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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 ( >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%.

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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:SimplicityPeak 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 (>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?

• 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

Edo Berger, Brad Cenko & Alicia SoderberAvishay Gal-Yam, Derek Fox, Dae-Sek MoonFiona HarrisonDale Frail

The Great Caltech-Carnegie Axis

From smaller states:Paul Price (Hawaii)

Goal: Search for the Ultimate Explosions in the Universe

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 < tjet

high log f

log t

|

tjett > tjet

low

log f

log t|

tjetRhoads

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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– VLBA+Bonn 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

Berger et al in prep.

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

Jet break

Berger et al. 2003

Puzzle: A single fireball does not account for radio & X-ray emission

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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

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)

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Clue 3: Flat Early Light Curves

Fox

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Clue 4: First redshift is low (z=0.25)

Energy in the Explosion (Prompt): 1049 erg (low compared to GRBs)

Soderberg et al

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

Galama et al. E~1048 erg (isotropic)

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Clue 5b: Mildly Relativistic Ejecta in SN 1998bw

Kulkarni et al

E~1048 erg

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 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

28(Kulkarni et al., 1998; Weiler et al. 1998; Berger et al. 2002; Soderberg et al. 2004)

Summary of Radio Observations (1998-2004)

29Conclusion: Hyperkinetic or Hyperenergetic optical events

appear not to have special engines

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SN2003bg – Multiple Episodes of Energy

Input ?

SN2003bg:Energy~3

SN1998bw:Energy=2.6

(Soderberg et al., 2004)

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Explosion Energies of Local Ibc & GRBs

2003

L &

200

3bg

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

=> Superonovae explosions are two-parameter family: nucleosynthesis and engine

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Scenarios for SN1998bw

GRB/SN < 7%Soderberg et al. 2004

GRB/SN < 3%Berger 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 => 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

Case 1: off-axis (0.5 %)

Case2 : quasi-spherical relativistic ejecta(unknown %)

observer

observer observer

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(Kulkarni et al., 1998; Weiler et al. 1998)

Type Ibc RadioLightcurves

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(Soderberg et al. in prep.)

Type Ibc RadioLightcurves

1999-2002:28 limits& SN2002ap

2003-present:23 limits& SN2003L

SN/GRB < 2%

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(Berger et al. 2002)

Type Ibc RadioLightcurves

1999-2002:28 limits& SN2002ap

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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)M

V = -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/scf: SN1998bw: v~15,000 - 30,000 km/scf: SN2003dh: v~20,000 - 40,000 km/s

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SN2003L Modeling Results

(Soderberg et al. in prep.)