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GRBGamma Ray Bursts

An Ongoing Mystery, Evolving Quickly

John G. LearnedUniversity of Hawaii

with slides from many folks,Particularly Kevin Hurley and Guido Barbiellini

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GRBs First Seen 1967Vela satellites, Seeking atom bomb testsSecret at first

Clearly a lot of Energy, depending upon distance and solid angle of emission

Distance, years of debate:

Very local? Galaxy halo? Not so far away? Cosmic Scale?

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CGRO-BATSE Tagged ManyDistribution: Isotropic

By early 90’s became clear

Not associated withour galaxy: no clustering in planeno tilt towards GC

Still models for near solar system

Sentiment towards cosmological distances

BATSE could not tag fast enough or withsufficient accuracy (1’)for telescopes

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Beppo-SAX Does the Job in 1997

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THREE INTERESTING GAMMA-RAY BURST/SUPERNOVA

PARAMETERS GRBs SUPERNOVAE

UNIVERSE-WIDE RATE 100’s-1000/day 100000/day

RATE PER GALAXY 1/105 years 1/50-100 years

ENERGY 1051-52 erg 1051-52 erg

Beaming Factor ~340 (100-1000)

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SOME ABSOLUTELY INCONTROVERTIBLE GRB PROPERTIES THAT NO REASONABLE

PERSON COULD POSSIBLY DISAGREE WITH

1. There are two morphological classes of GRBs, long bursts (~20 s duration) and short bursts (~0.2 s duration)

2. Counterparts and redshifts have been found for many long bursts

3. No counterpart or redshift has been found for any short burst

4. Most of the long bursts display long-wavelength (radio and optical) “afterglows”; but some of them have no detectable optical or radio counterparts (“dark” bursts)

5. There is good evidence which links some long bursts to the deaths of massive stars

K. Hurley, Moriond 2005

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6. The energy spectra of the long bursts form a continuum, from X-ray flashes (with few or no γ-rays), X-ray rich bursts, and GRBs

7. There is no experimental evidence to suggest that any class of burst (long/short, X-ray rich, dark) has a different origin, or a different spatial distribution, from any other class – but there are many theories which do suggest different origins.

8. The energy spectra of the long bursts form a continuum, from X-ray flashes (with few or no γ-rays), X-ray rich bursts, and GRBs

9. There is no experimental evidence to suggest that any class of burst (long/short, X-ray rich, dark) has a different origin, or a different spatial distribution, from any other class – but there are many theories which do suggest different origins

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6 7 8 9 10TIME, s

20

40

60

80

CO

UN

TS

/0.0

64 S

ULYSSESGRB00060725-150 keV

SHORT BURST

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LONG BURST

0 10 20 30 40TIME, S

40

60

80

100

120C

OU

NT

S/0

.12

5 S

ULYSSESGRB92050125-150 keV

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0.01 0.1 1 10 100 1000DURATION, SECONDS

0

40

80

120

160

NU

MB

ER

OF

BU

RS

TS

THE GRB DURATION DISTRIBUTION

SHORTBURSTS(~25%)

LONGBURSTS

~75%

HARDERENERGYSPECTRA

SOFTERENERGYSPECTRA

WE ONLYKNOW ABOUT

THE ORIGINOF THE LONG

BURSTS

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ENERGY SPECTRA OF THE LONG BURSTS

10 100 1000EN ER GY, keV

PH

OT

ON

S/C

M2

S k

eV

1

10-1

10-2

10-3

10-4

10-5

10-6

PO W ER LAW W ITHEXPO N E N TIAL C U TO FF

SM O O TH BR E AK

PO W ER LAW

B AN D SPEC TR U M

…OBSERVED UP TO 18 GeV

10 100 1000EN ER GY, keV

101

102

103

keV

/CM

2 S

keV

Epeak~100’s of keV

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THE ENERGY SPECTRA OF THE LONG BURSTS FORM A CONTINUUM, FROM SOFT-SPECTRUM X-RAY FLASHES TO HARD-SPECTRUM GAMMA-RAY BURSTS (BeppoSAX, HETE)

