Madrid, 26 (European press)
X-ray pulsars are strongly magnetized neutron stars driven by accretion of gas from a nearby companion star and are among the most prominent sources in the X-ray sky. NASA, which began operations in late 2021, is now offering a new perspective on these objects. IXPE measures X-ray polarization and is used to measure the polarization of an X-ray pulsar for the first time, allowing its basic geometry to be restricted.
Viktor Doroshenko of the University of Tübingen, Germany, lead author of the Astronomy in Nature paper, says in a statement.
The average degree of polarization of about 9% measured by IXPE at very high resolution has been shown to be well below 80% optimistically by some theorists.
“This significant discrepancy indicates that current models of radiation transmission in strongly magnetized plasma are limited to the poles of a neutron star and that our ideas about the geometry and structure of the emission region in Hercules X-1 and possibly other pulsars must be largely revised…in light of the IXPE findings,” Adds Juri Potanin of the University of Turku in Finland, chair of the IXPE working group that studies neutron star accretion.
By observing the differences in the angle of polarization during the spin phase, it was possible to measure the angle between the spin axes and the magnetic dipole, an elementary piece of information for any emission model for such objects. Combined modeling of the new X-ray polar observations and older optical polarization measurements obtained at the Scandinavian optical telescope also unequivocally showed that the pulsar’s rotation axis is not parallel to the orbital angular momentum, a strong indication that the neutron star is advancing like a propeller wheel. .
The Neutron Star-Free Initiative was previously called upon to explain the observed quasi-uniform variations of pulsar flux and pulsar shape over a period of about 35 days, and has some important consequences for our understanding of the internal structure of neutron stars. neutron stars, but so far only indirect evidence for this hypothesis is available. The final clue is expected to come later when IXPE observes the Hercules X-1 at another stage in its head start cycle.
Says Sergei Tsygankov of the University of Turku, one of the most important authors of the publication.
IXPE was launched on a Falcon 9 rocket from Cape Canaveral in December 2021 and is now orbiting 600 km above the Earth’s surface. The mission is a collaboration between NASA and the Italian Space Agency with scientific partners and collaborators in 13 countries, including Finland.
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