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Rapid follow-up of gammaray bursts with Watcher
John French
School of Physics
University College Dublin
Overview
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Background on multi-wavelength
observations of GRBs and their afterglows
and what we can learn from them
Where robotic telescopes fit into the picture,
and some results obtained from small robotic
telescopes
The Watcher instrument, software and site
Multi-wavelength observations of GRBs
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Most astrophysical sources are studied over
a broad spectral range during a long
observational period
GRBs were discovered in late 60’s, no
counterparts at other wavelengths observed
until 1997
Multi-wavelength observations constrained
models and continue to provide new
information
First afterglow detections
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Italian-Dutch satellite
BeppoSAX first to
accurately localise
GRBs
First multi-wavelength
counterparts detected:
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X-ray: 970111
Optical: 970228
Radio: 970508
BeppoSAX X-ray afterglow
of 970228
Information from afterglows
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Measurement of redshifts finally confirmed
cosmological origin of GRBs
Fireball model fits observations
GRBs occur in galaxies
Ejecta moves relativistically
Some GRBs may be associated with death of
high-mass stars
Fireball model
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Large quantity of energy (~ 1051 - 1054 ergs)
released very rapidly (~ 0.1 - 100 sec.) in a
compact source (~ 106 cm)
Jet of highly relativistic ejecta emitted (Γ >
100)
Collisions within ejecta produce γ-rays and
prompt optical/X-ray emission
Blast wave created when ejecta meets local
medium produces afterglow
Fireball model
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Internal shocks:
γ-rays / prompt optical
Reverse shock:
prompt optical / X-rays
Forward shock:
afterglow (optical / Xray / radio)
The role of robotic telescopes
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HETE and INTEGRAL missions provided
accurate localisations rapidly
Unpredictable transient nature, short duration
Bright (mv~9–18 mag.) optical flash predicted
Ideally suited to follow-ups with small robotic
telescopes
ROTSE, LOTIS, RAPTOR, PROMPT, TAROT
Prompt emission: GRB990123
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First GRB with optical detection while burst
was still in progress
ROTSE, 4 x 200mm telephoto lenses
First image 22 s. after trigger (T90=110 s.)
8.9 mag. optical flash, z = 1.6 → brightest
object ever observed
Optical emission uncorrelated with γ-rays
→ reverse shock
ROTSE Observations of GRB990123
GRB 041219
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First prompt optical detection since 990123
RAPTOR, 40cm, New Mexico
First image 115 s. after trigger (T90 = 520s),
peak mr = 18.6
Similar γ-ray light curve to 990123, but with
correlated optical emission
Internal shocks driven into burst ejecta by
variations in central engine
041219 and 990123 in γ-rays and optical
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041219: Optical flash
(red) during primary γray peak (black)
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990123: Optical flash
comes after secondary
γ-ray peak
High redshift: GRB 050904
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z = 6.29, second most distant object ever
observed, universe at 6% of current age
TAROT 25cm, 86 s. after trigger (T90 = 200s),
peak mI = 14.1
Extremely bright X-ray peak temporally
coincident with optical flash
Possible reactivation of central engine
Afterglow: GRB 060206
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Afterglow observed by RAPTOR beginning
48.1 min. after trigger (T90 ~ 7 s)
Flux rises sharply by ~1 mag., peak at ~16.4
mag. 60 min. after trigger → never seen
before in optical
Subsequent decay fit by power-law model
The SWIFT mission
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Launched 11/04, multiwavelength mission
γ-ray (BAT), X-ray (XRT),
UV & optical (UVOT)
Rapid localisations ~ 3
arcmin. with BAT
0.3 – 0.5 arcsec. with
XRT/UVOT
148 Bursts detected since
launch ~ one every 3 days
(61 with optical transients)
Gamma-ray burst Coordinates Network
(GCN)
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Automated system
to rapidly distribute
GRB positions to
sites worldwide via
the internet
Reporting of
observations via
GCN Circulars
allows
coordination of
subsequent
observations
Watcher: Site
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Boyden Observatory, South Africa (29°S ,26°E)
Altitude 1387m, ~300 clear nights/year
Accessible: 24km from Bloemfontein
Manned site, support from University of the
Free State Physics Dept. and technicians
Microwave link to University network (64 KB/s)
1.6m telescope available for coordinated
observations
Watcher: Site
Watcher Schematic
Watcher: Instrument
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40cm, f/14.25
Cassegrain telescope
Apogee AP6e CCD,
1024x1024 24µm
pixels, ~1.5 s. readout
15’ x 15’ FOV,
0.85”/pixel
Fast-slewing robotic
mount (Paramount ME)
Focuser, filter wheel
(BVRI filters)
Watcher: Hardware
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Motorised roll-back roof with custom control
electronics
Weather station: precipitation, wind,
cloud cover
Uninterruptible power supply
Webcam
2 PCs running Linux (400 GB storage
capacity)
RTS2 Software
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Developed since 2000 by Czech BART group
Sophisticated, reliable, controls wide range of
hardware
Currently runs 6 telescopes on 3 continents
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BART: Czech Republic
BOOTES-1A & 1B: Spain (under repair)
BOOTES-IR: 60cm, Spain
FRAM: Pierre-Auger South, Argentina
Watcher: South Africa
RTS2 Features
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Enables fully automatic operation of a remote
observatory without human intervention
2 observational modes: autonomous or userspecified schedules
Database of targets, observations, image data
Customisable target-specific scripting
Automatic astrometry of images (JIBARO)
Communication with users via email/SMS
RTS2 Structure
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Groups of C++ executables communicating
over TCP/IP via custom library
rts2-centrald (observatory control centre)
device daemons (hardware interface)
executing daemons (selector, executor,
process images / GRB alerts)
client-side monitoring programs
database querying & update tools
Watcher Commissioning
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Operational since late
March ‘06
Rapid response times
(11 s. and 18 s.)
during installation
GRB 060413, first
observations 4h13m
after trigger, no new
source down to 16.5
mag. (GCN 4960)
First light image of M42
Future
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Extra-solar planet
transits / microlensing
events
Blazar monitoring
Observations of
INTEGRAL sources
Coordinate with other
robotic telescopes