151 research outputs found
A Precessing Jet in the CH Cyg Symbiotic System
Jets have been detected in only a few symbiotic binaries to date, and CH Cyg
is one of them. In 2001, a non-relativistic jet was detected in CH Cyg for the
first time in X-rays. We carried out coordinated Chandra, HST, and VLA
observations in 2008 to study the propagation of this jet and its interaction
with the circumbinary medium. We detected the jet with Chandra and HST and
determined that the apex has expanded to the South from about 300 AU to about
1400 AU, with the shock front propagating with velocity < 100 km/s. The shock
front has significantly slowed down since 2001. Unexpectedly, we also
discovered a powerful jet in the NE-SW direction, in the X-ray, optical and
radio. This jet has a multi-component structure, including an inner jet and a
counter-jet at about 170 AU, and a SW component ending in several clumps
extending out to approximately 750 AU. The structure of the jet and the
curvature of the outer portion of the SW jet suggest an episodically powered
precessing jet, or a continuous precessing jet with occasional mass ejections
or pulses. We carried out detailed spatial mapping of the X-ray emission and
correlation with the optical and radio emission. X-ray spectra were extracted
of the central source, inner NE counter jet, and the brightest clump at a
distance of approximately 500 AU from the central source. We discuss the
initial results of our analyses, including the multi-component spectral fitting
of the jet-components and of the central source.Comment: 15 pages with 4 figures, Accepted by ApJ Letter
Two new species of Exobasidium causing Exobasidium diseases on Vaccinium spp. in Japan
Abstract Two new Exobasidium species on Vaccinium
spp. in Japan are described and discussed. Exobasidium
kishianum, which causes Exobasidium leaf blight on I/.
hirtum var. pubescens and V. smallii, is characterized by its
ellipsoid to ovoid basidiospores with (0-)1-3 septa. Its systemic
infection is also observed. Exobasidium inconspicuum,
cansing Exobasidium leaf blister on V. hirtum vat.
pubescens, is characterized by its obovoid or ellipsoid to
oval basidiospores with 0-4 septa. Mode of germination of
the basidiospores is by germ tube in both species
High-resolution X-ray Spectra Of The Symbiotic Star SS73 17
SS73 17 was an innocuous Mira-type symbiotic star until Integral and Swift
discovered its bright hard X-ray emission, adding it to the small class of
"hard X-ray emitting symbiotics." Suzaku observations in 2006 then showed it
emits three bright iron lines as well, with little to no emission in the 0.3-2
keV bandpass. We present here followup observations with the Chandra HETG and
Suzaku that confirm the earlier detection of strong emission lines of Fe Kalpha
fluorescence, Fe XXV and Fe XXVI but also show significantly more soft X-ray
emission. The high resolution spectrum also shows emission lines of other
highly ionized ions as Si XIV and possibly S XVI. In addition, a reanalysis of
the 2006 Suzaku data using the latest calibration shows that the hard (15-50
keV) X-ray emission is brighter than previously thought and remains constant in
both the 2006 and 2008 data.
The G ratio calculated from the Fe XXV lines shows that these lines are
thermal, not photoionized, in origin. With the exception of the hard X-ray
emission, the spectra from both epochs can be fit using thermal radiation
assuming a differential emission measure based on a cooling flow model combined
with a full and partial absorber. We show that acceptable fits can be obtained
for all the data in the 1-10 keV band varying only the partial absorber. Based
on the temperature and accretion rate, the thermal emission appears to be
arising from the boundary layer between the accreting white dwarf and the
accretion disk.Comment: 7 pages, 5 figures. Accepted by the Astrophysical Journa
The X-ray Pulse Profile of BG CMi
We present an analysis of the X-ray data of a magnetic cataclysmic variable,
BG CMi, obtained with ROSAT in March 1992 and with ASCA in April 1996. We show
that four peaks clearly exist in the X-ray pulse profile, unlike a single peak
found in the optical profile. The fluxes of two major pulses are
times larger than those of two minor pulses. The fraction of the total pulsed
flux increases from 51% to 85% with increasing energy in 0.1 2.0 keV,
whereas it decreases from 96% to 22% in 0.8 10 keV. We discuss the
implications of our findings for the origin of the pulse profile and its energy
dependence.Comment: To appear in New Astronom
A precessing accretion disc in the intermediate polar XY Ari?
