Astronomy 305/Frontiers in Astronomy

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: lynnc@charmian.sonoma.edu Prof. Lynn Cominsky

Group 8 Congratulations, Group 8! Prof. Lynn Cominsky

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

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

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

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

Making a Neutron Star Prof. Lynn Cominsky

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Thermonuclear Flash Model movie Prof. Lynn Cominsky

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

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

Making a magnetar Prof. Lynn Cominsky

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Astronomy 305/Frontiers in Astronomy