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 22.06.2012

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

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

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

optical afterglows in Swift era Kann et al. 2010

major rebrightenings at t>t0+500 s

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. 2010) late time engine activity, refreshed shocks (e.g., Vlasis et al. 2011)

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

GRB 050408 energy injection (at 2.9 days) seen off-axis de Ugarte Postigo et al. 2007

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

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

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

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

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

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

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

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

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

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

GRB 060206, 081029, 100901A

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

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

variation of microphysics Kong et al. 2010

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

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

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

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

collision of two shells Vlasis et al. 2011

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.

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

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

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