5,969 research outputs found
Large amplitude oscillation of an erupting filament as seen in EUV, H-alpha and microwave observations
We present multiwavelength observations of a large-amplitude oscillation of a polar-crown filament on 15 October 2002, which has been reported by Isobe and Tripathi (Astron. Astrophys. 449, L17, 2006). The oscillation occurred during the slow rise (≈1 km s−1) of the filament. It completed three cycles before sudden acceleration and eruption. The oscillation and following eruption were clearly seen in observations recorded by the Extreme-Ultraviolet Imaging Telescope (EIT) onboard the Solar and Heliospheric Observatory (SOHO). The oscillation was seen only in a part of the filament, and it appears to be a standing oscillation rather than a propagating wave. The amplitudes of velocity and spatial displacement of the oscillation in the plane of the sky were about 5 km s−1 and 15 000 km, respectively. The period of oscillation was about two hours and did not change significantly during the oscillation. The oscillation was also observed in Hα by the Flare Monitoring Telescope at the Hida Observatory. We determine the three-dimensional motion of the oscillation from the Hα wing images. The maximum line-of-sight velocity was estimated to be a few tens of kilometers per second, although the uncertainty is large owing to the lack of line-profile information. Furthermore, we also identified the spatial displacement of the oscillation in 17-GHz microwave images from Nobeyama Radio Heliograph (NoRH). The filament oscillation seems to be triggered by magnetic reconnection between a filament barb and nearby emerging magnetic flux as was evident from the MDI magnetogram observations. No flare was observed to be associated with the onset of the oscillation. We also discuss possible implications of the oscillation as a diagnostic tool for the eruption mechanisms. We suggest that in the early phase of eruption a part of the filament lost its equilibrium first, while the remaining part was still in an equilibrium and oscillated
Adaptive Sampling Approach to the Negative Sign Problem in the Auxiliary Field Quantum Monte Carlo Method
We propose a new sampling method to calculate the ground state of interacting
quantum systems. This method, which we call the adaptive sampling quantum monte
carlo (ASQMC) method utilises information from the high temperature density
matrix derived from the monte carlo steps. With the ASQMC method, the negative
sign ratio is greatly reduced and it becomes zero in the limit
goes to zero even without imposing any constraint such like the constraint path
(CP) condition. Comparisons with numerical results obtained by using other
methods are made and we find the ASQMC method gives accurate results over wide
regions of physical parameters values.Comment: 8 pages, 7 figure
A new Comptonization model for low-magnetized accreting neutron stars in low mass X-ray binaries
We developed a new model for the X-ray spectral fitting \xspec package which
takes into account the effects of both thermal and dynamical (i.e. bulk)
Comptonization. The model consists of two components: one is the direct
blackbody-like emission due to seed photons which are not subjected to
effective Compton scattering, while the other one is a convolution of the
Green's function of the energy operator with a blackbody-like seed photon
spectrum. When combined thermal and bulk effects are considered, the analytic
form of the Green's function may be obtained as a solution of the diffusion
Comptonization equation. Using data from the BeppoSAX, INTEGRAL and RXTE
satellites, we test our model on the spectra of a sample of six persistently
low magnetic field bright neutron star Low Mass X-ray Binaries, covering three
different spectral states. Particular attention is given to the transient
powerlaw-like hard X-ray (> 30 keV) tails that we interpret in the framework of
the bulk motion Comptonization process. We show that the values of the best-fit
delta-parameter, which represents the importance of bulk with respect to
thermal Comptonization, can be physically meaningful and can at least
qualitatively describe the physical conditions of the environment in the
innermost part of the system. Moreover, we show that in fitting the thermal
Comptonization spectra to the X-ray spectra of these systems, the best-fit
parameters of our model are in excellent agreement with those of COMPTT, a
broadly used and well established XSPEC model.Comment: 15 pages, 8 figures, accepted for publication in Ap
Vertex operator approach for correlation functions of Belavin's (Z/nZ)-symmetric model
Belavin's -symmetric model is considered on the
basis of bosonization of vertex operators in the model and
vertex-face transformation. The corner transfer matrix (CTM) Hamiltonian of
-symmetric model and tail operators are expressed in
terms of bosonized vertex operators in the model. Correlation
functions of -symmetric model can be obtained by
using these objects, in principle. In particular, we calculate spontaneous
polarization, which reproduces the result by myselves in 1993.Comment: For the next thirty days the full text of this article is available
at http://stacks.iop.org/1751-8121/42/16521
Energy dependence of transverse mass spectra of kaons produced in p+p and p+pbar interactions.A compilation
The data on m_T spectra of K0S K+ and K- mesons produced in all inelastic p+p
and p+pbar interactions in the energy range sqrt(s)NN=4.7-1800GeV are compiled
and analyzed. The spectra are parameterized by a single exponential function,
dN/(m_T*dm_T)=C exp(-m_T/T), and the inverse slope parameter T is the main
object of study. The T parameter is found to be similar for K0S, K+ and K-
mesons. It increases monotonically with collision energy from T~30MeV at
sqrt(s)NN=4.7GeV to T~220MeV at sqrt(s)NN=1800GeV. The T parameter measured in
p+p and p+pbar interactions is significantly lower than the corresponding
parameter obtained for central Pb+Pb collisions at all studied energies. Also
the shape of the energy dependence of is different for central Pb+Pb
collisions and p+p(pbar) interactions.Comment: more differential analysis adde
Advection-Dominated Accretion and Black Hole Event Horizons
The defining characteristic of a black hole is that it possesses an event
horizon through which matter and energy can fall in but from which nothing
escapes. Soft X-ray transients (SXTs), a class of X-ray binaries, appear to
confirm this fundamental property of black holes. SXTs that are thought to
contain accreting black holes display a large variation of luminosity between
their bright and faint states, while SXTs with accreting neutron stars have a
smaller variation. This difference is predicted if the former stars have
horizons and the latter have normal surfaces.Comment: 11 pages, including 2 tables and 2 figures. To appear in The
Astrophysical Journal Letter
Supersonic Downflows in a Sunspot Light Bridge
We report the discovery of supersonic downflows in a sunspot light bridge
using measurements taken with the spectropolarimeter on board the Hinode
satellite. The downflows occur in small patches close to regions where the
vector magnetic field changes orientation rapidly, and are associated with
anomalous circular polarization profiles. An inversion of the observed Stokes
spectra reveals velocities of up to 10 km/s, making them the strongest
photospheric flows ever measured in light bridges. Some (but not all) of the
downflowing patches are cospatial and cotemporal with brightness enhancements
in chromospheric Ca II H filtergrams. We suggest that these flows are due to
magnetic reconnection in the upper photosphere/lower chromosphere, although
other mechanisms cannot be ruled out.Comment: 4 pages, 5 figures, Published in ApJ Letter
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