X-RAY FLASH

GAMMA-RAYBURST

Epeak~keV

Epeak~200 keV

1 10 100 1000EN ER GY, keV

100

101

102

103

keV

/CM

2 S

keV

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GAMMA-RAY BURSTS ARE FOLLOWED BY X-RAY

AFTERGLOWS…

BeppoSAX: Costa et al. 1997

T0+8h T0+2d

1-10 keV

1’

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…OPTICAL AFTERGLOWS…

Pandey et al. 2004

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…AND RADIO AFTERGLOWS

1 10 100 1000 Time after GRB970508, days

Flu

x de

nsit

y, μ

Jy 100

10

1

Frail et al. 2003

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FIREBALL MODEL

ISM

INTERNALSHOCK

RAYS

EXTERNALSHOCK

X-RAYS

OPTICALRADIO

20 km

1-6 AU

1000-2000 AU

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SIMULTANEOUS OPTICAL/GAMMA-RAY EMISSION HAS NOW BEEN DETECTED TWICE

GRB990123(BATSE)

ROTSE (www.rotse.net)

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dGRB041219(INTEGRAL)

RAPTOR (http://www.raptor.lanl.gov/index.htm)

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990705 (z=0.8424)990506

980613 (z=1.0964)

980519 980329000301(z=2.0335)

GRB HOST GALAXIES

•Aren’t pretty; but they are normal•Not active galaxies•Indistinguishable from field galaxies with similar ages

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REDSHIFT DISTRIBUTION OF 34 LONG GAMMA-RAY BURSTS

LOWEST REDSHIFT=0.104 (INTEGRAL, GRB031203); HIGHEST=4.5 (IPN, GRB000131); AVERAGE=1.4

ONLY ONE REDSHIFT HAS BEEN MEASURED FOR AN X-RAY FLASH

z=0.25

0 1 2 3 4 5REDSHIFT, z

0

2

4

6

8

NU

MB

ER

OF

BU

RS

TS

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GRB ENERGETICS

• Isotropic gamma-ray energies range from >1051 to >1054 erg

• Two possibilities for liberating large amounts of energy:1. Merging neutron stars (short bursts?)2. Collapsars (also called hypernovae, or energetic

supernovae; long bursts)

• In either case, beaming is also required; there is observational evidence in afterglow light curves that it occurs in some cases

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THE OPTICAL AFTERGLOW CAN GIVE INFORMATION ABOUT BEAMING

OBSERVER

TIME

AFTERGLOWINTENSITY

BREAK

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BEAMING CAN TURN GRBs INTO (MODEL-DEPENDENT) STANDARD CANDLES

• Beaming angles range from ~1º to ~25º; average ~ 4º

• Distribution of energy assumed uniform within the beam

• Energy ~ 1.3x1051 erg

Isotropic energies,no beaming

Correctedfor beaming

Frail et al. 2001

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HOW IS THE ENERGY DISTRIBUTED?

keV rays: 65%

2 1-10 keV X-rays: 7%

3 Optical: 0.1%

4 Radio ?

5 MeV/GeV/TeV ? >10%?

6 Gravitational radiation ?

keV rays: 7%

2 1-10 keV X-rays: 9%

3 Optical: 2%

4 Radio: 0.05%

DURING THE BURST AFTERGLOW

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GRB030329 – THE “POSTER CHILD”* FOR THE GRB-SUPERNOVA CONNECTION

• GRB030329 was a bright (top 1%) nearby (z=0.17) burst, discovered by HETE

• It is the best-studied GRB to date (>>100 observations)

• Its optical afterglow light curve and spectrum point to an underlying supernova component (SN2003dh)

• These signatures have been observed before in numerous GRBs, starting with GRB980425 (=SN1998bw, peculiar Type Ic – the previous poster child), but GRB030329 is the most convincing case

*Poster child n. A child afflicted by some disease or deformity whose picture is used onposters to raise money for charitable purposes

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Matheson et al. 2004

• Optical afterglow spectrum resembles that of SN1998bw

• Broad, shallow absorption lines imply large expansion velocities

• Afterglow light curve can be decomposed into two components: power law decay + supernova

Some long GRB’s are associated with the deaths of massive stars (>30M)

Stanek et al. 2003

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MYSTERY OF THE OPTICALLY DARK BURSTS

DARKBURSTS

Fox et al. 2003Fox et al. 2003

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THE MYSTERY OF THE OPTICALLY DARK BURSTS IS BEING SOLVED

• 35% of the GRBs detected by BeppoSAX and the IPN had no detectable optical counterparts – why?

