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Gamma Ray Burstsand Swift
Julian Osborne
University of Leicester
UK Space Conference - Charterhouse School March 28 2008
Cnt
s/s
BAT
UVOT
XRT
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GRB introduction
Swift observatory
GRB afterglows
Short GRBs The most distant GRBs
Breaking News: GRB 080319B
Outline
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GRB introduction
Swift observatory
GRB afterglows
Short GRBs The most distant GRBs
Braking News: GRB 080319B
The first gamma-ray burst (1969)Klebesadel et al 1973
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Gamma R ay B urst discoveryGamma R ay B urst discovery
• Cold war at its height
• USA/Soviets think the other side may be testing nuclear bombs in space
• USA ‘Vela’ satellite programme designed to detect nuclear detonations
• Data indicate Data indicate ‘interesting signals’ that ‘interesting signals’ that do not originate from the do not originate from the Earth, Sun or MoonEarth, Sun or Moon
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Flash ForwardFlash Forward
Over time, it became clear that nothing was clear. • Some GRBs are relatively smooth, others spiky• Durations range from 30 milliseconds to 1000 seconds
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BeppoSAXX-ray afterglow
discovery1997
CGRO BATSESky distribution
1991-2000
GR B recent historyGR B recent history
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GR B B ack ground cont.
Discovery of host galaxies allowed measurement of distance and energy
Typical redshift (pre-Swift) z ~ 1(i.e. distance ~ 8 billion light years)
Huge explosions: E ~ 1051 ergs(the Sun’s lifetime output in a few sec) Signatures of black hole birth
Ultra-relativistic outflows (0.99999c)
Two types of burst: short and longShort Long
Kouveliotou et al.
hostgalaxy
GRB
GRB 990123 - HST
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Collision with surroundings
Fireball Model of GRBs
XO
R
Internal Shock
cm1014≈ cm1016>
Collisions in different parts of the flow
The Flow decelerating into the surrounding medium
GRB Afterglow
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• Massive star (>30 M) dies – center collapses to BH
• Get Supernova + hyper-accreting disk “feeding Black Hole”
• In some cases get very fast jets (>0.9999c) emitted ⇒ GRB
Long GRBs – Hypernovae
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L ong GR B H ostsL ong GR B H osts
• GRBs trace brightest regions in hosts
• Hosts are sub-luminous irregular galaxies
⇒ Concentrated in regions of most massive stars
⇒ Restricted to low metallicity galaxies
Fruchter 2005
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Short GR B s – NS-NS merger?Short GR B s – NS-NS merger?
• 2005 May 9 – first short burst located accurately on the sky
• In a (fairly) nearby elliptical galaxy not currently making stars
• No supernova – so what is it?
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GRB introduction
Swift observatory GRB afterglows
Short GRBs
The most distant GRBs
Breaking News: GRB 080319B
Swift wins 2005 Best of What’s New award from Popular Science
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What’s the problem? - The Time Gap
Swift
Beppo SAX data
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BAT
XRT
Spacecraft
UVOT
BAT
UVOT
XRT
Whats’s the solution? - The Swift Observatory
Burst Alert Telescope (BAT) - 32,000 CdZnTe detectors - 2 sr field of view
X-Ray Telescope (XRT) - CCD spectroscopy - Arcsec GRB positions
UV-Optical Telescope (UVOT) - Sub-arcsec position - 22 mag sensitivity
Spacecraft slews XRT & UVOT to GRB in <100 s
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November 20, 2004
Swift on rocket
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Swift communication
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XRFShortGRB
XRF
ShortGRB
XRF
XRFXRF
XRF
XRF
ShortGRB
XRF
ShortGRB
ShortGRB
ShortGRB
ShortGRBXRF
XRFXRF
ShortGRB Short
GRB
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GRB introduction
Swift observatory GRB afterglows
Short GRBs
The most distant GRBs
Breaking News: GRB 080319B
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Swift A fterglows – complicated Swift A fterglows – complicated
Canonical Lightcurve
Shape
GRB 051001 - XRT
AfterglowFlare
GRB 050502B - XRT
Curves &Breaks
GRB 050525AUVOT
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Paul O’Brien / UL
BAT
XRT
Swift X -ray L ightcurves - The M ovieSwift X -ray L ightcurves - The M ovie
BAT
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Afterglow featuresAfterglow features
1. Light travel time effect from curved radiating surface (internal)
3. Plateau due to on-going energy injection to shock (external)
5. Flare due to central engine accretion event (internal)
7. Standard decay of shock (external)
9. Steeper decay as shock slows: after ‘jet-break’ (external)
1
2
3
4
5
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Afterglow features: New implicationsAfterglow features: New implications
Existence of Plateau and Flares out to beyond 10,000 sec
• Many orders of magnitude longer than accretion disk dynamical timescale – something is holding up the accretion
Very few jet-breaks seen
• Jets narrower or wider than thought before Swift• X-ray jet is narrower than optical jet• Jet model wrong?
