Origin of the in-orbit instrumental background of the Hard X-ray Imager onboard Hitomi
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47 OTHER INSTRUMENTATION↗
Engineering topics
Makishima, Kazuo
Publications and source records attributed to Makishima, Kazuo.
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↗
Suzaku Studies of the Supernova Remnant CTB 109 Hosting the Magnetar 1E 2259+586
Ages of the magnetar 1E 2259+586 and the associated supernova remnant CTB 109 were studied. Analyzing the Suzaku data of CTB 109, its age was estimated to be ∼14 kyr, which is much younger than the measured characteristic age of 1E 2259+586, 230 kyr. This reconfirms the previously reported age discrepancy of this magnetar/remnant association, and suggests that the characteristic ages of magnetars are generally over-estimated as compared to their true ages. This discrepancy is thought to arise because the former are calculated without considering decay of the magnetic fields. This novel view is supported independently by much stronger Galactic-plane concentration of magnetars than other pulsars. The process of magnetic field decay in magnetars is mathematically modeled. It is implied that magnetars are much younger objects than previously considered, and can dominate new-born neutron stars.
Nakano, Toshio↗
Spectral and Timing Nature of the Symbiotic X-Ray Binary 4U 1954+319: The Slowest Rotating Neutron Star in AN X-Ray Binary System
The symbiotic X-ray binary (SyXB) 4U 1954+319 is a rare system hosting a peculiar neutron star (NS) and an M-type optical companion. Its approx. 5.4 hr NS spin period is the longest among all known accretion-powered pulsars and exhibited large (is approx. 7%) fluctuations over 8 yr. A spin trend transition was detected with Swift/BAT around an X-ray brightening in 2012. The source was in quiescent and bright states before and after this outburst based on 60 ks Suzaku observations in 2011 and 2012. The observed continuum is well described by a Comptonized model with the addition of a narrow 6.4 keV Fe-K alpha line during the outburst. Spectral similarities to slowly rotating pulsars in high-mass X-ray binaries, its high pulsed fraction (approx. 60%-80%), and the location in the Corbet diagram favor high B-field (approx. greater than 10(exp12) G) over a weak field as in low-mass X-ray binaries. The observed low X-ray luminosity (10(exp33)-10(exp35) erg s(exp−1)), probable wide orbit, and a slow stellar wind of this SyXB make quasi-spherical accretion in the subsonic settling regime a plausible model. Assuming a approx. 10(exp13) G NS, this scheme can explain the approx. 5.4 hr equilibrium rotation without employing the magnetar-like field (approx. 10(exp16) G) required in the disk accretion case. The timescales of multiple irregular flares (approx. 50 s) can also be attributed to the free-fall time from the Alfv´en shell for a approx. 10(exp13) G field. A physical interpretation of SyXBs beyond the canonical binary classifications is discussed.
accretion disks aEuro" binaries: symbiotic aEuro" ↗
Suzaku View of the Neutron Star in the Dipping Source 4U 1822-37
The dipping X-ray source 4U 1822−37 was observed by Suzaku on 2006 Octrober 20 for a net exposure of 37 ks. The source was detected with the XIS at a 1-10 keV flux of 5.5 ×10(exp −10) erg per square centimeter per second, and with the HXD (HXD-PIN) at a 10-50 keV flux of 8.9 ×10(exp −10) erg per square centimeter per second. With HXD-PIN, the pulsation was detected at a barycentric period of 0.592437 seconds, and its change rate was reconfirmed as −2.43 × 10(exp −12) seconds per second. The 1-50 keV spectra of 4U 1822-37 were found to be very similar to those of Her X- 1 in the slopes, cutoff and iron lines. Three iron lines (Fe Kalpha, Fe XXV, and Fe XXVI) were detected, on top of a 1-50 keV continuum that is described by an NPEX model plus a soft blackbody. In addition, a cyclotron resonance scattering feature was detected significantly ( greater than 99% confidence), at an energy of 33+/-2 keV with a depth of 0.4(sup +0.6)/(sub −0.3). Therefore, the neutron star in this source is concluded to have a strong magnetic field of 2.8 × 10(exp 12) G. Further assuming that the source has a relatively high intrinsic luminosity of several times 10(exp 37) erg per second, its spectral and timing properties are consistently explained.
