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