Short GRB afterglows have same features as long GRB afterglows
• Explosion dynamics & environmentsimilar in spite of different origin
GRB 060729: Jet wider than 56°
Grupe et al
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GRB introduction
Swift observatory
GRB afterglows
Short GRBs The most distant GRBs
Breaking News: GRB 080319B
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GRB 050509B GRB 050724
• elliptical hosts• low SF rates• offset positions• redshifts z ~ 0.2
>> inconsistent with collapsar model>> supportive of NS-NS model
2 Short GR B s - 2 E lliptical H osts2 Short GR B s - 2 E lliptical H osts
BAT
XRT XRT
Chandra
35 kpc offset 4 kpc offset
Gehrels et al. 2005 Barthelmy et al. 2005
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GR B 050724GR B 050724
Host:- Elliptical- L = 1.7 L*- z = 0.258- SFR < 0.02 MO yr-1
BAT - 250 ms hard spike- 6x10-7 erg/cm2 fluence
Afterglow- bright afterglow with flares - detected by Chandra- optical & radio
Barthelmy et al. 2005
Evidence for NS-BH ?
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Fox et al. 2005
HETE-2 GRB 050709HST Image
Swift GRB 051221BAT Lightcurve
Parsons et al. 2005
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Short GR B ObservationsShort GR B Observations
Name Redshift Afteglow Host Eiso(15-150keV) What might it be? (erg) ___________________________________________________________________________
050202 - no slew - - -050509B 0.225 X Elliptical@ 1x1048 NS-NS merger050709* 0.161 X, O SF galaxy 6x1049 NS-NS merger050724 0.258 X, O, R Elliptical 3x1050 NS-NS / NS-BH merger050813 ? 1.8 X galaxy@ ? 2x1051 ? NS-NS merger050906 ? 0.03 - ? galaxy - ? minimal afterglow 050925# - - in gal. plane - ? possible new SGR051105A - - - - ? minimal afterglow051210 ? 0.11 X ? cluster@ ? 2x1048 ? NS-NS merger051221 0.547 X, O, R SF galaxy 9x1050 -060121* - X - - -060313 - X, O ? cluster@ - ? NS-NS merger
* HETE GRB # soft spectrum@ galaxy in cluster
short GRBs
long GRBs
1055
1054
1048
1053
1052
1049
1050
1051
1047
10-2 10-1 100 101 102 103
T90 / (1+z) (s)
Eis
o (e
rg)
Swift GRBs
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B eaming for Short GR B sB eaming for Short GR B s
Grupe, Burrows, et al.
Lack of jet break impliesθ > 25˚
Other hints of jet breaksgive θ ~ 10 - 20˚ ˚
Long bursts have θ ~5˚
Conclusion: θshort > θlong
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Short GR B Summary Short GR B Summary
Strong evidence that short GRBs associated with old stellar populations
Rapid fluctuations imply compact source origin. Energetics suggest collapse to BH
Could be NS-NS or NS-BH mergers, or accretion-induced collapse of NS.