1. Absorbed by dust within the host galaxy?

2. Intrinsically faint and/or rapidly fading?

3. High redshift?

• Only ~10% of the bursts detected by HETE are optically dark– HETE gets positions out to the astronomers faster than

BeppoSAX and the IPN did– Swift is now doing the same, and carrying out optical

observations within minutes– Some Swift bursts do appear to be optically dark

Confirmed byobservation? Not so far

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OBSERVATIONS OF SWIFT BURSTS

DARKBURSTS

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WHAT ARE X-RAY FLASHES?

1.GRBs observed away from the jet axis?

2.Explosions with less relativistic ejecta?

3.GRBs at high redshift?

• We have only one XRF redshift (XRF020903, z=0.251); in this case, the answer is clearly 2 (Soderberg et al. 2004)

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ARE THE SHORT GRBS NEARBY MAGNETAR FLARES?

GIANT FLARE FROM SGR1806-20RHESSI DATA

•Giant flares begin with ~0.2 s long, hard spectrum spikes

•Their energy can be ~1047 erg

•The spike is followed by a pulsating tail with ~1/1000th of the energy

•Viewed from a large distance, only the initial spikes would be visible

•They would resemble the short GRBs

•Swift can detect them out to 100 Mpc

•Are all short GRBs magnetar flares?–Uncertainties are the progenitors of magnetars and the number-intensity relation for giant flares

0 100 200 300 400Tim e, s

10

100

1000

10000

100000

Co

un

ts/0

.5 s

0 100 200 300 400Tim e, s

10

100

1000

10000

100000

Co

un

ts/0

.5 s

6 7 8 9 10TIME, s

20

40

60

80

CO

UN

TS

/0.0

64

S

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CONCLUSIONS• Good evidence now links some of the long GRBs to Type Ic

supernovae and the deaths of massive stars

• The origin of one X-ray flash has been determined – but does this explain all of them?

• The origin of the short bursts is probably the most outstanding mystery – neutron star/neutron star mergers, magnetar flares in nearby galaxies, both, something else?

• The mystery of the dark bursts is being solved – but are some at high redshift?

• GRB’s are bright enough to be detected out to z>10 – but are they actually generated there?

• HETE, INTEGRAL, and Swift may solve these mysteries

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GRB

UHEcosmic ray

acceleration;

Quantumgravity Mass extinctions,

morbid curiosityof the

general public

Earlyuniverse,

reionization

Merging neutronstars, GW

Stellarcollapse

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THE Epeak-Eisotropic energy RELATION

• Amati (2002) found that the peak energy in a GRB spectrum is related to the isotropic equivalent energy: EpeakEiso

0.52 (BeppoSAX results)

• Lamb (2004) has begun to extend this relation down to the XRF’s using HETE results: the relation holds also for XRF’s

• There are still several possible explanations for this, but in any case it strongly suggests that XRF’s and GRB’s are related

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B field Vacuum Breakdown

Blandford-Znajek mechanism

Blandford & Znajek (1977)Brown et al. (2000)Barbiellini & Longo (2001)Barbiellini, Celotti & Longo (2003)

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Vacuum Breakdown

Polar cap BH vacuum breakdown

Figure from Heyl 2001

The GRB energy emission is attributed to an high magnetic field that breaks down the vacuum around the BH and gives origin to a e fireball.

