577 research outputs found
1-(Butan-2-ylÂidene)-2-(2-nitroÂphenÂyl)hydrazine
Crystals of the title compound, C10H13N3O2, were obtained from a condensation reaction of butan-2-one and 1-(2-nitroÂphenÂyl)hydrazine. The molÂecule exhibits a nearly coplanar structure, except for the methyl and methylÂene H atoms, the largest deviations from the mean plane defined by all non-H atoms, except for the nitro group, being 0.120 (2) Å for one of the nitro O atoms. IntraÂmolecular N—H⋯O hydrogen bonding helps to establish the molÂecular configuration
Multi-epoch, multi-frequency VLBI study of the parsec-scale jet in the blazar 3C 66A
We present the observational results of the Gamma-ray blazar, 3C 66A, at 2.3,
8.4, and 22 GHz at 4 epochs during 2004-05 with the VLBA. The resulting images
show an overall core-jet structure extending roughly to the south with two
intermediate breaks occurring in the region near the core. By model-fitting to
the visibility data, the northmost component, which is also the brightest, is
identified as the core according to its relatively flat spectrum and its
compactness. As combined with some previous results to investigate the proper
motions of the jet components, it is found the kinematics of 3C 66A is quite
complicated with components of inward and outward, subluminal and superluminal
motions all detected in the radio structure. The superluminal motions indicate
strong Doppler boosting exists in the jet. The apparent inward motions of the
innermost components last for at least 10 years and could not be caused by
new-born components. The possible reason could be non-stationarity of the core
due to opacity change.Comment: 24 pages, 4 figure
An hourglass model for the flare of HST-1 in M87
To explain the multi-wavelength light curves (from radio to X-ray) of HST-1
in the M87 jet, we propose an hourglass model that is a modified two-zone
system of Tavecchio & Ghisellini (hereafter TG08): a slow hourglass-shaped or
Laval nozzle-shaped layer connected by two revolving exponential surfaces
surrounding a fast spine, through which plasma blobs flow. Based on the
conservation of magnetic flux, the magnetic field changes along the axis of the
hourglass. We adopt the result of TG08---the high-energy emission from GeV to
TeV can be produced through inverse Compton by the two-zone system, and the
photons from radio to X-ray are mainly radiated by the fast inner zone system.
Here, we only discuss the light curves of the fast inner blob from radio to
X-ray. When a compressible blob travels down the axis of the first bulb in the
hourglass, because of magnetic flux conservation, its cross section experiences
an adiabatic compression process, which results in particle acceleration and
the brightening of HST-1. When the blob moves into the second bulb of the
hourglass, because of magnetic flux conservation, the dimming of the knot
occurs along with an adiabatic expansion of its cross section. A similar broken
exponential function could fit the TeV peaks in M87, which may imply a
correlation between the TeV flares of M87 and the light curves from radio to
X-ray in HST-1. The Very Large Array (VLA) 22 GHz radio light curve of HST-1
verifies our prediction based on the model fit to the main peak of the VLA 15
GHz radio light curve.Comment: 14 pages, 2 figures, accepted for publication in A
N′-(2-FurylmethylÂene)nicotinohydrazide
The asymmetric unit of the title compound, C11H9N3O2, contains two independent molÂecules: the dihedral angles between the pyridine ring and the furyl ring are 17.00 (16) and 34.12 (15)°. The crystal structure involves interÂmolecular C—H⋯O, N—H⋯N and N—H⋯O hydrogen bonds
Magnetar giant flares in multipolar magnetic fields. III. Multipolar magnetic field structure variations
We have analyzed the multipolar magnetic field structure variation at neutron
star surface by means of the catastrophic eruption model, and find that the
variation of the geometry of multipolar fields on the magnetar surface could
result in the catastrophic rearrangement of the magnetosphere, which provides
certain physical mechanism for the outburst of giant flares. The magnetospheric
model we adopted consists of two assumptions: a helically twisted flux rope is
suspended in an ideal force-free magnetosphere around the magnetar, and a
current sheet emerges during the flux rope evolution. Magnetic energy
accumulates during the flux rope's gradual evolution along with the variation
of magnetar surface magnetic structure before the eruption. The two typical
behaviors, either state transition or catastrophic escape, would take place
once the flux rope loses equilibrium, thus tremendous accumulated energy is
radiated. We have investigated the equilibrium state of the flux rope and the
energy release affected by different multipolar structures, and find structures
that could trigger violent eruption and provide the radiation approximately
0.5 of the total magnetic energy during the giant flare outburst. Our
results provide certain multipolar structures of the neutron star's magnetic
field with an energy release percentage 0.42 in the state transition and
0.51 in the catastrophic escape case, which are sufficient for the
previously reported energy release from SGR 1806-20 giant flares
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