11

John Nousek (Penn State University)

ly Searching the Sky:

The First Three Years of theSwift Gamma-Ray Burst Explorer

III Cosmic Ray & Astrophysics School - Arequipa, Peru – 1 Sep 2008

22

GRBs – Pre-Swift GRB Phenomenon Pre-Swift GRB Paradigm

Swift Era Swift satellite Swift discoveries

Challenges to the GRB Paradigm Short GRBs ‘Canonical’ X-ray light curves Lack of jet breaks/chromatic jet breaks X-ray ‘flares’

Swift & GRB science in the future What to do with Swift for the next four years?

Talk Outline

33

GRBs – Pre-Swift

What did we know about GRBs before Swift?

44

• GRBs discovered in 1969 by Ray Klebesadel of LANL– Vela satellites: monitored Nuclear Test Ban treaty– Data published in 1973

History of GRBs

– BATSE: 2609 bursts in 8.5 years

• Compton Gamma-Ray Observatory launched on 5 April 1991

Compton Observatory Era

Sof

tH

ard

Har

dn

ess

Rat

io

Duration (s)

short

long

GRB 971214 - Keck

GRB 970228 - BeppoSAX

Beppo-SAX & HETE-2 Era

Fireball Model(Meszaros & Rees 1997)

-raysafterglow

77

The Time Gap

Swift

Beppo SAX data

GRB Progenitors

Hypernova Merging Neutron Stars

99

The Swift Era

What have we learned so far from Swift?

1010

Swift launch:

20 Nov 2004 !!

1111

MOC Facility

Has continuously operated Has continuously operated SwiftSwift successfully from L+80 minutes successfully from L+80 minutes to now!to now!

Located in State College, PA

~ 4 km. from Penn State campus

Flight Operations Team (FOT)

– responsible for observatory Health & Safety

Science Operations Team (SOT)

- responsible for scientific operation of Swift

1212

Observing Scenario

2. Spacecraft autonomously slews to GRB position in 20-70 s

3. X-Ray Telescope determines position to ~2-3 arcseconds

4. UV/Optical Telescope images field, transmits finding chart to ground

BAT Burst Image

T<20 sec

1. Burst Alert Telescope triggers on GRB, calculates position on sky to ~ 1 arcmin

BAT Error Circle

XRT Image

T<90 sec T<300 sec

UVOT Image

1313

BAT GRB Position AccuracyGRB 050215b GRB 050315 GRB 050319

GRB 050406 GRB 050416a GRB 050509a

BAT FSW (3’ radius)

XRT

Mean BAT position error: 52 arcseconds

T. Sakamoto

1414

FRED

Fast Rise Exponential Decay

Short GRB

Short GRB

Swift Statistics:~300 GRB discovered 85% with X-ray detections 95% with XRT @ T<200 ks ~60% with optical detection (UVOT + ground) ~9% short GRBs

>400 non-GRB TOOs>100,000 slews

1515

Average Redshift- Pre-Swift: z = 1.2- Swift: z = 2.3

Redshift and Time Distributions

Redshift (z)

Num

ber

o f G

RB

s

5

10

Pre-Swift

0.1 1.0 10.00

Swift

Long GRBs

Lookback Time (G yr)1.0 10.0

Era of GRBs

0

5

10

15

20

Analysis by Neil Gehrels

1616

72 Swift Long GRB Redshifts

6.29 0509045.47 0609275.3 0508145.11 0605224.9 060510B4.41 060223A4.27 0505054.05 0602063.97 0507303.91 0602103.71 0606053.69 0609063.63 070721B3.53 0601153.44 061110B3.43 0607073.36 061222B3.34 0509083.24 0503193.22 0605263.20 0609263.08 060607A2.95 0704112.90 0504012.82 0506032.71 0607142.69 0710312.68 0606042.61 050820A2.50 0705292.45 0708022.43 0609082.35 051109A2.35 0701102.31 0705062.30 060124

2.20 050922C2.17 0708102.15 0710202.04 0706111.95 0503151.56 0508011.55 0511111.55 0701251.51 060502A1.50 0703061.49 0604181.44 0503181.31 0611211.29 0501261.26 0610071.17 0702081.16 0611260.98 0710100.97 070419A0.95 071010B0.94 051016B0.84 0608140.84 0703180.83 0508240.78 0602020.76 061110A0.70 060904B0.65 050416A0.61 050525A0.59 0502230.54 0607290.44 0605120.30 0508260.125 0606140.089 0605050.033 060218

< z > = 2.3

0.001 0.01 0.1 1 10 Redshift

Swift Redshift Distribution

N

umbe

r

Gehrels et al. 2007

1717

GRBs – now in the Swift era

How has the paradigm changed with the Swift discoveries?

