3,830 research outputs found
Relation of cyclotron resonant energy and luminosity in a strongly magnetized neutron star GRO J1008-57 observed by Insight-HXMT
Cyclotron line scattering features are detected in a few tens of X-ray
pulsars (XRPs) and used as direct indicators of a strong magnetic field at the
surface of accreting neutron stars (NSs). In a few cases, cyclotron lines are
known to be variable with accretion luminosity of XRPs. It is accepted that the
observed variations of cyclotron line scattering features are related to
variations of geometry and dynamics of accretion flow above the magnetic poles
of a NS. A positive correlation between the line centroid energy and luminosity
is typical for sub-critical XRPs, where the accretion results in hot spots at
the magnetic poles. The negative correlation was proposed to be a specific
feature of bright super-critical XRPs, where radiation pressure supports
accretion columns above the stellar surface. Cyclotron line in spectra of
Be-transient X-ray pulsar GRO J1008-57 is detected at energies from keV, the highest observed energy of cyclotron line feature in XRPs. We
report the peculiar relation of cyclotron line centroid energies with
luminosity in GRO J1008-57 during the Type II outburst in August 2017 observed
by Insight-HXMT. The cyclotron line energy was detected to be negatively
correlated with the luminosity at 3.2\times 10^{37}\,\ergs, and positively correlated at L\gtrsim 5\times
10^{37}\,\ergs. We speculate that the observed peculiar behavior of a
cyclotron line would be due to variations of accretion channel geometry.Comment: 9 pages. 5 figures, 2 tables, accept for publication in Ap
Multistage Random Growing Small-World Networks with Power-law degree Distribution
In this paper, a simply rule that generates scale-free networks with very
large clustering coefficient and very small average distance is presented.
These networks are called {\bf Multistage Random Growing Networks}(MRGN) as the
adding process of a new node to the network is composed of two stages. The
analytic results of power-law exponent and clustering coefficient
are obtained, which agree with the simulation results approximately.
In addition, the average distance of the networks increases logarithmical with
the number of the network vertices is proved analytically. Since many real-life
networks are both scale-free and small-world networks, MRGN may perform well in
mimicking reality.Comment: 3 figures, 4 page
Reanalysis of the X-ray burst associated FRB 200428 with Insight-HXMT observations
A double-peak X-ray burst from the Galactic magnetar SGR J1935+2154 was
discovered as associated with the two radio pulses of FRB 200428 separated by
28.97+-0.02 ms. Precise measurements of the timing and spectral properties of
the X-ray bursts are helpful for understanding the physical origin of fast
radio bursts (FRBs). In this paper, we have reconstructed some information
about the hard X-ray events, which were lost because the High Energy X-ray
Telescope (HE) onboard the Insight-HXMT mission was saturated by this extremely
bright burst, and used the information to improve the temporal and spectral
analyses of the X-ray burst. The arrival times of the two X-ray peaks by
fitting the new Insight-HXMT/HE lightcurve with multi-Gaussian profiles are
2.77+-0.45 ms and 34.30+-0.56 ms after the first peak of FRB 200428,
respectively, while these two parameters are 2.57+-0.52 ms and 32.5+-1.4 ms if
the fitting profile is a fast rise and exponential decay function. The spectrum
of the two X-ray peaks could be described by a cutoff power-law with cutoff
energy ~60 keV and photon index ~1.4, the latter is softer than that of the
underlying bright and broader X-ray burst when the two X-ray peaks appeared.Comment: 11 pages, 7 figure
In-orbit demonstration of X-ray pulsar navigation with the Insight-HXMT satellite
In this work, we report the in-orbit demonstration of X-ray pulsar navigation
with Insight-Hard X-ray Modulation Telescope (Insight-HXMT), which was launched
on Jun. 15th, 2017. The new pulsar navigation method 'Significance Enhancement
of Pulse-profile with Orbit-dynamics' (SEPO) is adopted to determine the orbit
with observations of only one pulsar. In this test, the Crab pulsar is chosen
and observed by Insight-HXMT from Aug. 31th to Sept. 5th in 2017. Using the
5-day-long observation data, the orbit of Insight-HXMT is determined
successfully with the three telescopes onboard - High Energy X-ray Telescope
(HE), Medium Energy X-ray Telescope (ME) and Low Energy X-ray Telescope (LE) -
respectively. Combining all the data, the position and velocity of the
Insight-HXMT are pinpointed to within 10 km (3 sigma) and 10 m/s (3 sigma),
respectively.Comment: Accepted by the Astrophysical Journal Supplemen
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