Gamma Ray Bursts

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Gamma Ray Bursts

• S. R. Kulkarni
• California Institute of Technology

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Acknowledgements

• Alicia Soderberg
• Caltech/NRAO/Carnegie gang
• Berger, Cenko, Fox, Frail, Harrison, Price,
  Schmidt
• T. Sakamoto R. Yamazaki

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Quasars A Historical Analogy, I

• Astonished Impressed The immense power and
  energy of quasars resulting from Schmidts
  discovery of redshift.
• Amused and Educated Relativistic effects such as
  super-luminal motion were anticipated by Rees.
• Ruthless Exploitation Ask not why quasars quase
  but simply use them as light beacons to study the
  IGM.

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Quasars A Historical Analogy, II

• Scintillation Interplanetary Scintillation
  showed that quasars were compact
• The Central Engine After three decades we have a
  working model involving black holes
• The Pesky Jets Questions remain
• FRI and FRII
• What is the difference between radio quiet and
  radio loud AGN?
• Unification The desire to unify various classes
  of quasars drove much of quasar research.

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Unification Working Model
Jet
BLR
Torus
NLR
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AGN Empirical Classification

• Radio Luminosity
• Radio Loud
• Radio Quiet
• Optical Emission Lines
• Broad Emission Lines (Type 1)
• Narrow Emission Lines (Type 2)
• Roughy speaking these two may map to the type of
  host galaxy and the type of black hole
• What are the equivalent physical parameters for
  GRBs?

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Outline

• GRB Phenomenon
• Long Duration GRBs
• Jets
• Energetics
• SN Connection
• Jets in nearby SNe?
• Where do we stand at unification?

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Two classes of GRBs
Short - Hard
Long - Soft
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Jets

• Decrease Total Energy (by beaming fraction)
• Increase the event rate (by inverse beaming
  fraction)

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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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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 980703 Non-relativistic Transition
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Complications

• Evidence for continued or additional injection of
  energy
• Evidence for additional components in the jet
  (wide angle, low Gamma)

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Early Light Curves
Fox
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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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Long Duration GRB-SN Connection
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SN 1998bw/GRB 980425, a severely underluminous
GRB
E?1048 erg (isotropic)
Galama et al.
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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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Direct Spectroscopic Evidence
MMT (Stanek et al)
VLT (Hjorth et al)
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X-ray Flashes
Heise
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XRF 020903 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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Collapsar Model
Woosley, Heger, MacFadyen
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GRB-SN Grand 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, Yamazaki
• In favor
• Simplicity
• Peak energy-luminosity correlation

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SN-GRB Meek Diversity

• 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).
• No evidence for early rise in the afterglow

Kulkarni, Soderberg, Sakamoto
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Putting it altogether Engine
Soderberg
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SUMMARY Peak SN magnitudes
(Soderberg et al. 2005b)
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Do nearby core collapse SNe have strong jets that
materially affect the explosion?
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VLA ATCA Program

• Radio emission traces both relativistic and
  mildly relativistic ejecta (cf SN 1998bw)
• Relativistic aberration is less of an issue for
  mildly relativistic ejecta
• Motivated by 1998bw we began a program of
  monitoring all known nearby Ib/c
• Monitored SNe from day to a year

Soderberg thesis
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Radio Light-curves of Cosmic Explosions Ibc
Survey 11 detections 73 upper limits No GRBs or
98bws lt 1.2 GRB/SN
c.f. 1 beaming fraction for GRBs 5
hypernova rate
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Explosion Energies of Local Ibc GRBs
2003L 2003bg
Conclusion SN 1998bw-like events are rare
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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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Progenitors of Ibc SNe A Hot Result
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Progenitor of SN 2004gt (Ic SN)
Mv gt -5.5
Gal-Yam
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Summary Cosmological GRBs

• Long duration GRBs are highly collimated
  explosions and possess central engines which
  drive the explosion
• Searches with good sensitivity have almost always
  found associated SNe of type Ib/c (or at least
  not of Type II)
• Not all associated SNe are bright (-19 mag)
• XRFs are likely simply low energy explosions
  (relative to cosmological GRBs but comparble to
  low energy GRBs)

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Summary Nearest Events

• There is growing evidence of underenergetic GRBs
  (e.g. 980425, 030329, 031203) with engines
  releasing a mix of ejecta
• ultra-relativistic (? gt100),
• relativistic(? gt10)
• mildly relativistic (? gt2) ejecta
• Some of these events are dominated by mildly
  relativistic ejecta (GRB 030329). Some are X-ray
  Flashes (I.e. dominated by X-ray and not
  gamma-ray emission).

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GRBs as 2-parameter Explosions

• GRBs clearly manifest an essentially spherical
  explosions (supernova) and narrow jets (few to
  tens of degrees)
• There is wide variation in properties of both
  components.
• There is little evidence for universal jet or
  universal supernova model.

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Nearest Ib/c SNe

• Other than SN 1998bw we have not identified a
  single similar example
• No strong emission (indicative) is seen in any of
  the nearly one hundred local Ib/c SNe on
  timescales of days to years.
• Significant variation in peak optical emission as
  well as spectro-velocity peculiarities (e.g
  2003jd, Mazzali et al)

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Open Issues

• What accounts for the variation in opening angles
  of GRB jets?
• Do jets play a significant role in exploding
  typical core collapse events?
• Attractive hypothesis but little evidence (so
  far)
• Alternate explanations must be sought for
  variation in optical diversity.
• Are short hard bursts strongly jetted?

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GRB050509b Short Hard Burst

• Rapidly fading X-ray afterglow (Gehrels et al)
• No optical/radio afterglow
• Seen against z0.22 cluster

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GRB 050509b Constraining an associated moderate
nova
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