Central Engines of Gamma-Ray Bursts

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Central Engines of Gamma-Ray Bursts Supernovae

• S. R. Kulkarni
• California Institute of Technology
• http//www.astro.caltech.edu/srk

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My summary of what we know about GRBs

• GRBs are highly collimated explosions and possess
  central engines which drive the explosion
• Long duration GRBs are deaths of massive stars
  (SN Ib/c connection)
• There is growing evidence of underenergetic GRBs
  (e.g. 980425, 030329, 031203) with engines
  outputing a mix of ejecta ultra-relativistic (?
  gt100), relativistic(? gt10) and mildly
  relativistic (? gt2) ejecta
• The fraction of nearby Ib/c supernovae with
  features indicative of a central engine is small,
  less than 10.

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GRB-SN Complete Unification

• All core collapse events are the same.
• GRBs are explosions viewed on axis
• XRFs are explosions viewed off axis
• GRB 980425 is an off-axis GRB
• In all cases, underlying SNe
• 
  Lamb,
  Nakamura,
• In favor
• Simplicity
• Peak energy-luminosity correlation

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SN-GRB No Unification

• GRBs are not standard explosions (energy, opening
  angle)
• XRFs are not GRBs viewed sideways and likely
  lower energy explosions
• SN 1998bw is an engine driven SN but with a weak
  engine
• In most core collapses the influence of engines
  is likely to be small or subtle.
• In favor
• The existence of sub-energetic events (e.g.
  031203, SN 1998bw).

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Related Issues The Engine

• What is the energy release of GRB engines? Are
  all GRBs hyper-energetic (gt1 FOE)?
• Gamma-ray emission arises from ultra-relativistic
  ejecta (?gt100). There is clear evidence for
  collimation of this ejecta.
• Is there energy released at lower Lorentz
  factors?
• Lorentz factor, ? gt 10 (relativistic ejecta) -gt
  X-ray
• Lorenta factor, ? gt 2 (moderately relativistic
  ejecta) -gt Radio
• If so, is this energy released with the same
  opening angle as the relativistic ejecta?
• Similar questions can be raised about XRFs

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Related Issues The Supernova

• Do all long duration GRBs have an underlying SN?
• What is special about SNe associated with GRBs?
• Are these SNe always hyper-energetic or
  hyper-kinetic (cf SN 1998bw)?
• In ordinary core collapse, nucleosynthesis
  (radioactive Nickel) is a major byproduct of the
  explosion and in turn influence the subsequent
  evolution. How about for GRB explosions?
• What is the connection between nearby Ibc SNe and
  GRBs?
• Is asymmetry essential for a supernova to
  explode?
• Where do XRFs, which share many attributes with
  GRBs, fit in the current framework of long
  duration GRBs?

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Coalition of the Willing Dedicated
Goal Search for the Ultimate Explosions in the
Universe
Edo Berger, Brad Cenko Alicia Soderber Avishay
Gal-Yam, Derek Fox, Dae-Sek Moon Fiona
Harrison Dale Frail The Great Caltech-Carnegie
Axis From smaller states Paul Price (Hawaii)
The Bad Guys The Rest of the World (Baltimore,
Europe, East Coast) etc
Now is the time for Penn State to be with us or
against us
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Energetics
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Light Curves provide Evidence for Collimation
t lt tjet high ?
log f
tjet
log t
t gt tjet low ?
log f
log t
tjet
Rhoads
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GRB Energetics Tiger becomes Lamb
Before the beaming correction
(isotropic)
After the beaming correction
(Frail et al.)
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Radio Light Curves at 8.5 GHz
Radio Afterglows Angular Size and Calorimetry
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Calorimetry

• Afterglow estimates sensitive to jet opening
  angles
• At late times the blast wave becomes
  non-relativistic and rapidly becomes spherical.
  Thus one can apply minimum energy method (or
  variations) with confidence.
• Radio observations have confirmed that the
  overall energetics scale is correct and in some
  cases evidence for copious amount of mildly
  relativistic ejecta.

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GRB 980703 Non-relativistic Transition
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GRB 030329 Non-relativistic Transition
Scaled to nu-0.6
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and the latest .

• GRB 030329, 24 days after the burst
• VLBABonn at 22 GHz
• Marginally resolved at 0.08 milliarcsec
• In line with expectations from the fireball model
• superluminal expansion (5c)

0.45 x 0.18 mas
Taylor et al.
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GRB 030329 No proper motion
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Conclusion Energetics inferred from afterglow
modeling are reasonable
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The Clues
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Clue 1 The second nearest GRB 030329 is peculiar
Puzzle A single fireball does not account for
radio X-ray emission

• A possible solution
• a narrow, ultra-relativistic jet with low energy
  which produces X-ray optical
• a wide, mildly relativistic jet carrying the bulk
  of the energy and powering the radio

Berger et al in prep.
Berger et al. 2003
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Clue 2 The nearest GRB 031203 is a cosmic analog
of GRB 980425

• Localized by IBIS (Gotz et al)
• XMM TOO observations (Watson)
• Plethora of ground-based optical
• Radio afterglow candidate identified (1 arcsec)
• Putative host galaxy coincident with radio source
  at z0.1 identified (Bloom)
• Discovery of X-ray scattered halo from XMM
  observations (Vaughn)
• Continued VLA monitoring shows event is weak and
  a weak explosion (Soderberg et al. 2004)

