654 research outputs found
ASCA Observation of the Low-Luminosity Seyfert 1.5 Galaxy NGC 5033
We present the results of an ASCA observation of the low-luminosity Seyfert
1.5 galaxy NGC 5033. A point-like X-ray source with a luminosity of 2.3x10^{41}
erg s^{-1} in the 2--10 keV band (at 18.7 Mpc; Tully 1988, AAA045.002.054) was
detected at the nucleus. The X-ray light curve shows variability on a timescale
of ~10^4 s with an amplitude of ~20%. The X-ray continuum is represented by a
weakly absorbed (N_H~9x10^{20} {cm^{-2}) power-law with a photon index of
1.72+/-0.04, which is quite similar to Seyfert 1 galaxies with higher
luminosities. A Fe Kalpha emission line is detected at 6.40^{+0.08}_{-0.06} keV
(redshift corrected) and the equivalent width is 290+/-100 eV. The line width
is unresolved. The narrower line width and larger equivalent width compared to
Seyfert 1s imply that fluorescent Fe Kalpha emission from matter further out
from the center than the accretion disk significantly contributes to the
observed Fe Kalpha line. We suggest that fluorescent Fe Kalpha emission from
the putative torus contributes to the observed Fe Kalpha line.Comment: 17 pages, To appear in PASJ, Vol. 51, No.
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
Iron K-alpha line profiles driven by non-axisymmetric illumination
Previous calculations of Fe K-alpha line profiles are based on axisymmetric
emissivity laws. In this paper, we show line profiles driven by non-axial
symmetric illumination which results from an off-axis X-ray point source. We
find that source location and motion have significant effects on the red wing
and blue horn of the line profiles. The disk region under the source will
receive more flux, which is the most important factor to affect the line
profiles. We suggest that at least part of the variation in Fe K-alpha line
profiles is caused by the motion of X-ray sources. Future observations of Fe
K-alpha line profiles will provide more information about the distribution and
motion of the X-ray sources around black holes, and hence the underlying
physics.Comment: 10 pages, 3 figures, accepted for the publication in MNRA
Similarity In Phase Diagrams Between Ionic And Nonionic Surfactant Solutions At Constant Temperature
Detection of an X-ray periodicity in the Seyfert galaxy IRAS18325-5926
We report the detection of a 58 ks (16 hr) periodicity in the 0.5-10 keV
X-ray light curve of the Seyfert galaxy IRAS18325-5926 (Fairall49), obtained
from a 5-day ASCA observation. Nearly 9 cycles of the periodic variation are
seen; it shows no strong energy dependence and has an amplitude of about 15 per
cent. Unlike most other well-studied Seyfert galaxies, there is no evidence for
strong power-law red noise in the X-ray power spectrum of IRAS18325-5926.
Scaling from the QPOs found in Galactic black hole candidates suggests that the
mass of the black hole in IRAS18325-5926 is (6-40) million solar masses.Comment: 5 pages, 4 Postscript figures, to be published in MNRA
The Infocus Hard X-ray Telescope: Pixellated CZT Detector/Shield Performance and Flight Results
The CZT detector on the Infocus hard X-ray telescope is a pixellated
solid-state device capable of imaging spectroscopy by measuring the position
and energy of each incoming photon. The detector sits at the focal point of an
8m focal length multilayered grazing incidence X-ray mirror which has
significant effective area between 20--40 keV. The detector has an energy
resolution of 4.0keV at 32keV, and the Infocus telescope has an angular
resolution of 2.2 arcminute and a field of view of about 10 arcminutes. Infocus
flew on a balloon mission in July 2001 and observed Cygnus X-1. We present
results from laboratory testing of the detector to measure the uniformity of
response across the detector, to determine the spectral resolution, and to
perform a simple noise decomposition. We also present a hard X-ray spectrum and
image of Cygnus X-1, and measurements of the hard X-ray CZT background obtained
with the SWIN detector on Infocus.Comment: To appear in the proceedings of the SPIE conference "Astronomical
Telescopes and Instrumentation", #4851-116, Kona, Hawaii, Aug. 22-28, 2002.
12 pages, 9 figure
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
Combined Analysis of X-Ray Spectra of NGC 3227
The 1.5 Seyfert galaxy NGC 3227 has been observed by several X-ray missions.
We carried out combined analysis of the data obtained by more recent major
observations of this source - two observations performed by XMM-Newton in 2000
and 2006 and six observations performed by Suzaku in 2008.
A unified model was constructed which is consistent with all eight of the
observations by the two satillites with large intensity and spectral changes.
The model consists of a hard power law with the spectral index of
Gamma_Hard=1.4-1.7 which is interpreted as the Comptonized emission from the
corona above an accretion disk. In the high flux states an additional soft
excess component dominates, which is consistent with a model with either a
steeper power law with Gamma_Soft=3.3-3.85 or the warm Comptonization
component. These emissions from the central engine are absorbed by a neutral
partial covering material and warm absorbers. A reflection component and
several emission lines are also present. We examined the relationship between
the intrinsic luminosity and the absorbers' physical parameters such as the
column density, which suggests that the source expanded significantly during
the bright states where the soft excess is greatly enhanced.Comment: 24 pages, 5 tables, and 17 figure
ASCA PV observations of the Seyfert 1 galaxy MCG-6-30-15 : rapid variability of the warm absorber
We present a detailed re-analysis of the two {\it ASCA} Performance
Verification observations of the nearby Seyfert 1 galaxy MCG-6-30-15.
Confirming the results of Fabian et al. (1994), we find definite evidence for
the {\sc O\,vii} and {\sc O\,viii} K-shell absorption edges of the warm
absorber and a doubling of the warm absorber column density within the 3 weeks
separating the two observations. No intra-day {\it flux-correlated} variability
of the warm absorber is found. However, we report the discovery of an `event'
in which the warm absorber parameters temporarily change for
\sim10\,000\thinspace s before returning to their original values. Possible
interpretations are discussed but a contradiction remains: the constancy of the
ionization state of the warm absorber argues that it lies at large distances
from the central source whereas the short term change in column density argues
for small distances. Fluorescent iron emission is examined. As found by Fabian
et al. (1994), the iron line is broad and strong (equivalent width
\sim300\thinspace eV). The line profile is also suggestive of it being skewed.
Such a line would be expected from a relativistic accretion disk. We also find
very rapid primary X-ray variability. Assuming relativistic beaming to be
unimportant, the derived efficiency is comparable to the maximum obtainable
from accretion onto a Schwarzschild black hole. Correlated variability outside
of the energy range of {\it ASCA} might exceed this maximum, thus requiring
efficient accretion onto a Kerr hole.Comment: uuencoded compressed postscript. The preprint is also available at
http://www.ast.cam.ac.uk/preprint/PrePrint.htm
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