Swift Spacecraft and Instruments
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Spacecraft Design
Star Trackers
Gyros
1 of 6 Reaction wheels
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Swift
Swift Overview
Catching Gamma Ray Bursts on the Fly
Capabilities
 ~ 1000 GRBs studied over a three-year period
 0.3–2.5 arc-second positions for each GRB
 Multiwavelength observatory (gamma, X-ray,
UV, and Optical) to monitor afterglows
 20–70 s reaction time
 Five times more sensitive than BATSE
 Spectroscopy from 0.2 to 150 keV
 Six colors covering 170–650 nm
 UV and optical spectroscopy with R ~ 300–600
for Mb < 17
 Capability to directly measure redshift
 Results publicly distributed within seconds
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Swift Mission Features
 Multi-wavelength observatory
 Burst Alert Telescope (BAT): 10-150 keV
 detect ~ 300 gamma ray bursts per year
 onboard computation of positions
 arc-minute positional accuracy
 Dedicated telescopes for X-rays, UV, and optical
afterglow follow up:
 Rapid response satellite
 0.3-10 keV X-ray Telescope (XRT)
 170-650 nm UV/Optical Telescope (UVOT)
 0.3-2.5 arc-second locations
 existing hardware from JET-X and XMM
 determine redshifts from X-ray absorption,
lines, and Lyman-a cutoff
 20 - 70 sec to slew within FOV of BAT
 autonomous operations
 factor of > 100 improved response time
 continue monitoring of fading afterglow for days to weeks after the event
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Swift Instrumentation
I. Burst Alert Telescope (BAT)
 Real time gamma ray burst positions
half coded 2 steradian FOV
5200 cm2 CdZnTe pixel array
10–150 keV band
based on INTEGRAL Imager design
4 mm
BAT CdZnTe
8 x 16 element
detector module
5 times more sensitive than BATSE
~ 1 burst per day detected
(depends of logN-logS extrapolation)
angular resolution of 22 arc-minute
giving positions of 1–4 arc-minute
onboard processing to provide prompt
arc-minute position to satellite ACS and
to the ground
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Swift Instrumentation
II. X-ray Telescope (XRT)
 Flight spare JET-X module
 15 arc-second half energy width
sharp core will yield arc-second locations
 3.5 m focal length
 Total effective area
110 cm2 at 1.5 keV
65 cm2 at 6 keV
XRT Mirror Module
 CCD array covers 0.2-10 keV band
use spare XMM chip
24 x 24 arc-minute field of view
Cooled to -80 degrees C
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Swift Instrumentation
III. UV-Optical Telescope (UVOT)
 Based on XMM OM to minimize cost and risk
 Covers 170 nm to 650 nm
 30 cm Ritchey-Chretien telescope
 24 mag in 1000 s with 17 arc-minute FOV
 Detector is image intensified CCD array
 Unique coverage 20-70 s after
burst trigger
 Positions to 0.3 arc-seconds using onboard
image registration
XMM OM
Filter Wheel
 UVOT will be simple reproduction of
XMM OM
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UVOT Performance
 Positions to 0.3 arc-seconds using onboard image registrations
 Filters give spectral/color information and allow redshift determination from Lyman edge detection
Measured UVOT Response
UVOT Sensitivity
Percent Transmittance
For V = 20 B star in 1000 s
get:
UVW2
UVM2
UVW1
680 cts
800 cts
1000 cts
Sensitivity to Ly-a cutoff:
UVM1 - UVM2
UVM1 - UVM1
U - UVW1
B-U
z ~ 1.5
z~2
z ~ 2.7
z ~ 3.5
Wavelength
UV and optical grisms with Dl of 0.5 nm and 1.0 nm, respectively, for Mb < 17
• IUE type resolution
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Swift
Multiwavelength Cascade of Images
Gamma Ray (arc-minute)
X-ray (2.5 arc-second)
HST, Keck,
etc.
UVOT
(0.3 arc-second)
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Observing Strategy
 Allow both onboard and external triggers (from, e.g., INTEGRAL)
 Slew to new burst as soon as possible
Time
S/C Event
Time
POC Event
0 s GRB
10 s Slew Begins
12 s BAT location distributed
~ 50 s GRB acquired
55 s XRT image
150 s UVOT finding
chart
1200 s XRT spectrum
62 s XRT location, BAT
lightcurves distributed
200 s Optical finding chart
distributed
1210 s XRT spectra distributed
7200 s UVOT filters
complete
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~ 10 s Ground station
pass
All burst data, New
observing program
uploaded
 Follow all afterglows for as long as they are visible
 typically Swift will be monitoring a few afterglows
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