Gamma Ray BurstsGamma Ray Bursts João Braga - INPE

Dark ages of GRBs BATSE/CGRO: some light GRBs x SGRs, magnetars BeppoSAX: afterglows and IDs Progenitors Host galaxies and cosmology HETE, SWIFT and the future

Dark AgesDark Ages

July 1967: Vela satellites detect gamma ray outbursts

16 peculiar events of cosmic origin short (~s) photon flashes with E > 100 MeV publication only in 1973

Dark AgesDark Ages

After ~30 ys

only a reasonable idea of what they are

Phenomenology of bursts in the DAs:

almost no association with known objects statistically poor distribution

no clue

Dark AgesDark Ages

Burst of March 5th, 1979

SNR N49 in LMC (~10,000 ys) 8 s oscillations in ~200 s

Nature of GRBs associated with Galactic neutron stars: rapid variability compact object (light-seconds) cyclotron lines @ tens of keV B ~ 1012 G : = eB/mc emission lines @ hundreds of KeV redshifted 511 keV

zobs = z0 (1 – 2GM/c2 R)

periodicity rotation of a NS : R3 < (GM/42) T2

BATSE – COMPTON GROBATSE – COMPTON GRO• ~3000 bursts (~1 each day)• Isotropic distribution

- No concentration towards LMC, M31 or nearby clusters

- No dipole and quadupole moments• No spectral lines• No periodicity

Hundreds of models proposed

BATSE – COMPTON GROBATSE – COMPTON GRO• Bimodal distribution

— most are longer than 2 s— ~1/3 are shorter than 2 s

• Spectra: combination of two power-laws- spectrum softens with time

- Ep decreases with time (in the E.f(E) x E plot)

• Fluence: ~ 10-6 — 10-4 erg cm-2

long duration and hard spectrum bursts deviate more from a 3-D Euclidean brightness distribution

Euclidean

Soft Gamma Ray Repeaters Soft Gamma Ray Repeaters SGR SGR

Burst of March 9Burst of March 9thth, 1979, 1979

SNR N49 in LMC (~10,000 ys)

8 s oscillations in ~200 s

SOFT GAMMA RAY REPEATERSSOFT GAMMA RAY REPEATERS bursts repeat soft spectra (E 100 keV) short duration (~100 ms) Galactic “distribution”, associated with SNRs

Soft Gamma Ray Repeaters Soft Gamma Ray Repeaters SGR SGR

Soft Gamma Ray Repeaters Soft Gamma Ray Repeaters SGR SGR

Rotating magnetized Rotating magnetized neutron stars neutron stars

dE B2 R6 4 sin2 = dt 6 c3

Erot= I 2/2 ; P = 2 /

dE . = I dt . c 3/2 3IPP 1/2 B =B = RR33 sin sin 2 2

Rotating magnetized Rotating magnetized neutron stars neutron stars

for SGR 0525-66 (5/3/79):~1 ms 8 s in ~10 kys . P ~ 3 x 10-11 s s-1

B ~1015 G !!

MAGNETARMAGNETAR

Rotating magnetized Rotating magnetized neutron stars neutron stars

Very high fields

Fast spindown

SGRs are young NSs which should still be associated to

SNRs

MAGNETARSMAGNETARS

QuickTime Movie

MAGNETARSMAGNETARS

How do the bursts happen? NS crust brakes due to EM tensions (starquakes) Alfvén waves injected in the magnetosphere particle acceleration optically thick pair plasma forms gamma-ray emission

MAGNETARSMAGNETARS

Problems:

In 1900+14, RXTE measured a much . smaller P 2 ys before the 1998 active period

EB increased by more than 100%

Spindown is not magnetic and may be due

to relativistic winds (no magnetar!)

BeppoSAX and AfterglowsBeppoSAX and Afterglows

BeppoSAX:- 4 narrow field instruments(.1 to 300 keV; ~arcminute res.)- Wide Field Camera(2 to 25 keV; 200 x 200 ; 5’; coded-mask)- Gamma Ray Burst Monitor(60 to 600 keV; side shield)