Pair production rate

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Two phase expansion

• Phase 1 (acceleration and collimation) ends when:

• Assuming a dependence of the B field:

this happens at

• Parallel stream with

• Internal “temperature”

collrand tt 3 RB

cm1091 R

acc301

1'

1

The first phase of the evolution occurs close to the engine and is responsible of energizing and collimating the shells. It ends when the external magnetic field cannot balance the radiation pressure.

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Two phase expansion

• Phase 2 (adiabatic expansion) ends at the radius: Fireball matter dominated:

• R2 estimation

• Fireball adiabatic expansion

20 Mc

ERR

02 100RR

0

2'

'2

1R

R

The second phase of the evolution is a radiation dominated expansion.

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Jet Angle estimation

Figure from Landau-Lifšits (1976)

• Lorentz factors

• Opening angle

• Result:

The fireball evolution is hypothized in analogy with the in-flight decay of an elementary particle.

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Energy Angle relationship

Predicted Energy-Angle relation

The observed angular distribution of the fireball Lorentz factor is expected to be anisotropic.

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Spectral Energy correlations

Amati et al. (2002)Ghirlanda et al. (2004)

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GRB for Cosmology

Ghirlanda et al. (2004)

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GRB for Cosmology

Ghirlanda et al. 2005

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Testing the correlations

(Band and Preece 2005)

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GRB fluence distributionGRB RATESFR

Madau & Pozzetti 2000

zz

1)(R

dzdV

~dzdtdN GRB

FLUENCE DISTRIBUTIONUSING AMATI RELATION

By random extraction of Epeak (Preece et al. 2000) and GRB redshift for a sample of GRBs we reproduce bright GRB fluence distribution. Bosnjak et al. (2004)

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Testing the correlations

Ghirlanda et al. astro-ph/0502186

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SN- GRB connection

SN 1998bw - GRB 980425 chance coincidence O(10-4)(Galama et al. 98)

SN evidence

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GRB 030329: the “smoking gun”?

(Matheson et al. 2003)

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Bright and Dim GRB(Connaughton 2002)

Q = cts/peak cts

BRIGHT GRB DIM GRB

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GRB tails• Connaughton (2002), ApJ 567, 1028 • Search for Post Burst emission in prompt GRB

energy band• Looking for high energy afterglow (overlapping with

prompt emission) for constraining Internal/External Shock Model

• Sum of Background Subtracted Burst Light Curves• Tails out to hundreds of seconds decaying as

temporal power law = 0.6 0.1 • Common feature for long GRB • Not related to presence of low energy afterglow

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GRB tailsSum of 400 long GRB bkg subtracted peak alligned curve

Connaughton 2002

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GRB tails

Connaughton 2002

Dim Bursts

Bright Bursts

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Bright and Dim Bursts

• 3 equally populated classes• Bright bursts

– Peak counts >1.5 cm-2 s-1 – Mean Fluence 1.5 10-5 erg cm-2

• Dim bursts – peak counts < 0.75 cm-2 s-1 – Mean fluence 1.3 10-6 erg cm-2

• Mean fluence ratio = 11

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Recent evidence

Piro et al. (2005)

GRB 011121

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Effect of Attenuation

Epeak

Egamma

Ep ~ Eg0.7

Ep ~ Eg

Preliminary

Tau = 1.5 +- 0.5 Caution: scaling fluence and Epeak

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Effects on Hubble Plots

Luminositydistance

Redshift

Reducing the scatter

Preliminary

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Effects on Hubble PlotsLuminositydistance

Redshift

Preliminary

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Conclusions

• Cosmology with GRB requires: – Spectral Epeak

determination– Measurement of Jet

Opening Angle– Evaluation of

environment material• Waiting for Swift results

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COMPARISON OF CURRENT MISSIONS

FOV,sr

# BURSTS/YEAR

LOCALIZATIONACCURACY

IPN 4π 100 5’

HETE 1.6 25 1’

INTEGRAL 0.02 8 1.5’

Swift 1.4 84 3’

NO NO

NO NO

ONBOARD FOLLOWUPX-RAYS? OPTICAL?

NO NO

YES YES

Should be an exciting year for GRB results!