Soft X-ray Polarimeter Concepts
A Narrow-band Approach
The PLEXAS design was proposed to NASA as
a small explorer in 1998. A paper on this approach was presented at the
2002 SPIE meeting.
A Broad-band Approach
The basic concept was outlined in
Paper 1 (pdf),
presented at the SPIE meeting in 2007.
This approach could be used to measure X-ray polarization across
the band from 0.2 to 0.8 keV.
Paper 2 (pdf)
was presented at the SPIE meeting in 2008,
was presented at the Rome X-ray Polarimetry meeting held in April, 2009,
and Paper 3 (pdf)
was presented at the SPIE meeting in 2010.
This approach could be implemented as a small mission or used on
a large X-ray astronomy mission such as
Examples of targets for both instruments:
- BL Lac Objects with relativistic, magnetized jets which
should be polarized up to 60 %
- Isolated pulsars such as PSR 0656+14, which have a strong magnetic
field which will polarize the surface emission at the 20-50% level
- Quasars and Active Galactic Nuclei (AGN) whose disks will show
polarized emission due to electron scattering up to 12%
A laboratory for demonstrating critical components of this design
is also described in Paper 3. A small scale version of the laboratory work was
started in the summer of 2009 with MIT Kavli internal funding
and now has NASA APRA funding.
pdf for a presentation at the 2013 SPIE meeting in San Diego and
see this pdf
for the submitted paper with more details.
A successful polarization test, as
published in 2013.
The polarization source is 100% polarized
and its orientation was rotated through 150 degrees to demonstrate that the
system can produce, rotate, and measure polarized X-rays.
More recently, we have entered Phase III, where we are using
laterally graded multilayer coated mirrors (LGMLs). We show results
paper, published in the proceedings of the
2014 SPIE meeting (volume 9144), held in Montreal, Canada.
New LGMLs were obtained from Reflective X-ray Optics
and measured at the
(Advanced Light Source in Berkeley.
published in 2015.
A sounding rocket proposal has been submitted to NASA. Some
of the engineering renderings and raytrace results are shown in a
to the eXTP Mission Design Coordination Meeting (held 3/21-23/17 in Beijing, PRC)
about providing a similar instrument for
The MIT X-ray Polarimetry Beamline. The polarizing source is at left, the grating
chamber is in the center of the beamline and the detector chamber is at right.
The entire beamline is about 19 m long.
The polarizing source. The (unpolarized) X-ray source is the chamber at right
that is horizontal and parallel to the beamline. A laterally graded
multilayer coated mirror is installed in a chamber at the intersection of
the source output and the beamline. The mirror is mounted at
the end of a vertical shaft, rotatable by the manipulator that is pointed slightly
to the left of the camera. A linear drive (at right) compresses the bellows,
moving the mirror's position in the chamber to select different multilayer
coating periods for optimal reflectivity and polarizing the reflected X-rays.
The detector chamber. The X-ray sensitive CCD is at the left end of the system,
to which is attached a liquid nitrogen feed line for cooling to -75deg C.
The detector electronics are in the foreground on a cart with four power
supplies. The detector control and analysis computer is on the table.
For more information, see
Herman Marshall, or send e-mail
to hermanm -at- space.mit.edu.
Updated: March 22, 2017