108 research outputs found
Discovery of 101-s Pulsations from AX J0057.4-7325 in the SMC with ASCA
The results from two ASCA observations of AX J0057.4-7325 = RX J0057.3-7325
are presented. Coherent pulsations with a barycentric period of 101.45 +/- 0.07
s were discovered in the second observation. The X-ray spectrum was found to be
hard (photon index ~ 0.9) and unchanged through these observations, except for
the flux. The ROSAT archival data show that AX J0057.4-7325 exhibits a flux
variation with a factor >~ 10. A discussion on a possible optical counterpart
is given.Comment: 4 pages, 4 figures, to be published in PASJ. Also available at
http://www-cr.scphys.kyoto-u.ac.jp/member/jun/job
Suzaku Observation of the Anomalous X-ray Pulsar 1E 1841-045
We report the results of a Suzaku observation of the anomalous X-ray pulsar
(AXP) 1E 1841-045 at a center of the supernova remnant Kes 73. We confirmed
that the energy-dependent spectral models obtained by the previous separate
observations were also satisfied over a wide energy range from 0.4 to ~70 keV,
simultaneously. Here, the models below ~10 keV were a combination of blackbody
(BB) and power-law (PL) functions or of two BBs wit h different temperatures at
0.6 - 7.0 keV (Morii et al. 2003), and that above ~20 keV was a PL function
(Kuiper Hermsen Mendez 2004). The combination BB + PL + PL was found to best
represent the phase-averaged spectrum. Phase-resolved spectroscopy indicated
the existence of two emission regions, one with a thermal and the other with a
non-thermal nature. The combination BB + BB + PL was also found to represent
the phase-averaged spectrum well. However, we found that this model is
physically unacceptable due to an excessively large area of the emission region
of the blackbody. Nonetheless, we found that the temperatures and radii of the
two blackbody components showed moderate correlations in the phase-resolved
spectra. The fact that the same correlations have been observed between the
phase-averaged spectra of various magnetars (Nakagawa et al. 2009) suggests
that a self-similar function can approximate the intrinsic energy spectra of
magnetars below ~10 keV.Comment: Accepted for publication in the PAS
Development and Performance of Kyoto's X-ray Astronomical SOI pixel (SOIPIX) sensor
We have been developing monolithic active pixel sensors, known as Kyoto's
X-ray SOIPIXs, based on the CMOS SOI (silicon-on-insulator) technology for
next-generation X-ray astronomy satellites. The event trigger output function
implemented in each pixel offers microsecond time resolution and enables
reduction of the non-X-ray background that dominates the high X-ray energy band
above 5--10 keV. A fully depleted SOI with a thick depletion layer and back
illumination offers wide band coverage of 0.3--40 keV. Here, we report recent
progress in the X-ray SOIPIX development. In this study, we achieved an energy
resolution of 300~eV (FWHM) at 6~keV and a read-out noise of 33~e- (rms) in the
frame readout mode, which allows us to clearly resolve Mn-K and
K. Moreover, we produced a fully depleted layer with a thickness of
. The event-driven readout mode has already been successfully
demonstrated.Comment: 7pages, 12figures, SPIE Astronomical Telescopes and Instrumentation
2014, Montreal, Quebec, Canada. appears as Proc. SPIE 9147, Space Telescopes
and Instrumentation 2014: Ultraviolet to Gamma Ra
X-ray Spectral Study of the Photoionized Stellar Wind in Vela~X-1
We present results from quantitative modeling and spectral analysis of the
high mass X-ray binary Vela X-1 obtained with the Chandra HETGS. The spectra
exhibit emission lines from H-like and He-like ions driven by photoionization,
as well as fluorescent emission lines from several elements in lower charge
states. In order to interpret and make full use of the high-quality data, we
have developed a simulator, which calculates the ionization and thermal
structure of a stellar wind photoionized by an X-ray source, and performs Monte
Carlo simulations of X-ray photons propagating through the wind. The emergent
spectra are then computed as a function of the viewing angle accurately
accounting for photon transport in three dimensions including dynamics. From
comparisons of the observed spectra with the simulation results, we are able to
find the ionization structure and the geometrical distribution of material in
Vela X-1 that can reproduce the observed spectral line intensities and
continuum shapes at different orbital phases remarkably well. It is found that
a large fraction of X-ray emission lines from highly ionized ions are formed in
the region between the neutron star and the companion star. We also find that
the fluorescent X-ray lines must be produced in at least three distinct regions
--(1)the extended stellar wind, (2)reflection off the stellar photosphere, and
(3)in a distribution of dense material partially covering and possibly trailing
the neutron star, which may be associated with an accretion wake. Finally, from
detailed analysis of the emission lines, we demonstrate that the stellar wind
is affected by X-ray photoionization.Comment: 22 pages, 7 tables, 24 figures, accepted for publication in The
Astrophysical Journa
Radiation-Induced Degradation Mechanism of X-ray SOI Pixel Sensors with Pinned Depleted Diode Structure
The X-ray Silicon-On-Insulator (SOI) pixel sensor named XRPIX has been
developed for the future X-ray astronomical satellite FORCE. XRPIX is capable
of a wide-band X-ray imaging spectroscopy from below 1 keV to a few tens of keV
with a good timing resolution of a few tens of s. However, it had a major
issue with its radiation tolerance to the total ionizing dose (TID) effect
because of its thick buried oxide layer due to the SOI structure. Although new
device structures introducing pinned depleted diodes dramatically improved
radiation tolerance, it remained unknown how radiation effects degrade the
sensor performance. Thus, this paper reports the results of a study of the
degradation mechanism of XRPIX due to radiation using device simulations. In
particular, mechanisms of increases in dark current and readout noise are
investigated by simulation, taking into account the positive charge
accumulation in the oxide layer and the increase in the surface recombination
velocity at the interface between the sensor layer and the oxide layer. As a
result, it is found that the depletion of the buried p-well at the interface
increases the dark current, and that the increase in the sense-node capacitance
increases the readout noise.Comment: 7 pages, 10 figures, accepted for publication in IEEE-TN
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