2DARK天文志

We numerically evolve turbulence driven by the magnetorotational instability (MRI) in a 3D, unstratified shearing box and study its structure using two-point correlation functions. We confirm Fromang and Papaloizou's result that shearing box models with zero net magnetic flux are not converged; the dimensionless shear stress $\alpha$ is proportional to the grid scale. We find that the two-point correlation of the magnetic field shows that it is composed of narrow filaments that are swept back by differential rotation into a trailing spiral. The correlation lengths along each of the correlation function principal axes decrease monotonically with the grid scale. For mean azimuthal field models, which we argue are more relevant to astrophysical disks than the zero net field models, we find that: $\alpha$ increases weakly with increasing resolution at fixed box size; $\alpha$ increases slightly as the box size is increased; $\alpha$ increases linearly with net field strength, confirming earlier results; the two-point correlation function of the magnetic field is resolved and converged, and is composed of narrow filaments swept back by the shear; the major axis of the two-point increases slightly as the box size is increased; these results are code independent, based on a comparison of ATHENA and ZEUS runs. The velocity, density, and magnetic fields decorrelate over scales larger than $\sim H$, as do the dynamical terms in the magnetic energy evolution equations. We conclude that MHD turbulence in disks is localized, subject to the limitations imposed by the absence of vertical stratification, the use of an isothermal equation of state, finite box size, finite run time, and finite resolution

The dark cloud Lynds 1622 is one of a few specific sites in the Galaxy where, relative to observed free-free and vibrational dust emission, there is a clear excess of microwave emission. In order to constrain models for this microwave emission, and to better establish the contribution which it might make to ongoing and near-future microwave background polarization experiments, we have used the Green Bank Telescope to search for linear polarization at 9.65 Ghz towards Lynds 1622. We place a 95.4%upper limit of 88 micro-Kelvin (123 micro-Kelvin at 99.7 confidence) on the total linear polarization of this source averaged over a 1'.3 FWHM beam. Relative to the observed level of anomalous emission in Stokes I these limits correspond to fractional linear polarizations of 3.2% and 4.1%.

We conduct global galactic--scale magnetohydrodynamical (MHD) simulations of the cosmic--ray driven dynamo. We assume that exploding stars deposit small--scale, randomly oriented, dipolar magnetic fields into the differentially rotating ISM, together with a portion of cosmic rays, accelerated in supernova shocks. Our simulations are performed with the aid of a new parallel MHD code PIERNIK. We demonstrate that dipolar magnetic fields supplied on small SN--remnant scales, can be amplified exponentially by the CR--driven dynamo to the present equipartition values, and transformed simultaneously to large galactic--scales by an inverse cascade promoted by resistive processes.

We review basic features of cosmological models with large-scale classical non-Abelian Yang-Mills (YM) condensates. There exists a unique SU(2) YM configuration (generalizable to larger gauge groups) compatible with homogeneity and isotropy of the three-space which is parameterized by a single scalar field. In the past various aspects of Einstein-Yang-Mills (EYM) cosmology were discussed in the context of the Early Universe. Due to conformal invariance, solvable EYM FRW models exist both on the classical and quantum levels. To develop the YM model for dark energy one has to find mechanisms of the conformal symmetry breaking. We discuss the Born-Infeld generalization and some phenomenological models motivated by quantum corrections exploring possibility of transient DE and phantom regimes.

We present new developments on the Cosmic--Ray driven, galactic dynamo, modeled by means of direct, resistive CR--MHD simulations, performed with ZEUS and PIERNIK codes. The dynamo action, leading to the amplification of large--scale galactic magnetic fields on galactic rotation timescales, appears as a result of galactic differential rotation, buoyancy of the cosmic ray component and resistive dissipation of small--scale turbulent magnetic fields. Our new results include demonstration of the global--galactic dynamo action driven by Cosmic Rays supplied in supernova remnants. An essential outcome of the new series of global galactic dynamo models is the equipartition of the gas turbulent energy with magnetic field energy and cosmic ray energy, in saturated states of the dynamo on large galactic scales.

Aims. High angular resolution N-band imaging is used to discern the torus of active galactic nuclei (AGN) from its environment in order to allow a comparison of its mid-infrared properties to the expectations of the unified scenario for AGN. Methods. We present VLT-VISIR images of 25 low-redshift AGN of different Seyfert types, as well as N-band SEDs of 20 of them. In addition, we compare our results for 19 of them to Spitzer IRS spectra. Results. We find that at a resolution of ~ 0.35", all the nuclei of our observed sources are point-like, except for 2 objects whose extension is likely of instrumental origin. For 3 objects, however, we observed additional extended circumnuclear emission, even though our observational strategy was not designed to detect it. Comparison of the VISIR photometry and Spitzer spectrophotometry indicates that the latter is affected by extended emission in at least 7 out of 19 objects and the level of contamination is (0.20 ~ 0.85) * F_IRS. In particular, the 10 um silicate emission feature seen in the Spitzer spectra of 6 type I AGN, possibly 1 type II AGN and 2 LINERs, also probably originates not solely in the torus but also in extended regions. Conclusions. Our results generally agree with the expectations from the unified scenario, while the relative weakness of the silicate feature supports clumpy torus models. Our VISIR data indicate that, for low-redshift AGN, a large fraction of Spitzer IRS spectra are contaminated by extended emission close to the AGN.

