168 research outputs found
A First Look at the Nuclear Region of M31 with Chandra
We report on the first observation of the nuclear region of M31 with the
Chandra X-ray Observatory. The nuclear source seen with the Einstein and ROSAT
HRIs is resolved into five point sources. One of these sources is within 1'' of
the M31 central super-massive black hole. As compared to the other point
sources in M31, this nuclear source has an unusual x-ray spectrum. Based on the
spatial coincidence we identify this source with the central black hole, and
note that the unusual spectrum is a challenge to current theories. A bright
transient is detected ~26'' to the west of the nucleus, which may be associated
with a stellar mass black hole.Comment: Submitted to ApJ Letters, 4 pages, 4 figures. email:
garcia,ssm,fap,wrf,jem,cjf, @head-cfa.harvard.ed
Prevalence of Toxoplasma gondii in Belgian wildlife
De Craeye, S., Speybroeck, N., Baert, K., Ajzenberg, D., Dardé, M.L., Collinet, F., Tavernier, P., Van Gucht, S., Dorny, P., Dierick, K
A comparison of the strong lensing properties of the Sersic and the NFW profiles
We investigate the strong lensing properties of the Sersic profile as an
alternative to the NFW profile, focusing on applications to lens modelling of
clusters. Given an underlying Sersic dark matter profile, we study whether an
NFW profile can provide an acceptable fit to strong lensing constraints in the
form of single or multiple measured Einstein radii. We conclude that although
an NFW profile that fits the lensing constraints can be found in many cases,
the derived parameters may be biased. In particular, we find that for n~2,
which corresponds to massive clusters, the mass at r_200 of the best fit NFW is
overestimated (by a factor of ~2) and the concentration is very low (c~2). The
differences are important enough to warrant the inclusion of Sersic profile for
future analysis of strong lensing clusters.Comment: 19 pages (single column format), 11 figures. Accepted for publication
by JCA
A Chandra X-ray Study of NGC 1068: II. The Luminous X-ray Source Population
We present an analysis of the compact X-ray source population in the
Seyfert~2 galaxy NGC 1068, imaged with Chandra. We find a total of 84 compact
sources, of which 66 are projected onto the galactic disk of NGC 1068. Spectra
of the brightest sources have been modeled with both multi-color disk blackbody
and power-law models. The power-law model provides the better description of
the spectrum for most of these sources. Five sources have 0.4-8 keV intrinsic
luminosities greater than 10^{39} erg/s, assuming that their emission is
isotropic and that they are associated with NGC 1068. We refer to these sources
as Intermediate Luminosity X-ray Objects (IXOs). If these five sources are
X-ray binaries accreting with luminosities that are both sub-Eddington and
isotropic, then the implied source masses are >7 solar masses, and so they are
inferred to be black holes. The brightest source has a much harder spectrum
(Gamma = 0.9\pm0.1) than that found in Galactic black hole candidates and other
IXOs. It also shows large-amplitude variability on both short-term and
long-term timescales. The ratio of the number of sources with luminosities
greater than 2.1 x 10^{38} erg/s in the 0.4-8 keV band to the rate of massive
star formation is the same, to within a factor of two, for NGC 1068, the
Antennae, NGC 5194 (the main galaxy in M51), and the Circinus galaxy. This
suggests that the rate of production of X-ray binaries per massive star is
approximately the same for galaxies with currently active star formation,
including ``starbursts''.Comment: 33 pages, 10 figures. To appear in The Astrophysical Journal, v591
n1, July 1, 2003 issu
Chandra Observation of Abell 2142: Survival of Dense Subcluster Cores in a Merger
We use Chandra data to map the gas temperature in the central region of the
merging cluster A2142. The cluster is markedly nonisothermal; it appears that
the central cooling flow has been disturbed but not destroyed by a merger. The
X-ray image exhibits two sharp, bow-shaped, shock-like surface brightness edges
or gas density discontinuities. However, temperature and pressure profiles
across these edges indicate that these are not shock fronts. The pressure is
reasonably continuous across these edges, while the entropy jumps in the
opposite sense to that in a shock (i.e. the denser side of the edge has lower
temperature, and hence lower entropy). Most plausibly, these edges delineate
the dense subcluster cores that have survived a merger and ram pressure
stripping by the surrounding shock-heated gas.Comment: Latex, 9 pages, 5 figures (including color), uses emulateapj.sty.
Submitted to Ap
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
Building solids inside nano-space: from confined amorphous through confined solvate to confined âmetastableâ polymorph
The nanocrystallisation of complex molecules inside mesoporous hosts and control over the resulting structure is a significant challenge. To date the largest organic molecule crystallised inside the nano-pores is a known pharmaceutical intermediate â ROY (259.3 g mol1). In this work we demonstrate smart manipulation of the phase of a larger confined pharmaceutical â indomethacin (IMC, 357.8 g mol1), a substance with known conformational flexibility and complex polymorphic behaviour. We show the detailed structural analysis and the control of solid state transformations of encapsulated molecules inside the pores of mesoscopic cellular foam (MCF, pore size ca. 29 nm) and controlled pore glass (CPG, pore size ca. 55 nm). Starting from confined amorphous IMC we drive crystallisation into a confined methanol solvate, which upon vacuum drying leads to the stabilised rare form V of IMC inside the MCF host. In contrast to the pure form, encapsulated form V does not transform into a more stable polymorph upon heating. The size of the constraining pores and the drug concentration within the pores determine whether the amorphous state of the drug is stabilised or it recrystallises into confined nanocrystals. The work presents, in a critical manner, an application of complementary techniques (DSC, PXRD, solid-state NMR, N2 adsorption) to confirm unambiguously the phase transitions under confinement and offers a comprehensive strategy towards the formation and control of nano-crystalline encapsulated organic solids
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