Engineering topics

Kawai, Nobuyuki

Publications and source records attributed to Kawai, Nobuyuki.

8 records

NASA NTRS2018

Temperature Structure in the Perseus Cluster Core Observed with Hitomi

The present paper investigates the temperature structure of the X-ray emitting plasma in the core of the Perseus cluster using the 1.8-20.0 keV data obtained with the Soft X-ray Spectrometer (SXS) onboard the Hitomi Observatory. A series of four observations were carried out, with a total effective exposure time of 338 ks and covering a central region _ 7′ in diameter. The SXS was operated with an energy resolution of _5 eV (full width at half maximum) at 5.9 keV. Not only fine structures of K-shell lines in He-like ions but also transitions from higher principal quantum numbers are clearly resolved from Si through Fe. This enables us to perform temperature diagnostics using the line ratios of Si, S, Ar, Ca, and Fe, and to provide the first direct measurement of the excitation temperature and ionization temperature in the Perseus cluster. The observed spectrum is roughly reproduced by a single temperature thermal plasma model in collisional ionization equilibrium, but detailed line ratio diagnostics reveal slight deviations from this approximation. In particular, the data exhibit an apparent trend of increasing ionization temperature with increasing atomic mass, as well as small differences between the ionization and excitation temperatures for Fe, the only element for which both temperatures can be measured. The best-fit two-temperature models suggest a combination of 3 and 5 keV gas, which is consistent with the idea that the observed small deviations from a single temperature approximation are due to the effects of projection of the known radial temperature gradient in the cluster core along the line of sight. Comparison with the Chandra/ACIS and the XMM-Newton/RGS results on the other hand suggests that additional lower-temperature components

Aharonian, Felix↗

NASA NTRS2016

The ASTRO-H (Hitomi) X-Ray Astronomy Satellite

The Hitomi (ASTRO-H) mission is the sixth Japanese X-ray astronomy satellite developed by a large international collaboration, including Japan, USA, Canada, and Europe. The mission aimed to provide the highest energy resolution ever achieved at E greater than 2 keV, using a microcalorimeter instrument, and to cover a wide energy range spanning four decades in energy from soft X-rays to gamma-rays. After a successful launch on 2016 February 17, the spacecraft lost its function on 2016 March 26, but the commissioning phase for about a month provided valuable information on the on-board instruments and the spacecraft system, including astrophysical results obtained from first light observations. The paper describes the Hitomi (ASTRO-H) mission, its capabilities, the initial operation, and the instruments/spacecraft performances confirmed during the commissioning operations for about a month.

Hard X-ray↗

NASA NTRS2012

Future of Space Astronomy: A Global Road Map for the Next Decades

The use of space techniques continues to play a key role in the advance of astrophysics by providing access to the entire electromagnetic spectrum from the radio observations to the high energy gamma rays. The increasing size, complexity and cost of large space observatories places a growing emphasis on international collaboration. Furthermore, combining existing and future datasets from space and ground based observatories is an emerging mode of powerful and relatively inexpensive research to address problems that can only be tackled by the application of large multi-wavelength observations. If the present set of space and ground-based astronomy facilities today is impressive and complete, with space and ground based astronomy telescopes nicely complementing each other, the situation becomes concerning and critical in the next 10-20 years. In fact, only a few main space missions are planned, possibly restricted to JWST and, perhaps, WFIRST and SPICA, since no other main facilities are already recommended. A "Working Group on the Future of Space Astronomy" was established at the 38th COSPAR Assembly held in Bremen, Germany in July 2010. The purpose of this Working Group was to establish a roadmap for future major space missions to complement future large ground-based telescopes. This paper presents the results of this study including a number of recommendations and a road map for the next decades of Space Astronomy research.

Ubertini, Pietro↗

NASA NTRS2011

Combined Spectral and Timing Analysis of the Black Hole Candidate MAXI J1659-152 Discovered by MAXI and Swift

