Gamma Ray Bursts: open Gamma Ray Bursts: open issuesissues

Brief historyBrief historyPowerPowerShort history of the paradigm: Short history of the paradigm:

internal vs external shocksinternal vs external shocksAfterglows: external shocksAfterglows: external shocksThe spectral-energy relationsThe spectral-energy relationsGRBs for cosmologyGRBs for cosmology

Gabriele Ghisellini – Osservatorio di Gabriele Ghisellini – Osservatorio di Brera Brera

Gamma-Ray Bursts: The story Gamma-Ray Bursts: The story beginsbegins

Treates banning nuclear tests between USA and USSR in early 60s

VELA Satellites: X and soft -ray detectors

Klebesadel R.W., Strong I.B., Olson R., 1973, Astrophysical Journal, 182, L85

`Observations of Gamma-Ray Bursts of Cosmic Origin’

Brief, intense Brief, intense flashes of flashes of -rays-rays

Shortest 6 msGRB 910711

Longest ~2000 sGRB 971208

Paciesas et al (2002)Briggs et al (2002) Koveliotou (2002)

SHORT LONG

Short – HardShort – Hard Long - SoftLong - Soft

Two flavours, long and Two flavours, long and shortshort

SpectraSpectra

Non thermal Non thermal spectraspectra

featureless continuumfeatureless continuum

power-laws - peak in power-laws - peak in FF F ~ E F ~ E

Epeak

1997: The BeppoSAX satellite

Slewing in several hoursSlewing in several hours

Italian-Dutch

“Satellite per l’ Astronomia X”

InstrumentsInstruments

Wide Field Cameras:Wide Field Cameras:

5% of sky – positioning ~ 5% of sky – positioning ~ 4’ 4’

+ +

Narrow Field InstrumentsNarrow Field Instruments

arcmin resolutionarcmin resolution

NFI

Discovery of first Discovery of first afterglow!afterglow!

GRB 28 9702

3 March3 March28 February28 February

Optical id. host galaxy: redshiftsOptical id. host galaxy: redshifts

Cosmological origin !

~120 / 3000 with z: <0.1 – 6.3~120 / 3000 with z: <0.1 – 6.3

(Batse, SAX, HETE-II, Integral, Swift, …) (Batse, SAX, HETE-II, Integral, Swift, …)

Huge Huge isotropicisotropic equivalent equivalent

energy!energy!

119 GRBs with 119 GRBs with zz

GRB typical Fluence GRB typical Fluence (i.e. time int. flux) is (i.e. time int. flux) is 1010-8 -8 – 10– 10-4 -4 erg/cmerg/cm2 2

(1keV – 10 MeV)(1keV – 10 MeV)

Assume Assume IsotropyIsotropy

Energy and PowerEnergy and Power

GRB are powerfulGRB are powerful

• AGN: L < 10AGN: L < 104848 erg/s erg/s• SN: L < 10SN: L < 104545 erg/s erg/s (in photons)(in photons)

• GRB: L < 10GRB: L < 105353 erg/s erg/s

Planck Planck power: power:

McMc22 cc55

RRgg/c /c GG

= = 3.6x10= = 3.6x105959 erg/s erg/s

“first light” & PopIII

chemical evolution

large scale structures

cover the epoch of re-ionization

Star Formation Rate

Probes of far universe

SNIa

Huge energyHuge energySmall VolumeSmall Volume

FireballFireball

Invented even before knowing that GRBs are Invented even before knowing that GRBs are cosmological….cosmological….

A short history of fireballsA short history of fireballs

19781978 Cavallo & Rees: fireball: photons trapped by their own Cavallo & Rees: fireball: photons trapped by their own pairs pairs

19781978 Rees: internal shocks in M87 to transport energy along Rees: internal shocks in M87 to transport energy along the jetthe jet

19861986 Paczynski: Cosmological GRB Paczynski: Cosmological GRB L=10 L=105151 erg/s and T~1 erg/s and T~1 MeV MeV

19861986 Goodman: T Goodman: Tobsobs remains T during expansion. Doppler remains T during expansion. Doppler

balances adiabatic cooling balances adiabatic cooling

19921992 Pure fireball made by Pure fireball made by e+e- . Focussing by e+e- . Focussing by gravitationgravitation

NS

e+e-

A short history of fireballsA short history of fireballs

19781978 Cavallo & Rees: fireball: photons trapped by their own Cavallo & Rees: fireball: photons trapped by their own pairs pairs

19781978 Rees: internal shocks in M87 to transport energy along Rees: internal shocks in M87 to transport energy along the jetthe jet

19861986 Paczynski: Cosmological GRB Paczynski: Cosmological GRB L=10 L=105151 erg/s and T~1 erg/s and T~1 MeV MeV

19861986 Goodman: T Goodman: Tobsobs remains T during expansion. Doppler remains T during expansion. Doppler

balances adiabatic cooling balances adiabatic cooling

19921992 Pure fireball made by Pure fireball made by e+e- . Focussing by e+e- . Focussing by gravitationgravitation

19921992 Dirty fireball polluted by baryons. Re-conversion of Dirty fireball polluted by baryons. Re-conversion of bulk kinetic into radiation through shocks with external bulk kinetic into radiation through shocks with external mediummedium

19941994 Internal shocks due to shells moving with different Internal shocks due to shells moving with different

Why internal shocks?Why internal shocks?