BeppoSAX and AfterglowsBeppoSAX and Afterglows

97 Feb 28: GRB 970228 Discovered by GRBM and WFC NFIs observe 1SAX J0501.7+1146

First clear evidence of a GRB X-ray tail

Non-thermal spectra X-ray fluence is 40% of -ray fluence

BeppoSAX and AfterglowsBeppoSAX and Afterglows

BeppoSAX and RXTE discovered several other afterglows

Optical transients: Observed in appr. ½ of the well localized

bursts GRB 990123 is the only one observed in the

optical when the gamma-ray flash was still going on

GRB 990123GRB 990123

GRB 011121GRB 011121

GRB 011121GRB 011121

Host galaxiesHost galaxies Optical IDs distant galaxies (low luminosity, blue) ~20 measured redshifts All in the z = 0.3 – 4.5 range, with the

exception of GRB 980425, possibly associated with SN 1998bw @ z = 0.008

OT is never far from center

redshiftsredshifts

ProgenitorsProgenitors Long GRBs are probably associated with

massive and short-lived progenitorsmassive and short-lived progenitors

GRBs may be associated with rare types of supernovae

Hypernovae: colapse of rotating massive star black hole accreting from a toroid

Collapsar: coalescence with a compact companion GRBs and SN-type remnant

ProgenitorsProgenitors Short GRBs are probably associated with

mergers of compact objectsmergers of compact objects

The fireball modelThe fireball model Observed fluxes require 1054 erg emitted in

seconds in a small region (~km)

Relativistic expanding fireball (e± , )Problem: energy would be converted into Ek of

accelerated baryons, spectrum would be quasi-thermal, and events wouldn’t be much longer than ms.

Solution: fireball shock modelfireball shock model: shock waves will inevitably occur in the outflow (after fireball becomes transparent) reconvert Ek into

nonthermal particle and radiation energy.

The fireball modelThe fireball model Complex light curves are due to internal shocks

caused by velocity variations. Turbulent magnetic fields built up behind the

shocks synchrotron power-law radiation spectrum Compton scattering to GeV range.

Jetted fireballJetted fireball: fireball can be significantly collimated if progenitor is a massive star with rapid rotation escape route along the rotation axis jet formation alleviate energy requirements higher burst rates

High Energy Transient ExplorerHigh Energy Transient Explorer

First dedicated GRB mission, X- and -rays Equatorial orbit, antisolar pointing launched on Oct 9th, 2000 - Pegasus 3 instruments, 1.5 sr common FOV

SXC (0.5-10 keV) - < 30” localization

WXM (2 –25 keV) - < 10’ localization FREGATE (6-400keV) - sr localization Rapid dissemination ( 1s) of GRB positions

(Internet and GCN)

HETEHETE

HETE Investigator TeamHETE Investigator Team

UC BerkeleyUC BerkeleyKevin Hurley J. Garrett Jernigan

MITMITGeorge R. Ricker (PI) Geoffrey Crew John P.Doty Al Levine Roland Vanderspek Joel Villasenor

LANLLANLEdward E. Fenimore Mark Galassi

RIKENRIKENMasaru Matsuoka Nobuyuki Kawai Atsumasa Yoshida

CESRCESRJean-Luc Atteia Gilbert Vedrenne Jean-Francois Olive

Michel Boer

UChicagoUChicagoDonald Q. LambCarlo Graziani

INPEINPEJoão Braga

UC Santa CruzUC Santa CruzStanford Woosley

CNESCNESJean-Luc Issler

SUP’AEROSUP’AEROChristian Colongo

CNRCNRGraziella Pizzichini

TIRFTIRFRavi Manchanda

HETE in the PegasusHETE in the Pegasus

Ground station networkGround station network

GRB 010921GRB 010921 Bright (>80) burst detected on Sept 21, 2001

05:15:50.56 UT by FREGATE First HETE-discovered GRB with counterpart Detected by WXM, giving good X position (10o x 20’ strip) Cross-correlation with Ulysses time history

IPN annulus (radius 60o ± 0.118o)

intersection gives error region with 310 arcmin2 centered at

~ 22h55m30s, ~ 40052’

GRB 010921GRB 010921

GRB 010921GRB 010921 Highly symmetric at high

energies Lower S/N for WXM due to

offset Durations increase by 65% at

lower energies Hard-to-soft spectral evolution Peak energy flux in the 4-25

keV band is 1/3 of 50-300 keV Peak photon flux is ~4 times

higher in the 4-25 keV

DiscussionDiscussion Long duration GRB X-ray rich, but no XRF (high 50-300 keV flux) z = 0.450 isotropic energy of 7.8 x 1051 erg

(M=0.3, =0.7, H0=65 km s-1 Mpc-1) - less if

beamed Second lowest z strong candidate for extended

searches for possible associated supernova Final position available 15.2h after burst

ground-based observations in the first night counterpart established well within HETE-IPN error region

ConclusionsConclusions

GRBs occur at a rate of (no beaming)

a few/day/universe or 1/few million ys/average galaxy or ~10-91 cm-3 s-1

(since observed GRBs are detectable out to z ~10) New missions are very important

SWIFT: 3 instruments, 250-300 bursts/yr, coverage from optical to gamma-rays, arcsecond positions,

will detect bursts up to z ~20.INTEGRAL, EXIST, MIRAX

Cosmology: burts can proble early universe and some could be related to Pop III stars

metal enrichment and ionization of the primordial gas.