1,970 research outputs found
Discovery of disc precession in the M31 dipping X-ray binary Bo 158
We present results from three XMM-Newton observations of the M31 low mass
X-ray binary XMMU J004314.4+410726.3 (Bo 158), spaced over 3 days in 2004,
July. Bo 158 was the first dipping LMXB to be discovered in M31. Periodic
intensity dips were previously seen to occur on a 2.78-hr period, due to
absorption in material that is raised out of the plane of the accretion disc.
The report of these observations stated that the dip depth was anti-correlated
with source intensity. However, our new observations do not favour a strict
intensity dependance, but rather suggest that the dip variation is due to
precession of the accretion disc. This is to be expected in LMXBs with a mass
ratio <~ 0.3 (period <~ 4 hr), as the disc reaches the 3:1 resonance with the
binary companion, causing elongation and precession of the disc. A smoothed
particle hydrodynamics simulation of the disc in this system shows retrograde
rotation of a disc warp on a period of ~11 P_orb, and prograde disc precession
on a period of ~29 P_orb. This is consistent with the observed variation in the
depth of the dips. We find that the dipping behaviour is most likely to be
modified by the disc precession, hence we predict that the dipping behaviour
repeats on a 81+/-3 hr cycle.Comment: 9 pages, 6 figures, accepted for publication by MNRAS, changed
conten
Energy-dependent evolution in IC10 X-1: hard evidence for an extended corona and implications
We have analyzed a ~130 ks XMM-Newton observation of the dynamically confirmed black hole + Wolf-Rayet (BH+WR) X-ray binary (XB) IC10 X-1, covering ~1 orbital cycle. This system experiences periodic intensity dips every ~35 hr. We find that energy-independent evolution is rejected at a >5Ï level. The spectral and timing evolution of IC10 X-1 are best explained by a compact disk blackbody and an extended Comptonized component, where the thermal component is completely absorbed and the Comptonized component is partially covered during the dip. We consider three possibilities for the absorber: cold material in the outer accretion disk, as is well documented for Galactic neutron star (NS) XBs at high inclination; a stream of stellar wind that is enhanced by traveling through the L1 point; and a spherical wind. We estimated the corona radius (r ADC) for IC10 X-1 from the dip ingress to be ~106 km, assuming absorption from the outer disk, and found it to be consistent with the relation between r ADC and 1-30 keV luminosity observed in Galactic NS XBs that spans two orders of magnitude. For the other two scenarios, the corona would be larger. Prior BH mass (M BH) estimates range over 23-38 M â, depending on the inclination and WR mass. For disk absorption, the inclination, i, is likely to be ~60-80°, with M BH ~ 24-41 M â. Alternatively, the L1-enhanced wind requires i ~ 80°, suggesting ~24-33 M â. For a spherical absorber, i ~ 40°, and M BH ~ 50-65 M â
The comet 17P/Holmes 2007 outburst: the early motion of the outburst material
Context. On October 24, 2007 the periodic comet 17P/Holmes underwent an
astonishing outburst that increased its apparent total brightness from
magnitude V\sim17 up to V\sim2.5 in roughly two days. We report on Wendelstein
0.8 m telescope (WST) photometric observations of the early evolution stages of
the outburst. Aims. We studied the evolution of the structure morphology, its
kinematic, and estimated the ejected dust mass. Methods. We analized 126 images
in the BVRI photometric bands spread between 26/10/2007 and 20/11/2007. The
bright comet core appeared well separated from that one of a quickly expanding
dust cloud in all the data, and the bulk of the latter was contained in the
field of view of our instrument. The ejected dust mass was derived on the base
of differential photometry on background stars occulted by the moving cloud.
Results. The two cores were moving apart from each other at a relative
projected constant velocity of (9.87 +/- 0.07) arcsec/day (0.135 +/-0.001
km/sec). In the inner regions of the dust cloud we observed a linear increase
in size at a mean constant velocity of (14.6+/-0.3) arcsec/day (0.200+/-0.004
km/sec). Evidence of a radial velocity gradient in the expanding cloud was also
found. Our estimate for the expanding coma's mass was of the order of 10^{-2}-1
comet's mass implying a significant disintegration event. Conclusions. We
interpreted our observations in the context of an explosive scenario which was
more probably originated by some internal instability processes, rather than an
impact with an asteroidal body. Due to the peculiar characteristics of this
event, further observations and investigations are necessary in order to
enlight the nature of the physical processes that determined it.Comment: 5 pages, 3 figures, A&A accepte
On the artificial nature of aperiodic variability in XMM-Newton observations of M 31 X-ray sources and the ultraluminous X-ray source NGC 4559 ULX-7
Context: Power density spectra (PDS) that are characteristic of low mass X-ray binaries (LMXBs) have been previously reported for M 31 X-ray sources, observed by XMM-Newton. However, we have recently discovered that these PDS result from the improper addition/subtraction of non-simultaneous lightcurves.
