Italian participation to the SVOM mission for GRB studies

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Italian participation to the SVOM mission for GRB
studies

• S.Mereghetti
• INAF-IASF Milano

M.Fiorini, A.De Luca, A.Tiengo, N.La Palombara,
M.Uslenghi, G.Vianello, A.Zambra, P.Caraveo,
F.Perotti, A.Paizis (IASF-Milano) S.Campana,
V.Cotroneo, S.Covino, G.Ghirlanda, G.Ghisellini
(Oss.Astrononico Brera) L. Amati, M.Trifoglio,
A.Bulgarelli, F.Gianotti (IASF-Bologna) L.Stella,
D.Guetta, A.Antonelli (Oss. Astronomico Roma)

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• Gamma-ray bursts are remarkable 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 (zgt10)

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GRB are useful for many topics, including -
mechanisms driving the explosions of massive
stars and the formation of stellar mass black
holes - physics of relativistic jets - history
of the Star Formation Rate - composition of the
ISM in young galaxies - cosmological probes
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SVOM

• CNES (France) CNSA (China) mission for GRB
  studies
• Launch in 2012
• Heritage of the ECLAIRs microsatellite studied
  in 2004-2006 by CNES
• Italian groups participated to the ECLAIRs study
  and expressed interest in a participation to SVOM
  
• Study funded by this ASI contract in the New
  Opportunities workpackage

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Main SVOM scientific driver
QUALITY rather than QUANTITY
Large samples of GRBs are already available, but
detailed spectral information and redshift are
known only for a limited number of GRBs ?
Multiwavelength approach with dedicated ground
based facilities
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• SVOM scientific requirements
• 1) Obtain the redshift for the majority of the
  detected bursts
• ? Provide quickly accurate GRB positions
• Optimize pointing strategy for ground telescopes
• Optimize detection of high redshift GRBs
  (trigger logic, soft E range)

Swift detected a larger number of high redshift
GRBs than previous missions But z is known for
only lt30 of Swift GRBs !!
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• SVOM scientific requirements
• 1) Obtain the redshift for the majority of the
  detected bursts
• ? Provide quickly accurate GRB positions
• Optimize pointing strategy for ground telescopes
• (cfr. redshift is known for only lt30
  of Swift GRBs !!)
• 2) Derive the GRB spectral parameters, E peak
• Broad energy range
• high-energy spectrometer
• (cfr Epeak is measured only for 15 of
  Swift GRBs )

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Epeak is a fundamental quantity in all empirical
correlations to use GRBs as standard candles
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GRB with 15-150 keV fluence 10-6 erg cm-2 and
Ep300 keV.
Pow.law fit
Pow.law fit
Spectral studies with Swift/BAT (and INTEGRAL )
suffer from the limited energy range and poor
sensitivity at high E
Addition of a high E detector (e.g. Scintillator)
is required to measure spectral curvature
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• SVOM scientific requirements
• 1) Obtain the redshift for the majority of the
  detected bursts
• ? Provide quickly accurate GRB positions
• Optimize pointing strategy for ground telescopes
• (cfr. redshift is known for only lt30
  of Swift GRBs !!)
• 2) Derive the GRB spectral parameters, E peak
• Broad energy range
• high energy spectrometer
• (cfr Epeak is measured only for 15 of
  Swift GRBs )
• 3) Allow afterglows detection with a telescope
  optimized in the red part of the optical range
• (cfr. Swift UVOT is sensible only in the
  blue / UV)

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Prompt dissemination of the GRB parameters
GRB
VHF network of ground stations X band
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Pointing strategy anti solar
SVOM orbit (i 30)
The center of the SVOM field of view will be well
above the horizon
of large ground based telescopes all located at
tropical latitudes
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Possible Italian Contributions

• full responsibility for the realization of an
  imaging Soft X-ray Telescope on SVOM
• design and procurement of the digital electronics
  of the CXG instrument.
• contribution to the design and development of the
  on-board triggering software for the CXG
• contribution to the design and calibration of the
  GRM
• contribution to the realization and operations of
  a network of ground based robotic telescopes
• participation to the ground segment with the
  Malindi antenna and ASI Science Data Center

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CXG 4-300 keV
The main requirement for the SXC was to improve
the GRB localizations
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Proposal for Italian contribution to the SVOM
payload
X
Replace the coded mask SXC with a soft
X-ray telescope
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Focal length 1 m
Radiator
X-ray Imager for Afterglow Observations
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Swift showed that virtually all GRB have bright
X-ray afterglows
X-rays detected in 90 of GRB (non detections
only when rapid repointing not done)
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PRELIMINARY OPTICS DESIGN H 30 cm Ø 14 22
cm Au coating Ang. Resol 30 HEW 11 shells
0.3 mm thickness 5 kg (mirrors only)

Focal length 100 cm
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XIAO expected count rates(0.2- 5 keV)

• 1 mCrab (2x10-11 erg /cm2/s 2-10 keV)
• NH 0 ? 4 ct/s
• NH 3 1020 cm-2 ? 1 ct/s
• NH 3 1021 cm-2 ? 0.4 ct/s

