55 research outputs found
超解像X線望遠鏡のイメージ再構成法
Open House, ISM in Tachikawa, 2018.6.15統計数理研究所オープンハウス(立川)、H30.6.15ポスター発
Data Compression for optical movie data of the Tomo-e Gozen
Open House, ISM in Tachikawa, 2017.6.16統計数理研究所オープンハウス(立川)、H29.6.16ポスター発
Geographic Variations in the Toxin Profile of the Xanthid Crab Zosimus aeneus in a Single Reef on Ishigaki Island, Okinawa, Japan
Toxic crabs of the family Xanthidae contain saxitoxins (STXs) and/or tetrodotoxin (TTX), but the toxin ratio differs depending on their habitat. In the present study, to clarify within reef variations in the toxin profile of xanthid crabs, we collected specimens of the toxic xanthid crab Zosimus aeneus and their sampling location within a single reef (Yoshihara reef) on Ishigaki Island, Okinawa Prefecture, Japan, in 2018 and 2019. The STXs/TTX content within the appendages and viscera or stomach contents of each specimen was determined by instrumental analyses. Our findings revealed the existence of three zones in Yoshihara reef; one in which many individuals accumulate extremely high concentrations of STXs (northwestern part of the reef; NW zone), another in which individuals generally have small amounts of TTX but little STXs (central part of the reef; CTR zone), and a third in which individuals generally exhibit intermediate characteristics (southeastern part of the reef; SE zone). Furthermore, light microscopic observations of the stomach contents of crab specimens collected from the NW and CTR zones revealed that ascidian spicules of the genus Lissoclinum were dominant in the NW zone, whereas those of the genus Trididemnum were dominant in the CTR zone. Although the toxicity of these ascidians is unknown, Lissoclinum ascidians are considered good candidate source organisms of STXs harbored by toxic xanthid crabs
Outburst of LS V+44 17 Observed by MAXI and RXTE, and Discovery of a Dip Structure in the Pulse Profile
We report on the first observation of an X-ray outburst of a Be/X-ray binary
pulsar LS V +44 17/RX J0440.9+4431, and the discovery of an absorption dip
structure in the pulse profile. An outburst of this source was discovered by
MAXI GSC in 2010 April. It was the first detection of the transient activity of
LS V +44 17 since the source was identified as a Be/X-ray binary in 1997. From
the data of the follow-up RXTE observation near the peak of the outburst, we
found a narrow dip structure in its pulse profile which was clearer in the
lower energy bands. The pulse-phase-averaged energy spectra in the 3100 keV
band can be fitted with a continuum model containing a power-law function with
an exponential cutoff and a blackbody component, which are modified at low
energy by an absorption component. A weak iron K emission line is also
detected in the spectra. From the pulse-phase-resolved spectroscopy we found
that the absorption column density at the dip phase was much higher than those
in the other phases. The dip was not seen in the subsequent RXTE observations
at lower flux levels. These results suggest that the dip in the pulse profile
originates from the eclipse of the radiation from the neutron star by the
accretion column.Comment: 18 pages, 7 figures, accepted for publication in PAS
Bright X-ray flares from the BL Lac object Mrk 421, detected with MAXI in 2010 January and February
Strong X-ray flares from the blazar Mrk 421 were detected in 2010 January and
February through the 7 month monitoring with the MAXI GSC. The maximum 2 -- 10
keV flux in the January and February flares was measured as 120 +- 10 mCrab and
164 +- 17 mCrab respectively; the latter is the highest among those reported
from the object. A comparison of the MAXI and Swift BAT data suggests a convex
X-ray spectrum with an approximated photon index of about 2. This spectrum is
consistent with a picture that MAXI is observing near the synchrotron peak
frequency. The source exhibited a spectral variation during these flares,
slightly different from those in the previous observations, in which the
positive correlation between the flux and hardness was widely reported. By
equating the halving decay timescale in the January flare, s, to the synchrotron cooling time, the magnetic field was
evaluated as B = 0.045 G , where is the jet
beaming factor. Assuming that the light crossing time of the emission region is
shorter than the doubling rise time, s,
the region size was roughly estimated as cm
. These are consistent with the values previously reported. For
the February flare, the rise time, s, gives a
loose upper limit on the size as cm ,
although the longer decay time s, indicates
B = 0.015 G , which is weaker than the previous results.
