On late time rebrightenings in GRB optical afterglows

1. On late time rebrightenings in GRB optical afterglows A. Gomboc (UL, CE SPACE-SI, Slovenia) with S. Kobayashi (LJMU), A. Pozanenko (IKI), A. Melandri (INAF Brera), J. Japelj (UL), D. Kopač (UL), C. Guidorzi (UF), C. Mundell (LJMU), I. Steele (LJMU), K. Wiersema (UL), O. Hartoog (UA), and more... Liverpool GRBsin the Era of Rapid Follow-up 22.06.2012

2. Outline • late time rebrightenings in optical afterglows • possible theoretical interpretations • focus: steep rebrightenings

3. standard model • power law decay: • forward + reverse shock • Mimica's talk yesterday Gomboc et al. 2009

4. thick shell, slow cooling • reverse shock: steep decay: α ≈ 1.7 thin shell, slow cooling Kobayashi 2000

5. optical afterglows in Swift era Kann et al. 2010

6. major rebrightenings at t>t0+500 s

7. theoretical interpretations • late forward shock • passage of • inhomogeneous circum-burst medium (density bumps) (e.g., Lazzatiet al. 2002, Mimica'stalk) • multi-component jet(e.g., Granot et al. 2006; Racusin et al. 2008) • varying micro-physical parameters (e.g., Kong et al. 2010) • late time engine activity, refreshed shocks (e.g., Vlasis et al. 2011)

8. GRB 970508 • αrise≈-3 • αdecay≈1.2 • refreshed shock (Panaitescu et al. 1998, Sari&Mészáros 2000, Kumar&Piran 2000) • density jump (Wang&Loeb 2000, Dai&Lu 2002, Nakar et al 2003) • patchy shell (Nakar et al. 2003) Pedersen et al. 1998, Galama et al. 1998

9. GRB 050408 • energy injection (at 2.9 days) seen off-axis de UgartePostigo et al. 2007

10. GRB 060210 • αrise≈ -0.9 • αdecay≈1.15 • density bump? (fine tuning) Curran et al. 2007

11. GRB 060614 • αrise depends on λ • colour evolution • passage of break frequency or Mangano et al. 2007

12. GRB 070311 • refreshed shock • density bump (less likely) Guidorzi et al. 2007

13. GRB 070419A • αrise≈-1.5 • αdecay≈0.6,1.5, 0.4 • long-lived central engine with a finely tuned energy injection rate Melandri et al. 2009

14. GRB 071003 • late-time refreshed shock or • wide-angle secondary jet Perley et al. 2008

15. GRB 071010A • energy injection • or density bump, structured jet Covino et al. 2008

16. GRB 071031 • onset of the forward shock emission + some bumps (also in X-rays) • common origin: late central engine activity Krühler et al. 2008

17. GRB 080129 • optical flare (RS) • rebrightening: • αrise≈-1.3 • αdecay≈0.5 • emerging afterglow Greiner et al. 2009

18. GRB 091024 Francisco Virgili's talk Virgili et al., in prep.

19. GRB 100418A • similar to 060614 • long-lasting energy injection • two component jet Lan-Wei et al. 2012 Marshall et al. 2011

20. GRB 060206, 081029, 100901A

21. GRB 060206 • αrise≈ -8 • αdecay≈ 1 • late energy injection Monfardini et al. 2006

22. variation of microphysics • Kong et al. 2010: region 1: region 2: Kong et al. 2010

23. variation of microphysics • Kong et al. 2010

24. GRB 060206 – cont. • variation of microphysics: Kong et al. 2010

25. GRB 081029 • αrise≈ -8 • αdecay≈ 0.4, 2.5 • no simultaneous rebrightening in X-rays • SED: SPL opt/NIR –X Nardini et al. 2011

26. GRB 081029 – cont. • seen in 7 bands Nardini et al. 2011

27. GRB 081029 – cont. • colour evolution • Nardini et al. 2011: long lasting activity/reactivation of central engine • Holland et al. 2012: two component jet and two shell collision Nardini et al. 2011

28. collision of two shells • Vlasis et al. 2011

29. GRB 100901A • afterglow onset • αrise≈ -3.9, -0.5 • αdecay≈ 1.5 • rebrightening in X-ray (not as steep) • SED: BPL opt-X • no obvious colour evolution Gomboc et al. in prep.

30. GRB 100901A – cont. • variation of microphysics • late time energy injection/two shell collision detail modeling of multi-wavelength afterglow behaviour

31. GRB 100621 • αrise≈ -14 (!) challenge? Nardini, Munich conf., 2012

32. Conclusions • late time optical (NIR) rebrightenings • diverse • (some) chromatic • steep rise: difficult to explain Thank you!