Exploses Csmicas Bursts de Raios Gama Novidades 20042005

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Explosões Cósmicas (Bursts) de Raios Gama
Novidades 2004/2005
Nova Física no Espaço 2005
João Braga INPE

• eventos recentes e implicações para os modelos de
  GRBs
• SWIFT e perspectivas

20/11/2004
17/10/2002
09/10/2000
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Recent GRBs
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GRB 031203

• Discovered by Integral (T 30s) on Dec. 3, 2003
• Optical and NIR (9hs after) show faint AG
• superimposed to host galaxy at z0.1055
• Rebrightening detected in all bands
• peaking at 18 rest-frame days,
• resembling light curve of SN 1998bw
• Spectra taken close to maximum show extremely
• broad features as in SN 1998bw ? SN 2004lw

? Strong support to GRB/energetic Ic SN
(hypernova) association (after GRB 030329/SN
2003dh)
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GRB 030329
Reminder
(Discovered by HETE-2, Vanderspek et al. 2003)

• GRB030329 is among the brightest 1 of bursts
  ever seen
• typical long burst (25s), fluence of 1.6 x 10-4
  erg cm-2
• E?,iso 1.3 x 1052 erg
• optical AG had magnitude 12 after 1.5 h (more
  than 3 mag brighter
• than GRB 990123 and GRB 021004)
• optical AG observed by an unprecedented number
  of telescopes (65)
• GRB030329 was the nearest cosmological GRB, at
  z 0.17
• (obtained 16h after the burst by the VLT and
  8h later by Keck)
• 10 days after the GRB, the spectral signature
  of an energetic
• Type Ic supernova emerged (SN 2003dh).

z 0.1675 ? probability of detecting a GRB this
close by is 1/3000 gt unlikely that HETE-2 or
Swift will see another such event
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Optical light curve of SN 2003dh
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Spectrum of SN 2003dh
Stanek et al. (2003)
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Spectrum of SN 2003lw
Malesani et al. (2004)
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SN2003lw

• Type Ic SNe
• absence of broad H lines ? Type I
• weak or absent Si II ?6150 ? not Ia or Ib
• unusually broad features and blended lines
• remarkably similar to SN1998bw
• very large expansion velocities similar to
  SN1998bw
• ( 23000 km/s _at_ 10 days)
• SN2003lw is yet another case of a hypernova,
• albeit much less energetic than SN2003dh
• GRB 031203 may be a cosmic analogue of GRB
  980425 sub-energetic GRBs with faint afterglows

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Evidence for SNconnection for GRBs

• In 29 GRB/XRF with measured redshifts
• 18 have light curve bumps ? photometric evidence
  for SNe
• 4 cases have spectroscopic evidence for a SN
• SNR W49B GRB in the Milky Way _at_ 12 kpc?
  (Chandra)
• Barrel-shaped nebula with bright IR rings and a
  bar of intense X-ray emission
• X-rays flare out at hot caps surrounded by IR
  emission
• ? Jets produced in the SN collided with a cloud
  of gas and dust ?

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GRB 041006

• Discovered by HETE-2
• Position available 42 s after the burst
• Light curve and spectrum very similar to GRB
  030329, but 20 times fainter
• OT absorption lines z0.716
• Jet break tb at 0.14 days (earliest known)
• Deep optical photometry over 65 days shows bump
  well fitted by SN1998bw corrected light curve ?
  another hypernova (Stanek et al. 2004)

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GRB 041006
SN 1998bw light curve corrected for z0.716
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Soft Gamma Ray Repeaters SGR
reminder

• 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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GRB duration distribution
reminder
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Progenitors
reminder

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

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Giant flare from SGR 1806-20

• SGRs are thought to be magnetars neutron stars
  with observable
• emissions (up to 100 keV) powered by
  magnetic dissipation
• Giant flare from SGR 1806-20 detected on
  December 27, 2004
• 380s long, 106 brighter than typical GRBs
  (emission followed
• by hard X-ray tail modulated by the period
  of the neutron star 7.56s)
• energy greatly exceeds previous events
• initial (200 ms) spike has blackbody spectrum,
  characteristic of
• relativistic pair/photon outflow
• observed light curve is well explained by
  emission from relativistic
• expanding fireballs, like GRBs (Yamazaki et
  al., astro-ph 0502320)
• rapidly fading after 600 ms ? emission from
  relativistic jet
• extreme energy suggests catastrophic instability
  involving global
• crust failure and magnetic reconnection,
  perhaps with significant
• large-scale untwisting of the magnetosphere
  (new physics !!)
• from a great distance this event would appear to
  be a
• short-hard GRB ! (Hurley et al. 2005, subm.
  Nature)

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Giant flare from SGR 1806-20
Terasawa et al. 2005 (Nature, subm.)
Yamazaki et al. 2005 (Nature, subm.)
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GRB models

• Observations favor the collapsar model
• collapsar high mass WR star, high rotation,
  make black hole
• 1 of supernovae are collapsars
• Maybe 1 GRB/galaxy/10.000 years

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The fireball model
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The fireball model

• Complex light curves are due to internal shocks
  caused by velocity variations blobs with
  different ?s
• Turbulent magnetic fields build 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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GRBs as a probe for cosmology

• Earliest massive stars form at z 20
• GRBs may mark the moment of first light
• (end of the dark ages, from z1100)
• ? indeed, some calculations (Lamb
  Reichart 2000)
• suggest that 10-40 of GRBs may lie at
  z gt 5
• GRBs have ?-ray luminosities 10 billion times
  greater than the associated SNe and host galaxies
  
• ? GRBs are easily detectable out to z 20
• HETE-2 has shown that Liso and Eiso are
  correlated with z
• ? GRBS evolve with redshift bursts at z5
  are 1000
• times more luminous than at z0 !

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GRBs as a probe for cosmology

• Strong correlation found
• Epeak ? Epeak (1z) ? E2/3
• (Guirlanda, Ghisellini Lazzati 2004)

obs
?
Epeak is the peak of the ? F? spectrum
E? is the collimation-corrected GRB energy E?
(1 cos ?j ) E?,iso
Underlying physical reason is not known, but the
radiation process (and photon energy) should be
related to the energy content
The correlation makes GRBs important cosmological
tools, because they probe redshifts not
accessible by Ia SNe
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Rapid slewing satellite for transient astronomy

• Launched on Nov. 20, 2004
• (2-year mission)
• Detailed X-ray, UV/optical AG
• observations from 1 min to days after the
  burst

Instruments 1. 15-150 keV burst detector (BAT)
with 1-4 arcmin position triggers
autonomous spacecraft slews 2. narrow-field X-ray
telescope (XRT), spectroscopy from 0.2 to
10 keV with 5 arcsec positions 3.
narrow-field UV/optical telescope,
170-600 nm, 0.3 arcsec positions, optical
finding-charts

• Redshift determination for most bursts
• 1 mCrab hard X-ray survey

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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 could be validated
  by future data
• With accumulation of a large sample 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?

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For theorists who may wish to enter this broad
and growing field, I should point out that there
are a considerable number of combinations, for
example, comets of antimatter falling onto
white holes, not yet claimed.
M. Ruderman