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Chandra Searches for Late-Time Jet Breaks in GRB Afterglows

Chandra Searches for Late-Time Jet Breaks in GRB Afterglows. David Burrows, Judith Racusin , Gordon Garmire , George Ricker, Mark Bautz , John Nousek , & Dirk Grupe. GRB followup. GRBs are the biggest, brightest explosions in the Universe since the Big Bang, with E iso ≥ 10 54 ergs

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Chandra Searches for Late-Time Jet Breaks in GRB Afterglows

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  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 Eiso ≥ 1054 ergs • Powered by collapse of massive stars with total energy ~ 1053 ergs => GRB outflows must be highly collimated ~ t -1.3 ~ t -2.3 tj Jet Relativistic beaming: θ ~ Γ-1, Γ > 100 2θj Torus

  3. GRB followup • GRBs are the biggest, brightest explosions in the Universe since the Big Bang, with Eiso ≥ 1054 ergs • Powered by collapse of massive stars with total energy ~ 1053 ergs => GRB outflows must be highly collimated Frail et al. 2001, ApJ, 562, L55

  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) • 10GRBs in sample • 4 have late-time breaks in LC • 6 do not

  5. Example: GRB 061121 Swift XRT follows the light curves to ~10-14 cgs, but usually does not see a clear jet break α = 0.99 α = 1.55 29.5 ks Blue: Swift/XRT WT mode Red: Swift/XRT PC mode 10 102 103 104 105 106 107 Time since BAT trigger (s) Burrows et al. 2010, in prep

  6. Example: GRB 061121 Swift XRT follows the light curves to ~10-14 cgs, but usually does not see a clear jet break Blue: Swift/XRT WT mode Red: Swift/XRT PC mode Green: Chandra/ACIS 10 102 103 104 105 106 107 Time since BAT trigger (s) Burrows et al. 2010, in prep

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

  8. 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, ApJ 105 106 107 108 Burrows et al. 2010, in prep

  9. 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 3.8 x107 Grupe et al. 2010 105 106 107 108 Burrows et al. 2010, in prep

  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 1.4 x 107 Grupe et al. 2010 105 106 107 108 Burrows et al. 2010, in prep

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

  12. Jet Break times in observed frame 1 1000 100 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

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