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Astronomy 305/Frontiers in Astronomy Class web site: http://glast.sonoma.edu/~lynnc/courses/a305 Office: Darwin 329A and NASA E/PO (707) 664-2655 Best way to reach me: [email protected] 10/21/03 Prof. Lynn Cominsky 1 Group 8 10/21/03 Prof. Lynn Cominsky 2 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 10/21/03 Prof. Lynn Cominsky 3 Exploding Stars Supernova 1987A in Large Magellanic Cloud HST/WFPC2 At the end of a star’s life, if it is large enough, it will end with a bang (and not a whimper!) 10/21/03 Prof. Lynn Cominsky 4 Supernova Remnants Vela Region CGRO/Comptel Radioactive decay of chemical elements created by the supernova explosion 10/21/03 Prof. Lynn Cominsky 5 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 10/21/03 Prof. Lynn Cominsky 6 Making a Neutron Star 10/21/03 Prof. Lynn Cominsky 7 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 10/21/03 Prof. Lynn Cominsky 8 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) 10/21/03 Prof. Lynn Cominsky 9 Accretion Matter transfers through inner Lagrange point from normal star onto compact companion Swirls around in accretion disk movie 10/21/03 Prof. Lynn Cominsky Blondin 1998 10 Accretion movies Roche lobe overflow Stellar wind capture 3D Simulations by John Blondin 10/21/03 Prof. Lynn Cominsky 11 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 reasoning behind your classification scheme 10/21/03 Prof. Lynn Cominsky 12 Aitoff Projection & Galactic Coordinates (1) 10/21/03 Prof. Lynn Cominsky 13 Aitoff Projection & Galactic Coordinates (2) 10/21/03 Prof. Lynn Cominsky 14 Answers (1) X-ray Bursters 10/21/03 0748-67 Soft GammaRay Repeaters 0526-66 Gamma ray bursts 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 Prof. Lynn Cominsky 15 Answers (2) X = Gamma Ray Bursts = Soft Gamma Ray Repeaters = X-ray Bursters 10/21/03 Prof. Lynn Cominsky 16 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 10/21/03 Prof. Lynn Cominsky 17 What makes Gamma-ray Bursts? X-ray Bursts Soft Gamma Repeaters Properties Thermonuclear Flash Model Properties Magnetar model Gamma-ray Bursts Properties Models Afterglows Future Mission Studies 10/21/03 Prof. Lynn Cominsky 18 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) 10/21/03 Prof. Lynn Cominsky 19 X-ray Burst Sources Locations in Galactic Coordinates bursters non-bursters Globular Clusters • Most bursters are located in globular clusters or near the Galactic center • They are therefore relatively older systems 10/21/03 Prof. Lynn Cominsky 20 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 10/21/03 Prof. Lynn Cominsky 21 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 10/21/03 Prof. Lynn Cominsky 22 Thermonuclear Flash Model movie 10/21/03 Prof. Lynn Cominsky 23 X-ray Burst Sources Burst spectra are thermal black-body L(t) = 4 p R2 s T(t)4 Temperature Radius Expansion c2 10/21/03 Prof. Lynn Cominsky 24 Cominsky PhD 1981 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 SGR 1627-41 LMC 10/21/03 Prof. Lynn Cominsky 25 Making a magnetar 10/21/03 Prof. Lynn Cominsky 26 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 10/21/03 Prof. Lynn Cominsky 27 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 10/21/03 Prof. Lynn Cominsky 28 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! 10/21/03 Prof. Lynn Cominsky 29 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) 10/21/03 Prof. Lynn Cominsky 30 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 10/21/03 Prof. Lynn Cominsky 31 The first Gamma-ray Burst Vela satellite Discovered in 1967 while looking for nuclear test explosions - a 30+ year old mystery! 10/21/03 Prof. Lynn Cominsky 32 Compton Gamma Ray Observatory BATSE • Eight instruments on corners of spacecraft • NaI scintillators 10/21/03 Prof. Lynn Cominsky 33 CGRO/BATSE Gamma-ray Burst Sky Once a day, somewhere in the Universe 10/21/03 Prof. Lynn Cominsky 34 The GRB Gallery When you’ve seen one gamma-ray burst, you’ve seen…. one gamma-ray burst!! 