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XIAO Focal Plane
Back-thinned (40 mm) back illuminated CCD Frame
transfer 256 x 256 pixels Pixel size 26
mm 5.4 arcsec
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Simulations of different time intervals assuming
the X-ray lightcurve of a typical afterglow (GRB
050219A)
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Very low background

• Short Focal Length ? small spot area
• HEW30 arcsec ? 0.2 arcmin2 0.017 mm2
• BACKGROUND components
• Particles 2 10-3 cts / cm2 s keV ? 5
  10-7 ct/s (0.5-2 keV)
• 
  16 10-7 ct/s (0.2-5 keV)
• CXB (extragalactic) 2.3 10-5 ct/s
  (0.2-5 keV)
• Soft diffuse (local galactic)
  3.5 10-5 ct/s (0.2-5 keV)
• ? Particle BKG negligible compared to sky bkg
• Total bkg lt 6 10-5 ct/s ? 6 counts in 100
  ksec !!

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Example of NON-GRB Science 1 - Blazars
Simultaneous X-ray and optical observations to
understand origin of second peak in spectral
energy distribution
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Example of NON-GRB Science 2 - Active
stellar coronae
Flares are the most spectacular manifestation of
stellar magnetic activity Simultaneous multi-l
observations of flares crucial to test flare
models very relevant to understand coronal
heating mechanisms Very few simultaneous data
secured so far because of logistic/observational
difficulties (only 3 cases so far!!)SVOM
multi-l capabilities will allow simultaneous
optical-X-ray obsevations of flares for different
classes of active stars
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Example of NON-GRB Science 3 - Cataclysmic
Variables
Dwarf Novae show recurrent (from weeks to
months), large outbursts
Multi-l simultanoeus observations, unveiling time
behaviors in different ranges (including QPOs),
crucial to test disk instability model for
outbursts.
So far only fragmented (nearly) simultaneous data
available due to difficulties in scheduling
175 dwarf Novae known at bgt30º
SS Cyg X-rays delayed wrt. Optical Soft/Hard
X-ray anticorrelation
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Summary of XIAO performances

• Energy range 0.3-2 keV
• Field of view 23 x 23 arcmin2
• Ang. Resolution 30 arcsec HEW
• Effective area 80 cm2 _at_ 1.5 keV
• Localiz. Accuracy 10 arcsec for 5s
  source lt 5 arcsec for gt10s source
• Sensitivity (5s) 10 mCrab in 10 s 5-10
  mCrab in 10 ks
• Throughput 1 mCrab 0.4 ct/s for NH3x1021
  1 ct/s for NH3x1020
• Energy resolution 150 eV FWHM _at_ 1.5 keV
• Time resolution 10 ms in standard
  mode 0.1 ms in timing mode

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Summary of SVOM mission

• Mission design
• Orbit lt30 deg inclination, lt600km altitude,
  circular
• Mission lifetime 3 years 2 years( extend life
  time)
• Anti-Solar Pointing strategy.
• Spacecraft Platform, 3 axis stabilized
• Mass Payload 360 kg
• Power payload 312 W
• 68 passes per day on X-band, 2 passes per day on
  S-band, real time VHF link
• Instruments
• GRM Provide GRB detection in gamma-ray band, FOV
  89ºx89º , 2 detectors
• CXG generate GRB alert in hard X-ray band, FOV
  90ºx90º, 10 arcmin location accuracy.
• XIAO localize GRB afterglow in X-ray band, FOV
  23x23 arcmin,
• VT GRB onboard follow up observation. 21x21
  arcmin FOV, 2 bands.

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Conclusion

• Addition of XIAO is a major improvement of SVOM
  capabilities for both GRB and non-GRB science
• Relatively small investment allows a qualified
  participation with a large scientific return to a
  mission of great interest for the Italian
  community

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EXTRA SLIDES
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XIAO X-ray Imager for Afterglows
Observations
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CXG Camera X - Gamma
Coded mask imaging ? GRB trigger and
localization Same concept of SAX/WFC -
INTEGRAL/ISGRI - Swift/BAT
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2-D coded mask (30 transparency)
Passive shield to block X-ray background
200 modules of 48 CdTe semi-
conductor detectors (4mm4mm)
Useful area 1024 cm2
Field of view 2 sterad (90x90)
Energy range 4 to 300 keV
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CXG anticipated performances
GRBs detected with SNR gt 5 localized with an
error lt 10 arcmin
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GRM the Gamma-Ray Monitor
Scintillation (phoswich) detector
NaI (10 mm thick) CsI (40 mm thick)
Useful area 280 cm2 per module
Spectral domain 200 keV to 5 MeV
Enable measurements of Epeak up to 500 keV
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VT the Visual Telescope
Aperture size 450 mm
F number 9
Field of view 21' 21'
Spectral domain 400-600 nm 650-900 nm
Afterglow emission detection up to MV 23 (300 s
exposure)
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Development plan
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• XIAO proposal consortium

• Industries
• Thales Alenia Space Italia (ex Laben)
• Media Lario
• BCV Progetti

• INAF
• IASF Milano
• Osservatorio Astronomico Brera
• IASF Bologna
• Osservatorio Astronomico Roma

• Participation of other INAF structures is welcome