71 research outputs found
Discovery of a short plateau phase in the early evolution of a gamma-ray burst afterglow
We report optical observations during the first hour of the gamma-ray burst
(GRB) afterglow of GRB021004. Our observation revealed the existence of a short
plateau phase, in which the afterglow remained at almost constant brightness,
before an ordinary rapid fading phase. This plateau phase lasted for about 2
hours from 0.024 to 0.10 d after the burst, which corresponds to a missing
blank of the early afterglow light curve of GRB990123. We propose that the
plateau phase can be interpreted as the natural evolution of synchrotron
emission from the forward shock region of a blast wave. The time when the
typical frequency of the synchrotron emission passes through the optical range
has been predicted to be about 0.1 d after the burst, which is consistent with
the observed light curve. Our scenario hence implies that the observed feature
in GRB021004 is a common nature of GRB afterglows.Comment: 3 pages, 1 figure, accepted for publication in PAS
Large-Amplitude 2.65-d Oscillation in the VY Scl-Type star V425 Cas
From long-term photometry of a VY Scl-type star, V425 Cas, between 1998 and
2000, we discovered a short-term, large-amplitude (up to 1.5 mag) variations.
The variation was well represented by a single period of 2.65 d. The large
amplitude and the profile of the folded light curve suggest that the dwarf
nova-type disk instability is responsible for this variation. The shortness of
the period is unprecedented in hydrogen-rich cataclysmic variables. Given the
recent emerging evidence that the irradiation from white dwarfs in VY Scl-type
systems affect their light behavior, we propose a possibility that this unique
variation in V425 Cas can be explained by the combination of the dwarf
nova-type disk instability and irradiation. Similar short-period "outbursts"
have been known in X-ray transients (V518 Per), and helium cataclysmic
variables (CR Boo and V803 Cen). We discuss the possibility that these
phenomena have a common origin to the unique variation in V425 Cas.Comment: 6 pages, 5 figures, accepted for publication in Publ. Astron. Soc.
Japa
Rapid Optical Fluctuations in the Black Hole Binary, V4641 Sgr
We report on unprecedented short-term variations detected in the optical flux
from the black hole binary system, V4641 Sgr. Amplitudes of the optical
fluctuations were larger at longer time scales, and surprisingly reached ~60%
around a period of ~10 min. The power spectra of fluctuations are characterized
by a power law. It is the first case in black hole binaries that the optical
emission was revealed to show short-term and large-amplitude variations given
by such a power spectrum. The optical emission from black hole binaries is
generally dominated by the emission from the outer portion of an accretion
disc. The rapid optical fluctuations however indicate that the emission from an
inner accretion region significantly contributes to the optical flux. In this
case, cyclo-synchrotron emission associated with various scales of magnetic
flares is the most promising mechanism for the violently variable optical
emission.Comment: 5 pages, 2 figures, accepted for publication in PAS
Photometric Studies of New Southern SU UMa-type dwarf novae, FL Triangulum Australe and CTCV J0549-4921
We report time-resolved optical CCD photometry on newly discovered SU
UMa-type dwarf novae, FL TrA and CTCV J0549-4921. During the 2006 August
outburst, we detected superhumps with a period of 0.59897(11) days for FL TrA,
clarifying the SU UMa nature of the system. On the first night of our
observations on FL TrA, the object showed no superhumps. This implies that it
takes a few days for full development of superhumps. The superhump period
variation diagram of FL TrA was similar to that observed in some WZ Sge stars
and short period SU UMa-type stars. This indicates that the system is closely
related to WZ Sge stars and SU UMa stars having short orbital periods. For CTCV
J0549-4921, the candidates of the mean superhump period are 0.083249(10) days
and 0.084257(8) days, respectively. Due to a lack of the observations, we
cannot determine the true superhump period, but the latter period is favorable.