Aims: To understand the properties and origins of the artefact.
Methods: We re-analysed our XMM-Newton observations of M 31 with non-simultaneous and simultaneous lightcurves, then combined simulated lightcurves at various intensities with various offsets and found that the artefact is more dependent on the offset than the intensity.
Results: The lightcurves produced by the XMM-Newton Science Analysis Software (SAS) are non-synchronised by default. This affects not only the combination of lightcurves from the three EPIC detectors (MOS1, MOS2 and pn), but also background subtraction in the same CCD. It is therefore imperative that all SAS-generated lightcurves are synchronised by time filtering, even if the whole observation is to be used. We also find that the reported timing behaviour for NGC 4559 ULX-7 was also contaminated by the artefact; there is no significant variability in the correctly-combined lightcurves of NGC 4559 ULX-7. Hence, the classification of this source as an intermediate-mass black hole is no longer justified.
Conclusions: While previous timing results from M 31 have been proven wrong, and also the broken power law PDS in NGC 4559 ULX-7, XMM-Newton was able to detect aperiodic variability in just 3 ks of observations of NGC 5408 ULX1. Hence XMM-Newton remains a viable tool for analysing variability in extra-galactic X-ray sources
NGC300 X-1 and IC10 X-1: a new breed of black hole binary?
[ABRIDGED] IC10 X-1 has recently been confirmed as a black hole (BH) +
Wolf-Rayet (WR) X-ray binary, and NGC300 X-1 is thought to be. IC10 X-1 and
NGC300 X-1 have similar X-ray properties, with luminosities ~10^38 erg/s, and
orbital periods ~30 hr. We investigate similarities between these two, as well
as differences between them and the known Galactic BH binary systems. We have
examined XMM-Newton observations of NGC300 X-1 and IC10 X-1. We extracted
lightcurves and spectra; power density spectra (PDS) were constructed from the
lightcurves, and the X-ray emission spectra were modeled. Each source exhibits
PDS that are characteristic of disc-accreting X-ray binaries (XBs) in the high
state. In this state, Galactic XBs with known BH primaries have soft, thermal
emission; however the emission spectra of our targets are predominantly
non-thermal. Furthermore, the Observation 1 spectrum of NGC300 X-1 is
strikingly similar to that of IC10 X-1. The remarkable similarity between the
behaviour of NGC300 X-1 in Observation 1 and that of IC10 X-1 lends strong
evidence for NGC300 X-1 being a (BH+WR) binary. The unusual spectra of NGC300
X-1 and IC10 X-1 may be due to these systems existing in a persistently high
state, whereas all known BH LMXBs are transient. BH XBs in a persistent high
state could retain their corona, and hence exhibit a large non-thermal
component. LMC X-1 is a BH XB that has only been observed in the high state,
and its spectrum is remarkably similar to those of our targets. We therefore
classify NGC300 X-1, IC10 X-1 and perhaps LMC X-1 as a new breed of BH XB,
defined by their persistently high accretion rates and consequent stable disc
configuration and corona. This scenario may also explain the lack of
ultraluminous X-ray sources in the canonical soft state.Comment: Approved for publication in A&A. 8 pages, 5 figure
Discovery and modelling of disc precession in the M31 X-ray binary Bo 158?
The low mass X-ray binary (LMXB) associated with the M31 globular cluster Bo
158 is known to exhibit intensity dips on a ~2.78 hr period. This is due to
obscuration of the X-ray source on the orbital period by material on the outer
edge of the accretion disc. However, the depth of dipping varied from <10% to
\~83% in three archival XMM-Newton observations of Bo 158. Previous work
suggested that the dip depth was anticorrelated with the X-ray luminosity.
