Exploses Csmicas de Raios Gama GammaRay Bursts

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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

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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 gt 100 MeV
• publication only in 1973 (classified before that)

• Phenomenology of bursts before the 90s
• almost no association with known objects
• statistically poor distribution
• ?
• no clue

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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 _at_ tens of keV ? B 1012 G ?
  eB/mc
• emission lines _at_ hundreds of KeV ? redshifted
  511 keV
• zobs z0 (1 2GM/c2 R)
• periodicity ? rotation of a NS R3 lt (GM/4?2)
  T2

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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

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BATSE 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

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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

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Soft Gamma Ray Repeaters SGR
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BeppoSAX and 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)

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BeppoSAX and Afterglows

• 97 Feb 28 GRB 970228
• Discovered by GRBM and WFC
• NFIs observe 1SAX J0501.71146
• ?
• First clear evidence of a GRB X-ray tail
• ? Non-thermal spectra
• ? X-ray fluence is 40 of ?-ray fluence

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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

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GRB 990123
HST image host is an irregular, possibly
merging system
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GRBs observed by BeppoSAX
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GRB 011121
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GRB 011121
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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 _at_ z 0.008
• OT is never far from center

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redshifts
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Energy (isotropy)
redshifts
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redshifts cosmology
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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 (XRFs) little or no emission
• above 25 keV. Possibly related to X-ray
  rich
• GRBs.

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Types of Bursts
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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

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Progenitors

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

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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 wouldnt 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.

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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

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The fireball model
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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

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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) - lt 30 localization
• WXM (2 25 keV) - lt 10 localization
• FREGATE (6-400keV) - ? sr localization
• Rapid dissemination (? 1s) of GRB positions
• (Internet and GCN)

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HETE
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HETE Investigator Team
RIKEN Masaru Matsuoka Nobuyuki Kawai Atsumasa
Yoshida
UC Berkeley Kevin Hurley J. Garrett Jernigan
MIT George R. Ricker (PI) Geoffrey Crew John
P.Doty Al Levine Roland Vanderspek Joel
Villasenor
UChicago Donald Q. LambCarlo 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
SUPAERO Christian Colongo
TIRF Ravi Manchanda
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Ground station network
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HETE resultsGRB 010921

• Bright (gt80?) burst detected on Sept 21, 2001
  051550.56 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

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GRB 010921
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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

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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
  (?M0.3, ??0.7, H065 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

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GRB 011211
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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

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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

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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

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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

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GRB 030115
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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.

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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.

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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 gt 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).

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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?