We report on X-ray spectral and timing results of the new black hole candidate (BHC) MAXI J1659-152 with the orbital period of 2.41 hours (shortest among BHCs) in the 2010 outburst from 65 Rossi X-ray Timing Explorer (RXTE) observations and 8 simultaneous Swift and RXTE observations. According to the definitions of the spectral states in Remillard & McClintock (2006), most of the observations have been classified into the intermediate state. All the X-ray broadband spectra can be modeled by a multi-color disk plus a power-law with an exponential cutoff or a multi-color disk plus a Comptonization component. During the initial phase of the outburst, a high energy cutoff was visible at 30-40 keV. The innermost radius of the disk gradually decreased by a factor of more than 3 from the onset of the outburst and reached a constant value of 35 d(sub 10)cos(i sup −1/2) km, where d(sub 10) is the distance in units of 10 kpc and i is the inclination. The type-C quasi-periodic oscillation (QPO) frequency varied from 1.6 Hz to 7.3 Hz in association with a change of the innermost radius, while the innermost radius remained constant during the type-B QPO detections at 1.6-4.1 Hz. Hence, we suggest that the origin of the type-B QPOs is different from that of type-C QPOs, the latter of which would originate from the disk truncation radius. Assuming the constant innermost radius in the latter phase of the outburst as the innermost stable circular orbit, the black hole mass in MAXI J1659-152 is estimated to be 3.6-8.0 solar mass for a distance of 5.3-8.6 kpc and an inclination angle of 60-75 degrees.

Timing↗

NASA NTRS1994

Discovery of the double Doppler-shifted emission-line systems in the X-ray spectrum of SS 433

We have used the CCD X-ray spectrometers on ASCA and resolved the X-ray emission line from the jet of SS 433 both into Doppler-shifted components with two distinct velocities, and into emission from different ionization states of iron, i.e., Fe XXV and Fe XXVI. This is the first direct detection of the two Doppler shifted beams in the X-ray spectra of SS 433 and allows the radial velocity of the jet along the line of sight to be determined with an accuracy comparable to the optical spectroscopy. We also found pairs of emission lines from other atomic species, such as ionized silicon and sulfur, with the Doppler shifts consistent with each other. This confirms the origin of the X-ray emission in the high temperature plasma in the jets.

Kotani, Taro↗

NASA NTRS1992

The high-energy transient experiment (HETE) - An international multiwavelength mission

The High Energy Transient Experiment (HETE), an international mission scheduled by NASA for launch on a Pegasus rocket in July 1994, is described. The prime objective of HETE is to carry out the first multiwavelength study of gamma-ray bursts with UV, X-ray, and gamma-ray instruments mounted on a single, compact spacecraft. A unique feature of the HETE mission is its capability to localize GRBs with about 10 arc second accuracy, in near real time aboard the spacecraft, and to transmit these positions directly to a network of receivers at existing ground-based observatories, enabling rapid, sensitive follow-up studies in the radio, IR, and optical bands.

Ricker, George R.↗

NASA NTRS1991

Decrease in the orbital period of Hercules X-1

From a pulse-timing analysis of Ginga observations of the binary X-ray pulsar Her X-1 obtained during the interval 1989 April-June local orbital parameters are determined for a short high state. An orbital epoch is also determined in the adjacent main high state. By comparing these orbital solutions with previously published results, a decrease is detected in the orbital period for Her X-1 over the interval 1971-1989. The value is substantially larger than the value predicted from current estimates of the mass-transfer rate, and motivates consideration of other mechanisms of mass transfer and/or mass loss. A second result from these observations is a close agreement between orbital parameters determined separately in main high and short high states. This agreement places strong constraints on the obliquity of the stellar companion, HZ Her, if undergoing forced precession with a 35-day period. As a consequence further doubt is placed on the slaved-disk model as the underlying cause of the 35-day cycle in Her X-1.

Deeter, John E.↗

NASA NTRS1991

Decrease in the Orbital Period of Hercules X-1

From a pulse-timing analysis of Ginga observations of the binary X-ray pulsar Her X-1 obtained during the interval 1989 April-June we have determined local orbital parameters for a Short High state. We have also determined an orbital epoch in the adjacent Main High state. By comparing these orbital solutions with previously published results, we have detected a decrease in the orbital period for Her X-1 at an average rate of dot-P/P = (- 1.32 +/- 0.16) x 10(exp -8) yr(exp -1) over the interval 1971-1989. This is substantially larger than the value predicted from current estimates of the mass transfer rate, and motivates consideration of other mechanisms of mass transfer and/or mass loss. A second result from these observations is a close agreement between orbital parameters determined separately in Main High and Short High states. This agreement places strong constraints on the obliquity of the stellar companion, HZ Her, if undergoing forced precession with a 35 day period. As a consequence further doubt is placed on the slaved-disk model as the underlying cause of the 35 day cycle in Her X-1.

Deeter, John E.↗