This could be reconciled by invoking a scenario that this flare is a
superposition of unresolved events with a shorter timescale.Comment: 14 pages, 4 figures, accepted for PASJ (Vol. 62 No. 6
MAXI GSC observations of a spectral state transition in the black hole candidate XTE J1752-223
We present the first results on the black hole candidate XTE J1752-223 from
the Gas Slit Camera (GSC) on-board the Monitor of All-sky X-ray Image (MAXI) on
the International Space Station. Including the onset of the outburst reported
by the Proportional Counter Array on-board the Rossi X-ray Timing Explorer on
2009 October 23, the MAXI/GSC has been monitoring this source approximately 10
times per day with a high sensitivity in the 2-20 keV band. XTE J1752-223 was
initially in the low/hard state during the first 3 months. An anti-correlated
behavior between the 2-4 keV and 4-20 keV bands were observed around January
20, 2010, indicating that the source exhibited the spectral transition to the
high/soft state. A transient radio jet may have been ejected when the source
was in the intermediate state where the spectrum was roughly explained by a
power-law with a photon index of 2.5-3.0. The unusually long period in the
initial low/hard state implies a slow variation in the mass accretion rate, and
the dramatic soft X-ray increase may be explained by a sudden appearance of the
accretion disk component with a relatively low innermost temperature (0.4-0.7
keV). Such a low temperature might suggest that the maximum accretion rate was
just above the critical gas evaporation rate required for the state transition.Comment: Publication of Astronomical Society of Japan Vol.62, No.5 (2010) [in
print
The MAXI Mission on the ISS: Science and Instruments for Monitoring All Sky X-Ray Images
The MAXI (Monitor of All-sky X-ray Image) mission is the first astronomical
payload to be installed on the Japanese Experiment Module-Exposed Facility
(JEM-EF) on the ISS. It is scheduled for launch in the middle of 2009 to
monitor all-sky X-ray objects on every ISS orbit. MAXI will be more powerful
than any previous X-ray All Sky Monitor (ASM) payloads, being able to monitor
hundreds of AGN. MAXI will provide all sky images of X-ray sources of about 20
mCrab in the energy band of 2-30 keV from observation on one ISS orbit (90
min), about 4.5 mCrab for one day, and about 1 mCrab for one month. A final
detectability of MAXI could be 0.2 mCrab for 2 year observations.Comment: 12 pages, 11 figures, accepted for publication in Publications of the
Astronomical Society of Japa
Long-term Monitoring of the Black Hole Binary GX 339-4 in the High/Soft State during the 2010 Outburst with MAXI/GSC
We present the results of monitoring the Galactic black hole candidate GX
339-4 with the Monitor of All-sky X-ray Image (MAXI) / Gas Slit Camera (GSC) in
the high/soft state during the outburst in 2010. All the spectra throughout the
8-month period are well reproduced with a model consisting of multi-color disk
(MCD) emission and its Comptonization component, whose fraction is <= 25% in
the total flux. In spite of the flux variability over a factor of 3, the
innermost disk radius is constant at R_in = 61 +/- 2 km for the inclination
angle of i = 46 deg and the distance of d=8 kpc. This R_in value is consistent
with those of the past measurements with Tenma in the high/soft state. Assuming
that the disk extends to the innermost stable circular orbit of a non-spinning
black hole, we estimate the black hole mass to be M = 6.8 +/- 0.2 M_sun for i =
46 deg and d = 8 kpc, which is consistent with that estimated from the Suzaku
observation of the previous low/hard state. Further combined with the mass
function, we obtain the mass constraint of 4.3 M_sun < M < 13.3 M_sun for the
allowed range of d = 6-15 kpc and i < 60 deg. We also discuss the spin
parameter of the black hole in GX 339-4 by applying relativistic accretion disk
models to the Swift/XRT data.Comment: 9 pages, 8 figures, accepted for publication in PASJ (Suzaku+MAXI
special issue
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