1. 1 Central Engines of Gamma-Ray Bursts & Supernovae S. R. Kulkarni California Institute of Technology http://www.astro.caltech.edu/~srk

2. 2 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%.

3. 3 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

4. 4 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).

5. 5 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

6. 6 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?

7. 7 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) 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

8. 8 Energetics

9. 9 Light Curves provide Evidence for Collimation t < t jet high  log f log t | t jet t > t jet low  log f log t | t jet Rhoads

10. 10 GRB Energetics: Tiger becomes Lamb Before the beaming correction (isotropic) After the beaming correction (Frail et al.)

11. 11 Radio Light Curves at 8.5 GHz Radio Afterglows: Angular Size and Calorimetry

12. 12 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.

13. 13 GRB 980703: Non-relativistic Transition

14. 14 GRB 030329: Non-relativistic Transition Scaled to nu -0.6

15. 15 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.

16. 16 GRB 030329: No proper motion

17. 17 Conclusion: Energetics inferred from afterglow modeling are reasonable

18. 18 The Clues

19. 19 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

20. 20 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)

21. 21 Clue 3: Flat Early Light Curves Fox

22. 22 Clue 4: First redshift is low (z=0.25) Energy in the Explosion (Prompt): 10 49 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

23. 23 Clue 5: SN 1998bw/GRB 980425, a severely underluminous GRB Galama et al. E  ~10 48 erg (isotropic)

24. 24

25. 25 Clue 5b: Mildly Relativistic Ejecta in SN 1998bw Kulkarni et al E  ~10 48 erg Mildly relativistic ejecta vastly exceeds gamma-ray energy relese

26. 26 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)

27. 27 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. 28 (Kulkarni et al., 1998; Weiler et al. 1998; Berger et al. 2002; Soderberg et al. 2004) Summary of Radio Observations (1998-2004)

29. 29 Conclusion: Hyperkinetic or Hyperenergetic optical events appear not to have special engines

30. 30 SN2003bg – Multiple Episodes of Energy Input ? SN2003bg:  Energy~3 SN1998bw:  Energy=2.6 (Soderberg et al., 2004)

31. 31 Explosion Energies of Local Ibc & GRBs 2003L & 2003bg Conclusion: SN 1998bw-like events are rare

32. 32

33. 33 Putting it altogether: Engine Soderberg

34. 34 Putting it altogether: Nucleosynthesis HST proposal approved!

35. 35 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

36. 36

37. 37 Scenarios for SN1998bw GRB/SN < 7% Soderberg et al. 2004 GRB/SN < 3% Berger et al. 2003

38. 38 VLA Radio Observations of SN 2003L

39. 39

40. 40 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?

41. 41 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.

42. 42 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!

43. 43 New Missions AGILE, GLAST (GeV Missions) Milagro (TeV Telescope) ICECUBE (neutrino) LIGO (gravitational wave) AUGER (ultra-high energy cosmic rays)

44. 44 SN1998bw – an engine-driven SN Case 1: off-axis (0.5 %) Case2 : quasi-spherical relativistic ejecta (unknown %) observer

45. 45 (Kulkarni et al., 1998; Weiler et al. 1998) Type Ibc Radio Lightcurves

46. 46 (Soderberg et al. in prep.) Type Ibc Radio Lightcurves 1999-2002: 28 limits & SN2002ap 2003-present: 23 limits & SN2003L SN/GRB < 2%

47. 47 (Berger et al. 2002) Type Ibc Radio Lightcurves 1999-2002: 28 limits & SN2002ap

48. 48 Radio Emission from SN 1998bw Kulkarni et al

49. 49 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)

50. 50 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/s cf: SN1998bw: v~15,000 - 30,000 km/s cf: SN2003dh: v~20,000 - 40,000 km/s

51. 51 SN2003L Modeling Results (Soderberg et al. in prep.)