Using the ASAS-3 archive, it turned out that the system shows only four
outbursts over the past 6 years. The outburst amplitude of CTCV J0549-4921 was
relatively small, with about 4.5 mag. One possibility is that mass evaporation
may play a role during quiescence.Comment: 7 pages, 8 figures, published for PASJ vol.6
Discovery of a new dwarf nova, TSS J022216.4+412259.9: WZ Sge-type dwarf novae breaking the shortest superhump period record
We report on the time-resolved CCD photometry of a newly discovered variable
star, TSS J022216.4+412259.9 during the outburst in 2005 November-December
brightening. The obtained light curves unambiguously showed 0.2-0.3 mag
modulations, which we confirmed to be the superhump observed among SU UMa-type
dwarf novae. We also performed a period search for the data obtained during the
outburst plateau phase, and revealed the existence of the two periodicities:
0.054868(98) days for the first two nights and 0.055544(26) days for the
following plateau phase. This bi-periodicity is hardly observed in usual SU
UMa-type dwarf novae, but characteristic of WZ Sge-type stars. We undoubtedly
detected a rebrightening in the post-outburst stage, which is typical of
short-period SU UMa-type dwarf novae including WZ Sge-type stars. These
observations suggests that TSS J022216.4+412259.9 may be a new WZ Sge stars
breaking the shortest superhump period of 0.05648 days for V592 Her among this
class with a known superhump period so far.Comment: 5 pages, 6 figures, accepted for PASJ lette
Severe accidental colchicine poisoning by the autumn crocus: A case of successful treatment
AbstractBackgroundThe common garden plant autumn crocus contains colchicine and its derivatives. Colchicine poisoning causes abdominal cramps and diarrhea within hours. Several days later, multiorgan failure, pancytopenia, and cardiovascular collapse occur.1,2 Severe colchicine poisoning is associated with high mortality.Case reportA 63-year-old woman who accidentally ingested an autumn crocus, which contained ∼0.38 mg colchicine, had severe vomiting and was taken to an emergency center. She presented with symptoms of gastroenterocolitis within 1 hour of ingestion, and bone marrow hypoplasia with pancytopenia developed on the 3rd day after ingestion. We continued administration of granulocyte colony-stimulating factor (300 μg) for 5 days until we confirmed that the patient's white blood cell count was increasing. Also, there was focal and segmental intestinal ischemia and some cakes of charcoal remained in the intestinal tract. Therefore, we presumed that nonocclusive mesenteric ischemia was caused by hypotension with severe dehydration, although pseudo-obstruction due to the activated charcoal may have been a contributing factor. We were able to promptly intervene to treat paralytic ileus and gastrointestinal edema before anticipated worsening of abdominal compartment syndrome, by conducting open peritoneal drainage. Despite severe poisoning, our patient survived with intensive care. Conclusion: Colchicine intoxication may lead to a sudden and extreme critical course. Therefore, as there is no means to predict prognosis from initial severity of symptoms at onset, we suggest that all patients suspected of colchicine intoxication should be managed in hospital with continuous vital sign monitoring and frequent laboratory testing for at least a few days after ingestion
Dwarf Nova-like Outburst of Short Period Intermediate Polar HT Camelopardalis
We report the first time-series observations of the short outburst of the
proposed intermediate polar HT Cam (=RX J0757.0+6306). On 2001 December 29, we
detected the object was undergoing a bright outburst at the magnitude of
. Following this detection, we started international joint
observations through VSNET. The light curve showed a gradual decline for the
first 0.5 d. Following this short plateau phase, the rate of decline
dramatically increased to more than 4 mag d. Within 1.5 d from the
outburst detection, the object almost declined to the quiescent level. During
the rapidly declining phase, long-term modulations with a period of 86 min and
strong pulses with a period of 8.6 min were observed. We concluded that 86 min
and 8.6 min are the orbital period and the spin period of HT Cam, respectively.
By the detection of the spin period, we confirmed the IP classification of HT
Cam. However, its outburst behavior rather resembles that of dwarf novae.
The discrepancy between the declining rates of the total flux and the pulse
flux strongly suggests that the disk instabilities were taking place during the
outburst.Comment: 7 pages, 8 figures, accepted for publication in PAS
Long-term monitoring of the short period SU UMa-type dwarf nova, V844 Herculis
We report on time-resolved CCD photometry of four outbursts of a short-period
SU UMa-type dwarf nova, V844 Herculis. We successfully determined the mean
superhump periods to be 0.05584(64) days, and 0.055883(3) for the 2002 May
superoutburst, and the 2006 April-May superoutburst, respectively. During the
2002 October observations, we confirmed that the outburst is a normal outburst,
which is the first recorded normal outburst in V844 Her. We also examined
superhump period changes during 2002 May and 2006 April-May superoutbursts,
both of which showed increasing superhump period over the course of the plateau
stage. In order to examine the long-term behavior of V844 Her, we analyzed
archival data over the past ten years since the discovery of this binary.
Although photometry is not satisfactory in some superoutbursts, we found that
V844 Her showed no precursors and rebrightenings. Based on the long-term light
curve, we further confirmed V844 Her has shown almost no normal outbursts
despite the fact that the supercycle of the system is estimated to be about 300
days. In order to explain the long-term light curves of V844 Her, evaporation
in the accretion disk may play a role in the avoidance of several normal
outbursts, which does not contradict with the relatively large X-ray luminosity
of V844 Her.Comment: 10 pages, 11 figures, accepted for PAS
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