169 research outputs found
Shear viscosity in magnetized neutron star crust
The electron shear viscosity due to Coulomb scattering of degenerate
electrons by atomic nuclei throughout a magnetized neutron star crust is
calculated. The theory is based on the shear viscosity coefficient calculated
neglecting magnetic fields but taking into account gaseous, liquid and solid
states of atomic nuclei, multiphonon scattering processes, and finite sizes of
the nuclei albeit neglecting the effects of electron band structure. The
effects of strong magnetic fields are included in the relaxation time
approximation with the effective electron relaxation time taken from the
field-free theory. The viscosity in a magnetized matter is described by five
shear viscosity coefficients. They are calculated and their dependence on the
magnetic field and other parameters of dense matter is analyzed. Possible
applications and open problems are outlined.Comment: 6 pages, 3 figures, EPL, accepte
Neutrino-pair bremsstrahlung in a neutron star crust
Based on the formalism by Kaminker et al. (Astron. Astrophys. 343 (1999)
1009) we derive an analytic approximation for neutrino-pair bremsstrahlung
emissivity due to scattering of electrons by atomic nuclei in the neutron star
crust of any realistic composition. The emissivity is expressed through
generalized Coulomb logarithm which we fit by introducing an effective
potential of electron-nucleus scattering. In addition, we study the conditions
at which the neutrino bremsstrahlung in the crust is affected by strong
magnetic fields. The results can be applied for modelling of many phenomena in
neutron stars, such as thermal relaxation in young isolated neutron stars and
in accreting neutron stars with overheated crust in soft X-ray transients.Comment: 6 pages, 3 figures, EPL, accepte
Constraints on neutron star superfluidity from the cooling neutron star in Cassiopeia A using all Chandra ACIS-S observations
Analysis of Chandra observations of the neutron star (NS) in the centre of
the Cassiopeia A supernova remnant taken in the subarray (FAINT) mode of the
ACIS detector performed by Posselt and collaborators revealed, after inclusion
of the most recent (May 2020) observations, a significant decrease of the
source surface temperature from 2006 to 2020. The obtained cooling rate is
consistent with those obtained from analysis of the 20002019 data taken in
the GRADED mode of the ACIS detector, which is potentially more strongly
affected by instrumental effects. We performed a joint spectral analysis using
all ACIS data to constrain the NS parameters and cooling rate. We constrain the
mass of the Cassiopeia A NS at , and its radius at
km. The surface temperature cooling rate is found to be per cent in 10 years if the absorbing hydrogen column density is allowed
to vary and per cent in 10 years if it is fixed. The observed
cooling can be explained by enhanced neutrino emission from the superfluid NS
interior due to Cooper Pair Formation (CPF) process. Based on analysis of all
ACIS data, we constrain the maximal critical temperature of triplet neutron
pairing within the NS core at K. In accordance with
previous studies, the required effective strength of the CPF neutrino emission
is at least a factor of 2 higher than existing microscopic calculations
suggest.Comment: 20 pages, 17 figures. Accepted for publication in MNRA
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