5,615 research outputs found
Redefining the boundaries of interplanetary coronal mass ejections from observations at the ecliptic plane
On 2015 January 6-7, an interplanetary coronal mass ejection (ICME) was
observed at L1. This event, which can be associated with a weak and slow
coronal mass ejection, allows us to discuss on the differences between the
boundaries of the magnetic cloud and the compositional boundaries. A fast
stream from a solar coronal hole surrounding this ICME offers a unique
opportunity to check the boundaries' process definition and to explain
differences between them. Using Wind and ACE data, we perform a complementary
analysis involving compositional, magnetic, and kinematic observations
providing relevant information regarding the evolution of the ICME as
travelling away from the Sun. We propose erosion, at least at the front
boundary of the ICME, as the main reason for the difference between the
boundaries, and compositional signatures as the most precise diagnostic tool
for the boundaries of ICMEs.Comment: 9 pages and 7 figures in the original forma
Obscuring Material around Seyfert Nuclei with Starbursts
The structure of obscuring matter in the environment of active galactic
nuclei with associated nuclear starbursts is investigated using 3-D
hydrodynamical simulations. Simple analytical estimates suggest that the
obscuring matter with energy feedback from supernovae has a torus-like
structure with a radius of several tens of parsecs and a scale height of about
10 pc. These estimates are confirmed by the fully non-linear numerical
simulations, in which the multi-phase inhomogeneous interstellar matter and its
interaction with the supernovae are consistently followed. The globally stable,
torus-like structure is highly inhomogeneous and turbulent. To achieve the high
column densities (> 10^{24} cm^{-2}) as suggested by observations of some
Seyfert 2 galaxies with nuclear starbursts, the viewing angle should be larger
than about 70 degree from the pole-on for a 10^8 solar mass massive black hole.
Due to the inhomogeneous internal structure of the torus, the observed column
density is sensitive to the line-of-sight, and it fluctuates by a factor of
order 100. The covering fraction for N > 10^{23} cm^{-2} is about 0.4. The
average accretion rate toward R < 1 pc is 0.4 solar mass/yr, which is boosted
to twice that in the model without the energy feedback.Comment: ApJL in press (4 pages, 3 figures) A gziped ps file with high
resolution figures is available at http://th.nao.ac.jp/~wada/AGN
A Carrington-like geomagnetic storm observed in the 21st century
In September 1859 the Colaba observatory measured the most extreme
geomagnetic disturbance ever recorded at low latitudes related to solar
activity: the Carrington storm. This paper describes a geomagnetic disturbance
case with a profile extraordinarily similar to the disturbance of the
Carrington event at Colaba: the event on 29 October 2003 at Tihany magnetic
observatory in Hungary. The analysis of the H-field at different locations
during the "Carrington-like" event leads to a re-interpretation of the 1859
event. The major conclusions of the paper are the following: (a) the global Dst
or SYM-H, as indices based on averaging, missed the largest geomagnetic
disturbance in the 29 October 2003 event and might have missed the 1859
disturbance, since the large spike in the horizontal component (H) of
terrestrial magnetic field depends strongly on magnetic local time (MLT); (b)
the main cause of the large drop in H recorded at Colaba during the Carrington
storm was not the ring current but field-aligned currents (FACs), and (c) the
very local signatures of the H-spike imply that a Carrington-like event can
occur more often than expected.Comment: 18 pages, 2 figures, accepted for publication in SWS
Effects of an extra gauge boson on the top quark decay
The effects of an extra gauge boson with family nonuniversal fermion
couplings on the rare top quark decay gamma10^{-8}m_{Z'}=500Z'B(t --> c
\gamma)\sim 10^{-6}m_{Z'}=1$ TeV.Comment: New paragraphs included to clarify our results, conclusion remains
unchange
Supergranular-scale magnetic flux emergence beneath an unstable filament
Here we report evidence of a large solar filament eruption on 2013, September
29. This smooth eruption, which passed without any previous flare, formed after
a two-ribbon flare and a coronal mass ejection towards Earth. The coronal mass
ejection generated a moderate geomagnetic storm on 2013, October 2 with very
serious localized effects. The whole event passed unnoticed to flare-warning
systems.
We have conducted multi-wavelength analyses of the Solar Dynamics Observatory
through Atmospheric Imaging Assembly (AIA) and Helioseismic and Magnetic Imager
(HMI) data. The AIA data on 304, 193, 211, and 94 \AA sample the transition
region and the corona, respectively, while HMI provides photospheric
magnetograms, continuum, and linear polarization data, in addition to the fully
inverted data provided by HMI.
[...]
We have observed a supergranular-sized emergence close to a large filament in
the boundary of the active region NOAA11850. Filament dynamics and magnetogram
results suggest that the magnetic flux emergence takes place in the
photospheric level below the filament. Reconnection occurs underneath the
filament between the dipped lines that support the filament and the
supergranular emergence. The very smooth ascent is probably caused by this
emergence and torus instability may play a fundamental role, which is helped by
the emergence.Comment: 9 pages, 6 figures, online material at Journa
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