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Central Engines of Gamma-Ray
Bursts & Supernovae
S. R. Kulkarni
California Institute of Technology
http://www.astro.caltech.edu/~srk
1
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 ( >100), relativistic( >10) and
mildly relativistic ( >2) ejecta
• The fraction of nearby Ib/c supernovae with features
indicative of a central engine is small, less than 10%.
2
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
3
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).
4
Related Issues: The Engine
• What is the energy release of GRB engines? Are all GRBs
hyper-energetic (>1 FOE)?
• Gamma-ray emission arises from ultra-relativistic ejecta
(Г>100). There is clear evidence for collimation
of this ejecta.
– Is there energy released at lower Lorentz factors?
• Lorentz factor, Г > 10 (relativistic ejecta) ->
X-ray
• Lorenta factor, Г > 2 (moderately
relativistic ejecta) -> Radio
– If so, is this energy released with the same opening
angle as the relativistic ejecta?
5
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?
6
Goal: Search for the Ultimate Explosions in the Universe
Coalition of the Willing & Dedicated
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 7
Energetics
8
Light Curves provide Evidence for Collimation
t < tjet
log f
high
|
t > tjet tjet log t
log f
low
| log t
9
Rhoads tjet
GRB Energetics: Tiger becomes Lamb
Before
the beaming
correction
(isotropic)
After
the beaming
correction
al.)
(Frail et 10
Radio Afterglows: Angular Size and Calorimetry
Radio Light Curves at 8.5 GHz
11
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.
12
GRB 980703: Non-relativistic Transition
13
GRB 030329: Non-relativistic Transition
Scaled to nu-0.6
14
and the latest ….
• GRB 030329, 24 days after
the burst
– VLBA+Bonn at 22 GHz
• Marginally resolved at 0.08
milliarcsec
• In line with expectations
from the fireball model
0.45 x 0.18 mas – superluminal expansion (5c)
Taylor et al.
15
GRB 030329: No proper motion
16
Conclusion: Energetics inferred
from afterglow modeling are
reasonable
17
The Clues
18
Clue 1: The second nearest GRB 030329 is
peculiar
Puzzle: A single fireball does not account for
radio & X-ray emission
A possible solution:
(1) a narrow, ultra-relativistic jet
with low energy which produces
X-ray & optical
(2) a wide, mildly relativistic jet
carrying the bulk of the energy
and powering the radio
Berger et alJet break
in prep.
2003
Berger et al.19
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 z=0.1 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)
20
Clue 3: Flat Early Light Curves
21
Fox
Clue 4: First redshift is low (z=0.25)
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
22
Clue 5: SN 1998bw/GRB 980425, a severely
underluminous GRB
E~1048 erg (isotropic)
Galama et al. 23
24
Clue 5b: Mildly Relativistic Ejecta in SN
1998bw
E~1048 erg
Kulkarni et al
Mildly relativistic ejecta vastly exceeds gamma-ray energy relese
25
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
26
(Soderberg, Frail, Wieringa 2004)
Clue 6:Studies 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
27
Summary of Radio Observations (1998-2004)
(Kulkarni et al., 1998; Weiler et al. 1998; Berger et al. 2002; Soderberg et al.
28
2004)
Conclusion: Hyperkinetic or Hyperenergetic optical events
29
appear not to have special engines
SN2003bg – Multiple Episodes of Energy
Input ?
SN2003bg:
Energy~3
SN1998bw:
Energy=2.6
30
(Soderberg et al., 2004)
Explosion Energies of Local Ibc & GRBs
2003L & 2003bg
Conclusion: SN 1998bw-like events are rare
31
32
Putting it altogether: Engine
Soderberg
33
Putting it altogether: Nucleosynthesis
34
HST proposal approved!
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
=> Superonovae explosions are two-parameter
family: nucleosynthesis and engine
35
36
Scenarios for
SN1998bw
GRB/SN < 7%
Soderberg et al. 2004
GRB/SN < 3%
Berger et al. 2003
37
VLA Radio Observations of SN
2003L
38
39
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?
40
SN 1998bw is UNUSUAL
Copious (mildly) relativistic outflow
Energy addition
Associated with gamma-ray burst
=> Engine Driven Explosion (“Hypernova”)
Kulkarni et al, Li & Chevalier, Pian e al.
41
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!
42
New Missions
• AGILE, GLAST (GeV Missions)
• Milagro (TeV Telescope)
• ICECUBE (neutrino)
• LIGO (gravitational wave)
• AUGER (ultra-high energy cosmic rays)
43
SN1998bw – an engine-driven
SN
Case2 : quasi-spherical
relativistic ejecta
(unknown %)
Case 1: off-axis (0.5 %) 44
observer observer
Type Ibc
Radio
Lightcurves
45
(Kulkarni et al., 1998; Weiler et al. 1998)
Type Ibc
Radio
Lightcurves
1999-2002:
28 limits
& SN2002ap
2003-present:
23 limits
& SN2003L
SN/GRB < 2% 46
(Soderberg et al. in prep.)
Type Ibc
Radio
Lightcurves
1999-2002:
28 limits
& SN2002ap
47
(Berger et al. 2002)
Radio Emission from SN 1998bw
48
Kulkarni et al
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)
49
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; v~5900 - 12,000 km/s
cf: SN1998bw: v~15,000 - 30,000 km/s
cf: SN2003dh: v~20,000 - 40,000 km/s
50
SN2003L Modeling Results
51
(Soderberg et al. in prep.)
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