Spikes have Spikes have same same durationduration

A process A process that that repeats repeats itselfitself

Relativ. eRelativ. e-- + B: + B: synchrotron??synchrotron??

Relativ. eRelativ. e-- + + B: B:

synchrotronsynchrotron

Shell still opaqueShell still opaque

““The” model:The” model:Internal/ExternInternal/Extern

al Shocksal ShocksRees-Meszaros-Piran

ProgenitProgenitorsors

Host galaxiesHost galaxiesFaint (mFaint (mRR ~ 25 ) galaxies~ 25 ) galaxiesSites of star formation Sites of star formation Low metallicitiesLow metallicities

Blo

om

et a

l. 20

02

GRBs associated with SN (Ib,c) GRBs associated with SN (Ib,c)

SN

afterglow

Math

eson

et a

l. 20

03

Afterglow re-brightening Afterglow re-brightening A few spectroscopic ident. (underluminous?)A few spectroscopic ident. (underluminous?)

ProgenitorsProgenitors

core collapse of massive stars (M > 30 Msun) long GRBs Collapsar or Hypernova (MacFadyen &

Woosley 1999) GRB simultaneous with SN

Supranova – two-step collapse (Vietri & Stella 1998)

GRB delayed by few months-years

Discriminants: host galaxies, location within host, duration, environment, redshift distribution, ...

compact object mergers (NS-NS, NS-BH) short GRBs

?

The engineThe engine

Accreting torus

Formation of a spinning BH + dense Formation of a spinning BH + dense torus, sustaining B ~ 10torus, sustaining B ~ 101414-10-101515 G G

Extraction BH spin energy (0.29 Extraction BH spin energy (0.29 MMBHBHcc22))

Extract E > 10Extract E > 105252 erg erg

ttGRBGRB ~ 10 ~ 1044 t tdyndyn

JetsJets

Jet half opening

angle

Jet effectJet effect

, Surf.

Relativistc beaming:

emitting surface

1/

1/1/

Log(t)

Log(F)

Jet Jet breakbreak

>> 1/

Israel et al. 1999

GRB Jet measureGRB Jet measure

“Jet break”

Jet break time tbreak

Jet opening angle

““True” energeticsTrue” energeticsFra

il e

t al.

2001

Isotropic equivalent Isotropic equivalent energyenergy

EEtruetrue = E = Eiso iso (1 – cos (1 – cos ))

Blo

om

et

al.

2003

EE peakpeak

was n

ot

was n

ot

consid

e

consid

e

red…

red…

Am

ati

et

al.

2002

Am

ati

et

al.

2002

9+2 BeppoSAX GRBs

EE peak

peak

E E

iso

iso

0.5

0.5

Peak energy – Isotropic energy Peak energy – Isotropic energy CorrelationCorrelation

EEp

eak

peak(1

+z

(1+

z))

Nava e

t al.

2006;

Gh

irla

nd

a e

t al.

2007

Nava e

t al.

2006;

Gh

irla

nd

a e

t al.

2007

“Am

ati”

(62)

“Ghi

rlan

da”

(25)

1- cos 1- cos jetjet

Gh

irla

nd

a,

Gh

isellin

i, L

azzati

& F

irm

an

i 2004

Gh

irla

nd

a,

Gh

isellin

i, L

azzati

& F

irm

an

i 2004

Lu

min

osit

y

Lu

min

osit

y

dis

tan

ce

dis

tan

ce

redshiftredshiftGRBs can b

e use

d as c

osmolo

gical

GRBs can b

e use

d as c

osmolo

gical

RULERS !

RULERS !

Supernovae

GRBsGRBs

Problems:Problems: 1: Efficiency 1: Efficiency

Efficiency=Radiated/total energyEfficiency=Radiated/total energyOnly the RELATIVE kinetic energy can be used!Only the RELATIVE kinetic energy can be used!