1818

Short vs Long GRBs

Short Long

GRB 990123 - BeppoSAXHST Image

BATXRT

GRB 050509B - SwiftVLT Image

Cn

ts/s

Short GRB Long GRB

Cn

ts/s

Short GRBsin non-SF

galaxies/regions

Long GRBsin SF

galaxies

GRB

Swift first to discover counterpart to short GRB!

1919 III Cosmic Ray & Astrophysics School – Arequipa, Peru – 1 Sep 2008

Comparing Short and Long GRBs

& GRB 061210

GRB 061121 = brightest long GRBGRB 061210 = brightest short GRB

Norris et al. 2006

2020 III Cosmic Ray & Astrophysics School – Arequipa, Peru – 1 Sep 2008

Comparing Short and Long GRBs

& GRB 061210

GRB 061121 = brightest long GRBGRB 061210 = brightest short GRB

Short GRB 051221A

Kouveliotou et al. 1993

2121

Long GRBs

Short GRBs

Gehrels et al. 2007

Prompt vs Afterglow Correlation Analysis

2222

Short GRBs - Opportunity

Progress on short GRBs - a tough nut to crack!

Swift statistics:

24 total short GRB (+ 3 questionable)

* ~4 firm redshifts * 8 OTs * ~4 host galaxy IDs

Short bursts versus Long bursts - Different physics - Different environments - Different population of stars - Different ages & distances

New tool for studying stellar evolution & binary formation

Direct tie-in to emerging GW field

CHALLENGE:

Short GRBs are weak in , X, opt

Current knowledge from few events

GRBs with afterglow - special subclass?

Which are short, which are long?

Needed: more short GRBs rapid, sensitive follow-up high resolution optical imaging

2323

Pre-Swift X-ray light curve

Swift

Beppo SAX data

Canonical Swift XRT Light Curve

1.0t

2.1t

7.0t

3.2t

6t (steep – due to light delay effects from end of prompt emission)

(plateau – due to energy injection into external shock)

(normal – external shock)

Flare

Jet Break

GRB060428A – Courtesy of D. Burrows

2525

Jet Break

Torus

Jet Relativistic beaming:θ ~ Γ-1

Frail et al. 2001, ApJ, 562, L55

2626

Jet Break

Frail et al. 2001, ApJ, 562, L55

Jet break knowledge is critical for GRB energetics:E γ = Eiso(1-cos θj)

GRB050416A

> 58 Days

α = 0.81

GRB060729 is also still going with no jet break after 2 months!

2828

Jet Break

Torus

Jet Relativistic beaming:θ ~ Γ-1

Frail et al. 2001, ApJ, 562, L55

For some Swift bursts there is either no jet break, or there is a chromatic break →

Either jet angle is very wide or

Density is very low or

Basic model is wrong

2929

Giant X-ray Flare: GRB 060526

> 100x increase!

Peak ~ 220 s

3030

Giant X-ray Flare: GRB 050502B

500x increase!

GRB Fluence:8E-7 ergs/cm2

Flare Fluence:9E-7 ergs/cm2

Burrows et al. 2005, Science; Falcone et al. 2005, ApJ

Peak ~ 700 s

Note establishment of AG before flare begins.

3131

Swift XRT X-ray Flares

GRB 050406GRB 050421 GRB 050502B

GRB 050712GRB 050607GRB 050713A

GRB 050714B

GRB 050716GRB 050726

GRB 050730

116 prompt afterglow detections

~ 50% have X-ray flares

Typically in first 20 min.

