2,342 research outputs found
The generalized parton distribution functions and the nucleon spin sum rules in the chiral quark soliton model
The theoretical predictions are given for the forward limit of the
unpolarized spin-flip isovector generalized parton distribution function within the framework of the chiral quark soliton model, with
full inclusion of the polarization of Dirac sea quarks. We observe that has a sharp peak around , which we interpret
as a signal of the importance of the pionic excitation with large
spatial extension in the transverse direction. Another interesting indication
given by the predicted distribution in combination with Ji's angular momentum
sum rule is that the -quark carries more angular momentum than the
-quark in the proton, which may have some relation with the physics of
the violation of the Gottfried sum rule.Comment: 23 pages, 2 figures, revised final version to appear in Phys. Rev.
A Systematic Study of X-Ray Flares from Low-Mass Young Stellar Objects in the Rho Ophiuchi Star-Forming Region with Chandra
We report on the results of a systematic study of X-ray flares from low-mass
young stellar objects, using Chandra observations of the main region of the Rho
Oph. From 195 X-ray sources, including class I-III sources and some young brown
dwarfs, we detected a total of 71 X-ray flares. Most of the flares have the
typical profile of solar and stellar flares, fast rise and slow decay. We
derived the time-averaged temperature (kT), luminosity (L_X), rise and decay
timescales (tau_r and tau_d) of the flares, finding that (1) class I-II sources
tend to have a high kT, (2) the distribution of L_X during flares is nearly the
same for all classes, and (3) positive and negative log-linear correlations are
found between tau_r and tau_d, and kT and tau_r. In order to explain these
relations, we used the framework of magnetic reconnection model to formulate
the observational parameters as a function of the half-length of the
reconnected magnetic loop (L) and magnetic field strength (B). The estimated L
is comparable to the typical stellar radius of these objects (10^{10-11} cm),
which indicates that the observed flares are triggered by solar-type loops,
rather than larger ones (10^{12} cm) connecting the star with its inner
accretion disk. The higher kT observed for class I sources may be explained by
a higher magnetic field strength (about 500 G) than for class II-III sources
(200-300 G).Comment: 33 pages, 7 figures, accepted for publication in PASJ, the complete
version of tables are available at
ftp://ftp-cr.scphys.kyoto-u.ac.jp/pub/crmember/kensuke/PASJ_RhoOph/KI_all.tar
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An Algebraic Model for the Multiple Meixner Polynomials of the First Kind
An interpretation of the multiple Meixner polynomials of the first kind is
provided through an infinite Lie algebra realized in terms of the creation and
annihilation operators of a set of independent oscillators. The model is used
to derive properties of these orthogonal polynomials
The nature of the fluorescent iron line in V 1486 Ori
The fluorescent 6.4 keV iron line provides information on cool material in
the vicinity of hard X-ray sources as well as on the characteristics of the
X-ray sources themselves. First discovered in the X-ray spectra of the flaring
Sun, X-ray binaries and active galactic nuclei (AGN), the fluorescent line was
also observed in a number of stellar X-ray sources. The young stellar object
(YSO) V1486 Ori was observed in the framework of the Chandra Ultra Deep Project
(COUP) as the source COUP 331. We investigate its spectrum, with emphasis on
the strength and time variability of the fluorescent iron K-alpha line, derive
and analyze the light curve of COUP 331 and proceed with a time-resolved
spectral analysis of the observation. The light curve of V 1486 Ori shows two
major flares, the first one lasting for (approx) 20 ks with a peak X-ray
luminosity of 2.6*10^{32} erg/s (dereddened in the 1-10 keV band) and the
second one -- only partially observed -- for >60 ks with an average X-ray
luminosity of 2.4*10^{31} erg/s (dereddened). The spectrum of the first flare
is very well described by an absorbed thermal model at high temperature, with a
pronounced 6.7 keV iron line complex, but without any fluorescent K-alpha line.
The X-ray spectrum of the second flare is characterized by even higher
temperatures (>= 10 keV) without any detectable 6.7 keV Fe XXV feature, but
with a very strong fluorescent iron K-alpha line appearing predominantly in the
20 ks rise phase of the flare. Preliminary model calculations indicate that
photoionization is unlikely to account for the entire fluorescent emission
during the rise phase.Comment: 4 pages, letter, accepted for publication in A&
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