth's upper atmosphere was bathed briefly by an invisible burst of gamma- and X-ray radiation. This pulse - the most powerful to strike Earth from beyond the solar system ever detected - had a significant effect on Earth's upper atmosphere, report Stanford researchers. It is the first time that a significant change in Earth's environment has been traced to energy from a distant star. (from the NASA press release) Prof. Lynn Cominsky

  31. Gamma Ray Burst Properties • A cataclysmic event of unknown origin • Unknown magnetic field • No repeatable periods seen in bursts • No orbital periods seen – not in binaries • Thousands of bursts seen to date – no repetitions from same location • Isotropic distribution • Afterglows have detectable redshifts which indicate GRBs are at cosmological distances (i.e., far outside our galaxy) • Lg= 1052 - 1053 erg/s at peak of bursts Prof. Lynn Cominsky

  32. The first Gamma-ray Burst • Discovered in 1967 while looking for nuclear test explosions - a 30+ year old mystery! Vela satellite Prof. Lynn Cominsky

  33. Compton Gamma Ray Observatory BATSE • Eight instruments on corners of spacecraft • NaI scintillators Prof. Lynn Cominsky

  34. CGRO/BATSE Gamma-ray Burst Sky • Once a day, somewhere in the Universe Prof. Lynn Cominsky

  35. The GRB Gallery When you’ve seen one gamma-ray burst, you’ve seen…. one gamma-ray burst!! Prof. Lynn Cominsky

  36. Near or Far? Isotropic distribution implications: Very close: within a few parsecs of the Sun Why no faint bursts? Very far: huge, cosmological distances What could produce such a vast amount of energy? Sort of close: out in the halo of the Milky Way A comet hitting a neutron star fits the bill Silly or not, the only way to be sure was to find the afterglow. Prof. Lynn Cominsky

  37. Breakthrough! In 1997, BeppoSAX detects X-rays from a GRB afterglow for the first time, 8 hours after burst Prof. Lynn Cominsky

  38. The View From Hubble/STIS 7 months later Prof. Lynn Cominsky

  39. On a clear day, you really can see forever 990123 reached 9th magnitude for a few moments! First optical GRB afterglow detected simultaneously Prof. Lynn Cominsky

  40. The Supernova Connection GRB011121 Afterglow faded like supernova Data showed presence of gas like a stellar wind Indicates some sort of supernova and not a NS/NS merger Prof. Lynn Cominsky

  41. Hypernova • A billion trillion times the power from the Sun • The end of the life of a star that had 100 times the mass of our Sun movie Prof. Lynn Cominsky

  42. Iron lines in GRB 991216 • Chandra observations show link to hypernova model when hot iron-filled gas is detected from GRB 991216 Iron is a signature of a supernova, as it is made in the cores of stars, and released in supernova explosions Prof. Lynn Cominsky

  43. Catastrophic Mergers • Death spiral of 2 neutron stars or black holes Prof. Lynn Cominsky

  44. Which model is right? The data seem to indicate two kinds of GRBs • Those with burst durations less than 2 seconds • Those with burst durations more than 2 seconds Short bursts have no detectable afterglows so far as predicted by the NS/NS merger model Long bursts are sometimes associated with supernovae, and all the afterglows seen so far as predicted by the hypernova merger model Prof. Lynn Cominsky

  45. Gamma-ray Bursts • Either way you look at it – hypernova or merger model • GRBs signal the birth of a black hole! Prof. Lynn Cominsky

  46. Gamma-ray Bursts • Or maybe the death of life on Earth? No, gamma-ray bursts did not kill the dinosaurs! Prof. Lynn Cominsky

  47. How to study Gamma rays? • Absorbed by the Earth’s atmosphere • Use rockets, balloons or satellites • Can’t image or focus gamma rays • Special detectors: crystals, silicon-strips GLAST balloon test Prof. Lynn Cominsky

  48. HETE-2 • Launched on 10/9/2000 • Operational and finding about 2 bursts per month Prof. Lynn Cominsky

  49. Swift Mission • Burst Alert Telescope (BAT) • Ultraviolet/Optical Telescope (UVOT) • X-ray Telescope (XRT) To be launched in 2004 Prof. Lynn Cominsky

  50. Swift Mission • Will study GRBs with “swift” response • Survey of “hard” X-ray sky • To be launched in 2003 • Nominal 3-year lifetime • Will see ~150 GRBs per year Prof. Lynn Cominsky