Kavli Affiliate: Herman Marshall
| First 5 Authors: Paolo Soffitta, Niccolò Bucciantini, Eugene Churazov, Enrico Costa, Michal Dovciak
| Summary:
Since the birth of X-ray Astronomy, spectacular advances have been seen in
the imaging, spectroscopic and timing studies of the hot and violent X-ray
Universe, and further leaps forward are expected in the future. On the other
hand, polarimetry is very much lagging behind: after the measurements of the
Crab Nebula and Scorpius X-1, obtained by OSO-8 in the 70s, no more
observations have been performed in the classical X-ray band, even if some
interesting results have been obtained in hard X-rays and in soft gamma-rays.
The NASA/ASI mission IXPE, scheduled for the launch in 2021, is going to
provide for the first time imaging X-ray polarimetry in the 2-8 keV band thanks
to its photoelectric polarimeter, coupled with ~25” angular resolution X-ray
mirrors. Its orders of magnitude improvement in sensitivity with respect to the
OSO-8 Bragg polarimeter implies scientifically meaningful polarimetric
measurements for at least the brightest specimens of most classes of X-ray
sources. In 2027, the Chinese-led mission eXTP should also be launched. In
addition to timing and spectroscopic instruments, eXTP will have on board
photoelectric polarimeters very similar to those of IXPE, but with a total
effective area 2-3 times larger. Building on IXPE results, eXTP will increase
the number of sources for which significant polarimetric measurements could be
obtained. However, further progresses, such as exploring a broader energy
range, considering a larger effective area, improving the angular resolution,
and performing wide-field polarization measurements, are needed to reach a
mature phase for X-ray polarimetry. In the first part of this White Paper we
will discuss a few scientific cases in which a next generation X-ray
Polarimetry mission can provide significant advances. In the second part, a
possible concept for a medium-class Next Generation X-ray Polarimetry (NGXP)
mission will be sketched.
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