482 research outputs found
Infrared/optical - X-ray simultaneous observations of X-ray flares in GRB 071112C and GRB 080506
We investigate the origin of short X-ray flares which are occasionally
observed in early stages of afterglows of gamma-ray bursts (GRBs). We observed
two events, GRB 071112C and GRB 080506, before the start of X-ray flares in the
optical and near-infrared (NIR) bands with the 1.5-m Kanata telescope. In
conjunction with published X-ray and optical data, we analyzed densely sampled
light curves of the early afterglows and spectral energy distributions (SEDs)
in the NIR-X-ray ranges. We found that the SEDs had a break between the optical
and X-ray bands in the normal decay phases of both GRBs regardless of the model
for the correction of the interstellar extinction in host galaxies of GRBs. In
the X-ray flares, X-ray flux increased by 3 and 15 times in the case of GRB
071112C and 080506, respectively, and the X-ray spectra became harder than
those in the normal decay phases. No significant variation in the optical-NIR
range was detected together with the X-ray flares. These results suggest that
the X-ray flares were associated with either late internal shocks or external
shocks from two-component jets.Comment: 10 pages, 5 figures, accepted to Astronomy and Astrophysic
Detection of Polarimetric Variations Associated with the Shortest Time-Scale Variability in S5 0716714
We present the result of near-infrared and optical observations of the BL Lac
object S5 0716714 carried out by the KANATA telescope. S5 0716714 has
both a long term high-amplitude variability and a short-term variability within
a night. The shortest variability (microvariability) time-scale is important
for understanding the geometry of jets and magnetic field, because it provides
a possible minimum size of variation sources. Here, we report the detection of
15-min variability in S5 0716714, which is one of the shortest time-scales
in optical and near-infrared variations observed in blazars. The detected
microvariation had an amplitude of mag in band and a blue
color of . Furthermore, we successfully detected
an unprecedented, short time-scale polarimetric variation which correlated with
the brightness change. We revealed that the microvariation had a specific
polarization component. The polarization degree of the variation component was
higher than that of the total flux. These results suggest that the
microvariability originated from a small and local region where the magnetic
field is aligned.Comment: 5 pages, 4 figures; Publications of the Astronomical Society of Japan
letter accepte
Dwarf Novae in the Shortest Orbital Period Regime: I. A New Short Period Dwarf Nova, OT J055717+683226
We report the observation of a new dwarf nova, OT J055717+683226, during its
first-ever recorded superoutburst in December 2006. Our observation shows that
this object is an SU UMa-type dwarf nova having a very short superhump period
of 76.67+/- 0.03 min (0.05324+/-0.00002 d). The next superoutburst was observed
in March 2008. The recurrence time of superoutbursts (supercycle) is, hence,
estimated to be ~480 d. The supercycle is much shorter than those of WZ
Sge-type dwarf novae having supercycles of >~ 10 yr, which are a major
population of dwarf novae in the shortest orbital period regime (<~85 min).
Using a hierarchical cluster analysis, we identified seven groups of dwarf
novae in the shortest orbital period regime. We identified a small group of
objects that have short supercycles, small outburst amplitudes, and large
superhump period excesses, compared with those of WZ Sge stars. OT
J055717+683226 probably belongs to this group.Comment: 14 pages, 11 figures, accepted for publication in PAS
Optical and Near-Infrared Photometry of Nova V2362 Cyg : Rebrightening Event and Dust Formation
We present optical and near-infrared (NIR) photometry of a classical nova,
V2362 Cyg (= Nova Cygni 2006). V2362 Cyg experienced a peculiar rebrightening
with a long duration from 100 to 240 d after the maximum of the nova. Our
multicolor observation indicates an emergence of a pseudophotosphere with an
effective temperature of 9000 K at the rebrightening maximum. After the
rebrightening maximum, the object showed a slow fading homogeneously in all of
the used bands for one week. This implies that the fading just after the
rebrightening maximum ( less or equal 1 week ) was caused by a slowly shrinking
pseudophotosphere. Then, the NIR flux drastically increased, while the optical
flux steeply declined. The optical and NIR flux was consistent with blackbody
radiation with a temperature of 1500 K during this NIR rising phase. These
facts are likely to be explained by dust formation in the nova ejecta. Assuming
an optically thin case, we estimate the dust mass of 10^(-8) -- 10^(-10)
M_solar, which is less than those in typical dust-forming novae. These results
support the senario that a second, long-lasting outflow, which caused the
rebrightening, interacted with a fraction of the initial outflow and formed
dust grains.Comment: 6 pages, 4 figures, 2010, PASJ, 62, 1103--1108, in pres
Histological Course of Nonalcoholic Fatty Liver Disease in Japanese Patients: Tight glycemic control, rather than weight reduction, ameliorates liver fibrosis