Dynamic range: 1.3x – 500x

Flare analysis courtesy of Dave Burrows

3232

Flares in Short GRBs

?

Mechanism for flares must also operate in the context of short GRBs.

3333

The Future

What to do with Swift for the next four years?

3434

High-z GRB - Opportunity

Prediction: - 7% - 10% of Swift GRBs at z>5 (Bromm & Loeb, Jakobbson et al., Lamb & Reichart)

- ~0.5% at z>10

Swift measurements: - 4 out of 72 = 6% Bromm & Loeb (2006)

Swift GRBRate

z GRB Optical Brightness

6.29 050904 J = 18 @ 3 hrs 5.6 060927 I = 16 @ 2 min 5.3 050814 K = 18 @ 23 hrs 5.11 060522 R = 21 @ 1.5 hrs

3535

High-z GRB - Opportunity

GRBs are briefly the most luminous sources in the universe .... across the E-M spectrum!

High-z GRBs offer unique tool for studying: - Reionization era - Abundance history of universe - First stars & first light - Star formation rate history - Gas and dust content of early galaxies

CHALLENGE:

Difficult to determine redshift for high-z bursts

Bursts not detected in optical can be common dark GRBs or rare high-z events.

Needed: rapid response, large telescope, IR spectrograph

Needed: redshift indicators, good position on sky for follow-up

Fraction with OT

Fraction with z

239 Swift GRBs with XRT

2005 2006 2007

GRB 060218: GRB + Supernova

Super-long GRB - ~35 minutes

BAT, XRT, UVOT during GRB

z = 0.033 d = 145 Mpc

SN 2006aj SN Ib/c

Eiso = few x 1049 erg - underluminous

Epeak = 4.9 keV - XRF

BAT 3 GRB SNeSN 2006aj

SNe Ic

Campana et al., Mazzali et al., Pian et al., Soderberg et al.

Pian et al. 2006

3737

Underluminous GRBs - Opportunity

Observations of nearby GRBs leading to breakthroughs in understanding of:

- GRB central engine - Jet outflows - CC supernovae

CHALLENGE:

Data are scarce and puzzling: 6 events, all different - 980425 underluminous - 031203 underluminous - 030329 normal GRB - 060219 XRF underluminous - 060505 no SN - 060614 no SN

Needed: better detection of faint GRBs

3838

The Year of High-z Bursts

Alerts from Swift data - BAT T90, variability, spectrum (Ukwatta & Sakamoto 2007)

- X-ray light curve flaring (Morris et al. 2007)

- X-ray NH correlations (Grupe et al. 2007)

- UVOT photometric data (Vanden Berk 2007)

Sun Angle - 50% of time with Swift pointing >9hr from sun

Follow-up Community - Small & medium telescopes to identify candidates - Large telescope for spectra of likely candidates

Sakamoto 2007

Pointing angle relative to SunAdvantage of high sun angle

2006

April2007

Nov.2007

9 hr3 hr

Sun Angle

1.0

Nu

mb

er o

f G

RB

s

Fraction of GRBs with z

All GRBs

Sun angle [deg]

4040

BAT Low Threshold Experiment

Lower BAT thresholds: ~2 triggers & slews per day

Observe with NFIs for 2 ks

Trigger is deemed a GRB if afterglow is detected

No Notices or Circulars for triggers without afterglow

Observers can sign up to receive all triggers, with suitable warnings

Experiment to last 1 month

Barthelmy, Palmer, Fenimore

4141

Opportunities for Joint Observations

JWST (2013)IR

ICECUBE (2009 -2011)neutrinos

LIGO (2014 - ALIGO)gravitational wave~30 NS-NS mergers per year

ALMA (2012)radio mm/submm

IR Afterglow

JWST sensitivity

Bromm & Loeb (2007)

z=15

z=5

AGILE & GLASTH.E. -rays

Dermer, Chiang & Mitman (2000)

H.E. -Ray

4242

GSFC

Swift Institutions

Executive Committee

G. Chincarini - Brera Obs.N. Gehrels - GSFCP. Giommi - ASI

K. Mason - MSSLJ. Nousek - PSU

J. Osborne - U. LeicesterA. Wells - U. Leicester

N. White - GSFC