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