金沢大学医薬保健研究域医学系OBJECTIVE - The goal of this study was to examine whether metabolic abnormalities are responsible for the histological changes observed in Japanese patients with nonalcoholic fatty liver disease (NAFLD) who have undergone serial liver biopsies. RESEARCH DESIGN AND METHODS - In total, 39 patients had undergone consecutive liver biopsies. Changes in their clinical data were analyzed, and biopsy specimens were scored histologically for stage. RESULTS - The median follow-up time was 2.4 years (range 1.0-8.5). Liver fibrosis had improved in 12 patients (30.7%), progressed in 11 patients (28.2%), and remained unchanged in 16 patients (41%). In a Cox proportional hazard model, decrease in A1C and use of insulin were associated with improvement of liver fibrosis independent of age, sex, and BMI. However, ΔA1C was more strongly associated with the improvement of liver fibrosis than use of insulin after adjustment for each other (χ2; 7.97 vs. 4.58, respectively). CONCLUSIONS - Tight glycemic control may prevent histological progression in Japanese patients with NAFLD. © 2010 by the American Diabetes Association
Optical and Near-Infrared Photometric Observation during the Superoutburst of the WZ Sge-Type Dwarf Nova, V455 Andromedae
We report on optical and infrared photometric observations of a WZ Sge-type
dwarf nova, V455 And during a superoutburst in 2007. These observations were
performed with the KANATA (V, J, and K_s bands) and MITSuME (g', Rc, and Ic
bands) telescopes. Our 6-band simultaneous observations allowed us to
investigate the temporal variation of the temperature and the size of the
emitting region associated with the superoutburst and short-term modulations,
such as early and ordinary superhumps. A hot (>11000 K) accretion disk suddenly
disappeared when the superoutburst finished, while blackbody emission, probably
from the disk, still remained dominant in the optical region with a moderately
high temperature (~8000 K). This indicates that a substantial amount of gas was
stored in the disk even after the outburst. This remnant matter may be a sign
of an expected mass-reservoir which can trigger echo outbursts observed in
several WZ Sge stars. The color variation associated with superhumps indicates
that viscous heating in a superhump source stopped on the way to the superhump
maximum, and a subsequent expansion of a low-temperature region made the
maximum. The color variation of early superhumps was totally different from
that of superhumps: the object was bluest at the early superhump minimum. The
temperature of the early superhump light source was lower than that of an
underlying component, indicating that the early superhump light source was a
vertically expanded low-temperature region at the outermost part of the disk.Comment: 14 pages, 12 figures, PASJ accepte
Early phase observations of extremely luminous Type Ia Supernova 2009dc
We present early phase observations in optical and near-infrared wavelengths
for the extremely luminous Type Ia supernova (SN Ia) 2009dc. The decline rate
of the light curve is , which is one of the
slowest among SNe Ia. The peak -band absolute magnitude is mag even if the host extinction is mag. It reaches
mag for the host extinction of mag as
inferred from the observed Na {\sc i} D line absorption in the host. Our
-band photometry shows that the SN is one of the most luminous SNe Ia
also in near-infrared wavelengths. These results indicate that SN 2009dc
belongs to the most luminous class of SNe Ia, like SN 2003fg and SN 2006gz. We
estimate the ejected Ni mass of \Msun for no host
extinction case (or 1.6 0.4 M for the host extinction of
mag). The C {\sc ii} 6580 absorption line keeps visible
until a week after maximum, which diminished in SN 2006gz before its maximum
brightness. The line velocity of Si {\sc ii} 6355 is about 8000 km
s around the maximum, being considerably slower than that of SN 2006gz,
while comparable to that of SN 2003fg. The velocity of the C {\sc ii} line is
almost comparable to that of the Si {\sc ii}. The presence of the carbon line
suggests that thick unburned C+O layers remain after the explosion. SN 2009dc
is a plausible candidate of the super-Chandrasekhar mass SNe Ia
The 2006 November outburst of EG Aquarii: the SU UMa nature revealed
We report time-resolved CCD photometry of the cataclysmic variable EG Aquarii
during the 2006 November outburst During the outburst, superhumps were
unambiguously detected with a mean period of 0.078828(6) days, firstly
classifying the object as an SU UMa-type dwarf nova. It also turned out that
the outburst contained a precursor. At the end of the precursor, immature
profiles of humps were observed. By a phase analysis of these humps, we
interpreted the features as superhumps. This is the second example that the
superhumps were shown during a precursor. Near the maximum stage of the
outburst, we discovered an abrupt shift of the superhump period by
0.002 days. After the supermaximum, the superhump period decreased at the rate
of =, which is typical for SU UMa-type dwarf
novae. Although the outburst light curve was characteristic of SU UMa-type
dwarf novae, long-term monitoring of the variable shows no outbursts over the
past decade. We note on the basic properties of long period and inactive SU
UMa-type dwarf novae.Comment: 9 pages, 7 figures, accepted for PAS
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