4 research outputs found
QED and the High Polarization of the Thermal Radiation from Neutron Stars
Get PDFThe thermal emission of strongly magnetized neutron-star atmospheres is
thought to be highly polarized. However, because of the different orientations
of the magnetic field over the surface of the neutron star (NS), it is commonly
assumed that the net observed polarization will be significantly reduced as the
polarization from different regions will cancel each other. We show that the
birefringence of the magnetized QED vacuum decouples the polarization modes in
the magnetosphere; therefore, the direction of the polarization follows the
direction of the magnetic field up to a large distance from the stellar
surface. At this distance, the rays that leave the surface and are destined for
our detectors pass through only a small solid angle; consequently, the
polarization direction of the emission originating in different regions will
tend to align together. The net observed polarization of the thermal radiation
of NSs should therefore be very large. Measurement of this polarization will be
the first direct evidence of the birefringence of the magnetized vacuum due to
QED and a direct probe of behavior of the vacuum at magnetic fields of order of
and above the critical QED field of 4.4 x 10 13 G. The large observable
polarization will also help us learn more about the atmospheric properties of
NSs.Comment: 6 pages, 2 figures, minor changes to reflect accepted versio
The X-ray Polarization Probe mission concept
Get PDFThe X-ray Polarization Probe (XPP) is a second generation X-ray polarimeter following up on the Imaging X-ray Polarimetry Explorer (IXPE). The XPP will offer true broadband polarimetery over the wide 0.2-60 keV bandpass in addition to imaging polarimetry from 2-8 keV. The extended energy bandpass and improvements in sensitivity will enable the simultaneous measurement of the polarization of several emission components. These measurements will give qualitatively new information about how compact objects work, and will probe fundamental physics, i.e. strong-field quantum electrodynamics and strong gravity
