chandra searches for late-time jet breaks in grb afterglows david burrows, judith racusin, gordon...
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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 Eiso ≥ 1054 ergs
• Powered by collapse of massive stars with total energy ~ 1053 ergs => GRB outflows must be highly collimated
Torus
Jet Relativistic beaming:θ ~ Γ-1, Γ > 100
2θj
tj
~ t -1.3
~ t -2.3
GRB followup
Frail et al. 2001, ApJ, 562, L55
• 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
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
Example: GRB 061121
Blue: Swift/XRT WT modeRed: Swift/XRT PC mode
10210Time since BAT trigger (s)
103 104 105 106 107
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 k
s
Example: GRB 061121
Blue: Swift/XRT WT modeRed: Swift/XRT PC modeGreen: Chandra/ACIS
10210Time since BAT trigger (s)
103 104 105 106 107
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
Jet Break Lower Limit
Force additional break with slope αlast+1
Find 90% confidence limit of earliest additional break buried in errors
GRBs w/ late breaks: GRB 060729
Black: Swift/XRTRed: 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±0.05Breaktime4=38.0+4.1
-5.3 MsPow5=4.59+1.7
-1.1
105 106 107 108
Burrows et al. 2010, in prep
GRBs w/ late breaks: GRB 060729
Black: Swift/XRTRed: Chandra/ACIS
Grupe et al. 2010
Pow3=1.31+0.02-0.03
Breaktime3=1.22+0.17-0.23 Ms
Pow4=1.65±0.05Breaktime4=38.0+4.1
-5.3 MsPow5=4.59+1.7
-1.1
105 106 107 108
Burrows et al. 2010, in prep
3.8
x 10
7
GRBs w/ late breaks: GRB 060729Pow3=1.31+0.02
-0.03
Breaktime3=1.22+0.17-0.23 Ms
Pow4=1.65±0.05Breaktime4=38.0+4.1
-5.3 MsPow5=4.59+1.7
-1.1
Black: Swift/XRTRed: Chandra/ACIS
Grupe et al. 2010
105 106 107 1081.
4 x
107
Burrows et al. 2010, in prep
1
Jet Break times in observed frame
Frail et al. 2001, ApJ, 562, L55
1
Jet Break times in observed frame
100 1000
Frail et al. 2001, ApJ, 562, L55
0.1 1.0 10.0 100.0 1000.00123456789
1011
Jet Break times
CXO_max
Jet_Break
Min_break
XRT_limit
Rest-frame time since burst (d)
Summary
GRB 091127GRB 090423GRB 090102
GRB 081007GRB 080913
GRB 050724GRB 091020GRB 071020GRB 061121GRB 060729
1.0 10.0 100.00123456789
1011
Jet Angles
CXO_max
Jet_break
Min_break
XRT_limit
Opening half-angle (degrees)
Summary
GRB 091127GRB 090423GRB 090102
GRB 081007GRB 080913
GRB 050724GRB 091020GRB 071020GRB 061121GRB 060729
48.5 49.0 49.5 50.0 50.5 51.0 51.5 52.0 52.50123456789
1011
log (E_gamma)
CXO_max
Jet_break
Min_break
XRT_limit
log(jet energy) (ergs)
Summary
GRB 091127GRB 090423GRB 090102
GRB 081007GRB 080913
GRB 050724GRB 091020GRB 071020GRB 061121GRB 060729
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