We present a new multi-fluid, grid MHD code PIERNIK, which is based on the Relaxing TVD scheme (Jin & Xin, 1995). The original scheme (see Trac & Pen (2003) and Pen et al. (2003)) has been extended by an addition of dynamically independent, but interacting fluids: dust and a diffusive cosmic ray gas, described within the fluid approximation, with an option to add other fluids in an easy way. The code has been equipped with shearing-box boundary conditions, and a selfgravity module, Ohmic resistivity module, as well as other facilities which are useful in astrophysical fluid-dynamical simulations. The code is parallelized by means of the MPI library. In this paper we present an extension of PIERNIK, which is designed for simulations of diffusive propagation of the Cosmic-Ray (CR) component in the magnetized ISM.

The measured redshifts of gamma-ray bursts (GRBs), which were first detected by the Swift satellite, seem to be bigger on average than the redshifts of GRBs detected by other satellites. We analyzed the redshift distribution of GRBs triggered and observed by different satellites (Swift[1], HETE2[2], BeppoSax, Ulyssses). After considering the possible biases significant difference was found at the p = 95.70% level in the redshift distributions of GRBs measured by HETE and the Swift.

We consider the secular dynamics of a binary and a planet in terms of non-restricted, hierarchical three-body problem, including the general relativity corrections to the Newtonian gravity. We determine regions in the parameter space where the relativistic corrections may be important for the long-term dynamics. We try to constrain the inclinations of putative Jovian planets in recently announced binary systems of HD 4113 and HD 156846.

Coronal loops are fundamental building blocks of the solar active regions and the corona. Therefore, a clear understanding of the physics of coronal loops will help us understand the physics of active region heating in particular and coronal heating in general. This requires a precise measurement of physical quantities such as electron densities and filling factors, temperatures, and flows in coronal loops. In this paper we have carried out an investigation of a spatially well resolved coronal loop using the EIS onboard Hinode to measure the above mentioned physical quantities. Based on this study we find that a nano-flare model could explain most of the observed characteristics of this loop.

We present a list of interstellar absorption lines in the direction of HD 37061 in the M 43 nebula. The lines were found in Hubble Space Telescope (HST) high resolution ultraviolet spectra and in the spectra obtained by the Ultraviolet-Visual Echelle Spectrograph (UVES) lacated in Paranal, Chile. Some of the absorption lines arise from atomic excited levels. Moreover, 34 absorption lines in the far UV could not be identified using popular catalogues of spectral lines. The excited levels of Fe II are populated by fluorescence.

An outburst of the accreting X-ray millisecond pulsar SAX J1808.4-3658 in October-November 2002 was followed by the RXTE for more than a month. For the first time, we demonstrate that the area covered by the hotspot at the neutron star surface as well as the reflection amplitude decrease during the outburst. This is in agreement with the scenario, where the disc inner edge is receding from the neutron star as the mass accretion rate drops. This is further supported by the variations of the pulse profiles, showing the presence of the secondary maximum at the late stages of the outburst after October 29, when the disc has moved sufficiently far from the neutron star to open the view of the lower magnetic pole. We estimate the disc inner radius, the inclination at i=60^o+-5^o and to put constraints on the stellar magnetic moment mu=(7+-3)x10^{25} G cm^3, which corresponds to the surface field of about 10^8 G, and is in agreement with the value obtained recently from the observed pulsar spin-down rate. The timing noise and sharp changes in the phase of the fundamental are intimately related to the variations of the pulse profile, which are associated with the varying obscuration of the antipodal spot. We also demonstrate that the strong dependence of the pulse profiles on photon energy and the observed soft time lags result from the different phase dependence of the two spectral components, the blackbody and the Comptonized tail. The pulse profile amplitude allows us to estimate the colatitude of the hotspot centroid to be 4^o-10^o.

The traditional celestial navigation system(CNS) is used the moon, stars, and planets as celestial guides. Then the star tracker(i.e. track one star or planet or angle between it) and star sensor(i.e. sense many star simultaneous) be used to determine the attitude of the spacecraft. Pulsar navigation also be introduced to CNS. Maser is another interested celestial in radio astronomy which has strong flux density as spectral line. Now I analysis the principle of maser navigation which base measure Doppler shift frequency spectra and the feasibility that use the exist instrument, and discuss the integrated navigation use maser, then give the perspective in the Milk Way and the intergalatic. Maser navigation can give the continuous position in deep space, that means we can freedom fly successfully in the Milk Way use celestial navigation that include maser, pulsar and traditional star sensor. Maser as nature beacon in the universe will make human freely fly in the space of the Milk Way, even outer of it. That is extraordinary in the human evolution to type III of Karadashev civilizations.

Based on minimal supersymmetric standard model, neutralino dark matter annihilation induced gamma ray emission from galaxy cluster 1E0657-56 is calculated. The merge of bullet-like subcluster with the main cluster is also investigated.

Recent observation of 850 micron sub-mm polarization from T Tauri disks opens up the possibility of studying magnetic field structure within protostellar disks. The degree of polarization is around 3 % and the direction of polarization is perpendicular to the disk. Since thermal emission from dust grains dominates the spectral energy distribution at the sub-mm/FIR regime, dust grains are thought to be the cause of the polarization. We discuss grain alignment by radiation and we explore the efficiency of dust alignment in T Tauri disks. Calculations show that dust grains located far away from the Central proto-star are more efficiently aligned. In the presence of a regular magnetic field, the aligned grains produce polarized emission in sub-mm/FIR wavelengths. The direction of polarization is perpendicular to the local magnetic field direction. When we use a recent T Tauri disk model and take a Mathis-Rumpl-Nordsieck-type distribution with maximum grain size of 500-1000 $\mu$m, the degree of polarization is around 2-3 % level at wavelengths larger than $\sim100\mu$m. Our study indicates that multifrequency infrared polarimetric studies of protostellar disks can provide good insights into the details of their magnetic structure. We also provide predictions for polarized emission for disks viewed at different wavelengths and viewing angles.