Shells of Shells of equal equal massesmasses

Shells of Shells of equal equal energiesenergies

final final ~ (~ (1122))1/21/2

Dyn

am

ical effi

cie

ncy

(%)

5%

Pir

o a

str

o-p

h/0

001436

Pir

o a

str

o-p

h/0

001436

A lot of kinetic energy should remain to power the A lot of kinetic energy should remain to power the afterglowafterglow

SAX X-ray SAX X-ray afterglow afterglow light curvelight curve

PromptPrompt

Willin

gale

et

al.

W

illin

gale

et

al.

2007

2007

SWIFTSWIFT

EEafterglowafterglow < E < Epromptprompt

EE afterg

low

afterg

low ~

0.1 E

~ 0.1 E pro

mpt

prompt

Problems:Problems:2: Early 2: Early

“afterglow”“afterglow”

Good old timesGood old timesP

iro a

str

o-p

h/0

001436

Pir

o a

str

o-p

h/0

001436

Now: a messNow: a mess

GRB 050904GRB 050904

z=6.29z=6.29

Pan

ait

escu

2006

Pan

ait

escu

2006

XX

OptOpt..

X-ray and optical behave X-ray and optical behave differentlydifferently

X-rays: X-rays: steep-flat-steep-flat-

steepsteep

TA

Is this “real” afte

rglow? i.e. e

xternal

Is this “real” afte

rglow? i.e. e

xternal

shock?

shock?

Early (normal) prompt: Early (normal) prompt: >>1/j

Late prompt: Late prompt: >1/j

Late prompt: Late prompt: =1/j

Late prompt: Late prompt: <1/j

”real” after-glow

Ghisellini et al. Ghisellini et al. 20072007

Long lasting engine??Long lasting engine??

• RRss/c ~ 10/c ~ 10-4-4 s (for a 10 solar mass s (for a 10 solar mass

BH)BH)• Even 10 s are 10Even 10 s are 1055 dynamical times dynamical times• Two-phase accretion? Two-phase accretion?

ConclusionsConclusions

““Paradigm”: internal+external shocks, Paradigm”: internal+external shocks, synchrotron for both: synchrotron for both: it helps, but it it helps, but it is limitingis limiting

Efficiency is an issueEfficiency is an issue

Progenitors for long: done. For short: Progenitors for long: done. For short: not yetnot yet

Central engine? How long does it live?Central engine? How long does it live?

GRBs as probes of the far universe GRBs as probes of the far universe (continue…)(continue…)

There can be a Black Body … butThere can be a Black Body … but

Time resolved Time resolved spectraspectra

Time integrated Time integrated spectrumspectrum

The same The same occurs for ALL occurs for ALL GRBs detected GRBs detected by BATSE and by BATSE and with WFCwith WFCG

hir

lan

da e

t al.

G

hir

lan

da e

t al.

2007b

2007b

MemoryMemory

Epeak

=509 keV

Epeak

=503 keV Epeak

= 416 keV

Time [sec]

cts/sec

Epeak

= 390 keV

EF(E)

EF(E)

EF(E)

GRB spectrum evolves with time within GRB spectrum evolves with time within single burstssingle bursts

Ghirlanda PhD Ghirlanda PhD thesisthesis

phot

/cm

^2 s

ec

Hard to Soft Hard to Soft evolutionevolution

Epe

ak

Epeak

, t), t)

Decrease Decrease independent of the independent of the rise and decay of rise and decay of the fluxthe flux

Epeak

time

Tracking Tracking evolutionevolution

Photon Photon fluxflux

Correlated with

EEpeakpeak(t)(t), , (t) (t) ,,(t)(t)

By construction, internal shocks By construction, internal shocks should all be equal.should all be equal.

Then, why does the spectrum Then, why does the spectrum evolve?evolve?

SpectraSpectraSpectra

Fis

hm

an

& M

eeg

an

1995

Fis

hm

an

& M

eeg

an

1995

EEpeakpeak

Prompt Prompt radiation: radiation:

Synchrotron?Synchrotron?

Energy spectrum of a cooling electronEnergy spectrum of a cooling electron

Fast cooling Fast cooling + synchro: + synchro:

E() -1/2

N() -3/2

Typical synchrotron Typical synchrotron frequencyfrequency

synsyn = 3.6x10 = 3.6x1066BB22/(1+z)/(1+z)HzHz

Magnetic field from: Magnetic field from:

LLB B = = BBLLkinkin R R2222BB22c = c = BBLLshellshell

Size from:Size from:

R ~ RR ~ R002 2 (internal shock) (internal shock)

Electron energy from: Electron energy from:

mmeecc22==eemmppcc22((’-1) ~ ’-1) ~ eemmppcc22

B B LLshellshell

RR00

BB ~

1/21/2 1/21/2

~ ~ eemmpp/m/mee

Synchrotron Synchrotron -ray -ray emission?emission?

