X-ray polarisation: Science

1
X-ray polarisation Science

• Accretion powered pulsars / high magnetic field
  neutron stars?X-ray beaming pattern
  (fan/pencil) is not known and will be determined
  from pulse phase resolved polarisation
  measurement.Rotation powered pulsars?The
  source of high energy emission is not known
  (polar cap / outer gap). Recent Fermi and Magic
  observations support outer gap model. Pulse phase
  resolved X-ray polarisation measurement of
  rotation powered pulsars is required.Black hole
  binariesMultiple sources of X-ray polarisation
  1) reflection of coronal hard X-rays from the
  accretion disk, 2) thermal disk emission can be
  partially polarised in highly inclined sources,
  3) in accretion disk around a highly spinning
  black hole, gravitational bending and reflection
  from the inner accretion disk can cause strong
  X-ray polarisation.SNR, Blazars, PWN can also
  have strong X-ray polarisation.Only one X-ray
  polarisation measurement of astronomical source,
  Crab (1976).

2
(No Transcript)
3
(No Transcript)
4
(No Transcript)
5
(No Transcript)
6
RRI Thomson X-ray Polarimeter

• Polarisation is unexplored in High Energy
  Astrophysics
• X-ray emission from the following processes
  should be polarised
• Cyclotron
• Synchrotron
• Non-Thermal Bremsstrahlung
• Scattering from non-spherical plasma
• These objects should produce polarised X-ray
  radiation
• Accretion powered pulsars
• Rotation powered pulsars
• Magnetars
• Pulsar wind nebulae
• Non-thermal supernova remnants
• Black holes, micro-quasars and active galactic
  nuclei

Measurement Technique Anisotropic Thomson
Scattering
Crab nebula is the only source for which X-ray
polarisation measurement exists. This was made in
1976 !! The GEMS mission, to be launched
in 2014 will work in a different energy band
of 2-10 keV
7
Development status

• A Thomson X-ray polarimeter has been designed,
  developed and successfully tested at RRI.
• These have been made
• Detectors
• Front end electronics
• Processing electronics
• Collimators with flat top response
• Test and calibration setup
• Rotational stage

Results
Power spectrum
Light Curve
Light Curve
Unpolarised source
Polarised source
Polarised source
8
X-ray polarimeter small satellite mission

• Key features of the polarimeter
• Minimum detectable Polarisation of 3
• at 5 sigma level for a 50 mCrab source
• No of sources 50
• Weight 110 kg
• Data rate 300 Mb per orbit
• Spacecraft
• Spinning satellite, 0.5 rpm
• Very long exposures, one week to one month
• Pointing accuracy 0.1 degree
• Equatorial orbit, less than 20 degree
• Altitude 500600 km

Collimator Scatterer Detectors