Explosões Cósmicas de Raios Gama (Gamma-Ray Bursts) Nova Física no Espaço 2003 João Braga – INPE breve história dos GRBs BeppoSAX: afterglows galáxias hospedeiras e redshifts modelos para os progenitores resultados recentes (HETE) SWIFT, MIRAX e o futuro

History 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

History 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/42) T2

BATSE – COMPTON GRO launched 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

BATSE – COMPTON GRO Bimodal distribution Euclidean 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

Soft Gamma Ray Repeaters SGR Burst of March 5th, 1979 (SGR 0526-66) SNR N49 in LMC (~10,000 ys)  SOFT 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

Soft Gamma Ray Repeaters SGR

BeppoSAX and Afterglows  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

BeppoSAX 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 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 990123 z=1.6 Keck OT spectrum HST image: host is an irregular, possibly merging system

GRBs observed by BeppoSAX

GRB 011121

GRB 011121

Host 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

redshifts GRB 990123 z=1.6 Keck OT spectrum

Energy (isotropy) redshifts

redshifts & cosmology

Types of 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: 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): little or no emission above ~ 25 keV. Possibly related to X-ray rich GRBs.

Types of Bursts  25% 20 30% no 30 20% 0.3 ? Burst Class Long (normal) Percentage of all bursts Typical duration (sec) Initial gamma-ray emission Afterglow X-ray emission Afterglow optical emission Long (normal) 25% 20  (dark) 30% no (X-ray rich or XRF) 30 Absent or weak short 20% 0.3 ?

GRBs may be associated with rare types of supernovae Progenitors Long GRBs are probably associated with massive 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

Progenitors Short GRBs - ?? associated with mergers of compact objects SGRs in external galaxies phase transition to strange stars

Relativistic expanding fireball (e± , ) The 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 model: shock waves will inevitably occur in the outflow (after fireball becomes transparent)  reconvert Ek into nonthermal particle and radiation energy.

The 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 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

The fireball model

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

HETE High Energy Transient Explorer space.mit.edu/HETE First dedicated GRB mission, X- and g-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)

HETE

HETE Investigator Team RIKEN Masaru Matsuoka Nobuyuki Kawai Atsumasa Yoshida MIT George R. Ricker (PI) Geoffrey Crew John P.Doty Al Levine Roland Vanderspek Joel Villasenor UC Berkeley Kevin Hurley J. Garrett Jernigan UChicago Donald Q. Lamb Carlo Graziani CESR Jean-Luc Atteia Gilbert Vedrenne Jean-Francois Olive Michel Boer INPE João Braga LANL Edward E. Fenimore Mark Galassi CNR Graziella Pizzichini CNES Jean-Luc Issler UC Santa Cruz Stanford Woosley SUP’AERO Christian Colongo TIRF Ravi Manchanda

Ground station network

IPN annulus (radius 60o ± 0.118o) HETE results GRB 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 010921

GRB 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

GRB 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

GRB 011211

GRB 020405 Highly significant polarization (9.9%) in the V band measured 1.3 days after the burst z = 0.695 based on emission lines of host galaxy High 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

GRB 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

GRB 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

GRB 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

GRB 030115

New missions 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): launched last year. Several instruments with high energy resolution. EXIST (US): huge area hard X-ray mission for 2010. GLAST (US): large area high energy gamma-ray mission; will study high energy afterglows. To be launched around 2007. 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.

What we do “know” about GRBs so far 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 to expect in the coming years 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).

Open questions 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?