ECLAIRs scientific objectives my biased view as of may 2005 JeanLuc Atteia LATOMP, Toulouse, France

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ECLAIRs scientific objectives(my biased view
as of may 2005) Jean-Luc AtteiaLAT/OMP,
Toulouse, France
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1 - Gamma-ray bursts

• Gamma-ray bursts are remarquable astrophysical
  events, connected with many important issues of
  modern astrophysics.
• They are associated with powerful stellar
  explosions which emit an ultra-relativistic jet
  in our direction.
• They are detectable out to large distances (z15
  ?)
• They can be used to
• - Study the mechanisms driving the explosions of
  massive stars and the formation of stellar mass
  black holes
• - Study the physics of relativistic jets
• - Measure the history of the Star Formation Rate
• - Analyze the composition of the MIS in young
  galaxies
• -

Credit Jimmy Cox
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1 - Some pending issues

• GRB diversity
• - What is the true extent of the GRB population ?
  
• - What is a GRB ?
• The physics of relativistic jets
• - Radiation mechanisms, efficiency, Ep-Eiso
  correlation, polarization of the prompt emission
  
• GRB progenitors the GRB-SN connection
• - Nature of the progenitors, nature and lifetime
  of the central engine
• GRBs and cosmology
• - GRB luminosity indicators
• - The SFR
• - GRBs from pop III stars ?
• - Constraints on the scale of the quantum gravity

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1 - Some pending issues

• The origin of Short / Hard bursts
• GRB emission outside the electromagnetic
  spectrum neutrinos, cosmic rays, gravitational
  waves

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2 - Some basic facts

• The study of GRBs will continue after SWIFT !
• All known GRBs have been detected in space need
  for a space-born mission after SWIFT ? ECLAIRs
• GRB alerts are currently distributed within a few
  tens seconds of the burst ? ECLAIRs should
  continue along this line
• Trigger criteria are fundamental, they determine
  which subsample of the GRB population will be
  available to observers on the ground.

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2 - Some basic facts

• GRB follow-up by ground observatories is
  absolutely required, GRBs are certainly the
  astrophysical events for which the synergy
  between the ground and space is the highest.
• Better localizations increase the rate of success
  of afterglow searches
• lt50 for 10 80 for 1-2
• GRBs without a redshift are not very useful.
• One out of 6 localized GRBs has a redshift in
  pre-SWIFT missions.
• High-z GRBs (z5-10) may exist, but have not been
  detected yet.

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2 - Observing GRBs

• Gamma-ray bursts are complex events, both
  temporally and spectroscopically.
• GRBs include various phases the prompt emission,
  the afterglow, the supernova (?).
• The environment of GRBs (the immediate
  surroundings and the host galaxy) plays an
  important role in the development of the
  afterglow (external and reverse shock) and in its
  detectability (dust).
• Observations must cover all these phases and be
  multi-wavelength. Large telescopes have been
  crucial in solving the GRB mystery.

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2 The prompt emission

• The detection of the prompt emission allows
• The detection in space
• The localization of the source
• The measure of the high energy energy spectrum
  Fluence Epeak
• The measure of the broad-band spectrum
• The measure of the light curve
• Scientific questions addressed with the prompt
  emission
• GRBs statistics
• The Epeak-Eiso correlation
• The radiation mechanisms
• Search for spectral components (thermal vs
  non-thermal)
• The emission of the reverse shock and the
  beginning of the afterglow

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3 - ECLAIRs

• Originally ECLAIRs had two main objectives
• Providing fast GRB localizations after SWIFT
• Measuring the broad-band spectrum (optical to
  100s keV) of the prompt emission
  (complementarity with GLAST)
• This led to a mission with a large effective area
  (to provide 50 GRBs/yr at least) and a low energy
  threshold (to measure the spectrum of the prompt
  emission at X-ray energies, where it was not well
  known).
• The discovery of X-Ray Flashes, which are faint
  soft events, strengthens the case for a mission
  with a large effective area and a low energy
  threshold.
• It is clear that ECLAIRs is also very well suited
  for the detection of GRBs at high redshift, which
  are also faint soft bursts

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3 - ECLAIRs and High-z GRBs

• The redshift range of GRBs with a redshift is 0.1
  to 4.5
• ( GRB 980425 at z0.0085)
• We have only two redshifts of XRFs (z0.25,
  z0.21)
• We have no redshift of a short/hard burst
• A mission with a large effective area and a low
  energy threshold is best suited to detect GRBs
  over a wide range of redshifts since
• XRFs are intrinsically faint and soft, and
  probably more abundant spatially than hard GRBs.
  ECLAIRs will detect many nearby XRFs.
• Bright GRBs at high redshift are seen as faint,
  soft events. ECLAIRs should be able to detect a
  few high-z GRBs.