Stars: magnetic field↗
Suzaku Observations of the HMXB 1A 1118-61
We present broad band analysis of the Be/X-ray transient lA 1118-61 by Suzaku at the peak of its 3rd observed outburst in January 2009 and 2 weeks later when the source flux had decayed by an order of magnitude. The continuum was modeled with a cutoffpl model as well as a compTT model, with both cases requiring an additional black body component at lower energies, We confirm the detection of a cyclotron line at approx. 55 keV and discuss the possibility of a first harmonic at approx. 110 keV. Pulse profile comparisons show a change in the profile structure at lower energies, an indication for possible changes in the accretion geometry, Phase resolved spectroscopy in the outburst data show a change in the continuum throughout the pulse period. The decrease in the CRSF centroid energy also indicates that the viewing angle on the accretion column is changing throughout the pulse period. Subject headings: X-rays: stars - X-rays: binaries - stars: pulsars: individual (lA 1118-61) - stars: magnetic fields
Suchy, Slawomir↗
Metal concentration and X-ray cool spectral component in the central region of the Centaurus cluster of galaxies
Spatially resolved energy spectra in the energy range 0.5-10 keV have been measured for the Centaurus cluster of galaxies with Advanced Satellite for Cosmology and Astrophysics (ASCA). Within 10 min (200 kpc) from the cluster center, the helium-like iron K emission line exhibits a dramatic increase toward the center rising from an equivalent width approximately 500 eV to approximately 1500 eV corresponding to an abundance change from 0.3 to 1.0 solar. The presence of strong iron L lines indicates an additional cool component (kT approximately 1 keV) within 10 min from the center. The cool component requires absorption in excess of the galactic value and this excess absorption increases towards the central region of the cluster. In the surrounding region with radius greater than 10 min, the spectra are well described by a single temperature thermal model with kT approximately 4 keV and spatially uniform abundances at about 0.3-0.4 times solar. The detection of metal-rich hot and cool gas in the cluster center implies a complex nature of the central cluster gas which is likely to be related to the presence of the central cD galaxy NGC 4696.
Fukazawa, Yasushi↗
ASCA observation of three bright early-type galaxies: NGC 4472, NGC 4406, and NGC 4636
We report Advanced Satellite for Cosmology and Astrophysics (ASCA) 0.3-10 keV and X-ray observations of three early type galaxies, NGC 4472, NGC 4406, and NGC 4636. The extended mission in these galaxies is well described by thin thermal eimssion from hot gas. The gas temperature is 0.92 +/- 0.02 keV for NGC 4472, 0.79 +/- 0.01 keV for NGC 4406, and 0.73 +/- 0.02 keV for NGC 4636. The metal abundance for NGC 4472, NGC 4406, and NGC 4636 are, under the assumption of solar ratios, 0.63 +/- 0.15, 0.45 +/- 0.10, and 0.38 +/- 0.07, respectively. Detailed analysis has allowed determination of the abundances of oxygen, silicon, sulfur, and iron. The observed abundances are consistent with the solar ratios. For NGC 4472 and NGC 4406 we also determined the mean temperature of the gas producing the Si lines from the ratio of the Si H to He-like lines and find it to be consistent with the continuum temperature. The X-ray temperature is in good agreement with the observed optical velocity dispersion, stellar density profile, and gas density profile. Our data indicates that the supernova rate should be less than one fifth of the nominal rate in early type galaxies. We derive the mass of these systems within fixed angular scales and find that M/L greater than 40, confirming that elliptical galaxies are dark matter dominated at large radii.
Awaki, Hisamitsu↗
Discovery of an obscured low luminosity active nucleus in the spiral galaxy NGC 4258
The spectra and images of the nearby jet galaxy NGC 4258 (M106) obtained with ASCA indicate presence of several distinct X-ray emission components. The emission above 3 keV is pointlike and coincident in position with the optical nucleus, exhibiting a hard (photon index approximately 1.78) and absorbed N(sub H) approximately 1.5 x 10(exp 23) cm(exp -2) spectrum. This provides clear evidence that NGC 4258 hosts an obscured active nucleus of low luminosity, about 4 x 10(exp 40) ergs s(exp -1) in 2-10 keV after removing the absorption. Iron K-line emission with an equivalent width 0.25 +/- 0.10 keV was detected. The emission below 1 keV is dominated by an extended approximately 4 min thin-thermal component with a temperature approximately 0.5 keV exhibiting atomic emission lines, possibly associated with the jet. There exists a third continuum component with an intermediate spectral hardness, which is brightest at approximately 1 min south-east of the nucleus.
