X-ray Eyes on the Universe’s Brightest Explosions:

Probing the GRB Afterglow Emission Mechanism with Chandra

Nat Butler [email protected]

Six Years of Science with Chandra Cambridge, MA — 11/2/2005 Collaborators

U. C. Berkeley MIT Josh Bloom, George Ricker, Alex Filippenko, Herman Marshall, Dave Pooley, Roland Vanderspek, Weidong Li, Peter Ford, Katherine Alatalo, Joel Villasenor, Daniel Perley, Geoff Crew, Dan Kocevski, Don Lamb (U. Chicago), Jason Prochaska (UCSC), and Garrett Jernigan (U. C. Berkeley). and Hsiao-Wen Chen (MIT).

Six Years of Science with Chandra — Cambridge, MA — 11/2/2005 — Slide 2 of 14 Outline

I. X-ray Afterglows Lines, Controversy, Resolution?

II. Uncovering the Short GRB Progenitors

...skipping... optically dark GRBs, afterglow synchrotron modelling, late-time energy injection, X-ray Flash Observations, GRB remnants.

Six Years of Science with Chandra — Cambridge, MA — 11/2/2005 — Slide 3 of 14 The Anatomy of a GRB

Six Years of Science with Chandra — Cambridge, MA — 11/2/2005 — Slide 4 of 14 X-ray Bright Afterglows and Chandra

Beppo-SAX, 90% detection of X-ray afterglow.

Chandra provides arcsecond positions for “optically dark” GRBs, spectra, curves. GRB970111 GRB970228 GRB970402 GRB970508 Chandra has observed GRBs for 1.07 Msec, GRB971214 GRB980329 since GRB 991216. 43 observations (6 gratings GRB980613 GRB991216 observations) of 28 fields.

5-10 times better sensitivity, spatial resolution, and spectral resolution than Swift XRT. Costa et al. (1999)

Six Years of Science with Chandra — Cambridge, MA — 11/2/2005 — Slide 5 of 14 I. X-ray Line Emission, Observational Background

Fe-group (i.e Fe, Ni, or Co) lines 970508, 000214 (SAX), 970828 (ASCA), 991216 (Chandra)

Emission lines have been claimed in the X-ray afterglow spectra for GRBs, taken from multiples missions.

Claims of moderately low significance ( 3σ). low-Z (e.g. Mg, Si, S, Ar Ca) lines ∼ 011211, 030227, 040106 (XMM), 020813 (Chandra) Subject of debate at the last 2 annual GRB conferences. (e.g., Rutledge & Sako 2002; Butler et al. 2003; Sako, Harrison, & Rutledge 2005)

Six Years of Science with Chandra — Cambridge, MA — 11/2/2005 — Slide 6 of 14 The X-ray Line Controversy, GRB 011211

et al. (2002) χ2 χ2 0,ν = 46.4/45; 0,ν = 27.1/39

2 0 ∆χ Set of low-Z emission lines claimed by Reeves -2 Mg Si S Ar Ca in first 5 ksec of GRB011211 XMM 0.20 Epic-PN spectrum. 0.1% significance. 0.15 0.10

Counts / s / keV 0.05

0.00 However, Rutledge & Sako (2002) “Matched- 2 0 ∆χ -2

Filter” approach finds 10% significance. 0.2 0.5 1.0 2.0 3.0 ∼ Energy [keV] Criticisms: 4.5 3.6σ [2.3σΝ] GRB011211 4 2.7σ [1.0σΝ] 1. Line associations not unique 2. Blind search 2.4σ [0.7σ ] Ν 3.5

necessary 3. Statistical methodology wrong. 3

2.5

2

Butler et al. (2005) uncovered the root of the Convolved Counts 1.5

1 discrepancy (NH parameter is important). 0.5 Mg Si S Ar Ca 0 0.3 0.5 1.0 2.0 Energy [keV]

Six Years of Science with Chandra — Cambridge, MA — 11/2/2005 — Slide 7 of 14 Claim of Low-Z Lines for GRB 030227

χ2 χ2 0,ν = 75.1/78; 0,ν = 44.1/68 Set of low-Z emission al. (2003) 2 lines claimed by Watson et 0 ∆χ in last 10 ksec of -2

GRB030227 XMM Epic-PN 0.20 Mg Si S Ar Ca spectrum. 0.15

Add 5 (unresolved) emission 0.10 lines to the power-law fit: 0.05 ∆χ2 Counts / s / keV 0 = 31.0, for 10 additional degrees of freedom. 0.00 2 0 ∆χ That corresponds to 0.06% -2 σ (3.4 ) significance. 0.3 0.5 1.0 2.0 3.0 4.0 Energy [keV]

