Studying the Galactic Ridge Emission with SIMBOL-X

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Studying the Galactic Ridge Emission with SIMBOL-X

• Sandro Mereghetti
• IASF - Milano

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Galactic Ridge X-ray Emission

• X-ray emission extending along the Galactic plane
• Longitude extent /- 40 deg ? Inner Galaxy
  R 4 kpc
• Latitude extent few deg ? small scale
  height 100 pc
• High peak at GC
• Luminosity 2 1038 erg/s
• Intense emission lines

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• Double T NEI model
• Soft component kT0.8 keV
• Hard component kT7 keV

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20-40 keV
Lebrun et al. 2004 Nature
40-60 keV
GRXE resolved by IBIS above 40 keV
60 120 keV
120-220 keV
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IMAGING DIFFUSE EMISSION
NO IMAGING DISCRETE SOURCES ?
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Simbol-X contribution

1. Population studies in hard X-rays
2. Mapping of emission lines
3. Imaging-spectroscopy at gt10 keV with point
   sources removed

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1 ) Population studies

• Several hundreds of pointings at low Galactic
  latitude
• FoV p (0.1)2 0.03 square deg ? Sky
  coverage several square deg
• ? Sensitivity tens of mCrabs
• (100 x better than IBIS)
• ? 10 sources/square deg
• (2-10 keV)

? 100 serendipitous sources ..but how many in
the 10-40 keV ?
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2 ) Mapping of emission lines
Compare with XMM / EPIC ? Effective area
larger than EPIC pn at E gt4-5 keV ?
similar energy resolution ? similar angular
resolution ? much lower instrumental
background Anticoincidence system Soft
protons magnetic diverter ? better modelling
of continuum emission thanks to extended
energy range
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3 ) Spectroscopy above 10 keV
Done up to now only with collimated instruments
Difficult to correctly estimate point sources
contribution Deep pointings of selected regions
in Galactic Plane can for the first time properly
measure the GRXE spectrum Also the spatial
distribution, e.g. latitude dependence, can be
directly measured

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Simulation of 500 ks pointing with
Simbol-X spectrum of diffuse emission from 6
arcmin radius extraction region
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3 ) Spectroscopy above 10 keV
Done up to now only with collimated instruments
Difficult to correctly estimate point sources
contribution Deep pointings of selected regions
in Galactic Plane can for the first time properly
measure the GRXE spectrum Also the spatial
distribution, e.g. latitude dependence, can be
directly measured CAVEAT Accuracy depends
ultimately on good knowledge of instrumental
background It is essential to control the
systematics uncertainties

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• Formation flight can help

Mirror field of view
detector
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• Formation flight can help

detector
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• Formation flight can help

detector
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• Formation flight can help

detector
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• Formation flight can help

Mirror field of view
The external parts of the detection plane can
monitor the instrumental background
detector
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Conclusions

• The spectral/imaging capabilities of SX will
  allow for the first time detailed studies of the
  GRXE above 10 keV
• It will be possible to determine the contribution
  of hard X-ray sources and verify if a hot plasma
  is really needed
• These studies have obvious implications on our
  understanding of the X-ray emission from the
  Galactic Center region
• Several dedicated long (500 ks) pointings
  required in addition to results from
  serendipitous sources
• A small background level is not enough It is
  essential to be able to reproduce its spatial and
  temporal variations