The signature of a wind reverse shock in GRB’s Afterglows Asaf Pe’er Ralph A.M.J. Wijers (Amsterdam) ApJ., 543, 1036 astro-ph/0511508 June 06

Outline Motivation: massive stars as GRB progenitors Complexities of the ambient density profile Interaction of relativistic blast wave and wind termination shock Plasma dynamics Resulting light curves

Motivation: wind from massive star Massive stars are progenitors of Long GRB’s (GRB-SN Ic connection, GRB’s in star forming regions..) Massive stars emit supersonic wind: ISM nISM~103 cm-3 Stellar wind Shocked stellar wind Massive star (reverse) shock wave (forward) shock wave Contact discontinuity

Graph #1: Density profile Pb>>Pa rb=4ra(r=R0) Castor et. al., 1975 Weaver et. al., 1977

Density profile numerical simulation by Chevalier, Li & Fransson (2004)

Blast wave propagation in region a: density profile Dr(ã)ob. ~ r/4G2 Blandford & McKee (1976) : n(r) r-2  G(r) r-1/2

GRB blast wave propagation in region a (relativistically-) shocked stellar wind (hot: Gmc2 per particle) Region a: Stellar wind (cold) Region b: Shocked stellar wind G(r) Compressed: Dr(ã)ob. ~ r/4G2 Relativistic blast wave Wind reverse shock

Interaction of shock waves Region ã Region a Region b Wind reverse shock G(r) (downstream) r<R0 G(r) Region b ~ Region c ~ Region ã: Region b G1G(r=R0) (upstream) GRS<G1 r>R0 New blast wave reverse shock New blast wave forward shock Contact discontinuity

Calculation of plasma properties during interaction Problem: reverse shock propagates into hot medium  not strong ! Region b: Region ã: Region b ~ Region c GRS<G1=? G1G(r=R0) G2=? We know: Boundary conditions: G1, nã, nb We find: Reverse shock jump conditions: - Conservation of particle number flux: [nGb] - Energy flux – [wG2b] - Momentum flux: [wG2b2 + P]

Schematic density profile during the existence of the reverse shock As long as the reverse shock exists – plasma in region ã is upstream  continues to move at G1  conditions in other regions are time independent !

Graph #2: Evolution of blast wave Lorentz factor G(r) r-1/2 G(r) r-3/2 R1 = 1.06R0 = radius where the reverse shock crossed region ã

Light curves calculations Synchrotron emission spectrum Calculation in 3 different regimes: (a) r < R0  Emission from region ã (b) R0<r<R1 Emission from regions ã , b, c (c) r>R1  Emission from region c ~ ~ (Sari, Piran & Narayan, 1998) ~

Graph #3: Resulting light curve Model predictions: (1) Jump in the light curve by a factor ~2 after ~day; (2) Change of spectral slopes at late times (3) Late times afterglow looks like explosion into constant density

Comparison with data: GRB030329 R-band afterglow of GRB030329 (corrected for the contribution of SN2003dh) (Taken from Lipkin et.al., 2004)

Summary Wind of massive star results in complex density structure GRB blast wave splits at R0, change its r- dependence Light curve is complex: shows jump by a factor of ~2 after ~ day, and change slope at late times