1,218 research outputs found
Suzaku investigation into the nature of the nearest ultraluminous X-ray source, M33 X-8
The X-ray spectrum of the nearest ultraluminous X-ray source, M33 X-8,
obtained by Suzaku during 2010 January 11 -- 13, was closely analyzed to
examine its nature. It is, by far, the only data with the highest signal
statistic in 0.4 -- 10 keV range. Despite being able to reproduce the X-ray
spectrum, Comptonization of the disk photons failed to give a physically
meaningful solution. A modified version of the multi-color disk model, in which
the dependence of the disk temperature on the radius is described as r^(-p)
with p being a free parameter, can also approximate the spectrum. From this
model, the innermost disk temperature and bolometric luminosity were obtained
as T_in = 2.00-0.05+0.06 keV and L_disk = 1.36 x 10^39 (cos i)^(-1) ergs/s,
respectively, where i is the disk inclination. A small temperature gradient of
p = 0.535-0.005+0.004, together with the high disk temperature, is regarded as
the signatures of the slim accretion disk model, suggesting that M33 X-8 was
accreting at high mass accretion rate. With a correction factor for the slim
disk taken into account, the innermost disk radius, R_in =81.9-6.5+5.9 (cos
i)^(-0.5) km, corresponds to the black hole mass of M \sim 10 M_sun (cos
i)^(-0.5). Accordingly, the bolometric disk luminosity is estimated to be about
80 (cos i)^(-0.5)% of the Eddington limit. A numerically calculated slim disk
spectrum was found to reach a similar result. Thus, the extremely
super-Eddington luminosity is not required to explain the nature of M33 X-8.
This conclusion is utilized to argue for the existence of intermediate mass
black holes with M > 100 M_sun radiating at the sub/trans-Eddington luminosity,
among ultraluminous X-ray sources with L_disk > 10^(40) ergs/s.Comment: 10 pages, 4 figures, PASJ accepte
Optimization by Smoothed Bandpass Calibration in Radio Spectroscopy
We have developed the Smoothed Bandpass Calibration (SBC) method and the best
suitable scan pattern to optimize radio spectroscopic observations. Adequate
spectral smoothing is applied to the spectrum toward OFF-source blank sky
adjacent to a target source direction for the purpose of bandpass correction.
Because the smoothing process reduces noise, the integration time for
OFF-source scans can be reduced keeping the signal-to-noise ratio. Since the
smoothing is not applied to ON-source scans, the spectral resolution for line
features is kept. An optimal smoothing window is determined by bandpass
flatness evaluated by Spectral Allan Variance (SAV). An efficient scan pattern
is designed to the OFF-source scans within the bandpass stability timescale
estimated by Time-based Allan Variance (TAV). We have tested the SBC using the
digital spectrometer, VESPA, on the VERA Iriki station. For the targeted noise
level of 5e-4 as a ratio to the system noise, the optimal smoothing window was
32 - 60 ch in the whole bandwidth of 1024 ch, and the optimal scan pattern was
designed as a sequence of 70-s ON + 10-s OFF scan pairs. The noise level with
the SBC was reduced by a factor of 1.74 compared with the conventional method.
The total telescope time to achieve the goal with the SBC was 400 s, which was
1/3 of 1200 s required by the conventional way. Improvement in telescope time
efficiency with the SBC was calculated as 3x, 2x and 1.3x for single-beam,
dual-beam, and on-the-fly (OTF) scans, respectively. The SBC works to optimize
scan patterns for observations from now, and also works to improve
signal-to-noise ratios of archival data if ON- and OFF-source spectra are
individually recorded, though the efficiency depends on the spectral stability
of the receiving system.Comment: 12 pages, 11 figures, to appear in the Publications of Astronomical
Society of Japan, Vol.64, No.
Pacemaker implantation via femoral vein and successful arrhythmia management in an elderly patient with Fontan circulation: a case report
Background The frequency of arrhythmias increases after the Fontan operation over time; atrial tachycardia (AT) and sinus node dysfunction (SND) are frequently observed. Case summary Our patient was 63-year-old woman who underwent a lateral tunnel Fontan operation for double outlet right ventricle at age 36. She experienced paroxysmal AT for 1 year, and antiarrhythmic medication was not feasible due to symptomatic SND. Computed tomography revealed a 45 mm-sized thrombus in the high right atrium (RA). The patient had three coexisting conditions: paroxysmal AT, symptomatic SND, and the right atrial thrombus, for which total cavopulmonary connection conversion and epicardial pacemaker implantation (PMI) would have been effective; however, given her age and comorbidities, surgical treatment was considered high risk. Catheter ablation was avoided because of the right atrial thrombus. Finally, a transvenous pacemaker was implanted via the right femoral vein to avoid the right atrial thrombus and severe venous tortuosity from the left subclavian vein to the RA. After PMI, the patient was prescribed amiodarone and bisoprolol for AT suppression. Atrial tachycardia occurred once in the third month after discharge. We increased the dose of amiodarone, and she has been tachycardia-free. Discussion Transvenous PMI must be considered in cases where open thoracic surgery or catheter ablation cannot be performed. This is the first report of transvenous PMI via the right femoral vein and successful AT and SND management in an elderly Fontan patient
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