rapid follow-up of gamma- ray bursts with watcher john french school of physics university college...
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Rapid follow-up of gamma-ray bursts
with WatcherJohn French
School of Physics
University College Dublin
Overview
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
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
Italian-Dutch satellite BeppoSAX first to accurately localise GRBs
First multi-wavelength counterparts detected: X-ray: 970111 Optical: 970228 Radio: 970508
BeppoSAX X-ray afterglow of 970228
Information from afterglows
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
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
Internal shocks:
γ-rays / prompt optical Reverse shock:
prompt optical / X-rays Forward shock:
afterglow (optical / X-ray / radio)
The role of robotic telescopes
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
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
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
041219: Optical flash (red) during primary γ-ray peak (black)
990123: Optical flash comes after secondary γ-ray peak
High redshift: GRB 050904
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
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
Launched 11/04, multi-wavelength 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)
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
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
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
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
Developed since 2000 by Czech BART group Sophisticated, reliable, controls wide range of
hardware Currently runs 6 telescopes on 3 continents
BART: Czech Republic BOOTES-1A & 1B: Spain (under repair) BOOTES-IR: 60cm, Spain FRAM: Pierre-Auger South, Argentina Watcher: South Africa
RTS2 Features
Enables fully automatic operation of a remote observatory without human intervention
2 observational modes: autonomous or user-specified schedules
Database of targets, observations, image data Customisable target-specific scripting Automatic astrometry of images (JIBARO) Communication with users via email/SMS
RTS2 Structure
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
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
Extra-solar planet transits / microlensing events
Blazar monitoring Observations of
INTEGRAL sources Coordinate with other
robotic telescopes