Gamma Ray Burstsand Swift

Julian Osborne

University of Leicester

UK Space Conference - Charterhouse School March 28 2008

Cnt

s/s

BAT

UVOT

XRT

GRB introduction

Swift observatory

GRB afterglows

Short GRBs The most distant GRBs

Breaking News: GRB 080319B

Outline

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

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

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

BeppoSAXX-ray afterglow

discovery1997

CGRO BATSESky distribution

1991-2000

GR B recent historyGR B recent history

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

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

• 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

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

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?

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

What’s the problem? - The Time Gap

Swift

Beppo SAX data

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

November 20, 2004

Swift on rocket

Swift communication

XRFShortGRB

XRF

ShortGRB

XRF

XRFXRF

XRF

XRF

ShortGRB

XRF

ShortGRB

ShortGRB

ShortGRB

ShortGRBXRF

XRFXRF

ShortGRB Short

GRB

GRB introduction

Swift observatory GRB afterglows

Short GRBs

The most distant GRBs

Breaking News: GRB 080319B

Swift A fterglows – complicated Swift A fterglows – complicated

Canonical Lightcurve

Shape

GRB 051001 - XRT

AfterglowFlare

GRB 050502B - XRT

Curves &Breaks

GRB 050525AUVOT

Paul O’Brien / UL

BAT

XRT

Swift X -ray L ightcurves - The M ovieSwift X -ray L ightcurves - The M ovie

BAT

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

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

GRB introduction

Swift observatory

GRB afterglows

Short GRBs The most distant GRBs

Breaking News: GRB 080319B

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

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 ?

Fox et al. 2005

HETE-2 GRB 050709HST Image

Swift GRB 051221BAT Lightcurve

Parsons et al. 2005

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

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

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.

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

Tanvir (2005)

GalaxiesQuasarsGRBs

10

12

13

8

Dis

tanc

e (B

illio

n L

ight

Yea

rs)

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

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)

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

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

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)

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

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.

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.

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.

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

GSFC

Swift Team