If NS-NS, some systems may be exchange captures in globular clusters
Gravitational Waves: Assuming short GRBs are NS-NS mergersAssuming 30 beaming˚⇒ A-LIGO detection rate of ~100 yr-1
Thorne et al.
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GRB introduction
Swift observatory GRB afterglows
Short GRBs
The most distant GRBs
Breaking News: GRB 080319B
The clearing of the fog – re-ionisation of the Universe
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Tanvir (2005)
GalaxiesQuasarsGRBs
10
12
13
8
Dis
tanc
e (B
illio
n L
ight
Yea
rs)
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Redshift z = 6.29distance ~ 12.8 billion light yr Universe 6.5% of current age
T90 = 225 secS (15-150 keV) = 5.4x10-6 erg cm-2
Eiso = 3.8x1053 erg
GR B 050904 – the record holderGR B 050904 – the record holder
Flux x100 of high-zluminous X-ray AGNCusumano et al. 2005
X-ray Afterglow
BATXRT- WTXRT- PC
flares
GRB 050904
Typical GRB
GRB 050904undilated by z+1
Prompt
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GR B 050904 Optical SpectroscopyGR B 050904 Optical Spectroscopy
Subaru Spectroscopy
Kawai et al. 2006
• Hydrogen Lyman absorption in the IR• Optically bright: J mag = 17.6 at 3.5 hours• Very low fraction of star-burned elements
Berger et al. 2006
z= 0 z ~ 1 z = 2.3
z = 6.3
Mgalaxy (mag)lo
g (m
etal
lici
ty)
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Lines are models with GRBsproportional to SFR
0.1 1.0 10.0
Redshift (z)
0
5
10
Num
ber Pre-Swift
Swift
Average Redshift- Pre-Swift: z = 1.2- Swift: z = 2.7
GRB Redshift Distributions
Jacobsson et al. 2005
Swift long GRBs Tracing SFR
H igh R edshift GR B sH igh R edshift GR B s
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GRB introduction
Swift observatory
GRB afterglows
Short GRBs Redshifts
Breaking News: GRB 080319B
The first naked eye gamma-ray burst
Arthur C Clarke 1917 – 2008
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The first ‘naked eye’ burst - GRB 080319B
The brightest and most energetic burst seen by Swift
The first burst that could have been seen without optical aid (mag 5.6)
z = 0.94 (7.5 billion light yrs)
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GRB 080319B
Pi of the Sky – stares at a large fraction of the sky all the time
• 2x 85 mm lenses with CCD cameras• FOV: 22x22 deg• 10 sec exposures - real-time flash search
Pi of the Sky
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GRB 080319B
A very bright burst, which was followed by many telescopes
High speed optical measurements within ~10 sec
Eiso ~ 10^54 ergs ~ 50% of the rest-mass energy of the Sun!
No beaming apparent
Bloom et al.
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GRB 080319B
Corrected for distance, this was the brightest burst seen at optical wavelengths
The brightest bursts seem to have an additional short-lived component, by 1 day the range of brightness is much less
Is this a ‘reverse shock’?
Bloom et al.
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GRB 080319BThe value of GRBs for exploring the Universe
GRBs are much more luminous than the most energetic quasars and supernovae
They could be seen in the ‘dark ages’, if they exist then (and are not too obscured)
In our Galaxy this burst would have appeared brighter than the Sun! Bloom et al.
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The Future
Swift will be in orbit well beyond 2012
Excellent for general rapid-reaction astrophysics as well as GRBs
GLAST & AGILE - New very high energy gamma-ray missions
Gravitational wave, neutrino & TeV gamma-ray observatories all searching for GRB signals
Combined observations will bring exciting new science
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GSFC
Swift Team