X-ray polarisation: Science Accretion powered pulsars / high magnetic field neutron stars: X-ray...

X-ray polarisation: ScienceAccretion 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 binaries:Multiple 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).

Accretion powered pulsars

Rotation powered pulsars & magnetars

X-ray polarisation in black hole accretion disk

Test of strong field gravity

X-ray polarisation measurement techniques

Bragg Reflection

Thompson Scattering

Photoelectron imaging

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

RRI Thomson X-ray Polarimeter

Measurement Technique Anisotropic Thomson Scattering

Crab nebula is the only source forwhich X-ray polarisation measurementexists. This was made in 1976 !! The GEMS mission, to be launched in 2014 will work in a different

energy band of 2-10 keV

A Thomson X-ray polarimeter has been designed, developed and successfully tested at RRI.These have been made:

DetectorsFront end electronicsProcessing electronicsCollimators with flat top responseTest and calibration setupRotational stage

Development status

Unpolarised source Polarised source

Power spectrum

ResultsLight Curve

Polarised source

Light Curve

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: 500—600 km

X-ray polarimeter small satellite mission

Collimator

Scatterer

Detectors