11 research outputs found
A Comment on "A note on polarized light from Magnetars: QED effects and axion-like particles" by L.M. Capparelli, L. Maiani and A.D. Polosa
The recent detection of a large polarization degree in the optical emission
of an isolated neutron star led to the suggestion that this has been the first
evidence of vacuum polarization in a strong magnetic field, an effect predicted
by quantum electrodynamics but never observed before. This claim was challanged
in a paper by Capparelli, Maiani & Polosa (2017), according to whom a much
higher polarization degree would be necessary to positively identify vacuum
polarization. Here we show that their conclusions are biased by several
inadequate assumptions and have no impact on the original claim.Comment: 10 pages, 2 figure
Evidence of vacuum birefringence from the polarisation of the optical emission from an Isolated Neutron Star
Isolated Neutron Stars are some of the most exciting stellar objects known to
astronomers: they have the most extreme magnetic fields, with values up to
G, and, with the exception of stellar-mass black holes, they are the
most dense stars, with densities of g cm. As such,
they are perfect laboratories to test theories of electromagnetism and nuclear
physics under conditions of magnetic field and density unattainable on Earth.
In particular, the interaction of radiation with strong magnetic fields is the
cause of the {\em vacuum birefringence}, an effect predicted by quantum
electrodynamics in 1936 but that lacked an observational evidence until now.
Here, we show how the study of the polarisation of the optical radiation from
the surface of an isolated neutron star yielded such an observational evidence,
opening exciting perspectives for similar studies at other wavelengths.Comment: 5 pages, 1 figure, Contributed to the 13th Patras Workshop on Axions,
WIMPs and WISPs, Thessaloniki, May 15 to 19, 201
Polarization of neutron star surface emission: a systematic analysis
New-generation X-ray polarimeters currently under development promise to open
a new window in the study of high-energy astrophysical sources. Among them,
neutron stars appear particularly suited for polarization measurements.
Radiation from the (cooling) surface of a neutron star is expected to exhibit a
large intrinsic polarization degree due to the star strong magnetic field
( G), which influences the plasma opacity in the
outermost stellar layers. The polarization fraction and polarization angle as
measured by an instrument, however, do not necessary coincide with the
intrinsic ones derived from models of surface emission. This is due to the
effects of quantum electrodynamics in the highly magnetized vacuum around the
star (the vacuum polarization) coupled with the rotation of the Stokes
parameters in the plane perpendicular to the line of sight induced by the
non-uniform magnetic field. Here we revisit the problem and present an
efficient method for computing the observed polarization fraction and
polarization angle in the case of radiation coming from the entire surface of a
neutron star, accounting for both vacuum polarization and geometrical effects
due to the extended emitting region. Our approach is fairly general and is
illustrated in the case of blackbody emission from a neutron star with either a
dipolar or a (globally) twisted magnetic field.Comment: 13 pages, 9 figures, accepted for publication in MNRA
Carbon Chain Anions and the Growth of Complex Organic Molecules in Titan's Ionosphere
Cassini discovered a plethora of neutral and ionized molecules in Titan's ionosphere including, surprisingly, anions and negatively charged molecules extending up to 13,800 u q-1. In this Letter, we forward model the Cassini electron spectrometer response function to this unexpected ionospheric component to achieve an increased mass resolving capability for negatively charged species observed at Titan altitudes of 950-1300 km. We report on detections consistently centered between 25.8 and 26.0 u q-1 and between 49.0-50.1 u q(-1) which are identified as belonging to the carbon chain anions, CN-/C3N- and/or C2H-/C4H-, in agreement with chemical model predictions. At higher ionospheric altitudes, detections at 73-74 u q-1 could be attributed to the further carbon chain anions C5N-/C6H- but at lower altitudes and during further encounters extend over a higher mass/charge range. This, as well as further intermediary anions detected at > 100 u, provide the first evidence for efficient anion chemistry in space involving structures other than linear chains. Furthermore, at altitudes below < 1100 km, the low-mass anions (< 150 u q-1) were found to deplete at a rate proportional to the growth of the larger molecules, a correlation that indicates the anions are tightly coupled to the growth process. This study adds Titan to an increasing list of astrophysical environments where chain anions have been observed and shows that anion chemistry plays a role in the formation of complex organics within a planetary atmosphere as well as in the interstellar medium
Constraining the Neutron Star Mass–Radius Relation and Dense Matter Equation of State with NICER
New Constraints on the Nuclear Equation of State from the Thermal Emission of Neutron Stars in Quiescent Low-mass X-Ray Binaries
The X-ray Polarization Probe mission concept
The 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