Six Years of Science with Chandra — Cambridge, MA — 11/2/2005 — Slide 8 of 14 A Weak Detection in a Chandra Gratings Spectrum ]

-1 CIE Plasma (kT = 9.2 keV) 10-3 Si XIV S XVI keV -1 s

Material (Si,S) characteristically produced -2

Fe during pre- nucleosynthesis in -4 10 Ni massive stars. Blue-shift (0.1c) typical for 10-4

Flux [Photons cm 2 3 4 5 inferred GRB-SN outflow velocities. 2 0 ∆χ -2

0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 Narrow lines require θjet 40◦. Energy [keV] ≤ Chandra HETGS Spectrum of Line duration (t 77 ksec) then gives: GRB 020813, Butler et al. (2004) ct 1 ≥ 16 R = 1+z 1 cos(θ ) 2 10 cm. ( 2 months − jet ≥ × ≥ between SN and GRB).

However, absence of Fe emission points toward ξ = L /nR2 10 100, nearby X ∼ − reprocessor model (Lazzati, Ramirez-Ruiz, & Rees 2002) .

Six Years of Science with Chandra — Cambridge, MA — 11/2/2005 — Slide 9 of 14 Recent Upper Limits from Chandra, No Lines!

Butler et al. (2005) 104 Gratings spectra for GRBs: 020405 (LETG 50 ksec), 3 θ o 021004 (HETG 90 ksec), 10 GRB 020405 ( jet=6 ) GRB 030328 (θ =4o) 030328 (LETG 90 ksec), jet GRB 041006 041006 (LETG 90 ksec). θ o GRB 021004 ( jet=13 ) 2 θ o 10 jet=10

The afterglow continuum GRB 010220

Source Frame EW [eV] GRB 001025A must be weak enough GRB 000214 1 θ o 10 jet=3 GRB 030227 not to over-power the θ o GRB 020813 ( jet=3 ) GRB 011211 (θ =5o) emission, peak EW’s at θjet o GRB 991216 ( jet=4 ) t 1 day. ∼ 0.1 1 10 . Time Since GRB [Source frame days] Simple photo-ionization model from Ballantyne & Ramirez-Ruiz (2001) .

Six Years of Science with Chandra — Cambridge, MA — 11/2/2005 — Slide 10 of 14 Are There Lines in the Swift XRT Data? (e.g., Gou, M esz´ aros,´ & Kallman 2004)

The Swift XRT data are accumulating!

First 7 months, 33 bright spectra (> 500 cts) in PC mode. (113 if time slice). Plus 30 (152) spectra in WT mode.

We are fitting these in a systematic (and autonomous) way, looking for lines. Nothing yet at > 4σ significance.

Six Years of Science with Chandra — Cambridge, MA — 11/2/2005 — Slide 11 of 14 II. Chasing Short GRBs Pre-Swift

Afterglow non-detections.

GRB970111 GRB970228 sGRB 020531 (HETE), 20 ksec (5 days) GRB970402 GRB970508 + 10 ksec (11 days). (Butler et al. 2002) GRB971214 GRB980329 GRB980613 sGRB 021201 (IPN), 20 ksec (8 days) + GRB991216 20 ksec (33 days). (Hurley et al. 2001) GRB020531 −> X

sGRB afterglows must be 10-100 times fainter than for GRBs.

Six Years of Science with Chandra — Cambridge, MA — 11/2/2005 — Slide 12 of 14 Enter Swift, The Short GRB Era

al. 2005; Bloom et al. 2005) sGRB 050709 sGRB 050509b (Swift) , 50 ksec, (non- , (Fox et al. 2005) 0 10 detection). Elliptical Host Galaxy? (Burrows et

−2 10

−4 al. 2005) 10 (mJy) ν

F −6 sGRB 050709 (HETE), 40 ksec (2.5 days) + 10

−8 20 ksec (16 days). Spiral Host Galaxy. (Fox et 10

Host Galaxy. −3 −2 −1 0 1 10 10 10 10 10 t (days) (a) Chandra Image. (b) Hubble Image. sGRB 050724 (Swift), 50 ksec. Elliptical (Burrows et al. 2005; Berger et al. 2005)

sGRBs appear to be associated with a variety of galaxy types, progenitor diversity.

Six Years of Science with Chandra — Cambridge, MA — 11/2/2005 — Slide 13 of 14 Conclusions

Chandra observations have enabled observations at longer wavelengths and have provided key insights.

Recent Observations show little evidence for X-ray lines.

Chandra is helping to close in on the progenitors of short GRBs.

Six Years of Science with Chandra — Cambridge, MA — 11/2/2005 — Slide 14 of 14