ON LATE TIME REBRIGHTENINGS IN GRB OPTICAL AFTERGLOWS

Liverpool GRBs in the Era of Rapid Follow-up 22.06.2012

A. Gomboc (UL, CE SPACE-SI, Slovenia)

withS. 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...

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

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F ∝ t−α

reverse shock: steep decay: α ≈ 1.7

Kobayashi 2000

thin shell, slow cooling

thick shell, slow cooling

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)

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νbreak

GRB 970508

Pedersen et al. 1998, Galama et al. 1998

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)

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 αrise

depends on λ

colour evolution

passage of break frequency

or Mangano et al. 2007

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ν i

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νc

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 shockor wide-angle secondary jet

Perley et al. 2008

GRB 071010A

energy injection or density bump, structured jetCovino et al. 2008

GRB 071031 onset of the forward shockemission + 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 afterglowGreiner et al. 2009

GRB 091024Francisco Virgili's talk

Virgili et al., in prep.

GRB 100418A similar to 060614

long-lasting energyinjection two component jet

Lan-Wei et al. 2012Marshall et al. 2011

GRB 060206, 081029, 100901A

GRB 060206 αrise≈ -8 αdecay≈ 1

late energy injection

Monfardini et al. 2006

variation of microphysics Kong et al.

2010:region 1:

region 2:Kong et al. 2010 €

εe = ε e,0γ−α1

ε B = εB ,0γ−α1

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εe = ε e,0γ−α 2

εB = ε B ,0γ−α 2

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 simultaneousrebrightening in X-rays

SED: SPL opt/NIR –XNardini 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.

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!