628 research outputs found
The Magellanic system X-ray sources
Using archival X-ray data from the second XMM-Newton serendipitous source
catalogue, we present comparative analysis of the overall population of X-ray
sources in the Large and Small Magellanic Clouds. We see a difference between
the characteristics of the brighter sources in the two populations in the X-ray
band. Utilising flux measurements in different energy bands we are able to sort
the X-ray sources based on similarities to other previously identified and
classified objects. In this manner we are able to identify the probable nature
of some of the unknown objects, identifying a number of possible X-ray binaries
and Super Soft Sources.Comment: 4 pages, 2 figures. Poster to appear in proceedings of IAU Symposium
256, The Magellanic System: Stars, Gas, and Galaxies. Keele Univeristy, U
Recurrent ~24 h Periods in RXTE ASM Data
Analysis of data from the Rossi X-ray Timing Explorer satellite's All Sky
Monitor instrument for several X-ray binary sources has identified a recurrent
\~24 h period. This period is sometimes highly significant, giving rise to the
possibility of it being identified as an orbital or super-orbital period.
Further analysis has revealed the same period in a number of other X-ray
sources. As a result this period has been discounted as spurious, described
variously as arising from daily variations in background levels and beating
between the sampling period and long-term secular trends in the light curves.
We present here an analysis of the spurious periods and show that the dominant
mechanism is in fact spectral leakage of low-frequency power present in the
light curves.Comment: 9 Pages, 10 figures, 1 table, submitted to PASA 20th December 2004.
Added 1 page of text and 3 figures to clarify results and discussion.
Resubmitted 16th May 2005. Accepted 25th June 200
The Cool Accretion Disk in ESO 243-49 HLX-1: Further Evidence of an Intermediate Mass Black Hole
With an inferred bolometric luminosity exceeding 10^42 erg/s, HLX-1 in ESO
243-49 is the most luminous of ultraluminous X-ray sources and provides one of
the strongest cases for the existence of intermediate mass black holes. We
obtain good fits to disk-dominated observations of the source with BHSPEC, a
fully relativistic black hole accretion disk spectral model. Due to
degeneracies in the model arising from the lack of independent constraints on
inclination and black hole spin, there is a factor of 100 uncertainty in the
best-fit black hole mass M. Nevertheless, spectral fitting of XMM-Newton
observations provides robust lower and upper limits with 3000 Msun < M < 3 x
10^5 Msun, at 90% confidence, placing HLX-1 firmly in the intermediate-mass
regime. The lower bound on M is entirely determined by matching the shape and
peak energy of the thermal component in the spectrum. This bound is consistent
with (but independent of) arguments based solely on the Eddington limit. Joint
spectral modelling of the XMM-Newton data with more luminous Swift and Chandra
observations increases the lower bound to 6000 Msun, but this tighter
constraint is not independent of the Eddington limit. The upper bound on M is
sensitive to the maximum allowed inclination i, and is reduced to M < 10^5 Msun
if we limit i < 75 deg.Comment: 10 pages, 7 figures, accepted for publication in Ap
Discovery of an Ultrasoft X-ray Transient Source in the 2XMM Catalog: a Tidal Disruption Event Candidate
We have discovered an ultrasoft X-ray transient source, 2XMMi
J184725.1-631724, which was detected serendipitously in two XMM-Newton
observations in the direction of the center of the galaxy IC 4765-f01-1504 at a
redshift of 0.0353. These two observations were separated by 211 days, with the
0.2-10 keV absorbed flux increasing by a factor of about 9. Their spectra are
best described by a model dominated by a thermal disk or a single-temperature
blackbody component (contributing >80% of the flux) plus a weak power-law
component. The thermal emission has a temperature of a few tens of eV, and the
weak power-law component has a photon index of ~3.5. Similar to the black hole
X-ray binaries in the thermal state, our source exhibits an accretion disk
whose luminosity appears to follow the relation. This would
indicate that the black hole mass is about 10^5-10^6 M_sun using the
