Transcript Astronomy 305/Frontiers in Astronomy - Fermi Gamma

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]
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Group 8
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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
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Exploding Stars
Supernova 1987A in
Large Magellanic Cloud
HST/WFPC2
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At the end of a star’s life, if it is large enough,
it will end with a bang (and not a whimper!)
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Supernova Remnants
Vela Region
CGRO/Comptel
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Radioactive decay of chemical elements
created by the supernova explosion
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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
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Making a Neutron Star
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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
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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)
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Accretion
Matter transfers
through inner
Lagrange point
from normal star
onto compact
companion
 Swirls around in
accretion disk
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movie
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Blondin 1998
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Accretion movies
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Roche lobe overflow
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Stellar wind capture
3D Simulations by John Blondin
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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
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Aitoff Projection & Galactic
Coordinates (1)
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Aitoff Projection & Galactic
Coordinates (2)
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Answers (1)
X-ray Bursters
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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
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Answers (2)
X = Gamma Ray Bursts
= Soft Gamma Ray Repeaters
= X-ray Bursters
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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
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What makes Gamma-ray Bursts?
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X-ray Bursts
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Soft Gamma Repeaters
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Properties
Thermonuclear Flash Model
Properties
Magnetar model
Gamma-ray Bursts
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Properties
Models
Afterglows
Future Mission Studies
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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)
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X-ray Burst Sources
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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
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X-ray Burst Source Properties
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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
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X-ray Emission
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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
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Thermonuclear Flash Model movie
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X-ray Burst Sources
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Burst spectra are thermal black-body
L(t) =
4 p R2 s T(t)4
Temperature
Radius Expansion
c2
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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
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SGR 1627-41
LMC
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Making a magnetar
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SGR Emission
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movie
Emission from
accretion can be
modulated by
magnetic fields
Modulation due to
spin of neutron star
can be seen within
the burst
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Soft Gamma Repeater Properties
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Young Neutron Stars near SNRs
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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
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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!
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SGR burst affects Earth
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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)
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Gamma Ray Burst Properties
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A cataclysmic event of unknown origin
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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
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The first Gamma-ray Burst
Vela satellite
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Discovered in 1967 while looking for nuclear test
explosions - a 30+ year old mystery!
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Compton Gamma Ray Observatory
BATSE
• Eight
instruments
on corners of
spacecraft
• NaI
scintillators
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CGRO/BATSE Gamma-ray Burst Sky
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Once a day, somewhere in the Universe
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The GRB Gallery
When you’ve
seen one
gamma-ray
burst, you’ve
seen….
one
gamma-ray
burst!!
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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.
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Breakthrough!
In 1997, BeppoSAX detects X-rays from a GRB
afterglow for the first time, 8 hours after burst
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The View From Hubble/STIS
7 months
later
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On a clear day, you really can see forever
990123 reached 9th magnitude for a few moments!
First optical GRB afterglow detected simultaneously
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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
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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
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Iron lines in GRB 991216
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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
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Catastrophic Mergers
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Death spiral of 2 neutron stars or black holes
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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
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Gamma-ray Bursts
Either way you
look at it –
hypernova or
merger model
 GRBs signal the
birth of a black
hole!
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Gamma-ray Bursts
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Or maybe
the death
of life on
Earth?
No, gammaray bursts did
not kill the
dinosaurs!
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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
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GLAST
balloon test
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HETE-2
Launched on 10/9/2000
 Operational and finding about 2 bursts
per month
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Swift Mission
To be launched in 2004
Burst Alert
Telescope (BAT)
 Ultraviolet/Optical
Telescope (UVOT)
 X-ray Telescope
(XRT)
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Swift Mission
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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
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Gamma-ray Large Area Space Telescope
 GLAST Burst
Monitor (GBM)
 Large Area
Telescope (LAT)
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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
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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
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http://gammaray.msfc.nasa.gov/gbm/
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Large Area Telescope (LAT)
PI Peter Michelson (Stanford)
 International Collaboration: USA NASA and
DoE, France, Italy, Japan, Sweden
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• LAT is a 4 x 4
array of towers
http://www-glast.stanford.edu
• Each tower is a
pair conversion
telescope with
calorimeter
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Pair Conversion Telescope
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LAT Schematic
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Tiled
Anticoincidence
Shield
Silicon strip
detectors
interleaved with
Tungsten
converter
Cesium Iodide
hodoscopic
calorimeter
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GLAST video
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A public outreach product from the
GLAST Education and Public Outreach
group
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Web Resources :
GLAST E/PO web site http://glast.sonoma.edu
 Swift E/PO web site http://swift.sonoma.edu
 Imagine the Universe!
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http://imagine.gsfc.nasa.gov
Science at NASA’s Marshall Space Flight
Center http://science.nasa.gov
 John Blondin’s accretion simulations
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http://www.physics.ncsu.edu/people/faculty
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http://science.msfc.nasa.gov
http://science.msfc.nasa.gov
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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/
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