1. PHASES OF SWIFT X-RAY AFTERGLOWS ( properties and theoretical interpretation ) A. Panaitescu Los Alamos National Laboratory

2. Four Afterglow Phases I II III IV

3. I. FAST X-RAY DECAY (1-100s → 300-500s) large-angle GRB emission - BAT-XRT continuity - decay as predicted F  t  -  Lorentz transf. →  x1 = 2+  x1 - faster decay: t < 2 t GRB or outflow structure on  - 1 - slower decay: forward shock or outflow structure

4. rel. boost  t -1   -2 : t = 1 → 10 t   for  = (1 → 3)  -1 softer fast-decay spectrum : 1. break at 10-50 keV (but BAT-extrapolated emission matches XRT) 2. outflow structure on  -1 Fast X-ray decay : spectrum 40% aglows:   ~  x1, 54% aglows:   <  x1

5. II. SLOW X-RAY DECAY (100-600 s → 10 3 -10 4.5 s) def: preceded by steeper decay or followed by steeper decay  x2  x2 incompatible with standard forward-shock model Possible reasons: 1. energy injection 2. structured outflow 3. time-varying micro-parameters

6. Г(t b ) = 610 (E k,52 /n 0 ) 1/8 (t b / [1+z] ) -3/8 Г i (t b ) = [ (e+8)/(e+4) ] 1/2 Г(t b ) E k = E 20keV-2MeV, n 0 = 1 Slow X-ray decay : energy injection a) long-lived engine or b) short-lived engine + range of Lorentz factors : E(>Г i )   i - e (  x2,  x2 ) → 0.5< e< 3

7. D. Eichler & J. Granot - astro-ph/05.09.857 Slow X-ray decay : structured outflow Expect L x2 -  x2  correlation & t x2 -  x2 anticorrelation Find L x2 -  x2  anticorrelation & t x2 -  x2 correlation ? t x2,L x2 t -  x2  offset 050315

8. Slow X-ray decay : evolving micro-parameters quantifying fraction of shock energy in - magnetic field  B   - electrons  e   Spectral characteristics ( peak flux + break frequencies ) depend on  B and  e ↓ Decay indices depend on evolution of  B and  e

9. III. PRE JET-BREAK PHASE (1-10 h → 1-10 d) def: preceded by slower decay or followed by steeper decay visible opening =  -1 <  jet (as if spherical)  x3  x3 compatible with 1. constant forward-shock energy 2. outflow without angular structure 3. constant micro-parameters → 1,2,3 may be all satisfied, though not necessarily so For some afterglows,  x3 –  o3 > 1 is too large (standard FS model :  x3 –  o3 = -1/4, 0, 1/4) → conditions 1, 2, or 3 not always satisfied

10. chromatic (not in optical) possibly chromatic achromatic (also in optical)

11. MECHANISMS for X-ray break at end of slow-decay phase and beginning of pre jet-break phase: a. cessation of energy injection → dynamics,  (t) b. structured outflow, average dE/d  stops increasing → evolution of blast-wave energy, E(  <  -1 )(t) c. micro-parameters become constant a,b,c affect evolution of all afterglow spectral characteristics ↓ simultaneous light-curve breaks at ALL frequencies ↓ a,b,c fail to explain alone the chromatic X-ray breaks at ~1 hour

12. CHROMATIC X-RAY BREAKS → evolving  B and  e No optical break at t b → evolutions of  B and  e at t b are correlated ?! SET-UP a) cessation of EI at t b → X-ray break b )  < c < x → decoupling of optical and X-ray decays c )  B and  e steadily evolving across t b to yield no optical break PROBLEM 4 CONSTRAINTS :  x &  o at t t b FOR 4 PARAMETERS : E(>Г )   - e  B   - b  e   - i n  r - s SOLUTION : 1) s = 1.9-2.3 all consistent with s=2 → grb progenitor = massive star 2) condition for lack of optical break : i/3 + b/4 ~ 0.9 ± 0.2 (?!) 3) t t b :  e  t - 0.4 ± 0.4 →  e larger by factor 2-6 during burst than at t b 4) t t b :  B  t 1.3 ± 0.2 →  B smaller by factor 10-50 during burst than at t b

13. IV. POST JET-BREAK DECAY (after ~1 d) visible opening =  -1 >  jet steep decay because of 1. jet boundary seen 2. jet lateral spreading → faster deceleration  x4  x3 compatible with standard JET model other simple tests for JET model 1. achromatic break 2. |  x4 –  o4 | ≤ 1/4

14. BEST PROOF FOR JET-BREAKS IS NOT SO GOOD t < t b :  x3 &  o3 cons. w/ SJM t > t b :  o4 too small for SJM →  B and  e start evolving at t b ? SJM = standard jet model ( with constant  B and  e ) is there an X-ray break ? same problem as for 050525A optical break at 0.5d & X-ray data are consistent with SJM

15. SUMMARY 1. fast-decay – large-angle GRB emission (internal shocks) short-lived, hard, Xray-only flares also from IS 2. slow-decay – forward shock + energy injection ( structured outflow ? ) 3. pre jet-break – standard (spherical) FS model BUT chromatic X-ray break at 2 → 3 requires evolving micro-parameters (bonus: wind medium) 4. post jet-break – standard jet model. To test pre-Swift: optical breaks, not enough X-ray coverage Swift: X-ray breaks, not enough optical coverage