explosões cósmicas de raios gama (gamma-ray bursts)

CEACEA

Explosões Cósmicas de Explosões Cósmicas de Raios Gama Raios Gama

(Gamma-Ray Bursts)(Gamma-Ray Bursts)

breve história dos GRBsbreve história dos GRBs BeppoSAX: afterglowsBeppoSAX: afterglows galáxias hospedeiras e galáxias hospedeiras e

redshiftsredshifts

modelos para os progenitoresmodelos para os progenitores resultados recentes (HETE)resultados recentes (HETE) SWIFT, SWIFT, MIRAXMIRAX e o futuro e o futuro

João Braga – INPEJoão Braga – INPE

Nova Física Nova Física no Espaço 2003no Espaço 2003

CEACEA HistoryHistory

July 1967: Vela satellites detect strong gamma ray signals coming from space 16 peculiar events of cosmic origin short (~s) photon flashes with E > 100 MeV publication only in 1973 (classified before that)

Phenomenology of bursts before the 90’s: almost no association with known objects statistically poor distribution

no clue

CEACEA HistoryHistory

Burst of March 5th, 1979 intense -ray pulse (0.2 s), ~100 times as intense as any previous burst SNR N49 in LMC (~10,000 ys) 8 s oscillations in ~200 s (softer emission)

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

CEACEABATSE – COMPTON GROBATSE – COMPTON GRO

launched on 1991 - ~10 yearslaunched on 1991 - ~10 years

• 2704 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

CEACEA

CEACEA 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

CEACEA

Soft Gamma Ray Repeaters Soft Gamma Ray Repeaters

SGR SGRBurst of March 5Burst of March 5thth, 1979, 1979 (SGR 0526-66) SNR N49 in LMC (~10,000 ys)

SOFT GAMMA RAY REPEATERSSOFT GAMMA RAY REPEATERS bursts repeat in random timescales (normally hundreds of times) (4, maybe 5 objects known) soft spectra (E 100 keV) short duration (~100 ms) Galactic “distribution”, associated with SNRs possibly associated with magnetars and AXPs

CEACEASoft Gamma Ray Repeaters Soft Gamma Ray Repeaters

SGR SGR

CEACEABeppoSAX BeppoSAX

and Afterglowsand Afterglows BeppoSAX:

4 narrow field instruments(.1 to 300 keV; ~arcminute res.) Wide Field Camera(2 to 28 keV; 200 x 200 ; 5’; coded-mask) Gamma Ray Burst Monitor(60 to 600 keV; side shield)

WFC

CEACEABeppoSAX and BeppoSAX and

AfterglowsAfterglows97 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

CEACEABeppoSAX and BeppoSAX and

AfterglowsAfterglows

BeppoSAX and RXTE discovered several other afterglows

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

bursts GRB 990123GRB 990123 is the only one observed in the

optical when the gamma-ray flash was still going on

CEACEA GRB 990123GRB 990123

z=1.6

Keck OT spectrumHST image: host is an irregular, possibly merging system

CEACEAGRBs observed by GRBs observed by BeppoSAXBeppoSAX

CEACEA Host galaxiesHost galaxies

Optical IDs distant galaxies (low luminosity, blue) ~30 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

CEACEA redshiftsredshifts

GRB 990123z=1.6

Keck OT spectrum

CEACEA Energy (isotropy)

redshiftsredshifts

CEACEA redshifts & cosmologyredshifts & cosmology

CEACEA Types of BurstsTypes of Bursts Long and short bursts:Long and short bursts: the normal ones. Bimodal distribution; short bursts are harder and have no counterparts; almost all long bursts have X-ray afterglows. Dark bursts:Dark bursts: long bursts with X-ray afterglows but no optical or radio afterglows (½ of them). Possible explanations:

Absorption in the host galaxy They are beamed away from the observer

X-ray flashes (XRF’s):X-ray flashes (XRF’s): little or no emission above ~ 25 keV. Possibly related to X-ray rich GRBs.

CEACEA Types of BurstsTypes of Bursts

BurstClass

Percentage of all

bursts

Typical duration

(sec)

Initial gamma-

ray emission

Afterglow X-ray

emission

Afterglow optical

emission

Long(normal)

25% 20 Long (dark)

30% 20 noLong (X-ray rich or XRF)

25% 30 Absent or weak no

short 20% 0.3 ? ?

CEACEA ProgenitorsProgenitors

Long GRBsLong GRBs are probably associated with massive and short-lived progenitorsmassive and short-lived progenitors

GRBs may be associated with rare types of

supernovaesupernovae Hypernovae:Hypernovae: colapse of rotating massive

star black hole accreting from a toroid Collapsar:Collapsar: coalescence with a compact

companion GRBs and SN-type remnant

CEACEA ProgenitorsProgenitorsShort GRBsShort GRBs - ??

associated with associated with mergers of compact objectsmergers of compact objects SGRs SGRs in external galaxiesin external galaxies phase transition to strange starsphase transition to strange stars

CEACEA The fireball modelThe fireball modelObserved fluxes require 1054 erg emitted in seconds

in a small region (~km)

Relativistic expanding fireball (e± , )Problem: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: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.

CEACEA The fireball modelThe fireball model

Complex light curves are due to internal shocksinternal shocks caused by velocity variations.

