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 GRBs in the Era of Rapid Follow-up

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. reverse shock: steep decay: α ≈ 1.7 thick shell, slow cooling
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., Lazzati et al. 2002, Mimica's talk)
multi-component jet (e.g., Granot et al. 2006; Racusin et al. 2008)
varying micro-physical parameters (e.g., Kong et al )
late time engine activity, refreshed shocks (e.g., Vlasis et al. 2011)

8. GRB 970508 refreshed shock density jump patchy shell 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 Ugarte Postigo et al. 2007

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

11. GRB 060614 colour evolution passage of break frequency or
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 A
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 emission + some bumps (also in X-rays) common origin:
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
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 , , A

21. GRB 060206 late energy injection αrise≈ -8 αdecay≈ 1
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 – 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 – 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. detail modeling of multi-wavelength afterglow behaviour
GRB A – cont.
variation of microphysics
late time energy injection/two shell collision
detail modeling of multi-wavelength afterglow behaviour

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

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