XY Ari is the only intermediate polar to show deep X-ray eclipses of its
white dwarf. Previously published observations with Ginga and Chandra have also
revealed a broad X-ray orbital modulation, roughly antiphased with the eclipse,
and presumed to be due to absorption in an extended structure near the edge of
an accretion disc. The X-ray pulse profile is generally seen to be
double-peaked, although a single-peaked pulse was seen by RXTE during an
outburst in 1996.We intended to investigate the cause of the broad orbital
modulation in XY Ari to better understand the accretion flow in this system and
other intermediate polars. We observed XY Ari with RXTE and analysed previously
unpublished archival observations of the system made with ASCA and XMM-Newton.
These observations comprise six separate visits and span about ten years. The
various X-ray observations show that the broad orbital modulation varies in
phase and significance, then ultimately disappears entirely in the last few
years. In addition, the X-ray pulse profile shows variations in depth and
shape, and in the recent RXTE observations displays no evidence for changes in
hardness ratio. The observed changes indicates that both the pulse profile and
the orbital modulation are solely due to geometrical effects at the time of the
RXTE observations, rather than phase-dependent variations in photoelectric
absorption as seen previously. We suggest that this is evidence for a
precessing, tilted accretion disc in this system. The precession of the disc
moves structures out of our line of sight both at its outer edge (changing the
orbital modulation) and at its inner edge where the accretion curtains are
anchored (changing the pulse profile).Comment: Accepted for publication in Astronomy & Astrophysic
Chandra High Energy Transmission Grating Spectrum of AE Aquarii
(Abridged) The results of a Chandra X-ray Observatory High-Energy
Transmission Grating (HETG) observation of the nova-like cataclysmic binary AE
Aqr are described. First, the X-ray spectrum is that of an optically thin
multi-temperature thermal plasma; the X-ray emission lines are broad, with
widths that increase with the line energy, from sigma~1 eV for O VIII to
sigma~5.5 eV for Si XIV; the X-ray spectrum is reasonably well fit by a plasma
model with a Gaussian emission measure distribution that peaks at log
T(K)=7.16, has a width sigma=0.48, an Fe abundance equal to 0.44 times solar,
and other metal (primarily Ne, Mg, and Si) abundances equal to 0.76 times
solar; and for a distance d=100 pc, the total emission measure EM=8.0E53 cm^-3
and the 0.5-10 keV luminosity L_X=1.1E31 erg/s. Second, based on the f/(i+r)
flux ratios of the forbidden (f), intercombination (i), and recombination (r)
lines of the He alpha triplets of N VI, O VII, and Ne IX measured by Itoh et
al. in the XMM-Newton Reflection Grating Spectrometer spectrum and those of O
VII, Ne IX, Mg XI, and Si XIII in the Chandra HETG spectrum, either the
electron density of the plasma increases with temperature by over three orders
of magnitude, from n_e~6E10 cm^-3 for N VI to n_e~1E14 cm^-3 for SI XIII,
and/or the plasma is significantly affected by photoexcitation. Third, the
radial velocity of the X-ray emission lines varies on the white dwarf spin
phase, with two oscillations per spin cycle and an amplitude K~160 km/s. These
results appear to be inconsistent with the recent models of Itoh et al.,
Ikhsanov, and Venter & Meintjes of an extended, low-density source of X-rays in
AE Aqr, but instead support earlier models in which the dominant source of
X-rays is of high density and/or in close proximity to the white dwarf.Comment: 13 pages including 1 table and 11 encapsulated postscript figure (3
in color); uses emulateapj.cls and apjfonts.sty; accepted on 2009 October 1
for publication in The Astrophysical Journa
Fe K line complex in the nuclear region of NGC 253
A bright, nearby edge-on starburst galaxy NGC 253 was studied using the
Suzaku, XMM and Chandra X-ray observatories. We detected with Suzaku and XMM
complex line structure of Fe K, which is resolved into three lines (Fe I at 6.4
keV, Fe XXV at 6.7 keV and Fe XXVI at 7.0 keV) around the center of NGC 253.
Especially, the Fe I and Fe XXVI lines are the first clear detections, with a
significance of >99.99 % and 99.89 % estimated by a Monte Carlo procedure.
