24 research outputs found
A Variable Partial Covering Model for the Seyfert 1 Galaxy MCG-6-30-15
We propose a simple spectral model for the Seyfert 1 Galaxy MCG-6-30-15 that
can explain most of the 1 - 40 keV spectral variation by change of the partial
covering fraction, similar to the one proposed by Miller et al. (2008). Our
spectral model is composed of three continuum components; (1) a direct
power-law component, (2) a heavily absorbed power-law component by mildly
ionized intervening matter, and (3) a cold disk reflection component far from
the black hole with moderate solid-angle ({\Omega}/2{\pi} \approx 0.3)
accompanying a narrow fluorescent iron line. The first two components are
affected by the surrounding highly ionized thin absorber with N_H \approx
10^{23.4}cm-2 and log {\xi} \approx 3.4. The heavy absorber in the second
component is fragmented into many clouds, each of which is composed of radial
zones with different ionization states and column densities, the main body (N_H
\approx 10^24.2cm-2, log {\xi} \approx 1.6), the envelope (N_H \approx
10^22.1cm-2, log {\xi} \approx 1.9) and presumably a completely opaque core.
These parameters of the ionized absorbers, as well as the intrinsic spectral
shape of the X-ray source, are unchanged at all. The central X-ray source is
moderately extended, and its luminosity is not significantly variable. The
observed flux and spectral variations are mostly explained by variation of the
geometrical partial covering fraction of the central source from 0 (uncovered)
to \sim0.63 by the intervening ionized clouds in the line of sight. The ionized
iron K-edge of the heavily absorbed component explains most of the seemingly
broad line-like feature, a well-known spectral characteristic of MCG-6-30-15.
The direct component and the absorbed component anti-correlate, cancelling
their variations each other, so that the fractional spectral variation becomes
the minimum at the iron energy band; another observational characteristic of
MCG-6-30-15 is thus explained.Comment: Accepted to Publications of the Astronomical Society of Japa
Origin of X-ray Spectral Variation and the Seemingly Broad Iron-Line Spectral Feature in Seyfert Galaxies
We present systematic X-ray data analysis of the Seyfert galaxies observed by Suzaku to study origin of their hard X-ray (2 - 40 keV) variations. In particular, we examine if the "Variable Partial Covering (VPC) model" proposed by Miyakawa, Ebisawa and Inoue (2012), which was successful to explain spectral variations of MCG{6-30-15, is also valid for other Seyfert galaxies or not. In this model, intrinsic X-ray luminosity of the AGN is not signicantly variable, and most observed flux and spectral variations are caused by change of the geometrical covering fraction of the extended X-ray source by ionized absorbing clouds in the line of sight. We found that the observed flux and spectral variations of 20 targets in addition to MCG{6-30-15 are successfully explained by the VPC model. The transmitted spectral component through the absorbing clouds has a characteristics spectral feature of the ionized iron K-edge, which is considered to be the origin of the seemingly broad iron-line feature commonly observed in Seyfert galaxies. Variation of the partial covering fraction of the constant X-ray luminosity source causes such an anti-correlation between the direct (non-obscured) component and the transmitted (obscured) component, that cancels their variations each other. The cancellation works most effectively at the energy band where intensities of the two components are the closest to each other, namely, just below the iron K-edge. This explains the signicantly small fractional variations in the iron K-energy band, another well-known observational characteristic of Seyfert galaxies
Luminosity dependence of the electron temperature in the bright hard state of the black hole candidate GX 339--4
We have analyzed 200 Rossi X-ray Timing Explorer observations of the black
hole candidate GX 339--4, all from the bright hard state periods between 1996
and 2005. Purpose of our study is to investigate the radiation mechanisms in
the hard state of GX 339--4. The broadband 3--200 keV spectra were successfully
modeled by a simple analytic model, power--law with an exponential cut-off
modified with a smeared edge. The obtained energy cut-off () was
distributed over 50--200 keV, and the photon index over 1.4--1.7. We found a
clear anti-correlation () between the
X-ray luminosity () in 2--200 keV and , when is larger
than erg s (assuming a distance of 8 kpc), while
is roughly constant at around 200 keV when is smaller than
erg s. This anti-correlation remained unchanged by
adopting a more physical thermal Comptonization model, which resulted in the
anti-correlation that can be expressed as . These anti-correlations can be quantitatively explained by a
picture in which the energy-flow rate from protons to electrons balances with
the inverse Compton cooling.Comment: Accepted by PASJ. 15 pages, 8 figure
Preoperative biliary drainage for biliary tract and ampullary carcinomas
We posed six clinical questions (CQ) on preoperative biliary drainage and organized all pertinent evidence regarding these questions. CQ 1. Is preoperative biliary drainage necessary for patients with jaundice? The indications for preoperative drainage for jaundiced patients are changing greatly. Many reports state that, excluding conditions such as cholangitis and liver dysfunction, biliary drainage is not necessary before pancreatoduodenectomy or less invasive surgery. However, the morbidity and mortality of extended hepatectomy for biliary cancer is still high, and the most common cause of death is hepatic failure; therefore, preoperative biliary drainage is desirable in patients who are to undergo extended hepatectomy. CQ 2. What procedures are appropriate for preoperative biliary drainage? There are three methods of biliary drainage: percutaneous transhepatic biliary drainage (PTBD), endoscopic nasobiliary drainage (ENBD) or endoscopic retrograde biliary drainage (ERBD), and surgical drainage. ERBD is an internal drainage method, and PTBD and ENBD are external methods. However, there are no reports of comparisons of preoperative biliary drainage methods using randomized controlled trials (RCTs). Thus, at this point, a method should be used that can be safely performed with the equipment and techniques available at each facility. CQ 3. Which is better, unilateral or bilateral biliary drainage, in malignant hilar obstruction? Unilateral biliary drainage of the future remnant hepatic lobe is usually enough even when intrahepatic bile ducts are separated into multiple units due to hilar malignancy. Bilateral biliary drainage should be considered in the following cases: those in which the operative procedure is difficult to determine before biliary drainage; those in which cholangitis has developed after unilateral drainage; and those in which the decrease in serum bilirubin after unilateral drainage is very slow. CQ 4. What is the best treatment for postdrainage fever? The most likely cause of high fever in patients with biliary drainage is cholangitis due to problems with the existing drainage catheter or segmental cholangitis if an undrained segment is left. In the latter case, urgent drainage is required. CQ 5. Is bile culture necessary in patients with biliary drainage who are to undergo surgery? Monitoring of bile cultures is necessary for patients with biliary drainage to determine the appropriate use of antibiotics during the perioperative period. CQ 6. Is bile replacement useful for patients with external biliary drainage? Maintenance of the enterohepatic bile circulation is vitally important. Thus, preoperative bile replacement in patients with external biliary drainage is very likely to be effective when highly invasive surgery (e.g., extended hepatectomy for hilar cholangiocarcinoma) is planned
Discharge Observation on Antenna Surface Radiating High-power Microwaves in Simulated Space Environment
The space solar power system (SSPS) transfers enormous amounts of electrical energy through microwaves. When high-power microwaves are irradiated from an antenna in a LEO plasma environment, there is a concern about discharge caused by interaction between the plasma and the microwaves. There has been no experimental observation of such an interaction phenomenon. Verification experiments are essential for SSPS to become a reality. We examine whether discharge or related phenomena occur or not on patch antennas under various conditions in the laboratory. We verify the hypothesis of discharge inception that the discharge is caused by multipactoring and breakdown of the outgas product. We compute the minimum electric field for the discharge inception