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High-z GRBs
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3 - The importance of High-z GRBs

• High-z GRBs have the potential to point to us
  some of the most distant objects in the universe.
  
• GRBs allow the observation of young star-forming
  galaxies otherwise inaccessible to observation.
• Detection of population III objects ?
• The history of the Star Formation Rate beyond
  redshift 5
• Luminosity evolution of GRBs
• Complementary of SN Ia for the determination of
  cosmological parameters

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3 - Identifying High-z GRBs

• GRBs beyond z 7 will have no detectable optical
  emission
• Present day data suggest that 10-15 of detected
  GRBs (at most) can have redshift gt 5.
• High-z GRBs can only be identified during the
  hours (at most days) following the burst (host
  galaxies may be too faint).
• Require the capability to trigger on long soft
  bursts.
• Redshift indicator to pre-select high-z
  candidates.
• Accurate localizations for NIR instruments and/or
  X-ray follow-up.

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Science studies during phase A

• Get reliable estimations of the number of GRBs
  detected and localized with the CXG, including
  XRFs, short/hard GRBs, and GRBs beyond z5. Check
  with SWIFT, INTEGRAL (coded mask), and HETE-2
  (XRFs).
• Analyze trade-offs between FOV, sensitivity, and
  localization accuracy.
• Study ways of improving the localization
  accuracy.
• Define the FOV of the optical instrument.
• Construct a redshift indicator for ECLAIRs GRBs.

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4 - Conclusions

• ECLAIRs must provide fast accurate GRB positions
  after SWIFT.
• ECLAIRs must detect all types of GRBs (classical,
  XRFs, S/H), and GRBs at high redshift.
• The physics of the prompt emission is a driver of
  the mission (in combination with GLAST) it
  requires a broad energy coverage (optical to
  100s keV), the capability of measuring Epeak
  (over more than one decade in Epeak), and the
  measure of the redshift.
• High-z GRBs may become a prime objective for
  ECLAIRs, thanks to its large effective area, and
  its energy range extended to low energies.
• The large effective area is required by all the
  scientific objectives above.
• The low energy threshold is required for the
  following goals
• Capture the physics of the prompt emission
• Detect High-z GRBs
• Detect and study XRFs
• Accurate localizations (1-2) are needed to
  identify High-z GRBs and XRFs.

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Outline

• 1- The astrophysics of GRBs
• 2 - Observing GRBs
• 3 ECLAIRs (and high-z GRBs)
• 4 - Conclusions

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2 - Observing GRBs

• The afterglow
• Photometry
• Spectroscopy redshift
• High resolution spectroscopy GRB surroundings
  MIS
• The host

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The diversity of GRBs

• The prompt emission, the afterglow and the
  underlying supernova exhibit a great diversity
• XRFs vs normal GRBs and short/hard GRBs
• Bright vs dark afterglows
• Presence or lack of supernova light
• Unifying relations
• Observations Amati relation ? Constant energy
  reservoir ?
• Theory jet opening angle ? Rotation of the
  progenitor ?

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GRB diversity prompt emission

• GRBs include long short bursts
• Long GRBs include hard soft bursts (XRFs, Ep lt
  50 keV)
• XRFs have been discovered recently
• The origin of Ep is not fully understood
• The boundary of the population has not been
  reached

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Unifying relations ?
Lamb et al. 2004
Berger et al. 2003
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Exploring The GRB Family

• GRBs / X-Ray Flashes / SN Ibc
• It is essential to fully sample the GRB family
• Look for faint soft bursts
• Optically selected GRB afterglows
• X-ray selected GRB afterglows
• Identify GRB progenitors
• Identify GRB descendants (W49B ?)
• Place of Short / Hard GRBs ?

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GRB diversity conclusions

• Even after SWIFT, and especially in the GLAST
  era, it will be important to fully sample the GRB
  family.
• ECLAIRs must allow the detection and localization
  of all types of GRBs with Epeak gt 10 keV (tbc),
  and the fast identification of their afterglow
  (redshift, spectro-temporal properties of the
  afterglow, SN light).
• ECLAIRs should allow the measure of Epeaks over a
  broad range (more than 1 decade).
• The sensitivity ECLAIRs should allow the
  detection and localization of 200 GRBs during the
  mission (tbc) and not less than 50 GRBs/yr (tbc).
• The precision of localization must permit the
  follow-up of ECLAIRs GRBs by medium size
  telescopes equiped with optical and NIR cameras.