Nature © Macmillan Publishers Ltd 19988 amounts of 56 Ni (ϳ0.7 solar masses) have to be synthesized in the explosion 16 ; the large energy and 56 Ni mass would be unprecedented for a core-collapse supernova.If one accepts the possibility that GRB980425 and SN1998bw are associated, one must conclude that GRB980425 is a rare type of GRB, and SN1998bw is a rare type of supernova. The radio properties 8,9 of SN1998bw show the peculiar nature of this event independent of whether or not it is associated with GRB980425.The consequence of an association is that the ␥-ray peak luminosity of GRB980425 is L ␥ ¼ ð5:5 Ϯ 0:7Þ ϫ 10 46 erg s −1 (in the 24-1,820 keV band) and its total ␥-ray energy budget is (8:1 ϫ 1:0Þ ϫ 10 47 erg. These values are much smaller than those of 'normal' GRBs which have peak luminosities of up to 10 52 erg s −1 and total energies 5 up to several times 10 53 erg. This implies that very different mechanisms can produce GRBs which cannot be distinguished on the basis of their ␥-ray properties, and that models explaining GRB980425/SN1998bw are unlikely to apply to 'normal' GRBs and vice versa. Ⅺ

Aims. We investigate the evolution of protoplanetary discs (PPDs hereafter) with magnetically driven disc winds and viscous heating. Methods. We considered an initially massive disc with ∼ 0.1M⊙ to track the evolution from the early stage of PPDs. We solved the time evolution of surface density and temperature by taking into account viscous heating and the loss of mass and angular momentum by the disc winds within the framework of a standard α model for accretion discs. Our model parameters, turbulent viscosity, disc wind mass-loss, and disc wind torque, which were adopted from local magnetohydrodynamical simulations and constrained by the global energetics of the gravitational accretion, largely depends on the physical condition of PPDs, particularly on the evolution of the vertical magnetic flux in weakly ionized PPDs.Results. Although there are still uncertainties concerning the evolution of the vertical magnetic flux that remains, the surface densities show a large variety, depending on the combination of these three parameters, some of which are very different from the surface density expected from the standard accretion. When a PPD is in a wind-driven accretion state with the preserved vertical magnetic field, the radial dependence of the surface density can be positive in the inner region < 1 − 10 au. The mass accretion rates are consistent with observations, even in the very low level of magnetohydrodynamical turbulence. Such a positive radial slope of the surface density strongly affects planet formation because it inhibits the inward drift or even causes the outward drift of pebble-to boulder-sized solid bodies, and it also slows down or even reversed the inward type-I migration of protoplanets. Conclusions. The variety of our calculated PPDs should yield a wide variety of exoplanet systems.

We show that the coronal heating and the fast solar wind acceleration in the coronal holes are natural consequence of the footpoint fluctuations of the magnetic fields at the photosphere, by performing onedimensional magnetohydrodynamical simulation with radiative cooling and thermal conduction. We initially set up a static open flux tube with temperature 10 4 K rooted at the photosphere. We impose transverse photospheric motions corresponding to the granulations with velocity dv ⊥ = 0.7km/s and period between 20 seconds and 30 minutes, which generate outgoing Alfvén waves. We self-consistently treat these waves and the plasma heating. After attenuation in the chromosphere by ≃ 85% of the initial energy flux, the outgoing Alfvén waves enter the corona and contribute to the heating and acceleration of the plasma mainly by the nonlinear generation of the compressive waves and shocks. Our result clearly shows that the initial cool and static atmosphere is naturally heated up to 10 6 K and accelerated to ≃ 800km/s. The mpeg movie for fig.

By performing local three-dimensional MHD simulations of stratified accretion disks, we investigate disk winds driven by MHD turbulence. Initially weak vertical magnetic fields are effectively amplified by magnetorotational instability and winding due to differential rotation. Large-scale channel flows develop most effectively at 1.5 -2 times the scale heights where the magnetic pressure is comparable to but slightly smaller than the gas pressure. The breakup of these channel flows drives structured disk winds by transporting the Poynting flux to the gas. These features are universally observed in the simulations of various initial fields. This disk wind process should play an essential role in the dynamical evaporation of protoplanetary disks. The breakup of channel flows also excites the momentum fluxes associated with Alfvénic and (magneto-)sonic waves toward the midplane, which possibly contribute to the sedimentation of small dust grains in protoplanetary disks.

