1. Low-luminosity GRBs and Relativistic shock breakouts Ehud Nakar Tel Aviv University Omer Bromberg Re’em Sari Tsvi Piran GRBs in the Era of Rapid Follow-up Liverpool, 2012

2. Low-luminosity GRBs ~10 -4 lower luminosity, <10 48 erg/s Much more frequent Smooth light curve E  << total energy Not highly collimated Mildly relativistic ejecta with energy ~ E  Delayed X-ray emission, with energy ~ E  Not “successful” jets Long Short Low luminosity Wanderman & Piran 2011 Low-luminosity GRB is NOT a regular GRB with low luminosity Connection to long GRBs is mainly via the common association to broad-line Ic SNe

3. Outline Propagation of a relativistic jet in a stellar envelope Why low-luminosity GRBs are not generated by “successful” jets (as long GRBs) Theory of relativistic shock breakout (  >0.5) Comparison of relativistic shock breakout predictions to low-luminosity GRB observations A note on short GRB classification

4. Jet propagation in a stellar envelope Numerical Macfadyan, Woosley, Zhang,Morsony, Lazzati, Mizuta, Aloy, Nagakura, Tominaga, Nagataki, Ioka... Analytic Begelman, Matzner, Meszaros, Waxman, Lazzati, Bromberg,...

5. JetMedium

6. JetMedium Head

7. Jet Medium Cocoon Head

8. Jet Medium Cocoon Head Collimation Shock

9. Morsony et al., 07

10. The head is slower than the jet material, and dissipates the jet energy. In order to propagate the head needs to be pushed by the jet material. The engine must work continuously until the jet breaks out. To observe a long GRB: the jet must break out

11. The head is slower than the jet material, and dissipates the jet energy. In order to propagate the head needs to be pushed by the jet material. The engine must work continuously until the jet breaks out – or it will fail. Breakout time: To observe a GRB: the jet must break out Failed jet ʘ ʘ Bromberg, EN, Piran & Sari 11

12. Are low-luminosity GRBs produced by “successful” jets? (Bromberg, EN & Piran 2011)

13. t γ = t e - t b tbtbtbtb tγtγtγtγ tetetete After the jet breaks out energy flows (relatively) freely to large distances where the prompt GRB emission is emitted.

14. tbtbtbtb tttt tetetete Less likely The engine is unaware that the jet breaks out

15. 0.01 0.11 10 T 90 /t b # of bursts Low-luminosity Long GRBs Low-luminosity GRBs are most likely (2  ) not produced by jets that successfully punches through their progenitor envelope Bromberg, EN & Piran 2012

16. If not a successful jet then what is the  -ray source of low-luminosity GRBs? Even “failed” jets drive shocks that breakout of the stellar surface! “failed” jets are much more frequent than successful ones What are the observed signatures of the resulting shock breakouts?

17. Relativistic shock breakout (EN & Sari 2012)

18. Shock breakout Shock accelerates while its energy decreases Shock width = distance to edge Radiation dominated shock:  =c/v Shock breakout radiation-dominated shock

19. Three hydrodynamic stages Shock breakout Shock width = distance to edge Planar expansion Before breakout layer doubles its radius Spherical expansion After Breakout layer doubles its radius

20. Relativistic shock breakout Main physical properties: Constant post shock rest frame temperature ~100-200 keV Temperature dependent (pair) opacity Significant post breakout acceleration T BB pairs Katz et. al., 10 Budnik et. al., 10

21. Three observables depend on two physical parameters: R and  Relativistic breakout relation for quasi-spherical breakout without wind The breakout emission - A flash of  -rays Colgate was correct after all (for wrong reasons)

22. The breakout emission - A flash of  -rays Colgate was correct after all (for wrong reasons) Important note The photosphere is not in thermal equilibrium The blackbody radius (R bb 2 = L/4  T 4 ) is meaningless

23. Emission following the shock breakout EN & Sari 12  -rays X-rays E p shifts from  -rays to X-rays (E x > E  ) ~

24. Are low-luminosity GRBs produced by relativistic shock breakouts? Colgate 1968, Kulkarni et al., 1998, Tan et al., 2001, Campana et al., 2006, Waxman et al., 2007, Wang et al., 2007, Katz et al., 2010

25. Predictions of relativistic shock breakouts from “failed” jets and a comparison to low luminosity GRBs: Smooth light curve E  << total energy Relativistic ejecta with energy ~ E  Delayed X-ray emission, with energy ~ E  (e.g., X-ray echo of GRB 031203) Relativistic breakout relation ?

26. Low luminosity GRBs GRBE bo (erg) T bo (keV) t bo (s) Relation t bo (s) R bo (cm)  bo 98042510 48 1503010 6  10 12 3 031203 5  10 49 >20030<35 2  10 13 >4 060218 5  10 49 4021001500 5  10 13 1 100316D 5  10 49 4013001500 5  10 13 1 Relativistic breakout relation

27. Shock breakout from long GRBs A short, hard and faint pulse at the beginning of the burst

28.  -ray flares from relativistic shock breakouts are expected in a range of other explosions. For example, White dwarf explosions (Type Ia and.Ia SNe and AIC): Extremely energetic and compact supernovae (e.g., SN 2002ap):

29. BATSE T 90 (50 - 300 keV) Swift T 90 (15 - 350 keV) The threshold duration for Swift sample must be shorter than for BATSE sample !!! We show that it is 0.6-0.7 s (Bromberg, EN, Piran & Sari 12) A note on short GRB classification

30. Summary Relativistic breakouts produce  -ray flares with characteristic properties: E bo – T bo – t bo relation (if quasi-spherical without wind) smooth a small fraction of total explosion energy  to X-ray evolution generate a relativistic outflow with E~E bo Low-luminosity GRBs, which are fundamentally different than long GRBs, show all these characteristics Failed jets is the most natural mechanism (explains also the high low luminosity GRB rate) Swift GRBs with 1s 50%) collapsars

31. Thanks

32. t 25 12 6 L 51 Zhang et al., 04 Comparison with simulations Bromberg, EN, Piran Sari 11

33. Which explosions are expected to have relativistic breakouts? EN & Sari 11