Shiro Ueno

ASCA Detection of a Superhot 100 Million K X‐Ray Flare on the Weak‐lined T Tauri Star V773 Tauri

We present results of a ≈ 40 ks ASCA observation of the active weak-lined T Tauri star V773 Tau (HD 283447) and the surrounding Barnard 209 dark cloud, obtained in 1995 February. During this observation, V773 Tau exhibited a dramatic X-ray flare, with the X-ray count rate increasing rapidly by a factor of ~20, then decreasing exponentially with an e-folding timescale of ≈ 2.3 hr. The peak flare luminosity was at least ~1033 ergs s-1 (0.7-10 keV; distance = 150 pc), which is among the highest X-ray luminosities observed to date for T Tauri stars. The total energy release was ~1037 ergs. However, the most spectacular aspect of this flare was its temperature, which reached a maximum value of at least 100 million K. Spectral fits near flare maximum give a temperature of ~10 keV, which slowly declined to a value ~6 keV at the end of the observation. These temperature measurements are based on high signal-to-noise ratio spectra, and provide the first unambiguous evidence for superhot flaring plasma at temperatures of ~108 K in T Tauri stars. A simple cooling-loop model gives electron densities that are similar to those of solar flares, but requires loop sizes that are comparable to or larger than the star itself. The flare showed other interesting behavior, including a high (and possibly variable) absorption column density, NH = 4 × 1022 cm-2, and an apparent increase in the global metal abundance during the flare.

Nonlinearity at the K-absorption-edge in the Xe-filled gas proportional counter

Abstract We measured the linearity of a Xe-filled gas proportional counter in the energy range between 10 and 40 keV at the synchrotron radiation facility. A clear gap at the Xe K-edge energy (34.5 keV) can be seen. We found that the equivalent width of this gap is about 170 ± 10 eV. In order to understand this value, we discussed the mean ionization energy during the X-ray photo absorption process.

An RXTE Observation of NGC 6300: A New Bright Compton Reflection-dominated Seyfert 2 Galaxy

Scanning and pointed Rossi X-Ray Timing Explorer (RXTE) observations of the nearby Seyfert 2 galaxy NGC 6300 reveal that it is a source of hard X-ray continuum and large equivalent-width Fe Kα emission. These properties are characteristic of Compton reflection-dominated Seyfert 2 galaxies. The continuum can be modeled as Compton reflection; subsolar iron abundance is required, and a high inclination is preferred. However, the poor energy resolution of RXTE means that this description is not unique, and the continuum can also be modeled using a dual absorber, i.e., a sum of absorbed power laws. Observations with higher energy resolution detectors will cleanly discriminate between these two models. Optical observations support the Compton reflection-dominated interpretation as LX/L is low. NGC 6300 is notable because with F2-10 ≈ 6.4 × 10-12 ergs cm-2 s-1, it is the second brightest such object known.

The X-ray spectrum and variability of the Seyfert 2 galaxy NGC 7172

We present evidence of flux variability, on both short (hours) and long (months) time-scales, of the Seyfert 2 galaxy NGC 7172. These results are based on the ASCA observation of NGC 7172 performed in 1996 May. The source was detected at a rather low flux level, about 3 times fainter than its usual state (including 1 yr before, when it was also observed by ASCA). xa0The source also varied by about 30 per cent during the observation, confirming the presence of a type 1 nucleus in its centre. However, its spectrum appears to be flatter than the typical Seyfert 1 spectrum (in agreement with findings on other Seyfert 2s), posing problems for the unification model unless complex absorption is invoked.

On the nature of the X-ray absorption in the Seyfert 2 galaxy NGC 4507

We present results of the ASCA observation of the Seyfert 2 galaxy NGC 4507. The 0.5–10 keV spectrum is rather complex and consists of several components: (i) a hard X-ray power law heavily absorbed by a column density of about 3-1023 cm−2, (ii) a narrow Fe Kα line at 6.4 keV, (iii) soft continuum emission well above the extrapolation of the absorbed hard power law and (iv) a narrow emission line at ∼0.9 keV. The line energy, consistent with highly ionized neon (Ne IX), may indicate that the soft X-ray emission is derived from a combination of resonant scattering and fluorescence in a photoionized gas. Some contribution to the soft X-ray spectrum from thermal emission, as a blend of Fe L lines, by a starburst component in the host galaxy cannot be ruled out with the present data.