10/21/03 Prof. Lynn Cominsky 35 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. 10/21/03 Prof. Lynn Cominsky 36 Breakthrough! In 1997, BeppoSAX detects X-rays from a GRB afterglow for the first time, 8 hours after burst 10/21/03 Prof. Lynn Cominsky 37 The View From Hubble/STIS 7 months later 10/21/03 Prof. Lynn Cominsky 38 On a clear day, you really can see forever 990123 reached 9th magnitude for a few moments! First optical GRB afterglow detected simultaneously 10/21/03 Prof. Lynn Cominsky 39 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 10/21/03 Prof. Lynn Cominsky 40 Hypernova movie 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 10/21/03 Prof. Lynn Cominsky 41 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 10/21/03 Prof. Lynn Cominsky 42 Catastrophic Mergers Death spiral of 2 neutron stars or black holes 10/21/03 Prof. Lynn Cominsky 43 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 10/21/03 Prof. Lynn Cominsky 44 Gamma-ray Bursts Either way you look at it – hypernova or merger model GRBs signal the birth of a black hole! 10/21/03 Prof. Lynn Cominsky 45 Gamma-ray Bursts Or maybe the death of life on Earth? No, gammaray bursts did not kill the dinosaurs! 10/21/03 Prof. Lynn Cominsky 46 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 10/21/03 Prof. Lynn Cominsky GLAST balloon test 47 HETE-2 Launched on 10/9/2000 Operational and finding about 2 bursts per month 10/21/03 Prof. Lynn Cominsky 48 Swift Mission To be launched in 2004 Burst Alert Telescope (BAT) Ultraviolet/Optical Telescope (UVOT) X-ray Telescope (XRT) 10/21/03 Prof. Lynn Cominsky 49 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 10/21/03 Prof. Lynn Cominsky 50 Gamma-ray Large Area Space Telescope GLAST Burst Monitor (GBM) Large Area Telescope (LAT) 10/21/03 Prof. Lynn Cominsky 51 GLAST Mission First space-based collaboration between astrophysics and particle physics communities Launch expected in 2006 Expected duration 5-10 years Over 3000 gamma-ray sources will be seen 10/21/03 Prof. Lynn Cominsky 52 GLAST Burst Monitor (GBM) PI Charles Meegan (NASA/MSFC) US-German secondary instrument 12 Sodium Iodide scintillators Few keV to 1 MeV Burst triggers and locations 2 bismuth germanate detectors 150 keV to 30 MeV Overlap with LAT http://gammaray.msfc.nasa.gov/gbm/ 10/21/03 Prof. Lynn Cominsky 53 Large Area Telescope (LAT) PI Peter Michelson (Stanford) International Collaboration: USA NASA and DoE, France, Italy, Japan, Sweden • LAT is a 4 x 4 array of towers http://www-glast.stanford.edu • Each tower is a pair conversion telescope with calorimeter 10/21/03 Prof. Lynn Cominsky 54 Pair Conversion Telescope 10/21/03 Prof. Lynn Cominsky 55 LAT Schematic Tiled Anticoincidence Shield Silicon strip detectors interleaved with Tungsten converter Cesium Iodide hodoscopic calorimeter 10/21/03 Prof. Lynn Cominsky 56 GLAST video A public outreach product from the GLAST Education and Public Outreach group 10/21/03 Prof. Lynn Cominsky 57 Web Resources : GLAST E/PO web site http://glast.sonoma.edu Swift E/PO web site http://swift.sonoma.edu Imagine the Universe! http://imagine.gsfc.nasa.gov Science at NASA’s Marshall Space Flight Center http://science.nasa.gov John Blondin’s accretion simulations http://www.physics.ncsu.edu/people/faculty 10/21/03 Prof. Lynn Cominsky http://science.msfc.nasa.gov http://science.msfc.nasa.gov 58 Web Resources Robert Duncan’s magnetar page http://solomon.as.utexas.edu/~duncan/magnetar.html Chandra observatory http://chandra.harvard.edu Jochen Greiner’s Gamma-ray bursts and SGR Summaries http://www.mpe.mpg.de/~jcg HETE-2 mission http://space.mit.edu/HETE/ Compton Gamma Ray Observatory http://cossc.gsfc.nasa.gov/ 10/21/03 Prof. Lynn Cominsky 59