1,052 research outputs found
Swift and Suzaku Observations of the X-Ray Afterglow from the GRB 060105
Results are presented of early X-ray afterglow observations of GRB 060105 by
Swift and Suzaku. The bright, long gamma-ray burst GRB 060105 triggered the
Swift Burst Alert Telescope (BAT) at 06:49:28 on 5 January 2006. The Suzaku
team commenced a pre-planned target of opportunity observation at 19 ks (5.3
hr) after the Swift trigger. Following the prompt emission and successive very
steep decay, a shallow decay was observed from T_0+187 s to T_0+1287 s. After
an observation gap during T_0 +(1.5-3) ks, an extremely early steep decay was
observed in T_0+(4-30) ks. The lightcurve flattened again at T_0+30 ks, and
another steep decay followed from T_0+50 ks to the end of observations. Both
steep decays exhibited decay indices of 2.3 - 2.4. This very early break, if it
is a jet break, is the earliest case among X-ray afterglow observations,
suggesting a very narrow jet whose opening angle is well below 1 degree. The
unique Suzaku/XIS data allow us to set very tight upper limits on line emission
or absorption in this GRB. For the reported pseudo-redshift of z=4.0+/-1.3 the
upper limit on the iron line equivalent width is 50 eV.Comment: 8 pages, 5 figures, Accepted for publication in PASJ Suzaku Special
Issue (vol. 58
Measurement of the forward-backward asymmetries for charm- and bottom-quark pair productions at =58GeV with electron tagging
We have measured, with electron tagging, the forward-backward asymmetries of
charm- and bottom-quark pair productions at =58.01GeV, based on
23,783 hadronic events selected from a data sample of 197pb taken with
the TOPAZ detector at TRISTAN. The measured forward-backward asymmetries are
and , which are consistent with the standard model
predictions.Comment: 19 pages, Latex format (article), 5 figures included. to be published
in Phys. Lett.
Measurement of the cross-section and forward-backward charge asymmetry for the b and c-quark in e+e- annihilation with inclusive muons at sqrt(s) = 58 GeV
We have studied inclusive muon events using all the data collected by the
TOPAZ detector at sqrt(s)=58 GeV with an integrated luminosity of 273pb-1. From
1328 inclusive muon events, we measured the ratio R_qq of the cross section for
qq-bar production to the total hadronic cross section and forward-backward
asymmetry A^q_FB for b and c quarks. The obtained results are R_bb =
0.13+-0.02(stat)+-0.01(syst), R_cc = 0.36+-0.05(stat)+-0.05(syst), A^b_FB =
-0.20+-0.16(stat)+-0.01(syst) and A^c_FB = -0.17+-0.14(stat)+-0.02(syst), in
fair agreement with a prediction of the standard model.Comment: To be published in EPJ C. 24 pages, 12 figure
Measurement of inclusive electron cross section in collisions at TRISTAN
We have studied open charm production in collisions with the
TOPAZ detector at the TRISTAN collider. In this study, charm
quarks were identified by electrons (and positrons) from semi-leptonic decays
of charmed hadrons. The data corresponded to an integrated luminosity of 95.3
pb at a center-of-mass energy of 58 GeV. The results are presented as
the cross sections of inclusive electron production in
collisions with an anti-tag condition, as well as the subprocess cross
sections, which correspond to resolved-photon processes. The latter were
measured by using a sub-sample with remnant jets. A comparison with various
theoretical predictions based on direct and resolved-photon processes showed
that our data prefer that with relatively large gluon contents in a photon at
small , with the next-to-leading order correction, and with a
charm-quark mass of 1.3 GeV.Comment: 26 pages, Latex format (article), 5 figures included, to be published
in Phys. Lett.
Production in Two-Photon Processes at TRISTAN
We have carried out an inclusive measurement of production
in two-photon processes at TRISTAN. The mean was 58 GeV and the
integrated luminosity was 199 pb. High-statistics samples were
obtained under such conditions as no-, anti-electron, and remnant-jet tags. The
remnant-jet tag, in particular, allowed us, for the first time, to measure the
cross sections separately for the resolved-photon and direct processes.Comment: 20 pages, Latex format, 4 figures and KEK-mark included. Table 1
revised. To be published in Phys. Lett.
Orbital characterization of GJ1108A system, and comparison of dynamical mass with model-derived mass for resolved binaries
We report an orbital characterization of GJ1108Aab that is a low-mass binary
system in pre-main-sequence phase. Via the combination of astrometry using
adaptive optics and radial velocity measurements, an eccentric orbital solution
of =0.63 is obtained, which might be induced by the Kozai-Lidov mechanism
with a widely separated GJ1108B system. Combined with several observed
properties, we confirm the system is indeed young. Columba is the most probable
moving group, to which the GJ1108A system belongs, although its membership to
the group has not been established. If the age of Columba is assumed for
GJ1108A, the dynamical masses of both GJ1108Aa and GJ1108Ab ( and ) are more massive than what an
evolutionary model predicts based on the age and luminosities. We consider the
discrepancy in mass comparison can attribute to an age uncertainty; the system
is likely older than stars in Columba, and effects that are not implemented in
classical models such as accretion history and magnetic activity are not
preferred to explain the mass discrepancy. We also discuss the performance of
the evolutionary model by compiling similar low-mass objects in evolutionary
state based on the literature. Consequently, it is suggested that the current
model on average reproduces the mass of resolved low-mass binaries without any
significant offsets.Comment: Accepted in Ap
SEEDS direct imaging of the RV-detected companion to V450 Andromedae, and characterization of the system
We report the direct imaging detection of a low-mass companion to a young,
moderately active star V450 And, that was previously identified with the radial
velocity method. The companion was found in high-contrast images obtained with
the Subaru Telescope equipped with the HiCIAO camera and AO188 adaptive optics
system. From the public ELODIE and SOPHIE archives we extracted available
high-resolution spectra and radial velocity (RV) measurements, along with RVs
from the Lick planet search program. We combined our multi-epoch astrometry
with these archival, partially unpublished RVs, and found that the companion is
a low-mass star, not a brown dwarf, as previously suggested. We found the
best-fitting dynamical masses to be and
M. We also performed spectral analysis of
the SOPHIE spectra with the iSpec code. The Hipparcos time-series photometry
shows a periodicity of d, which is also seen in SOPHIE spectra as an
RV modulation of the star A. We interpret it as being caused by spots on the
stellar surface, and the star to be rotating with the given period. From the
rotation and level of activity, we found that the system is
Myr old, consistent with an isochrone analysis ( Myr). This
work may serve as a test case for future studies of low-mass stars, brown
dwarfs and exoplanets by combination of RV and direct imaging data.Comment: 15 pages, 9 figures, 7 tables, to appear in Ap
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