Makishima, Kazuo↗
The broad band X-ray spectrum of SN 1978k and two other luminous X-ray sources in the spiral galaxy NGC 1313
We present preliminary results of our analysis of the Advanced Satellite for Cosmology and Astrophysics (ASCA) PV phase observation of the nearby spiral galaxy NGC 1313. ASCA cleanly resolves the three previously known luminous sources, one of which is the very luminous supernova, SN 1978k. The spectrum of SN 1978k is described by either a power law with a photon index gamma approximately 2.2 or a thermal model with temperature kT approximately 3.0 keV and abundances Z approximately 0.2 Z(sun). There is no evidence for strong line emission from it or from the other two sources. The spectrum of SN 1978k arises either in shocked gas in extreme departure from ionization equilibrium or from synchrotron processes associated with a newborn pulsar. A second source, near the galactic center, is well-fit by a power-law with a photon index of approximately 1.8. It is possibly an active nucleus-like source, but physically displaced from the optical nucleus of the galaxy. The spectrum of the third source, located 8 kpc south of the nucleus, along with the absence of an optical counterpart, suggests that it is a low mass X-ray binary; but its high X-ray luminosity clouds this interpretation. This observation demonstrates the ability of ASCA to perform effective broad band spectroscopic measurements of sources at a 2-10 keV flux level of 5 x 10(exp -13) erg cm(exp -2) s(exp -1).
Petre, Robert↗
The fluorescence-dominated X-ray spectrum of the spiral galaxy NGC 6552
A hard X-ray source with a 2-10 keV flux of approximately 6 x 10(exp -13) ergs/sec/sq cm was detected with ASCA in the north ecliptic pole region. It is identified with the spiral galaxy NGC 6552 at a redshift of z = 0.026, which is optically classified as a Seyfert 2 galaxy. The X-ray spectrum consists of a series of atomic K-emission lines from (nearly-) neutral species of at least seven abundant elements, and a heavily absorbed (N(sub H) approx. = 6 x 10(exp 23)/sq cm) hard continuum. The iron line has an equivalent width as large as approximately 0.9 keV. Our results show that NGC 6552 is an extreme type 2 Seyfert galaxy, in which the fluorescent lines are produced when hard X-rays from a hidden active nucleus are reflected off thick cool matter into our line of sight. The intrinsic 2-10 keV luminosity of the nucleus is estimated to be at least 6 x 10(exp 42) ergs/s.
Fukazawa, Yasushi↗
Detection os X-rays from SN 1993J with ASCA
ASCA observed SN 1993J seven times between April 5 and October 24 in 1993. The 1-10 keV luminosity 10d after the explosion was (15 +/- 4) x 10(exp 39) erg/s and decreased monotonicly to (1.3 +/- 0.4) x 10(exp 39) erg/s 210 d after the explosion, when a distance of 3.6 Mpc was assumed. The hardness ratio (2-10 keV/0.5-2 keV) significantly decreased during the course of the observations. The spectrum obtained from a sky region including not only SN 1993J but also the nearby X-ray source clearly shows an iron emission line. The correlation between the iron line flux with the SN 1993J flux suggests that the iron line emission originated in SN 1993J. These observational results are discussed in the context of thermal X-ray emission from a hot region behind the shock due to the collision of the supernova ejecta with the pre-supernova stellar wind.
Kohmura, Yoshiki↗
Discovery of a cyclotron absorption line in the spectrum of the binary X-ray pulsar 4U 1538 - 52 observed by Ginga
A cyclotron absorption line near 20 keV has been found in the spectrum of the massive eclipsing binary X-ray pulsar 4U 1538 - 52 in observations with the Ginga observatory. The line is detected throughout the 529 s pulse cycle with a variable equivalent width that has its maximum value during the smaller peak of the two-peak pulse profile. It is found that the profile of the pulse and the phase-dependence of the cyclotron line can be explained qualitatively by a pulsar model based on recent theoretical results on the properties of pencil beams emitted by accretion-heated slabs of magnetized plasma at the magnetic poles of a neutron star. The indicated field at the surface of the neutron star is 1.7 (1 + z) x 10 to the 12th G, where z is the gravitational redshift.
Clark, George W.↗