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Clue 3 Flat Early Light Curves
Fox
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Clue 4 First redshift is low (z0.25)
Soderberg et al
Energy in the Explosion (Prompt) 1049 erg (low
compared to GRBs)
No evidence for off-axis model (optical flux
declines) However, evidence for mildly
relativistic ejecta from radio afterglow
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Clue 5 SN 1998bw/GRB 980425, a severely
underluminous GRB
E?1048 erg (isotropic)
Galama et al.
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Clue 5b Mildly Relativistic Ejecta in SN 1998bw
E?1048 erg
Kulkarni et al
Mildly relativistic ejecta vastly exceeds
gamma-ray energy relese
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Was GRB 980425 an off-axis event?

• Six years of radio monitoring No evidence for
  off-axis jet.
• Off-axis jet (if present) requires a very low
  mass rate A 0.03, not consistent with
  inferred density

(Soderberg, Frail, Wieringa 2004)
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Clue 6Studies of Local Ibc SNe

• Questions
• 1 What is the fraction of SN 1998bw-like
  supernovae?
• 2 Are Ibc Sne powered by engines?
• 3 What is the fraction of off-axis GRBs?
• Alicia M. Soderberg
• (PhD Project)
• VLA ATCA (Radio)
• Palomar 60-inch (Optical Light Curves)
• Chandra

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Summary of Radio Observations (1998-2004)

(Kulkarni et al., 1998 Weiler et al. 1998
Berger et al. 2002 Soderberg et al. 2004)
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Conclusion Hyperkinetic or Hyperenergetic
optical events appear not to have special engines
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SN2003bg Multiple Episodes of Energy Input ?
SN2003bg ?Energy3 SN1998bw ?Energy2.6
(Soderberg et al., 2004)
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Explosion Energies of Local Ibc GRBs
2003L 2003bg
Conclusion SN 1998bw-like events are rare
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Putting it altogether Engine
Soderberg
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Putting it altogether Nucleosynthesis
HST proposal approved!
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Summing up

• A number of events are sub-energetic in the
  gamma-ray/X-ray band but more energy in the radio
  afterglow (by x10)
• Curiously these are the nearest events
• In only a small fraction of local Ib/c (100 Mpc)
  is there evidence for energy addition over
  extended time
• gt Superonovae explosions are two-parameter
  family nucleosynthesis and engine

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Scenarios for SN1998bw GRB/SN lt 7Soderberg
et al. 2004GRB/SN lt 3Berger et al. 2003
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VLA Radio Observations of SN 2003L
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SN 1998bw Hypernova?

• Large Velocity Width
• Larger Explosive Yield 3-10 FOE
• Iwamoto et al,
  Woosley et al, Hoefflich et al.
• Hypernova designation not well defined, yet.
• Large velocity width?
• Large Energy release?

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SN 1998bw is UNUSUAL

• Copious (mildly) relativistic outflow
  
• Energy addition
• Associated with gamma-ray burst
• gt Engine Driven Explosion (Hypernova)
• 
  
  Kulkarni et al, Li Chevalier, Pian e al.

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The Future is Bright

• HETE, Integral, IPN in operation
• Imminent launch of SWIFT (Sep 2004)
• Dedicated ground-based experiments
• ROTSE, TAROT, BOOTES, REM, NGAT
• Rapid Response by Premier
  Facilities (VLT, HST, Chandra..)
• At Palomar we have robotocized
  the 60-inch telescope and ready to go!

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New Missions

• AGILE, GLAST (GeV Missions)
• Milagro (TeV Telescope)
• ICECUBE (neutrino)
• LIGO (gravitational wave)
• AUGER (ultra-high energy cosmic rays)

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SN1998bw an engine-driven SN
Case2 quasi-spherical relativistic
ejecta (unknown )
Case 1 off-axis (0.5 )
observer
observer
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Type Ibc Radio Lightcurves
(Kulkarni et al., 1998 Weiler et al. 1998)
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Type Ibc Radio Lightcurves
1999-2002 28 limits SN2002ap
2003-present 23 limits SN2003L
SN/GRB lt 2
(Soderberg et al. in prep.)
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Type Ibc Radio Lightcurves
1999-2002 28 limits SN2002ap
(Berger et al. 2002)
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Radio Emission from SN 1998bw
Kulkarni et al
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What is SN 1998bw?

• An off-axis cosmological GRBf Nakamura
• A new beast, an under-energetic engine explosion
  Kulkarni, Chevalier
  Li
• Developments
• There is no evidence for energy addition on
  timescales of months to years (Soderberg et al)
• SN 1998bw is rare in the local population of
  Ibc SNe (based on Ibc VLA survey of Berger et al)

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Type Ic SN 2003L in NGC 3506
Optical Discovery Jan 12 2003 (Boles, IAUC
8048) MV -18.8 (before maximum) d 92
Mpc Spectroscopic ID Jan 25, 2003 (Valenti et
al. IAUC 8057 Matheson et al. GCN 1846) normal
Ic v5900 - 12,000 km/s cf SN1998bw v15,000 -
30,000 km/s cf SN2003dh v20,000 - 40,000 km/s
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SN2003L Modeling Results
(Soderberg et al. in prep.)