Late phase nebular spectra and photometry of Type Ib Supernova (SN) 2005bf taken by the Subaru telescope at ∼ 270 and ∼ 310 days since the explosion are presented. Emission lines ([OI] λλ6300, 6363, [CaII] λλ7291, 7324, [FeII] λ7155) show the blueshift of ∼ 1, 500 − 2, 000 km s −1 . The [OI] doublet shows a doubly-peaked profile. The line luminosities can be interpreted as coming from a blob or jet containing onlyNi synthesized at the explosion. To explain the blueshift, the blob should either be of unipolar moving at the center-ofmass velocity v ∼ 2, 000 − 5, 000 km s −1 , or suffer from self-absorption within the ejecta as seen in SN 1990I. In both interpretations, the low-mass blob component dominates the optical output both at the first peak (∼ 20 days) and at the late phase (∼ 300 days). The low luminosity at the late phase (the absolute R magnitude M R ∼ −10.2 mag at ∼ 270 days) sets the upper limit for the mass of 56 Ni ∼ < 0.08M ⊙ , which is in contradiction to the value necessary to explain the second, main peak luminosity (M R ∼ −18.3 mag at ∼ 40 days). Encountered by this difficulty in the 56 Ni heating model, we suggest an alternative scenario in which the heating source is a newly born, strongly magnetized neutron star (a magnetar) with the surface magnetic field B mag ∼ 10 14−15 gauss and the initial spin period P 0 ∼ 10 ms. Then, SN 2005bf could be a link between normal SNe Ib/c and an X-Ray Flash associated SN 2006aj, connected in terms of B mag and/or P 0 .

By constructing a global model based on 3D local magnetohydrodynamical (MHD) simulations, we show that the disk wind driven by magnetorotational instability (MRI) plays a significant role in the dispersal of the gas component of proto-planetary disks. Because the mass loss time scale by the MRI-driven disk winds is proportional to the local Keplerian rotation period, a gas disk dynamically evaporates from the inner region with possibly creating a gradually expanding inner hole, while a sizable amount of the gas remains in the outer region. The disk wind is highly time-dependent with quasi-periodicity of several times Keplerian rotation period at each radius, which will be observed as time-variability of protostar-protoplanetary disk systems. These features persistently hold even if a dead zone exists because the disk winds are driven from the surface regions where ionizing cosmic rays and high energy photons can penetrate. Moreover, the predicted inside-out clearing significantly suppresses the infall of boulders to a central star and the Type I migration of proto-planets which are favorable for the formation and survival of planets.

We present the magnetic landscape of the polar region of the Sun that is unprecedented in terms of high spatial resolution, large field of view, and polarimetric precision. These observations were carried out with the Solar Optical Telescope aboard Hinode. Using a Milne-Eddington inversion, we found many vertically-oriented magnetic flux tubes with field strength as strong as 1 kG that are scattered in latitude between 70 • ∼ 90 • . They all have the same polarity, consistent with the global polarity of the polar region. The field vectors were observed to diverge from the center of the flux elements, consistent with a view of magnetic fields that expand and fan out with height. The polar region is also covered with ubiquitous horizontal fields. The polar regions are the source of the fast solar wind channelled along unipolar coronal magnetic fields whose photospheric source is evidently rooted in the strong field, vertical patches of flux. We conjecture that vertical flux tubes with large expansion around the photospherecorona boundary serve as efficient chimneys for Alfvén waves that accelerate the solar wind.

We report results of three dimensional mangetohydrodynamical (MHD) simulations of global accretion disks threaded with weak vertical magnetic fields. We perform the simulations in the spherical coordinates with different temperature profiles and accordingly different rotation profiles. In the cases with a spatially constant temperature, because the rotation frequency is vertically constant in the equilibrium condition, general properties of the turbulence excited by magnetorotational instability (MRI) are quantitatively similar to those obtained in local shearing box simulations. On the other hand, in the cases with a radially variable temperature profile, the vertical differential rotation, which is inevitable in the equilibrium condition, winds up the magnetic field lines, in addition to the usual radial differential rotation. As a result, the coherent wound magnetic fields contribute to the Maxwell stress in the surface regions. Our global simulations give somewhat larger density fluctuation, δρ/ρ = 0.1 − 0.2, near the midplane than the values obtained in previous local shearing box simulations and global simulations without net vertical magnetic field. The velocity fluctuations, dominated by the radial component, are ≈ 0.1 − 0.2 of the local sound speed. The azimuthal power spectra of the magnetic fields show shallow slopes, ∝ m 0 ∼ m −1 , where m is an azimuthal mode number, which might be related to the energy injection by MRI from small scales. On the other hand, the power spectra of the velocities and density show steeper slopes, ∝ m −1 ∼ m −2 . We observe intermittent and structured disk winds driven by the Poynting flux associated with the MHD turbulence, with the slightly smaller mass fluxes than that obtained in our local simulations. The Poynting flux originating from magnetic tension is injected from the regions above a scale height toward both the midplane and the surfaces. Related to this, sound waves are directed to the midplane from the surface regions. The mass accretion mainly occurs near the surfaces and the gas near the midplane slowly moves outward in the time domain of the present simulations. The vertical magnetic fields are also dragged inward in the surface regions, while they stochastically move outward and inward around the midplane. The difference of the velocities at the midplane and the surfaces might cause large-scale meridional circulations. Applying to protoplanetary disks, these waves and circulation are supposed to play an important role in the dynamics of solid particles. We also discuss an observational implication of induced spiral structure in the simulated turbulent disks.