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Rapid follow-up of gamma-ray bursts with Watcher

Rapid follow-up of gamma-ray bursts with Watcher. John 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

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Rapid follow-up of gamma-ray bursts with Watcher

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  1. Rapid follow-up of gamma-ray bursts with Watcher John French School of Physics University College Dublin

  2. 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

  3. 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

  4. 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

  5. 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

  6. 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

  7. Fireball model • Internal shocks: γ-rays / prompt optical • Reverse shock: prompt optical / X-rays • Forward shock: afterglow (optical / X-ray / radio)

  8. 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

  9. 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

  10. ROTSE Observations of GRB990123

  11. 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

  12. 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

  13. 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

  14. Afterglow: GRB 060206 • Afterglow observed by RAPTOR beginning 48.1 min. after trigger (T90 ~ 7s) • 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

  15. 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)

  16. 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

  17. 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

  18. Watcher: Site

  19. Watcher Schematic

  20. 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)

  21. 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)

  22. 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

  23. 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

  24. 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

  25. 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

  26. Future • Extra-solar planet transits / microlensing events • Blazar monitoring • Observations of INTEGRAL sources • Coordinate with other robotic telescopes

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