7,400 research outputs found
Fermi Observation of the transitional pulsar binary XSS J12270-4859
Because of the disappearance of its accretion disk since the time period
around 2012 November--December, XSS J12270-4859 has recently been identified
as, in addition to PSR J1023+0038, another transitional millisecond pulsar
binary. We have carried out detailed analysis of the Fermi Large Area Telescope
data for the binary. While both spectra before and after the disk-disappearance
transition are well described by an exponentially cut-off power law, typical
for pulsars' emission in the Fermi's 0.2-300 GeV, a factor of 2 flux decrease
related to the transition is detected. A weak orbital modulation is seen, but
only detectable in the after-transition data, same to that found at X-rays. In
the long-term light curve of the source before the transition, a factor of 3
flux variations are seen. Comparing to the properties of J1023+0038, we disucss
the implications from these results. We suggest that since the modulation is
aligned with that at X-rays in orbital phase, it possibly arises due to the
occultation of the gamma-ray emitting region by the companion. The origin of
the variations in the long-term light curve is not clear, because the source
field also contains unidentified radio or X-ray sources and their contamination
can not be excluded. Multi-wavelength observations of the source field will
help identify the origin of the variations by detecting any related flux
changes from the in-field sources.Comment: 12 pages, 5 figures, 2 tables, submitted to Ap
On the significance of polarization charge and isomagnetic surface in the interaction between conducting fluid and magnetic field
From the frozen-in field lines concept, a highly conducting fluid can move
freely along, but not traverse to, magnetic field lines. We discuss this topic
and find that in the study of the frozen-in field lines concept, the effects of
inductive and capacitive reactance have been omitted. When admitted, the
relationships among the motional electromotive field, the induced electric
field, the eddy electric current, and the magnetic field becomes clearer and
the frozen-in field line concept can be reconsidered. We emphasize the
importance of isomagnetic surfaces and polarization charges, and show
analytically that whether a conducting fluid can freely traverse magnetic field
lines or not depends solely on the magnetic gradient in the direction of fluid
motion. If a fluid does not change its density distribution and shape (can be
regarded as a quasi-rigid body), and as long as it is moving along an
isomagnetic surface, it can freely traverse magnetic field lines without any
magnetic resistance no matter how strong the magnetic field is. When our
analysis is applied, the origin of the magnetic field of sunspots can be
interpreted easily. In addition, we also present experimental results to
support our analysis.Comment: 12 pages, 12 figures, 4 table
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