529 research outputs found
DIOS: the Diffuse Intergalactic Oxygen Surveyor
We present our proposal for a small X-ray mission DIOS (Diffuse Intergalactic
Oxygen Surveyor), consisting of a 4-stage X-ray telescope and an array of TES
microcalorimeters, cooled with mechanical coolers, with a total weight of about
400 kg. The mission will perform survey observations of warm-hot intergalactic
medium using OVII and OVIII emission lines, with the energy coverage up to 1.5
keV. The wide field of view of about 50' diameter, superior energy resolution
close to 2 eV FWHM, and very low background will together enable us a wide
range of science for diffuse X-ray sources. We briefly describe the design of
the satellite, performance of the subsystems and the expected results.Comment: 9 pages, 11 figures, a proceedings of SPIE "Astronomical Telescopes
and Instrumentation" 200
Formation of a Massive Black Hole at the Center of the Superbubble in M82
We performed 12CO(1-0), 13CO(1-0), and HCN(1-0) interferometric observations
of the central region (about 450 pc in radius) of M82 with the Nobeyama
Millimeter Array, and have successfully imaged a molecular superbubble and
spurs. The center of the superbubble is clearly shifted from the nucleus by 140
pc. This position is close to that of the massive black hole (BH) of >460 Mo
and the 2.2 micron secondary peak (a luminous supergiant dominated cluster),
which strongly suggests that these objects may be related to the formation of
the superbubble. Consideration of star formation in the cluster based on the
infrared data indicates that (1) energy release from supernovae can account for
the kinetic energy of the superbubble, (2) the total mass of stellar-mass BHs
available for building-up the massive BH may be much higher than 460 Mo, and
(3) it is possible to form the middle-mass BH of 100-1000 Mo within the
timescale of the superbubble. We suggest that the massive BH was produced and
is growing in the intense starburst region.Comment: 9 pages, 3 figures, to appear in ApJ Lette
The hardest X-ray source in the ASCA Large Sky Survey: Discovery of a new type 2 Seyfert
We present results of ASCA deep exposure observations of the hardest X-ray
source discovered in the ASCA Large Sky Survey (LSS) project, designated as AX
J131501+3141. We extract its accurate X-ray spectrum, taking account of the
contamination from a nearby soft source (AX J131502+3142), separated only by
1'. AX J131501+3141 exhibits a large absorption of NH = (6 +4 -2)x 10^22 H/cm^2
with a photon index \Gamma = 1.5 +0.7 -0.6. The 2--10 keV flux was about 5 x
10^-13 erg/s/cm^2 and was time variable by a factor of 30% in 0.5 year. From
the highly absorbed X-ray spectrum and the time variability, as well as the
results of the optical follow-up observations (Akiyama et al. 1998,
astro-ph/9801173), we conclude that AX J131501+3141 is a type 2 Seyfert galaxy.
Discovery of such a low flux and highly absorbed X-ray source could have a
significant impact on the origin of the cosmic X-ray background.Comment: 16 pages, 6 figures, requires AAS Latex macro v4.0, to appear in The
Astrophysical Journal, text and figures also available at
http://www-cr.scphys.kyoto-u.ac.jp/member/sakano/work/paper/index-e.htm
Conformations of Linear DNA
We examine the conformations of a model for under- and overwound DNA. The
molecule is represented as a cylindrically symmetric elastic string subjected
to a stretching force and to constraints corresponding to a specification of
the link number. We derive a fundamental relation between the Euler angles that
describe the curve and the topological linking number. Analytical expressions
for the spatial configurations of the molecule in the infinite- length limit
were obtained. A unique configuraion minimizes the energy for a given set of
physical conditions. An elastic model incorporating thermal fluctuations
provides excellent agreement with experimental results on the plectonemic
transition.Comment: 5 pages, RevTeX; 6 postscript figure
Explosive Nucleosynthesis in Hypernovae
We examine the characteristics of nucleosynthesis in 'hypernovae', i.e.,
supernovae with very large explosion energies ( \gsim 10^{52} ergs). We
carry out detailed nucleosynthesis calculations for these energetic explosions
and compare the yields with those of ordinary core-collapse supernovae. We find
that both complete and incomplete Si-burning takes place over more extended,
lower density regions, so that the alpha-rich freezeout is enhanced and
produces more Ti in comparison with ordinary supernova nucleosynthesis. In
addition, oxygen and carbon burning takes place in more extended, lower density
regions than in ordinary supernovae. Therefore, the fuel elements O, C, Al are
less abundant while a larger amount of Si, S, Ar, and Ca ("Si") are synthesized
by oxygen burning; this leads to larger ratios of "Si"/O in the ejecta.
