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