Hard X-Ray Luminosities of Multinuclei Infrared Luminous Galaxies Showing a Radio/Far-Infrared Excess

We report the results of hard X-ray observations of four multinuclei merging infrared luminous galaxies (IRLGs). We selected these four sources for their excess of radio-to-far-infrared luminosity ratio compared with starburst galaxies. This excess suggests that activity associated with a supermassive black hole (SMBH) contributes strongly to the IRLGs bolometric luminosities. Although we expect strong hard X-ray emission from the SMBH-driven activity, the radio-excess multinuclei merging IRLGs show considerably smaller hard X-ray luminosities relative to far-infrared (40-500 μm) and infrared (8-1000 μm) luminosities than active galactic nuclei (AGNs) showing a similar radio excess. This result may demonstrate that emission in the hard X-ray region from SMBH-driven activity in the multinuclei merging IRLGs is severely suppressed compared to a typical spectral energy distribution of SMBH-driven activity in AGNs. If this is a common property of merging IRLGs, without taking this into account, hard X-ray observations underestimate the contribution of SMBH-driven activity to the bolometric luminosities of merging IRLGs.

BeppoSAX observations of luminous IRAS galaxies

Abstract We have obtained hard X-ray spectra of four luminous IRAS galaxies, which were selected on the basis of their optical polarized broad lines. We have found prominent Fe K line emission from IRAS 20210+1121, suggesting that its observed X-ray continuum is scattered emission from a completely blocked AGN. The X-ray-[OIII]λ5007 ratios of our sources are in the range of moderately or heavily absorbed Seyfert 2s.

ASCA observations of Seyfert 2 galaxies

Abstract The Japanese X-ray satellite, ASCA has observed 6 Seyfert 2 galaxies. We found the evidence of obscured nuclei in all galaxies, i.e. heavy absorption feature for four galaxies and strong lines probably produced by fluorescence for two galaxies. This result supports the unified scheme of AGNs, and is very important to reveal the nature of type 2 Seyferts, e.g. obscured nucleus, scattering region, etc. The thermal component is found in low energy band as well as non thermal emission for two galaxies, and it would originate from starburst activity. It is very important, considering the connection between AGN and Starburst galaxy. It may give us a hint of the galaxy evolution.

STEADY AND TRANSIENT BEHAVIOR OF A DOUBLE-CONDENSER DESIGN LHP FOR MAXI

A loop heat pipe (LHP) is used as the heat transport device to reject heat from the Monitor of All-sky X-ray Image (MAXI). Since this LHP was designed exclusively for the MAXI system, it is different from conventional LHPs in configuration , a double -condenser design. We experimentall y investigated the effects of the particular design of this LHP on the heat transfer performance by using the LHP Ground Test Unit (GTU) on the ground. The steady heating experiment was carried out to investigate the steady state performance of LHP. When the two condensers were cooled at different temperatures under a steady heating condition, a quasi-periodic temperature oscillation was observed in the evaporator and accumulator area. We experimentally investigated the cause and mechanism of the temperature oscillation.

The BeppSAX observation of IRAS 20210+1121

Abstract We have obtained a hard X-ray spectrum of the ultraluminous infrared galaxy IRAS 20210+1121 (z = 0.056), whose optical spectrum is that of a Seyfert 2. The most significant feature is a strong Fe K line at 6.7 (6.5–7.0) keV in the rest-frame with equivalent width about 1 keV. This suggests that the observed X-ray continuum is scattered emission from a completely blocked AGN, a situation similar to that in NGC 1068. However, IRAS 20210+1121 has an observed 2–10 keV luminosity of 4 × 10 42 erg s −1 (assuming H 0 = 50km s −1 Mpc −1 ), about ten times higher than NGC 1068. If the scattering efficiencies of NGC 1068 and IRAS 20210 are similar, then this implies the presence of an extremely luminous X-ray source in IRAS 20210.