318 research outputs found
The Effect of Changes in the ASCA Calibration on the Fe-Kalpha Lines in Active Galaxies
The ASCA calibration has evolved considerably since launch and indeed, is
still evolving. There have been concerns in the literature that changes in the
ASCA calibration have resulted in the Fe-Kalpha lines in active galaxies (AGN)
now being systematically narrower than was originally thought. If this were
true, a large body of ASCA results would be impacted. In particular, it has
been claimed that the broad red wing (when present) of the Fe-Kalpha line has
been considerably weakened by changes in the ASCA calibration. We demonstrate
explicitly that changes in the ASCA calibration over a period of about eight
years have a negligible effect on the width, strength, or shape of the
Fe-Kalpha lines. The reduction in both width and equivalent width is only ~8%
or less. We confirm this with simulations and individual sources, as well as
sample average profiles. The average profile for type 1 AGN is still very
broad, with the red wing extending down to ~4 keV. The reason for the claimed,
apparently large, discrepancies is that in some sources the \fekalfa line is
complex, and a single-Gaussian model, being an inadequate description of the
line profile, picks up different portions of the profile with different
calibration. Single-Gaussian fits do not therefore model all of the line
emission in some sources, in which case they do not compare old and current
calibration since the models do not then describe the data.Comment: Accepted for publication in the Astrophysical Journal, Vol. 569, 10
April, 2002. 22 pages, 4 figure
Cessation of X-ray Pulsation of GX 1+4
We report results from our weekly monitoring campaign on the X-ray pulsar GX
1+4 with the {\em Rossi X-ray Timing Explorer} satellite. The spin-down trend
of GX 1+4 was continuing, with the pulsar being at its longest period ever
measured (about 138.7 s). At the late stage of the campaign, the source entered
an extended faint state, when its X-ray (2-60 keV) flux decreased significantly
to an average level of . It was
highly variable in the faint state; the flux dropped to as low as . In several observations during this
period, the X-ray pulsation became undetectable. We can, therefore, conclude
conservatively that the pulsed fraction, which is normally 70%
(peak-to-peak), must have decreased drastically in those cases. This is very
similar to what was observed of GX 1+4 in 1996 when it became similarly faint
in X-ray. In fact, the flux at which the cessation of X-ray pulsation first
occurred is nearly the same as it was in 1996. We suggest that we have, once
again, observed the propeller effect in GX 1+4, a phenomenon that is predicted
by theoretical models of accreting X-ray pulsars.Comment: 13 pages, 9 figures (available at
http://www.physics.purdue.edu/~cui/ftp/cuifigs.tar.gz). To appear in Ap
Evolution of Massive Haloes in non-Gaussian Scenarios
We have performed high-resolution cosmological N-body simulations of a
concordance LCDM model to study the evolution of virialized, dark matter haloes
in the presence of primordial non-Gaussianity. Following a standard procedure,
departures from Gaussianity are modeled through a quadratic Gaussian term in
the primordial gravitational potential, characterized by a dimensionless
non-linearity strength parameter f_NL. We find that the halo mass function and
its redshift evolution closely follow the analytic predictions of Matarrese et
al.(2000). The existence of precise analytic predictions makes the observation
of rare, massive objects at large redshift an even more attractive test to
detect primordial non-Gaussian features in the large scale structure of the
universe.Comment: 7 pages,3 figures, submitted to MNRA
On the Spin History of the X-ray Pulsar in Kes 73: Further Evidence For an Utramagnetized Neutron Star
In previous papers, we presented the discovery of a 12-s X-ray pulsar in the
supernova remnant Kes 73, providing the first direct evidence for an
ultramagnetized neutron star, a magnetar, with an equivalent dipole field of
nearly twenty times the quantum critical magnetic field. Our conclusions were
based on two epochs of measurement of the spin, along with an age estimate of
the host supernova remnant. Herein, we present a spin chronology of the pulsar
using additional GINGA, ASCA, XTE, & SAX datasets spanning over a decade.
Timing and spectral analysis confirms our initial results and severely limit an
accretion origin for the observed flux. Over the 10 year baseline, the pulsar
is found to undergo a rapid, constant spindown, while maintaining a steady flux
and an invariant pulse profile. Within the measurement uncertainties, no
systematic departures from a linear spin-down are found - departures as in the
case of glitches or simply stochastic fluctuations in the pulse
times-of-arrival (e.g. red timing noise). We suggest that this pulsar is akin
to the soft gamma-ray repeaters, however, it is remarkably stable and has yet
to display similar outbursts; future gamma-ray activity from this object is
likely.Comment: 6 pages with 3 embedded figures, LaTex, emulateapj.sty. Submitted to
the ApJ Letter
Broad band X-ray spectroscopy of A0535+262 with SUZAKU
The transient X-ray binary pulsar A0535+262 was observed with Suzaku on 2005
September 14 when the source was in the declining phase of the August-September
minor outburst. The ~103 s X-ray pulse profile was strongly energy dependent, a
double peaked profile at soft X-ray energy band (<3 keV) and a single peaked
smooth profile at hard X-rays. The width of the primary dip is found to be
increasing with energy. The broad-band energy spectrum of the pulsar is well
described with a Negative and Positive power-law with EXponential (NPEX)
continuum model along with a blackbody component for soft excess. A weak iron
K_alpha emission line with an equivalent width ~25 eV was detected in the
source spectrum. The blackbody component is found to be pulsating over the
pulse phase implying the accretion column and/or the inner edge of the
accretion disk may be the possible emission site of the soft excess in
A0535+262. The higher value of the column density is believed to be the cause
of the secondary dip at the soft X-ray energy band. The iron line equivalent
width is found to be constant (within errors) over the pulse phase. However, a
sinusoidal type of flux variation of iron emission line, in phase with the hard
X-ray flux suggests that the inner accretion disk is the possible emission
region of the iron fluorescence line.Comment: 21 pages, 6 figures. Accepted for publication in the Astrophysical
Journal, 2008 January issu
Reflection Shocked Gas in the Cygnus Loop Supernova Remnant
We performed spectroscopic X-ray observations of the eastern and northern
regions of the Cygnus Loop with the ASCA observatory. The
X-ray surface brightness of these regions shows a complex structure in the
ROSAT all-sky survey image. We carried out a spatially-resolved analysis for
both regions and found that did not increase toward the center
region, but showed inhomogeneous structures. Such variation cannot be explained
by a blast wave model propagating into a homogeneous interstellar medium. We
thus investigated the interaction between a blast wave and an interstellar
cloud. Two major emission mechanisms are plausible: a cloud evaporation model
and a reflection shock model. In both regions, only a reflection shock model
qualitatively explains our results. Our results suggest the existence of a
large-scale interstellar cloud. We suppose that such a large-scale structure
would be produced by a precursor.Comment: 27 pages, 15 figures. Accepted for publication of ApJ. High
resolution and color figures are available at
http://wwwxray.ess.sci.osaka-u.ac.jp/~miyata/paper/cygloop_reflection.pd
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