1. Chandra Searches for Late-Time Jet Breaks in GRB Afterglows David Burrows, Judith Racusin, Gordon Garmire, George Ricker, Mark Bautz, John Nousek, & Dirk Grupe

2. GRB followup GRBs are the biggest, brightest explosions in the Universe since the Big Bang, with E iso ≥ 10 54 ergs Powered by collapse of massive stars with total energy ~ 10 53 ergs => GRB outflows must be highly collimated Torus Jet Relativistic beaming: θ ~ Γ -1, Γ > 100 2θj2θj tjtj ~ t -1.3 ~ t -2.3

3. GRB followup Frail et al. 2001, ApJ, 562, L55 GRBs are the biggest, brightest explosions in the Universe since the Big Bang, with E iso ≥ 10 54 ergs Powered by collapse of massive stars with total energy ~ 10 53 ergs => GRB outflows must be highly collimated

4. Chandra GRB followup program Combination of GI and GTO time Sample of long-lived XRT afterglows chosen for followup with late-time Chandra observations – spectroscopic redshift – well-behaved XRT light-curve – extrapolated LC detectable in XRT for at least 10 d – Chandra observations performed at predicted fluxes of ~ 3e-15 cgs – trigger lead-time moderate (~ 2 weeks) 10 GRBs in sample – 4 have late-time breaks in LC – 6 do not

5. Example: GRB 061121 Blue: Swift/XRT WT mode Red: Swift/XRT PC mode 10 2 10 Time since BAT trigger (s) 10 3 10 4 10 5 10 6 10 7 Swift XRT follows the light curves to ~10 -14 cgs, but usually does not see a clear jet break Burrows et al. 2010, in prep α = 0.99 α = 1.55 29.5 ks

6. Example: GRB 061121 Blue: Swift/XRT WT mode Red: Swift/XRT PC mode Green: Chandra/ACIS 10 2 10 Time since BAT trigger (s) 10 3 10 4 10 5 10 6 10 7 Swift XRT follows the light curves to ~10 -14 cgs, but usually does not see a clear jet break Burrows et al. 2010, in prep

7. Jet Break Lower Limit Force additional break with slope α last +1 Find 90% confidence limit of earliest additional break buried in errors

8. GRBs w/ late breaks: GRB 060729 Black: Swift/XRT Red: Chandra/ACIS Grupe et al. 2010, ApJ Pow3=1.31 +0.02 -0.03 Breaktime3=1.22 +0.17 -0.23 Ms Pow4=1.65±0.05 Breaktime4=38.0 +4.1 -5.3 Ms Pow5=4.59 +1.7 -1.1 10 5 10 6 10 7 10 8 Burrows et al. 2010, in prep

9. GRBs w/ late breaks: GRB 060729 Black: Swift/XRT Red: Chandra/ACIS Grupe et al. 2010 Pow3=1.31 +0.02 -0.03 Breaktime3=1.22 +0.17 -0.23 Ms Pow4=1.65±0.05 Breaktime4=38.0 +4.1 -5.3 Ms Pow5=4.59 +1.7 -1.1 10 5 10 6 10 7 10 8 Burrows et al. 2010, in prep 3.8 x 10 7

10. GRBs w/ late breaks: GRB 060729 Pow3=1.31 +0.02 -0.03 Breaktime3=1.22 +0.17 -0.23 Ms Pow4=1.65±0.05 Breaktime4=38.0 +4.1 -5.3 Ms Pow5=4.59 +1.7 -1.1 Black: Swift/XRT Red: Chandra/ACIS Grupe et al. 2010 10 5 10 6 10 7 10 8 1.4 x 10 7 Burrows et al. 2010, in prep

11. 1 1 Jet Break times in observed frame Frail et al. 2001, ApJ, 562, L55

12. 1 1 Jet Break times in observed frame 100 1000 Frail et al. 2001, ApJ, 562, L55

13. Summary GRB 091127 GRB 090423 GRB 090102 GRB 081007 GRB 080913 GRB 050724 GRB 091020 GRB 071020 GRB 061121 GRB 060729

14. Summary GRB 091127 GRB 090423 GRB 090102 GRB 081007 GRB 080913 GRB 050724 GRB 091020 GRB 071020 GRB 061121 GRB 060729

15. Summary GRB 091127 GRB 090423 GRB 090102 GRB 081007 GRB 080913 GRB 050724 GRB 091020 GRB 071020 GRB 061121 GRB 060729

16. Summary Work in progress Late-time Chandra observations can – identify potential jet breaks in ~40% – put stronger limits on jet break times in ~60% Jets are occurring at much later times than seen in early optical studies We need IXO to follow X-ray light curves to significantly deeper limits