BB ee LLkin,shell,50kin,shell,50hhsynsyn ~ 400 ~ 400

keV keV

1/21/2 22 1/21/2

33 RR0,70,7 (1+z)(1+z)2

ttcoolcool ~ 10 ~ 10--

77

ee ( (/100)/100)

MeVMeV22

33

secsec

Extremely short - No way to make it longer

tcool << tdynamical ~ 10-2 sec

It must be short, if not, how can the flux vary?

0.2 0.2 msms

More than More than exponentialexponential

-2 -1 0 1 Low energy photon power law index N(E) =

kE-P

reece e

t al.

FF ~ ~ 1/31/3

FF ~ ~ -1/2-1/2

Can it be rescued Can it be rescued by:by:

Reacceleration?Reacceleration? NoNo, in ISS e- are , in ISS e- are accelerated only onceaccelerated only once

Adiabatic losses?Adiabatic losses? NoNo, too small , too small regions would be involved, too regions would be involved, too much ICmuch IC

Self absorption?Self absorption? NoNo, lots of e- , lots of e- needed, too much ICneeded, too much IC

Self Compton?Self Compton? NoNo, t, tcoolcool too small too small

even in this caseeven in this case

Clustering of the Clustering of the optical optical

luminositiesluminosities

Flux vs observed timeFlux vs observed time

=0.48=0.48

Nard

ini et

al.

2006

Nard

ini et

al.

2006

Luminosity vs rest frame Luminosity vs rest frame titimmee=0.28=0.28

Nard

ini et

al.

2006

Nard

ini et

al.

2006

Swift GRBsSwift GRBs

332121

552727

Pre-SwiftPre-Swift

+Swift+Swift

Dark??Dark??

Lx @ 12 Lx @ 12 hhoouurrss

pre-Swift (19)pre-Swift (19)

Including Including SSwwiifftt

(30)(30)

G1=100, G2=200G1=100, G2=200

Thompson, Meszaros & Rees 2007Thompson, Meszaros & Rees 2007

At R ~ RAt R ~ Rstarstar the fireball dissipates part of the fireball dissipates part of

its energy its energy BB BB

L ~L ~ 22 LLisoiso 22 ~ L/L ~ L/Lisoiso

LLisoiso ~ R ~ R22 22 T’ T’4 4

~ (~ (R/R/22 T T44

LLisoiso ~ R ~ R22 (L /L (L /Lisoiso)T)T

4 4 EEpeakpeak ~ L ~ Lisoiso1/21/2LL-1/4-1/4

A short history of fireballsA short history of fireballs

Short BurstsShort Bursts

The spectrum of short The spectrum of short burstsbursts

harder softer

Log Epeak Log Log Epeak Log

short

long

Gh

irla

nd

a e

t al.

2004

harder becausebecause

is harder, Epeak is

the same or even smaller

DensityDensity

Star forming regions are Star forming regions are densedense

GRB – Afterglow – Temporal PropertiesGRB emission in X, GRB emission in X, OpticalOpticalPanaitescu &

Kumar

Why densities a

re so

Why densities a

re so

small?

small?

Fir

man

i et

al.

2004

LL-1.5+-0.05-1.5+-0.05

No corr.No corr.

LLxx > L > Loptopt

LLoptopt more clustered than L more clustered than Lxx

vvcc between optical and X-rays between optical and X-rays

~same values of ~same values of BB, , ee, E, Ek,isok,iso

moderate cooling (small moderate cooling (small BB))

large Comptonization y large Comptonization y paraparametermeter

different pdifferent p

Universal energy Universal energy reservoir?reservoir?

Blo

om

et

al.

2003

Blo

om

et

al.

2003

Fra

il e

t al.

2001

Fra

il e

t al.

2001 Best n Best n

from fitsfrom fits

Fra

il e

t al.

Fra

il e

t al.

2001

2001

Fra

il e

t al.

2001

Same energy, different Same energy, different angles?angles?

Structured jetsStructured jets

viewview

jetjet

E()=const

E()=E0-2 L) = kLL) = kL-2-2

Universal EUniversal Epeakpeak??

Pre

ece e

t al.

~200 keV, ~200 keV, observerobserver frame frame

BATSEBATSE

HETE IIHETE II

X-ray fl

ashes

X-ray fl

ashes

Am

ati

et

al.

+Lam

b e

t A

mati

et

al.

+Lam

b e

t al.

al.

The “Amati et al.” relationThe “Amati et al.” relation

EEpeakpeak = 100 keV = 100 keV

EEiso,52 iso,52

++

EEisoiso = E = Etruetrue//22

EEpeakpeak = 1/ = 1/

1/21/2