Turbulent magnetic fields built up behind the shocks synchrotron power-lawsynchrotron power-law radiation spectrum Compton scattering to GeV rangeGeV 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 formationjet formation alleviate energy requirements higher burst rates

CEACEA The fireball modelThe fireball model

CEACEA The cannonball modelThe cannonball model

Bipolar jets of highly relativistic cannon balls are launched axially in core-collapse SNeThe CB front surfaces are collisionally heated to ~keV as they cross the SN shell and the wind ejecta from the SN progenitorA gamma-ray pulse in a GRB is the quasi- thermal radiation emitted when a CB becomes visible, boosted and collimated by its highly relativistic motionThe afterglow is mainly synchrotron radiation from the electrons the CBs gather by going through the ISM

CEACEAHETE HETE

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)

space.mit.edu/HETEspace.mit.edu/HETE

CEACEAHETEHETE

CEACEA 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

CEACEA Ground station network

CEACEAHETE resultsHETE resultsGRB 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’


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

CEACEA GRB 010921GRB 010921 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


Highly significant polarization (9.9%) in the V band measured 1.3 days after the burstz = 0.695 based on emission lines of host galaxyHigh polarization can be due to: line of sight at the very edge of the jet if the magnetic field is restricted to the plane of the shock alignment of the magnetic field over causally connected regions in the observed portion of the afterglow

CEACEA GRB 020531GRB 020531 Short, hard GRB detected by FREGATE and WXM on 31

May 2002 Short, intense peak followed by a marginal peak, which

is common on short, hard bursts T50 = 360 msec in the 85 – 300 keV band Preliminary localization 88min after burst, refined IPN localization 5 days after burst RA = +15h 15m 04s, Dec = -19o 24’ 51” (22 square arcmin hexagonal region) Follow-up at radio, optical and X-rays Duration increases with decreasing energy and spectrum evolves from hard to soft ► seem to indicate that short, hard bursts are closed related to long GRBs

CEACEA GRB 021004GRB 021004 detected by Fregate, WXM and SXC duration of ~100 sec (long GRB) GCN position notice (WXM) given 49 s after the beginning of the burst SXC location given 154 min after burst optical afterglow (R) detected in 9 min (15th mag) HST and Chandra observed in the following day best observed burst so far absorption redshift of 2.3 (C IV, Si IV, Ly) unusual brightenings seen in the light curve

CEACEA GRB 021211GRB 021211 Dark burst Duration of ~2.5 sec (“ transitional” GRB) GCN position notice (WXM) given 22 s after the beginning of the burst Raptor (LANL) observed 65 sec after burst Optical afterglow extremely faint after 2 hours GRB may have occurred on region with no surrouding gas or dust, so the shock wave had little material to smash into may support the binary merger theory for short GRB

CEACEANew missionsNew missions

SWIFT (US)SWIFT (US):: 3 instruments, large area, 250-300 bursts/yr, coverage from optical to gamma-rays, arcsecond positions, will detect bursts up to z ~20. Will be launched in 2003.INTEGRAL (Europe):INTEGRAL (Europe): launched last year. Several instruments with high energy resolution.EXIST (US):EXIST (US): huge area hard X-ray mission for 2010.GLAST (US):GLAST (US): large area high energy gamma-ray

mission; will study high energy afterglows. To be launched around 2007.

MIRAX (Brazil, US, Holland, Germany):MIRAX (Brazil, US, Holland, Germany): broadband imaging (6’) spectroscopy of a large source sample (1000 square degrees) in the central Galactic plane region. Expected to detect ~1 GRB/month. Two hard X-ray cameras and the flight model of the WFC. To be launched in ~2007.

CEACEA

Every GRB signals the birth of a sizable stellar-mass black hole somewhere in the observable universe.

Long GRBs occur in star forming galaxies at an average redshift of ~1.

There are now plausible or certain host galaxies found for all but 1 or 2 GRBs with X-ray, optical or radio afterglows positioned with arcsecond precision.

~30 redshifts have been measured for GRB hosts and/or afterglows, ranging from 0.25 (or maybe 0.0085) to 4.5.

BATSE results and current estimates for beaming imply that GRBs occur at a rate of 1000/day in the universe.

In a few cases, marginal evidence exist for transient X-ray emission lines and absorption features in the prompt and early afterglows.

What we do “know” What we do “know” about GRBs so farabout GRBs so far

CEACEA

Early afterglows will be carefully studied the missing link between the prompt emission and the afterglow will be identified;

The jet configuration will be identified universal structured jet model will be validated by future data;

With accumulation of a large sampe of spectral information and redshifts for GRB/XRF with Swift, we will know a lot more about the site(s) and mechanism(s) for the prompt emission;

Detection of GRB afterglows with z > 6 may provide a unique way to probe the primordial star formation, massive IMF, early IGM, and chemical enrichment at the end of the cosmic reionization era. (Djorgovski et al. 2003);

With Swift, we should get ~120 GRBs to produce Hubble diagrams free of all effects of dust extinction and out to redshifts impossible to reach by any other method (Schaefer 2003).

What to expect in What to expect in the coming yearsthe coming years

CEACEA

What is the exact nature of the central engine? Why does it work so intermittently, ejecting blobs

with large contrast in their bulk Lorentz factors? What is the radiation mechanism of the prompt

emission? What is the jet angle? If between 2o and 20o, the

energy can vary by ~500 (~1050 – 1052 erg) What is the efficiency of converting bulk motion

into radiation?

Open questionsOpen questions

explosões cósmicas de raios gama (gamma-ray bursts)

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