Enhancement of the mass ratio between complete and incomplete Si-burning
regions in the ejecta may explain the abundance ratios among iron-peak elements
in metal-poor stars. Also the enhanced "Si"/O ratio may explain the abundance
ratios observed in star burst galaxies. We also discuss other implications of
enhanced [Ti/Fe] and [Fe/O] for Galactic chemical evolution and the abundances
of low mass black hole binaries.Comment: Accepted for publication in the Astrophysical Journal (13 March 2001)
Tables 6 - 9 are available at
http://www.astron.s.u-tokyo.ac.jp/~nakamura/research/papers/nakamuratab.ps.g
The Asymmetric Wind in M82
We have obtained detailed imaging Fabry-Perot observations of the nearby
galaxy M82, in order to understand the physical association between the
high-velocity outflow and the starburst nucleus. The observed velocities of the
emitting gas in M82 reveal a bipolar outflow of material, originating from the
bright starburst regions in the galaxy's inner disk, but misaligned with
respect to the galaxy spin axis. The deprojected outflow velocity increases
with radius from 525 to 655 km/s. Spectral lines show double components in the
centers of the outflowing lobes, with the H-alpha line split by ~300 km/s over
a region almost a kiloparsec in size. The filaments are not simple surfaces of
revolution, nor is the emission distributed evenly over the surfaces. We model
these lobes as a composite of cylindrical and conical structures, collimated in
the inner ~500 pc but expanding at a larger opening angle of ~25 degrees beyond
that radius. We compare our kinematic model with simulations of
starburst-driven winds in which disk material surrounding the source is
entrained by the wind. The data also reveal a remarkably low [NII]/H-alpha
ratio in the region of the outflow, indicating that photoionization by the
nuclear starburst may play a significant role in the excitation of the optical
filament gas, particularly near the nucleus.Comment: 42 pages AASTeX with 16 figures; accepted for publication in ApJ;
figures reformatted for better printin
Starburst at the Expanding Molecular Superbubble in M82: Self-Induced Starburst at the Inner Edge of the Superbubble
We present high spatial resolution (2.3"x1.9" or 43 pc x 36 pc at D = 3.9
Mpc) 100 GHz millimeter-wave continuum emission observations with the Nobeyama
Millimeter Array toward an expanding molecular superbubble in the central
region of M82. The 100 GHz continuum image, which is dominated by free-free
emission, revealed that the four strongest peaks are concentrated at the inner
edge of the superbubble along the galactic disk. The production rates of Lyman
continuum photons calculated from 100 GHz continuum flux at these peaks are an
order of magnitude higher than those from the most massive star forming regions
in our Galaxy. At these regions, high velocity ionized gas (traced by H41a and
[Ne II]) can be seen, and H2O and OH masers are also concentrated. The center
of the superbubble, on the other hand, is weak in molecular and free-free
emissions and strong in diffuse hard X-ray emission. These observations suggest
that a strong starburst produced energetic explosions and resultant plasma and
superbubble expansions, and induced the present starburst regions traced by our
100 GHz continuum observations at the inner edge of the molecular superbubble.
These results, therefore, provide the first clear evidence of self-induced
starburst in external galaxies. Starburst at the center of the superbubble, on
the other hand, begins to cease because of a lack of molecular gas. This kind
of intense starburst seems to have occurred several times within 10^6-10^7
years in the central region of M82.Comment: 30 pages, 6 figures. To be appeared in ApJ, 617, 20 December 2004
issu
Wide band X-ray Imager (WXI) and Soft Gamma-ray Detector (SGD) for the NeXT Mission
The NeXT mission has been proposed to study high-energy non-thermal phenomena
in the universe. The high-energy response of the super mirror will enable us to
perform the first sensitive imaging observations up to 80 keV. The focal plane
detector, which combines a fully depleted X-ray CCD and a pixellated CdTe
detector, will provide spectra and images in the wide energy range from 0.5 keV
to 80 keV. In the soft gamma-ray band up to ~1 MeV, a narrow field-of-view
Compton gamma-ray telescope utilizing several tens of layers of thin Si or CdTe
detector will provide precise spectra with much higher sensitivity than present
instruments. The continuum sensitivity will reach several times 10^(-8)
photons/s/keV/cm^(2) in the hard X-ray region and a few times10^(-7)
photons/s/keV/cm^(2) in the soft gamma-ray region.Comment: 12 pages, 13 figures, to be published in the SPIE proceedings 5488,
typo corrected in sec.
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