However, we present results from three new XMM-Newton observations that suggest
that the evolution of dipping is instead due to precession of the accretion
disc. Such precession is expected in neutron star LMXBs with mass ratios <0.3
(i.e. with orbital periods <4 hr), such as the Galactic dipping LMXB 4U
1916-053. We simulated the accretion disc of Bo 158 using cutting-edge 3D
smoothed particle hydrodynamics (SPH), and using the observed parameters. Our
results show disc variability on two time-scales. The disc precesses in a
prograde direction on a period of 81+/-3 hr. Also, a radiatively-driven disc
warp is present in the inner disc, which undergoes retrograde precesson on a
\~31 hr period. From the system geometry, we conclude that the dipping
evolution is driven by the disc precession. Hence we predict that the dipping
behaviour repeats on a ~81 hr cycle.Comment: 6 pages, 4 figures, to appear in proceedings "The X-ray Universe
2005", San Lorenzo de El Escoriale (Madrid, Spain), 26-30 September 200
Comparison of established and emerging biodosimetry assays
Rapid biodosimetry tools are required to assist with triage in the case of a large-scale radiation incident. Here, we aimed to determine the dose-assessment accuracy of the well-established dicentric chromosome assay (DCA) and cytokinesis-block micronucleus assay (CBMN) in comparison to the emerging γ-H2AX foci and gene expression assays for triage mode biodosimetry and radiation injury assessment. Coded blood samples exposed to 10 X-ray doses (240 kVp, 1 Gy/min) of up to 6.4 Gy were sent to participants for dose estimation. Report times were documented for each laboratory and assay. The mean absolute difference (MAD) of estimated doses relative to the true doses was calculated. We also merged doses into binary dose categories of clinical relevance and examined accuracy, sensitivity and specificity of the assays. Dose estimates were reported by the first laboratories within 0.3-0.4 days of receipt of samples for the γ-H2AX and gene expression assays compared to 2.4 and 4 days for the DCA and CBMN assays, respectively. Irrespective of the assay we found a 2.5-4-fold variation of interlaboratory accuracy per assay and lowest MAD values for the DCA assay (0.16 Gy) followed by CBMN (0.34 Gy), gene expression (0.34 Gy) and γ-H2AX (0.45 Gy) foci assay. Binary categories of dose estimates could be discriminated with equal efficiency for all assays, but at doses ≥1.5 Gy a 10% decrease in efficiency was observed for the foci assay, which was still comparable to the CBMN assay. In conclusion, the DCA has been confirmed as the gold standard biodosimetry method, but in situations where speed and throughput are more important than ultimate accuracy, the emerging rapid molecular assays have the potential to become useful triage tools
From X-ray dips to eclipse: Witnessing disk reformation in the recurrent nova USco
The 10th recorded outburst of the recurrent eclipsing nova USco was observed
simultaneously in X-ray, UV, and optical by XMM-Newton on days 22.9 and 34.9
after outburst. Two full passages of the companion in front of the nova ejecta
were observed, witnessing the reformation of the accretion disk. On day 22.9,
we observed smooth eclipses in UV and optical but deep dips in the X-ray light
curve which disappeared by day 34.9, then yielding clean eclipses in all bands.
X-ray dips can be caused by clumpy absorbing material that intersects the line
of sight while moving along highly elliptical trajectories. Cold material from
the companion could explain the absence of dips in UV and optical light. The
disappearance of X-ray dips before day 34.9 implies significant progress in the
formation of the disk. The X-ray spectra contain photospheric continuum
emission plus strong emission lines, but no clear absorption lines. Both
continuum and emission lines in the X-ray spectra indicate a temperature
increase from day 22.9 to day 34.9. We find clear evidence in the spectra and
light curves for Thompson scattering of the photospheric emission from the
white dwarf. Photospheric absorption lines can be smeared out during scattering
in a plasma of fast electrons. We also find spectral signatures of resonant
line scattering that lead to the observation of the strong emission lines.
Their dominance could be a general phenomenon in high-inclination systems such
as Cal87.Comment: Submitted to ApJ. 16 pages, 16 figure
A Potential Supernova Remnant/X-ray Binary Association in M31
The well-studied X-ray/Optical/Radio supernova remnant DDB 1-15 (CXOM31
J004327.8+411829; r3-63) in M31 has been investigated with archival XMM-Newton
and Chandra observations. The timing data from XMM-Newton reveals a power
density spectrum (PDS) characteristic of accreting compact objects in X-ray
binaries (XRBs). The PDS shows features typical of Roche lobe overflow
accretion, hinting that the XRB is low-mass. The Chandra observations resolve
the SNR into a shell and show a variable count rate at the 94% confidence level
in the northwest quadrant. Together, these XMM-Newton and Chandra data suggest
that there is an XRB in the SNR r3-63 and that the XRB is located in the
northwestern portion of the SNR. The currently-available X-ray and optical data
show no evidence that the XRB is high-mass. If the XRB is low-mass, r3-63 would
be the first SNR found to contain a low-mass X-ray binary.Comment: 30 pages, 3 tables, 11 figures, accepted for publication in Ap
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