GammaRay Burst Afterglows Prospects for the NSU Rapid Response Robotic Telescope

1
Gamma-Ray Burst AfterglowsProspects for the
NSURapid Response Robotic Telescope

• David McDavid
• Department of Astronomy
• University of Virginia
• June 22, 2004

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Outline

• RRRT Collaboration
• Observatory plan
• The GRB Coordinates Network
• Examples of GRB optical afterglow monitoring
• The Supernova Connection
• Theory of the origin of GRB OAs
• Synchrotron radiation
• Why study polarization of OAs?
• A lesson from Kepler's Supernova Remnant
• Observational technique imaging polarimetry
• Reality Check
• Acknowledgements

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RRRT Collaboration

• Norfolk State University
• University of Virginia
• NASA Goddard Space Flight Center

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NSU RRRT ObservatoryFan Mountain, Virginia

• 0.6-m (24-in) aperture reflecting
  telescope
• CCD camera for optical imaging and
  polarimetry of GRB afterglows
• connection to Swift for rapid response to
  GRB trigger
• robotic (automatic) and remote (NSU)
  control modes

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GCNThe GRB Coordinates Network

• (an example based on pre-Swift configuration)

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Decay of an Optical Afterglow(HST Photometry
Example)

• GRB 990123
• power law decay of brightness f(t)
  f0t -a
• breaks (changes in value of a) give
  info on changes of physical conditions
  in radiation source

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Small Telescope Success Story!!GRB 030329 SN
Connection Burstnearby (2.3 Gly) ?
exceptionally bright

• monitoring with small telescopes
  beginning 76 min after the burst
• apertures 20-60cm (8-24in)
• continuous data for 11 hours
• result evidence for deviation from
  power-law decay in early afterglow

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The Supernova ConnectionGRB 030329 / SN 2003dh

• One of the most luminous supernovae
  on record, and the one with the highest
  measured velocities, was
  observed to accompany a GRB.
• This was interpreted as evidence that GRBs
  are associated with the deaths of massive
  stars (core collapse).

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Origin of Optical Afterglows(currently accepted
working hypothesis)

• rotating black hole remnant of a collapsed
  massive star (double?) produces jet of
  relativistic electrons, positrons, and ?-rays
• OA is synchrotron emission from shock front
  between jet and surrounding medium

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SynchrotronRadiation

• Synchrotron radiation is produced by
  relativistic charged particles in
  strong magnetic fields.
• The radiation is beamed along the velocity
  vector of the charged particle.
• A characteristic spectrum results from the
  frequency of pulsation of the beam across
  the line of sight with each spiral
  revolution.
• The radiation is linearly polarized
  perpendicular to the magnetic field.

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Why study polarization of OAs?

• Spectra and light curves of GRB afterglows
  match a synchrotron radiation
  model over a wide range of frequencies.
• Synchrotron radiation is highly polarized
  (up to 70), as verified in many
  astrophysical cases.
• Optical polarization of GRB afterglows
  is small, (rarely greater than 2),
  so theories of the origin of OAs must
  explain this.

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Kepler's Supernova Remnantpolarization dilution
by spatial averaging

• GRB afterglows appear as unresolved point
  sources of light because they are so distant.
• Localized patches may have strong magnetic
  fields and high polarization, but the net
  polarization is small unless the fields are
  globally aligned.

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Observational TechniqueImaging Polarimetry
UsingDouble Refraction

• An optically corrected calcite prism
  produces double polarized images
  which can be analyzed by aperture
  photometry to give the polarization of
  each object in the field.
• Errors from seeing and transparency
  variations vanish since they affect
  both images equally.

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Polarization of the OpticalAfterglow of GRB
030329
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Reality Check

• GRB afterglows are difficult to observe with
  small telescopes since most of them are faint.
• Swift pointing is an advantage.
• GRB polarimetry data are scarce, inconclusive,
  and subject to error in statistical analysis.
• There is much room for improvement.
• Interpretation of GRB polarimetry is complicated
  because multiple physical effects may be
  present
• intrinsic
• interstellar (Galactic host galaxy)
• associated supernova
• Any variability must be due either to the GRB or
  to the associated SN.

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Acknowledgements

• Official NASA Swift Home Page (http//swift.gsfc.n
  asa.gov/)
• The GRB Coordinates Network (http//gcn.gsfc.nasa.
  gov/)
• The Decay of an Optical Afterglow (HST
  Photometry)
• Andrew Fruchter, STScI
  
  (http//www-int.stsci.edu/fruchter/GRB/990123/
  index.html)
• Small Telescope Success Story
• Uemura et al. 2003, Nature, 423, 843
• Rie Sato, Tokyo Institute of Technology
  
  (http//www.hp.phys.titech.ac.jp/nkawai/030329/ind
  ex_e.html)
• The Supernova Connection
• Hjorth et al. 2003, Nature, 423, 847
• NASA Goddard Space Flight Center Top Story
  
  (http//www.gsfc.nasa.gov/topstory/2003/0618rosett
  aburst.html)
• Origin of Optical Afterglows
• Meszaros, P. 2001, Science, 291, 79
• Penn State Swift Page (http//www.swift.psu.edu/)
• Synchrotron spectra and light curves of GRB
  afterglows
• Panaitescu, A. and Kumar, P. 2001, ApJ, 554, 667
• Kepler's Supernova Remnant
• DeLaney et al. 2002, ApJ, 580, 914
• XMM-Newton X-ray Observatory
• Imaging Polarimetry by Double Refraction