2,158 research outputs found
A Multi-coloured survey of NGC 253 with XMM-Newton
There is a large body of work that has used the excellent Chandra
observations of nearby galaxies with neglible low mass X-ray binary (LMXB)
populations. This has culminated in a ``Universal'' X-ray luminosity function
(XLF) for high mass X-ray binaries (HMXBs). However, a number of methods have
been used to convert from source intensities to luminosities when creating
these XLFs. We have taken advantage of the XMM-Newton observations of the
nearby starbursting spiral galaxy NGC 253 to test some of these methods. We
find the luminosities derived from these various methods to vary by a factor of
3. We also find the most influential factor in the conversion from
intensity to luminosity to be the absorption. We therefore conclude that a more
consistent approach is required for determining the true Universal XLF for
HMXBs. Ideally, this would involve individual spectral fitting of each X-ray
source. Certainly, the line-of-sight absorption should be determined from the
observations rather than assuming Galactic absorption. We find the best
approach for obtaining an XLF from low-count data to be the splitting of the
X-ray sources into two or more intensity intervals, and obtaining a conversion
from intensity to flux for each group from spectral modelling of the summed
spectrum of that group.Comment: To appear in the proceedings of "X-rays from Nearby Galaxies", 4-7
Septembeer 2007, 4 page
Cumulative luminosity functions of the X-ray point source population in M31
We present preliminary results from a detailed analysis of the X-ray point
sources in the XMM-Newton survey of M31. These sources are expected to be
mostly X-ray binaries. We have so far studied 225 of the 535 sources found by
automated source detection. Only sources which were present in all three EPIC
images were considered. X-ray binaries are identified by their energy spectrum
and power density spectrum. Unlike in other surveys we have obtained source
luminosities from freely fit emission models. We present uncorrected luminosity
functions of the sources analysed so far.Comment: 2 pages, 1 figure. To appear in proceedings of IAUS23
XMM-Newton reveals ~100 new LMXBs in M31 from variability studies
We have conducted a survey of X-ray sources in XMM-Newton observations of
M31, examining their power density spectra (PDS) and spectral energy
distributions (SEDs). Our automated source detection yielded 535 good X-ray
sources; to date, we have studied 225 of them. In particular, we examined the
PDS because low mass X-ray binaries (LMXBs) exhibit two distinctive types of
PDS. At low accretion rates, the PDS is characterised by a broken power law,
with the spectral index changing from ~0 to ~1 at some frequency in the range
\~0.01--1 Hz; we refer to such PDS as Type A. At higher accretion rates, the
PDS is described by a simple power law; we call these PDS Type B. Of the 225
sources studied to date, 75 exhibit Type A variability, and are almost
certainly LMXBs, while 6 show Type B but not Type A, and are likely LMXBs. Of
these 81 candidate LMXBs, 71 are newly identified in this survey; furthermore,
they are mostly found near the centre of M31. Furthermore, most of the X-ray
population in the disc are associated with the spiral arms, making them likely
high mass X-ray binaries (HMXBs). In general these HMXBs do not exhibit Type A
variability, while many central X-ray sources (LMXBs) in the same luminosity
range do. Hence the PDS may distinguish between LMXBs and HMXBs in this
luminosity range.Comment: 4 pages, 2 figures. To appear in proceedings of IAUS230: "Populations
of High Energy Sources in Galaxies", 14-19 August 2005, Dublin, Eds E.J.A.
Meurs and G. Fabbian
Opioid prescribing for acute postoperative pain : an overview of systematic reviews related to two consensus statements relevant at patient, prescriber, system and public health levels
Peer reviewedPublisher PD
Analysis and design of on-grade reinforced concrete track support structures
For the improvement of rail service, the Department of Transportation, Federal Rail Administration, is sponsoring a test track on the Atchison, Topeka, and Santa Fe Railway. The test track will contain nine separate rail support structures, including one conventional section for control and three reinforced concrete structures on grade, one slab and two beam sections. The analysis and design of these latter structures was accomplished by means of the finite element method, NASTRAN, and is presented
Modifying the Rebound: It depends! Explaining Mobility Behaviour on the Basis of the German Socio-Economic Panel
Efficiency and distributional impacts of tradable white certificates compared to taxes, subsidies and regulations
A multi-coloured survey of NGC 253 with XMM-Newton: testing the methods used for creating luminosity functions from low-count data
NGC 253 is a local, star-bursting spiral galaxy with strong X-ray emission
from hot gas, as well as many point sources. We have conducted a spectral
survey of the X-ray population of NGC 253 using a deep XMM-Newton
observation.NGC 253 only accounts for ~20% of the XMM-Newton EPIC field of
view, allowing us to identify ~100 X-ray sources that are unlikely to be
associated with NGC\thinspace 253. Hence we were able to make a direct estimate
of contamination from e.g. foreground stars and background galaxies.
X-ray luminosity functions (XLFs) of galaxy populations are often used to
characterise their properties. There are several methods for estimating the
luminosities of X-ray sources with few photons. We have obtained spectral fits
for the brightest 140 sources in the 2003 XMM-Newton observation of NGC 253,
and compare the best fit luminosities of those 69 non-nuclear sources
associated with NGC 253 with luminosities derived using other methods.
We find the luminosities obtained from these various methods to vary
systematically by a factor of up to three for the same data; this is largely
due to differences in absorption.
We therefore conclude that assuming Galactic absorption is probably unwise;
rather, one should measure the absorption for the population.
A remarkable correlation has been reported between the XLFs of galaxies and
their star formation rates. However, the XLFs used in that study were obtained
using several different methods. If the sample galaxies were revisited and a
single method were applied, then this correlation may become stronger still.Comment: Accepted for publication in the Monthly Notices of the Royal
Astronomical Society (MNRAS). 17 pages, 7 figure
An X-ray spectral survey of the disc of M31 with XMM-Newton
We present the results of a complete spectral survey of the X-ray point
sources detected in five XMM-Newton observations along the major axis of M31
but avoiding the central bulge, aimed at establishing the population
characteristics of X-ray sources in this galaxy. We obtained background
subtracted spectra and lightcurves for each of the 335 X-ray point sources
detected across the five observations from 2002. We also correlate our source
list with those of earlier X-ray surveys and radio, optical and infra-red
catalogues. Sources with more than 50 source counts are individually spectrally
fit in order to create the most accurate luminosity functions of M31 to date.
Based on the spectral fitting of these sources with a power law model, we
observe a broad range of best fit photon index. From this distribution of best
fit index, we identify 16 strong high mass X-ray binary system candidates in
M31. We show the first cumulative luminosity functions created using the best
fit spectral model to each source with more than 50 source counts in the disc
of M31. The cumulative luminosity functions show a prominent, statistically
significant flattening in the X-ray luminosity LX interval 37.0 \lesssim log LX
erg s-1 \lesssim 37.5. Such a feature may also be present in the X-ray
populations of several other galaxies, but at a much lower statistical
significance. We investigate the number of AGN present in our source list and
find that above LX ~1.4x1036 erg s-1 the observed population is statistically
dominated by the point source population of M31.Comment: accepted by A&A. 24 pages, 6 figures, 7 table
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