best-fitting inner disk radius. Both XMM-Newton observations show variability
of about 21% on timescales of hours, which can be explained as due to fast
variations in the mass accretion rate. The source was not detected by ROSAT in
an observation in 1992, indicating a variability factor of >64 over longer
timescales. The source was not detected again in X-rays in a Swift observation
in 2011 February, implying a flux decrease by a factor of >12 since the last
XMM-Newton observation. The transient nature, in addition to the extreme
softness of the X-ray spectra and the inactivity of the galaxy implied by the
lack of strong optical emission lines, makes it a candidate tidal disruption
event. If this is the case, the first XMM-Newton observation would have been in
the rising phase, and the second one in the decay phase.Comment: 12 pages, 6 figures. Accepted for publication in Ap
X-ray Variability and Hardness of ESO 243-49 HLX-1: Clear Evidence for Spectral State Transitions
The ultra-luminous X-ray (ULX) source ESO 243-49 HLX-1 currently provides the
strongest evidence for the existence of intermediate mass black holes. We
conduct an ongoing monitoring campaign with the Swift X-ray Telescope and found
that HLX-1 showed two fast rise and exponential decay with increases in the
count rate of a factor ~40 separated by 375+/-13 days. We obtained new
XMM-Newton and Chandra dedicated pointings that were triggered at the lowest
and highest luminosities, respectively. The unabsorbed luminosities ranged from
1.9x10^40 to 1.25x10^42 erg/s. We confirm here the detection of spectral state
transitions from HLX-1 reminiscent of Galactic black hole binaries: at high
luminosities, the X-ray spectrum showed a thermal state dominated by a disk
component with temperatures of 0.26 keV at most, and at low luminosities the
spectrum is dominated by a hard power law with a photon index in the range
1.4-2.1, consistent with a hard state. The source was also observed in a steep
power law state. In the thermal state, the luminosity of the disk component
appears to scale with the fourth power of the inner disk temperature which
supports the presence of an optically thick, geometrically thin accretion disk.
The low fractional variability (rms of 9+/-9%) in this state also suggests the
presence of a dominant disk. The spectral changes and long-term variability of
the source cannot be explained by variations of the beaming angle and are not
consistent with the source being in a super-Eddington accretion state. HLX-1 is
thus an unusual ULX as it is similar to Galactic black hole binaries, which
have non-beamed and sub-Eddington emission, but with luminosities 3 orders of
magnitude higher. In this picture, a lower limit on the mass of the black hole
of >9000 M_sun can be derived, and the disk temperature in the thermal state
also suggests the presence of a black hole of a few 10^3 M_sun.Comment: accepted for publication in ApJ (October 10, 2011, v740-1); 11
figures, 13 pages with emulateapj styl
Seasonality and other risk factors for fleas infestations in domestic dogs and cats
Fleas in the genus Ctenocephalides are the most clinically important parasitic arthropods of dogs and cats worldwide yet risk factors that might increase the risk of infestation in small animals remains unclear. Here we developed a supervised text mining approach analysing key aspects of flea epidemiology using electronic health records from domestic cats and dogs seen at a sentinel network of 191 voluntary veterinary practices across Great Britain between March 2014 and July 2020. Our methods identified fleas as likely to have been present during 22,276 of 1,902,016 cat consultations (1.17%) and 12,168 of 4,844,850 dog consultations (0.25%). Multivariable logistic regression modelling found that animals originating from areas of least deprivation were associated with 50% reductions in odds of veterinaryârecorded flea infestation compared to the most deprived regions in England. Age of the animal was significantly associated with flea presentation in both cats and dogs, with cases peaking before animals reached 12 months. Cases were recorded through each study years, peaking between July and October, with fluctuations between each year. Our findings can be used towards healthcare messaging for veterinary practitioners and owners
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