769 research outputs found
The X-Ray Spectral Variability of Mrk 766
Analysis results from ASCA and ROSAT observations of the narrow-line Seyfert
1 galaxy Mrk 766 are reported. In the ASCA observation we observed rapid
variability with a doubling time scale of 1000 seconds. A spectral variability
event was observed in which the spectrum softened and hardened above and below
~1 keV, respectively, as the flux increased. The spectra could be modeled with
5 components: a power law, warm absorber, iron K(alpha) line and soft excess
component flux. The spectral variability resulted from a highly significant
change in the intrinsic photon law index from Gamma ~1.6 to ~2.0, an increase
in the warm absorber ionization, and a marginally significant decrease in the
soft component normalization. A ~100 eV equivalent width narrow iron K(alpha)
line was detected in the high state spectrum. Spectral hardening during flux
increases was observed in three ROSAT observations.
The change in intrinsic photon index and disappearance of the soft excess
component in the ASCA spectra can be explained as a transition from a first
order pair reprocessed spectrum to a pair cascade brought about by a sudden
increase in the injected electron Lorentz factor. The change in the ionization
of the warm absorber, though model dependent, could correspond to the increase
in flux at the oxygen edges resulting from the spectral index change. The ROSAT
spectral variability can be interpreted by variable intensity hard power law
and a relatively nonvarying soft component, possibly primary disk emission.
These results are compared with those reported from other narrow-line Seyfert 1
galaxies.Comment: 29 pages using (AASTeX) aaspp4.sty and 18 Postscript figures. To
appear in the September 1, 1996, issue of The Astrophysical Journa
Electrolyte jet machining for surface texturing of Inconel 718
Electrolyte jet machining is an emerging non-conventional machining process which is capable of selectively applying multi-scale surface textures. Surfaces processed in this way do not suffer from thermal damage and hence this technique is highly suited to finishing procedures in high value manufacturing across the aerospace and biomedical sectors. Furthermore, input variables can be modified dynamically to create functional graduation across component surfaces.
In this study, the development and design of a custom-built EJM system is described, and the capability of the EJM platform to machine and create surface textures in Inconel 718, a widely used nickel based super alloy, is investigated. Through control of machine path programming and parameter variation, multi-scale surface textures are created which have the potential to enhance bonding with subsequent coating layers and also provide fluid dynamic advantage
Theory of tunneling spectroscopy of normal metal/ferromagnet/spin-triplet superconductor junctions
We study the tunneling conductance of a ballistic normal metal / ferromagnet
/ spin-triplet superconductor junction using the extended
Blonder-Tinkham-Klapwijk formalism as a model for a -axis oriented Au /
SrRuO / SrRuO junction. We compare chiral -wave (CPW) and
helical -wave (HPW) pair potentials, combined with ferromagnet magnetization
directions parallel and perpendicular to the interface. For fixed ,
where is a direction of magnetization in the ferromagnet measured
from the -axis, the tunneling conductance of CPW and HPW clearly show
different voltage dependencies. It is found that the cases where the -vector
is perpendicular to the magnetization direction (CPW with
and HPW with ) are identical. The obtained results serve as a
guide to determine the pairing symmetry of the spin-triplet superconductor
SrRuO.Comment: 12 pages, 7 figures. There is also a supplementary (not uploaded
The variable OVIII Warm Absorber in MCG-6-30-15
We present the results of a 4 day ASCA observation of the Seyfert galaxy
MCG-6-30-15, focussing on the nature of the X-ray absorption by the warm
absorber, characterizd by the K-edges of the intermediately ionized oxygen,
OVII and OVIII. We confirm that the column density of OVIII changes on a
timescale of ~s when the X-ray continuum flux decreases. The
significant anti-correlation of column density with continuum flux gives direct
evidence that the warm absorber is photoionized by the X-ray continuum. From
the timescale of the variation of the OVIII column density, we estimate that it
originates from gas within a radius of about 10^{17}\cm of the central
engine. In contrast, the depth of the OVII edge shows no response to the
continuum flux, which indicates that it originates in gas at larger radii. Our
results strongly suggest that there are two warm absorbing regions; one located
near or within the Broad Line Region, the other associated with the outer
molecular torus, scattering medium or Narrow Line Region.Comment: 8 pages (including figures) uuencoded gziped PS file. Submitted to
Publications of the Astronomical Society of Japa
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
Design and tests of the hard X-ray polarimeter X-Calibur
X-ray polarimetry promises to give qualitatively new information about
high-energy astrophysical sources, such as binary black hole systems,
micro-quasars, active galactic nuclei, and gamma-ray bursts. We designed, built
and tested a hard X-ray polarimeter X-Calibur to be used in the focal plane of
the InFOCuS grazing incidence hard X-ray telescope. X-Calibur combines a low-Z
Compton scatterer with a CZT detector assembly to measure the polarization of
10-80 keV X-rays making use of the fact that polarized photons Compton scatter
preferentially perpendicular to the electric field orientation. X-Calibur
achieves a high detection efficiency of order unity.Comment: 9 pages, 5 figures, conference proceedings: SPIE 2011 (San Diego
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
X-ray Properties of the Weak Seyfert 1 Nucleus in NGC 4639
We obtained observations of NGC 4639 with ASCA in order to investigate its
mildly active Seyfert 1 nucleus at hard X-ray energies. Koratkar et al. (1995)
have previously shown that the nucleus is a pointlike source in the ROSAT soft
X-ray band. We detected in the 2-10 keV band a compact central source with a
luminosity of 8.3E+40 erg/s. Comparison of the ASCA data with archival data
taken with the Einstein and ROSAT satellites shows that the nucleus varies on
timescales of months to years. The variability could be intrinsic, or it could
be caused by variable absorption. More rapid variability, on a timescale of
\~10^4 s, may be present in the ASCA data. The spectrum from 0.5 to 10 keV is
well described by a model consisting of a lightly absorbed (N_H = 7.3E+20
cm^-2) power law with a photon index of 1.68. We find no evidence for
significant emission from a thermal plasma; if present, it can account for no
more than 25% of the flux in the 0.5-2.0 keV band. The limited photon
statistics of our data do not allow us to place significant limits on the
presence of iron K emission. (abridged)Comment: To appear in The Astrophysical Journal. LaTex, 18 pages including
embedded figures and table
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