719 research outputs found
The Reionization History and Early Metal Enrichment inferred from the Gamma-Ray Burst Rate
Based on the gamma-ray burst (GRB) event rate at redshifts of , which is assessed by the spectral peak energy-to-luminosity relation
recently found by Yonetoku et al., we observationally derive the star formation
rate (SFR) for Pop III stars in a high redshift universe. As a result, we find
that Pop III stars could form continuously at . Using the
derived Pop III SFR, we attempt to estimate the ultraviolet (UV) photon
emission rate at in which redshift range no observational
information has been hitherto obtained on ionizing radiation intensity. We find
that the UV emissivity at can make a noticeable contribution
to the early reionization. The maximal emissivity is higher than the level
required to keep ionizing the intergalactic matter at .
However, if the escape fraction of ionizing photons from Pop III objects is
smaller than 10%, then the IGM can be neutralized at some redshift, which may
lead to the double reionization. As for the enrichment, the ejection of all
metals synthesized in Pop III objects is marginally consistent with the IGM
metallicity, although the confinement of metals in Pop III objects can reduce
the enrichment significantly.Comment: 12 pages, 2 figures, ApJL accepte
Imprint of Gravitational Lensing by Population III Stars in Gamma Ray Burst Light Curves
We propose a novel method to extract the imprint of gravitational lensing by
Pop III stars in the light curves of Gamma Ray Bursts (GRBs). Significant
portions of GRBs can originate in hypernovae of Pop III stars and be
gravitationally lensed by foreground Pop III stars or their remnants. If the
lens mass is on the order of and the lens redshift is
greater than 10, the time delay between two lensed images of a GRB is s and the image separation is as. Although it is difficult to
resolve the two lensed images spatially with current facilities, the light
curves of two images are superimposed with a delay of s. GRB light
curves usually exhibit noticeable variability, where each spike is less than
1s. If a GRB is lensed, all spikes are superimposed with the same time delay.
Hence, if the autocorrelation of light curve with changing time interval is
calculated, it should show the resonance at the time delay of lensed images.
Applying this autocorrelation method to GRB light curves which are archived as
the {\it BATSE} catalogue, we demonstrate that more than half light curves can
show the recognizable resonance, if they are lensed. Furthermore, in 1821 GRBs
we actually find one candidate of GRB lensed by a Pop III star, which may be
located at redshift 20-200. The present method is quite straightforward and
therefore provides an effective tool to search for Pop III stars at redshift
greater than 10. Using this method, we may find more candidates of GRBs lensed
by Pop III stars in the data by the {\it Swift} satellite.Comment: 13 pages, 13 figures, accepted for publication in Ap
An X-Ray Microlensing Test of AU-Scale Accretion Disk Structure in Q2237+0305
The innermost regions of quasars can be resolved by a gravitational-lens
{\lq}telescope{\rq} on scales down to a few AU. For the purpose, X-ray
observations are most preferable, because X-rays originating from the innermost
regions, can be selectively amplified by microlensing due to the so-called
`caustic crossing'. If detected, X-ray variations will constrain the size of
the X-ray emitting region down to a few AU. The maximum attainable resolution
depends mainly on the monitoring intervals of lens events, which should be much
shorter than the crossing time. On the basis of this idea, we performe
numerical simulations of microlensing of an optically-thick, standard-type disk
as well as an optically-thin, advection-dominated accretion flow (ADAF).
Calculated spectral variations and light curves show distinct behaviors,
depending on the photon energy. X-ray radiation which is produced in optically
thin region, exhibits intensity variation over a few tens of days. In contrast,
optical-UV fluxes, which are likely to come from optically thick region,
exhibit more gradual light changes, which is consistent with the microlensing
events so far observed in Q2237+0305.
Currently, Q2237+0305 is being monitored in the optical range at Apache Point
Observatory. Simultaneous multi-wavelength observations by X-ray sattelites
(e.g., ASCA, AXAF, XMM) as well as HST at the moment of a microlens event
enable us to reveal an AU scale structure of the central accretion disk around
black hole.Comment: 10 pages LaTeX, 3 figures, accepted to ApJ Letter. e-mail:
[email protected]
The Formation of Population III Binaries
We explore the possibility for the formation of Population III binaries. The
collapse of a rotating cylinder is simulated with a three-dimensional,
high-resolution nested grid, assuming the thermal history of primordial gas.
The simulations are done with dimensionless units, and the results are
applicable to low-mass as well as massive systems by scaling with the initial
density. We find that if the initial angular momentum is as small as , where is the ratio of centrifugal force to pressure
force, then the runaway collapse of the cloud stops to form a
rotationally-supported disk. After the accretion of the envelope, the disk
undergoes a ring instability, eventually fragmenting into a binary. If the
initial angular momentum is relatively large, a bar-type instability arises,
resulting in the collapse into a single star through rapid angular momentum
transfer. The present results show that a significant fraction of Pop III stars
are expected to form in binary systems, even if they are quite massive or less
massive. The cosmological implications of Population III binaries are briefly
discussed.Comment: Astrophysical Journal Letter, in press. 10 pages, 2 color figures,
(full paper with high-resolution figures available at
http://yso.mtk.nao.ac.jp/~saigo/papers/saigo2004a/saigo2004.pdf
Rational Solutions of the Painleve' VI Equation
In this paper, we classify all values of the parameters , ,
and of the Painlev\'e VI equation such that there are
rational solutions. We give a formula for them up to the birational canonical
transformations and the symmetries of the Painlev\'e VI equation.Comment: 13 pages, 1 Postscript figure Typos fixe
Determinant Structure of the Rational Solutions for the Painlev\'e IV Equation
Rational solutions for the Painlev\'e IV equation are investigated by Hirota
bilinear formalism. It is shown that the solutions in one hierarchy are
expressed by 3-reduced Schur functions, and those in another two hierarchies by
Casorati determinant of the Hermite polynomials, or by special case of the
Schur polynomials.Comment: 19 pages, Latex, using theorem.st
Connection Formulae for Asymptotics of Solutions of the Degenerate Third Painlev\'{e} Equation. I
The degenerate third Painlev\'{e} equation, , where ,
and , and the associated tau-function are studied via the
Isomonodromy Deformation Method. Connection formulae for asymptotics of the
general as and solution and general regular as and solution are obtained.Comment: 40 pages, LaTeX2
The influence of octyl beta-D-glucopyranoside on cell lysis induced by ultrasonic cavitation
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98658/1/JAS003482.pd
On a q-difference Painlev\'e III equation: II. Rational solutions
Rational solutions for a -difference analogue of the Painlev\'e III
equation are considered. A Determinant formula of Jacobi-Trudi type for the
solutions is constructed.Comment: Archive version is already official. Published by JNMP at
http://www.sm.luth.se/math/JNMP
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