1,198 research outputs found
X-ray Development of the Classical Nova V2672 Ophiuchi with Suzaku
We report the Suzaku detection of a rapid flare-like X-ray flux amplification
early in the development of the classical nova V2672 Ophiuchi. Two
target-of-opportunity ~25 ks X-ray observations were made 12 and 22 days after
the outburst. The flux amplification was found in the latter half of day 12.
Time-sliced spectra are characterized by a growing supersoft excess with
edge-like structures and a relatively stable optically-thin thermal component
with Ka emission lines from highly ionized Si. The observed spectral evolution
is consistent with a model that has a time development of circumstellar
absorption, for which we obtain the decline rate of ~10-40 % in a time scale of
0.2 d on day 12. Such a rapid drop of absorption and short-term flux
variability on day 12 suggest inhomogeneous ejecta with dense blobs/holes in
the line of sight. Then on day 22 the fluxes of both supersoft and thin-thermal
plasma components become significantly fainter. Based on the serendipitous
results we discuss the nature of this source in the context of both short- and
long-term X-ray behavior.Comment: To appear in PASJ; 9 pages, 5 figures, 2 table
An X-Ray Dip in the X-Ray Transient 4U 1630-47
An x-ray dip was observed during a 1996 Rossi X-Ray Timing Explorer
observation of the recurrent x-ray transient 4U 1630-47. During the dip, the
2-60 keV x-ray flux drops by a factor of about three, and, at the lowest point
of the dip, the x-ray spectrum is considerably softer than at non-dip times. We
find that the 4U 1630-47 dip is best explained by absorption of the inner part
of an accretion disk, while the outer part of the disk is unaffected. The
spectral evolution during the dip is adequately described by the variation of a
single parameter, the column density obscuring the inner disk.Comment: 13 pages, 4 figures, Accepted for publication in Ap
A Method of Mass Measurement in Black Hole Binaries Using Timing and High Resolution X-ray Spectroscopy
In X-ray binaries, several percent of the compact object luminosity is
intercepted by the surface of the normal companion and re-radiated through
Compton reflection and the K-fluorescence. This reflected emission follows the
variability of the compact object with a delay approximately equal to the
orbital radius divided by the speed of light. This provides the possibility of
measuring the orbital radius and thus substantially refining the compact object
mass determination compared to using optical data alone. We demonstrate that it
may be feasible to measure the time delay between the direct and reflected
emission using cross-correlation of the light curves observed near the Kalpha
line and above the K-edge of neutral iron. In the case of Cyg X-1, the time
delay measurement is feasible with a 300--1000 ksec observation by a telescope
with a 1000 cm^2 effective area near 6.4 keV and with a ~5eV energy resolution.
With longer exposures, it may be possible to obtain mass constraints even if an
X-ray source in the binary system lacks an optical counterpart.Comment: ApJ Letters, in press. 4 pages, 3 figures, uses emulateapj.st
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
Infra-red effects of Non-linear sigma model in de Sitter space
We extend our investigation on a possible de Sitter symmetry breaking
mechanism in non-linear sigma models. The scale invariance of the quantum
fluctuations could make the cosmological constant time dependent signaling the
de Sitter symmetry breaking. To understand such a symmetry breaking mechanism,
we investigate the energy-momentum tensor. We show that the leading infra-red
logarithms cancel to all orders in perturbation theory in a generic non-linear
sigma model. When the target space is an N sphere, the de Sitter symmetry is
preserved in the large N limit. For a less symmetric target space, the
infra-red logarithms appear at the three loop level. However there is a counter
term to precisely cancel it. The leading infra-red logarithms do not cancel for
higher derivative interactions. We investigate such a model in which the
infra-red logarithms first appear at the three loop level. A nonperturbative
investigation in the large N limit shows that they eventually grow as large as
the one loop effect.Comment: 39page
Inclination Effects and Beaming in Black Hole X-ray Binaries
We investigate the dependence of observational properties of black hole X-ray
binaries on the inclination angle i of their orbits. We find the following: (1)
Transient black hole binaries show no trend in their quiescent X-ray
luminosities as a function of i, suggesting that the radiation is not
significantly beamed. This is consistent with emission from an accretion disk.
If the X-rays are from a jet, then the Lorentz factor gamma of the jet is less
than 1.24 at the 90% confidence level. (2) The X-ray binary 4U1543-47 with i of
order 21 degrees has a surprisingly strong fluorescent iron line in the high
soft state. Quantifying an earlier argument by Park et al. (2004), we conclude
that if the continuum X-ray emission in this source is from a jet, then gamma <
1.04. (3) None of the known binaries has cos i 75 degrees. This
fact, plus the lack of eclipses among the 20 black hole binaries in our sample,
strongly suggests at the 99.5% confidence level that systems with large
inclination angles are hidden from view. The obscuration could be the result of
disk flaring, as suggested by Milgrom (1978) for neutron star X-ray binaries.
(4) Transient black hole binaries with i ~ 70-75 degrees have significantly
more complex X-ray light curves than systems with i < 65 degrees. This may be
the result of variable obscuration and/or variable height above the disk of the
radiating gas.Comment: 26 pages, to appear in The Astrophysical Journal, vol. 624, May 1,
200
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
Development of a Schwarzschild-type x-ray microscope
This paper was published in Optics Letters and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: http://dx.doi.org/10.1364/OL.16.000109 Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law
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