434 research outputs found
The International X-ray Observatory
The International X-ray Observatory (IXO) is a joint ESA-JAXA-NASA effort to
address fundamental and timely questions in astrophysics: What happens close to
a black hole? How did supermassive black holes grow? How does large scale
structure form? What is the connection between these processes? To address
these questions IXO will employ optics with 3 sq m collecting area and 5 arc
sec angular resolution - 20 times more collecting area at 1 keV than any
previous X-ray observatory. Focal plane instruments will deliver a 100-fold
increase in effective area for high-resolution spectroscopy, deep spectral
imaging over a wide field of view, unprecedented polarimetric sensitivity,
microsecond spectroscopic timing, and high count rate capability. The mission
is being planned for launch in 2021 to an L2 orbit, with a five-year lifetime
and consumables for 10 years.Comment: 6 pages, 3 figures, for conference "X-ray Astronomy 2009 Present
status, multi-wavelength approach and future perspectives
The Suzaku Observation of NGC 3516: Complex Absorption and the Broad and Narrow Fe K Lines
We present results from a 150 ksec Suzaku observation of the Seyfert 1.5 NGC
3516 in October 2005. The source was in a relatively highly absorbed state. Our
best-fit model is consistent with the presence of a low-ionization absorber
which has a column density near 5 * 10^{22} cm^{-2} and covers most of the
X-ray continuum source (covering fraction 96-100%). A high-ionization absorbing
component, which yields a narrow absorption feature consistent with Fe K XXVI,
is confirmed. A relativistically broadened Fe K alpha line is required in all
fits, even after the complex absorption is taken into account; an additional
partial-covering component is an inadequate substitute for the continuum
curvature associated with the broad Fe line. A narrow Fe K alpha emission line
has a velocity width consistent with the Broad Line Region. The low-ionization
absorber may be responsible for producing the narrow Fe K alpha line, though a
contribution from additional material out of the line of sight is possible. We
include in our model soft band emission lines from He- and H-like ions of N, O,
Ne and Mg, consistent with photo-ionization, though a small contribution from
collisionally-ionized emission is possible.Comment: Accepted for publication in PASJ (Suzaku second special issue). 36
pages, 10 figure
The X-ray Spectrum of the Rapid Burster using the Chandra HETGS
We present observations of the Rapid Burster (RB, also known as MXB 1730-335)
using the Chandra High Energy Transmission Grating Spectrometer. The average
interval between type II (accretion) bursts was about 40 s. There was one type
I (thermonuclear flash) burst and about 20 "mini-bursts" which are probably
type II bursts whose peak flux is 10-40% of the average peak flux of the other
type II bursts. The time averaged spectra of the type II bursts are well fit by
a blackbody with a temperature of kT = 1.6 keV, a radius of 8.9 km for a
distance of 8.6 kpc, and an interstellar column density of 1.7e22 per sq. cm.
No narrow emission or absorption lines were clearly detected. The 3 sigma upper
limits to the equivalent widths of any features are < 10 eV in the 1.1-7.0 keV
band and as small as 1.5 eV near 1.7 keV. We suggest that Comptonization
destroys absorption features such as the resonance line of Fe XXVI.Comment: 10 pages, 4 figures, accepted for publication in AJ (with minor
changes and enhanced discussion of the instrument configuration
ASCA Observations of the Sgr B2 Cloud: An X-Ray Reflection Nebula
We present the ASCA results of imaging spectroscopy of the giant molecular
cloud Sgr B2. The X-ray spectrum is found to be very peculiar; it exhibits a
strong emission line at 6.4 keV, a low energy cutoff below about 4 keV and a
pronounced edge-structure at 7.1 keV. The X-ray image is extended and its peak
position is shifted from the core of the molecular cloud toward the Galactic
center by about 1--2 arcminute. The X-ray spectrum and the morphology are well
reproduced by a scenario that X-rays from an external source located in the
Galactic center direction are scattered by the molecular cloud Sgr B2, and come
into our line of sight. Thus Sgr B2 may be called an X-ray reflection nebula.
Possible implications of the Galactic center activity related to this unique
source are presented.Comment: 15 pages, 8 figures, AAS LaTeX, To be published in The Astrophysical
Journa
Detection of an iron K Emission Line from the LINER NGC 4579
We present the results of an ASCA observation of the LINER NGC 4579. A
point-like X-ray source is detected at the nucleus with a 2-10 keV luminosity
of 1.5x10^41 ergs/s assuming a distance of 16.8 Mpc. The X-ray spectrum is
represented by a combination of a power-law with a photon index of ~1.7 and
soft thermal component with kT~0.9 keV. An iron K emission line is detected at
6.73+/-0.13 keV (rest frame) with an equivalent width of 490 +180/-190 eV and
is statistically significant at more than 99.9 % confidence. The line center
energy is consistent with Helium-like iron and is significantly higher than 6.4
keV which is expected from fluorescence by "cold" (or a lower ionization state
of) iron. The iron line profile shows no significant red tail in contrast to
Seyfert 1 galaxies although the statistics are limited. The line center energy,
equivalent width, and profile are consistent with an origin in an ionized
accretion disk. However the large mass accretion rate necessary to ionize the
accretion disk is not consistent with the observed luminosity and normal
accretion models.Comment: 15 pages, 5 figures, to appear in The Astrophysical Journa
Log N - Log S Relations and Spectral Properties of Sources from the ASCA Large Sky Survey --- their Implications for the Origin of the Cosmic X-ray Background (CXB)
We carried out the first wide-area unbiased survey with the ASCA satellite in
the 0.7-10 keV band around a north Galactic-pole region covering a continuous
area of 7 square degrees (Large Sky Survey; LSS). To make the best use of ASCA
capability, we developed a new source-detection method where the complicated
detector responses are fully taken into account. Applying this method to the
entire LSS data independently in the total (0.7-7 keV), hard (2-10 keV), and
soft (0.7-2 keV) band, we detected 107 sources altogether with sensitivity
limits of 6 x 10E-14 (0.7-7 keV), 1 x 10E-13 (2-10 keV), and 2 x 10E-14 erg
sE-1 cmE-2 (0.7-2 keV), respectively. A complete list of the detected sources
is presented. Based on detailed studies by Monte Carlo simulations, we
evaluated effects of the source confusion and accurately derived Log N - Log S
relation in each survey band. The Log N - Log S relation in the hard band is
located on the extrapolation from the GINGA and HEAO1 results with the
Euclidean slope of -3/2, while that in the soft band is consistent with the
results by ROSAT. At these flux limits, 30 (+/- 3) percent of the CXB in the
0.7-7 keV band and 23 (+/- 3) percent in the 2-10 keV band have been resolved
into discrete sources. The average spectrum of faint sources detected in the
total band shows a photon index of 1.63 +/- 0.07 in the 0.7-10 keV range,
consistent with the comparison of source counts between the hard and the soft
energy band. Those detected in the hard band show a photon index of 1.49 +/-
0.10 in the 2-10 keV range. These spectral properties suggest that contribution
of sources with hard energy spectra become significant at a flux of 10E-13 erg
sE-1 cmE-2 (2-10 keV). The most plausible candidates are type-II AGNs, as
indicated by on-going optical identifications.Comment: 28 pages, 11 figures, to appear in ApJ 518, 1999; figure 1 replaced,
minor errors in text correcte
Minimization and Mitigation of Wire EDM Cutting Errors in the Application of the Contour Method of Residual Stress Measurement
- …