91 research outputs found
Search for Near-Infrared Pulsation of the Anomalous X-ray Pulsar 4U 0142+61
We have searched for pulsation of the anomalous X-ray pulsar (AXP) 4U 0142+61
in the K' band ( m) using the fast-readout mode
of IRCS at the Subaru 8.2-m telescope. We found no significant signal at the
pulse frequency expected by the precise ephemeris obtained by the X-ray
monitoring observation with RXTE. Nonetheless, we obtained a best upper limit
of 17% (90% C.L.) for the root-mean-square pulse fraction in the K' band.
Combined with i' band pulsation (Dhillon et al. 2005), the slope of the pulsed
component () was constrained to (90%
C.L.) for an interstellar extinction of .Comment: 11 pages, 3 figures, Accepted for publication in PAS
Power Spectrum Density of long-term MAXI data
Monitor of All-sky X-ray Image (MAXI) on the International Space Station has
been observing the X-ray sky since 2009 August 15. It has accumulated the X-ray
data for about four years, so far. X-ray objects are usually variable and their
variability can be studied by the power spectrum density (PSD) of the X-ray
light curves.We applied our method to calculate PSDs of several kinds of
objects observed with MAXI. We obtained significant PSDs from 16 Seyfert
galaxies.For blackhole binary Cygnus X-1 there was a difference in the shape of
PSD between the hard state and the soft state. For high mass X-ray binaries,
Cen X-3, SMC X-1, and LMC X-4, there were several peaks in the PSD
corresponding to the orbital period and the superorbital period.Comment: 4 pages, 4 figures, accepted for proceedings of The 12th Asia Pacific
Physics Conference of AAPP
On the Weak-Wind Problem in Massive Stars: X-ray Spectra Reveal a Massive Hot Wind in \mu\ Columbae
\mu\ Columbae is a prototypical weak-wind O-star for which we have obtained a
high-resolution X-ray spectrum with the Chandra LETG/ACIS-S instrument and a
low resolution spectrum with Suzaku. This allows us, for the first time, to
investigate the role of X-rays on the wind structure in a bona fide weak-wind
system and to determine whether there actually is a massive, hot wind. The
X-ray emission measure indicates that the outflow is an order of magnitude
greater than that derived from UV lines and is commensurate with the nominal
wind-luminosity relationship for O-stars. Therefore, the ``weak-wind
problem''---identified from cool wind UV/optical spectra---is largely resolved
by accounting for the hot wind seen in X-rays. From X-ray line profiles,
Doppler shifts, and relative strengths, we find that this weak-wind star is
typical of other late O dwarfs. The X-ray spectra do not suggest a magnetically
confined plasma---the spectrum is soft and lines are broadened; Suzaku spectra
confirm the lack of emission above 2 keV. Nor do the relative line shifts and
widths suggest any wind decoupling by ions. The He-like triplets indicate that
the bulk of the X-ray emission is formed rather close to the star, within 5
stellar radii. Our results challenge the idea that some OB stars are
``weak-wind'' stars that deviate from the standard wind-luminosity
relationship. The wind is not weak, but it is hot and its bulk is only
detectable in X-rays.Comment: Accepted for publication in ApJ Letter
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
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