Imaging spectroscopy with Chandra revealed that the emission is distributed in
~60 arcsec^2 region around the nucleus, which suggests that the source is not
only the buried AGN. The flux of highly ionized Fe lines can be explained by
the accumulation of 10-1000 supernova remnants that are the result of high
starforming activity, while the Fe I line flux is consistent with the
fluorescent line emission expected with the molecular clouds in the region.Comment: Accepted for publication in ApJ
A dwarf nova in the globular cluster M13
Dwarf novae in globular clusters seem to be rare with only 13 detections in
the 157 known Galactic globular clusters. We report the identification of a new
dwarf nova in M13, the 14th dwarf nova identified in a globular cluster to
date. Using the 2m Faulkes Telescope North, we conducted a search for stars in
M13 that show variability over a year (2005-2006) on timescales of days and
months. This led to the detection of one dwarf nova showing several outbursts.
A Chandra X-ray source is coincident with this dwarf nova and shows both a
spectrum and variability consistent with that expected from a dwarf nova, thus
supporting the identification. We searched for a counterpart in Hubble Space
Telescope ACS/WFC archived images and found at least 11 candidates, of which we
could characterize only the 7 brightest, including one with a 3 sigma H-alpha
excess and a faint blue star. The detection of one dwarf nova when more could
have been expected likely indicates that our knowledge of the global Galactic
population of cataclysmic variables is too limited. The proportion of dwarf
novae may be lower than found in catalogs, or they may have a much smaller duty
cycle in general as proposed by some population synthesis models and recent
observations in the field.Comment: Accepted for publication in ApJ, 12 pages, 12 figures, 5 tables (v2
contains corrections of the proofs
Near-infrared/optical identification of five low-luminosity X-ray pulsators
We present the identification of the most likely near-infrared/optical
counterparts of five low-luminosity X-ray pulsators (AX J1700.1-4157, AX
1740.1-2847, AX J1749.2-2725, AX J1820.5-1434 and AX J1832.3-0840) which have
long pulse periods (> 150 s). The X-ray properties of these systems suggest
that they are likely members of persistent high mass X-ray binaries or
intermediate polars. Using our Chandra observations, we detected the most
likely counterparts of three sources (excluding AX J1820.5-1434 and AX
J1832.3-0840) in their ESO - NTT near-infrared observations, and a possible
counterpart for AX J1820.5-1434 and AX J1832.3-0840 in the 2MASS and DSS
observations respectively. We also performed the X-ray timing and spectral
analysis for all the sources using our XMM-Newton observations, which further
helped us to constrain the nature of these systems. Our multiwavelength
observations suggest that AX J1749.2-2725 and AX J1820.5-1434 most likely
harbor accreting neutron stars while AX J1700.1-4157, AX J1740.1-2847 and AX
J1832.3-0840 could be intermediate polars.Comment: 11 pages, 5 figures, Submitted to MNRA
57 second oscillations in Nova Centauri 1986 (V842 Cen)
High speed photometry in 2008 shows that the light curve of V842 Cen
possesses a coherent modulation at 56.825 s, with sidebands at 56.598 s and
57.054 s. These have appeared since this nova remnant was observed in 2000 and
2002. We deduce that the dominant signal is the rotation period of the white
dwarf primary and the sidebands are caused by reprocessing from a surface
moving with an orbital period of 3.94 h. Thus V842 Cen is an intermediate polar
(IP) of the DQ Herculis subclass, is the fastest rotating white dwarf among the
IPs and is the third fastest known in a cataclysmic variable. As in other IPs
we see no dwarf nova oscillations, but there are often quasi-periodic
oscillations in the range 350 - 1500 s. There is a strong brightness modulation
with a period of 3.78 h, which we attribute to negative superhumps, and there
is an even stronger signal at 2.886 h which is of unknown origin but is
probably a further example of that seen in GW Lib and some other systems. We
used the Swift satellite to observe V842 Cen in the ultra-violet and in X-rays,
although no periodic modulation was detected in the short observations. The
X-ray luminosity of this object appears to be much lower than that of other IPs
in which the accretion region is directly visible.Comment: 6 pages, 10 figures, accepted for publication in MNRA
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