1,601 research outputs found
Spectroscopy of the brightest optical counterparts of X-ray sources in the direction of M~31 and M~33
Recent surveys of the Local Group spiral Galaxies M31 and M33 with XMM-Newton
yielded a large number of X-ray sources. As part of the effort to identify and
classify the objects responsible for this X-ray emission, we have obtained
optical spectra of the brightest optical counterparts of the identified X-ray
sources, using the 1.3m Skinakas Telescope. Most of these objects are
foreground star candidates. The purpose of the present study is to confirm this
identification and to explore the compatibility between the optical spectral
classification and the observed X-ray properties of the sources. We have
obtained optical spectra for the 14 brightest optical counterparts of X-ray
sources identified by XMM-Newton in the direction of M31 and for 21 optical
counterparts in the direction of M33, using the 1.3m Skinakas telescope in
Crete, Greece. All of the M31 sources and all but one of the M33 sources were
confirmed to be foreground stars, of spectral types between A and M. One of the
stars is a late M dwarf with H-alpha emission, a flare star, also displaying
strong X-ray variability. One of the M~33 sources (lying within the D25
ellipse) corresponds to a previously known background galaxy, LEDA 5899.Comment: 9 pages, 12 figures, accepted in A&
Deep XMM-Newton survey of M33
In an XMM-Newton raster observation of the bright local group spiral galaxy
M33 we study the population of X-ray sources (X-ray binaries, supernova
remnants, super-shells) down to a 0.5-10 keV luminosity of 10^35 erg s^-1 --
more than a factor of 10 deeper than earlier ROSAT observations. EPIC spectra
and hardness ratios are used to distinguish between different source classes.
We confirmed the 3.45 d orbital light curve of the X-ray binary M33 X7,
detected a transient super-soft source in M33, and searched for short term
variability of the brighter sources. We characterize the diffuse X-ray
component that is correlated with the inner disk and spiral arms. We will
compare the results with other nearby galaxies.Comment: Proceedings of the "X-ray surveys, in the light of the new
observatories" workshop, Astronomische Nachrichten, in the press (4 pages, 5
figures, uses an.cls
XMM-Newton survey of the Local Group galaxy M 33
In an XMM-Newton raster observation of the bright Local Group spiral galaxy M
33 we study the population of X-ray sources (X-ray binaries, supernova
remnants) down to a 0.2--4.5 keV luminosity of 10^35 erg/s -- more than a
factor of 10 deeper than earlier ROSAT observations. EPIC hardness ratios and
optical and radio information are used to distinguish between different source
classes. The survey detects 408 sources in an area of 0.80 square degree. We
correlate these newly detected sources with earlier M 33 X-ray catalogues and
information from optical, infra-red and radio wavelengths. As M 33 sources we
detect 21 supernova remnants (SNR) and 23 SNR candidates, 5 super-soft sources,
and 2 X-ray binaries (XRBs). There are 267 sources classified as hard, which
may either be XRBs or Crab-like SNRs in M 33 or background AGN. The 44
confirmed and candidate SNRs more than double the number of X-ray detected SNRs
in M 33. 16 of these are proposed as SNR candidates from the X-ray data for the
first time. On the other hand, there are several sources not connected to M 33:
five foreground stars, 30 foreground star candidates, 12 active galactic
nucleus candidates, one background galaxy and one background galaxy candidate.
Extrapolating from deep field observations we would expect 175 to 210
background sources in this field. This indicates that about half of the sources
detected are sources within M 33.Comment: 14 pages, 6 figures, accepted for publication in A&A, the images of
Figs. 1,2,3,4,6 are available in jpg format, a full version of the paper is
available at ftp://ftp.xray.mpe.mpg.de/people/fwh/docs/M33_AA0068.p
Diffusion of Mn interstitials in (Ga,Mn)As epitaxial layers
Magnetic properties of thin (Ga,Mn)As layers improve during annealing by
out-diffusion of interstitial Mn ions to a free surface. Out-diffused Mn atoms
participate in the growth of a Mn-rich surface layer and a saturation of this
layer causes an inhibition of the out-diffusion. We combine high-resolution
x-ray diffraction with x-ray absorption spectroscopy and a numerical solution
of the diffusion problem for the study of the out-diffusion of Mn interstitials
during a sequence of annealing steps. Our data demonstrate that the
out-diffusion of the interstitials is substantially affected by the internal
electric field caused by an inhomogeneous distribution of charges in the
(Ga,Mn)As layer.Comment: 11 pages, 5 figure
Mn incorporation in as-grown and annealed (Ga,Mn)As layers studied by x-ray diffraction and standing-wave uorescence
A combination of high-resolution x-ray diffraction and a new technique of
x-ray standing wave uorescence at grazing incidence is employed to study the
structure of (Ga,Mn)As diluted magnetic semiconductor and its changes during
post-growth annealing steps. We find that the film is formed by a uniform,
single crystallographic phase epilayer covered by a thin surface layer with
enhanced Mn concentration due to Mn atoms at random non-crystallographic
positions. In the epilayer, Mn incorporated at interstitial position has a
dominant effect on lattice expansion as compared to substitutional Mn. The
expansion coeffcient of interstitial Mn estimated from our data is consistent
with theory predictions. The concentration of interstitial Mn and the
corresponding lattice expansion of the epilayer are reduced by annealing,
accompanied by an increase of the density of randomly distributed Mn atoms in
the disordered surface layer. Substitutional Mn atoms remain stable during the
low-temperature annealing.Comment: 9 pages, 9 figure
The eclipsing massive X-ray binary M33 X-7: New X-ray observations and optical identification
The eclipsing X-ray binary M33 X-7 was in the field of view during several
observations of our XMM-Newton M33 survey and in the archival Chanfdra
observation 1730 which cover a large part of the 3.45 d orbital period. We
detect emission of M33 X-7 during eclipse and a soft X-ray spectrum of the
source out of eclipse that can best be described by bremsstrahlung or disk
blackbody models. No significant regular pulsations of the source in the range
0.25-1000 s were found. The average source luminosity out of eclipse is 5E37
erg/s (0.5-4.5 keV). In a special analysis of DIRECT observations we identify
as optical counterpart a B0I to O7I star of 18.89 mag in V which shows the
ellipsoidal heating light curve of a high mass X-ray binary with the M33 X-7
binary period. The location of the X-ray eclipse and the optical minima allow
us to determine an improved binary period and ephemeris of mid-eclipse as HJD
(2451760.61+-0.09)+- N * (3.45376+-0.00021). The mass of the compact object
derived from orbital parameters and the optical companion mass, the lack of
pulsations, and the X-ray spectrum of M33 X-7 may indicate that the compact
object in the system is a black hole. M33 X-7 would be the first detected
eclipsing high mass black hole X-ray binary.Comment: 9 pages including 6 figures, A&A accepte
Catalogue of high-mass X-ray binaries in the Galaxy ( edition)
We present a new edition of the catalogue of high-mass X-ray binaries in the
Galaxy. The catalogue contains source name(s), coordinates, finding chart,
X-ray luminosity, system parameters, and stellar parameters of the components
and other characteristic properties of 114 high-mass X-ray binaries, together
with a comprehensive selection of the relevant literature. The aim of this
catalogue is to provide the reader with some basic information on the X-ray
sources and their counterparts in other wavelength ranges (-rays, UV,
optical, IR, radio). About 60% of the high-mass X-ray binary candidates are
known or suspected Be/X-ray binaries, while 32% are supergiant/X-ray binaries.
Some sources, however, are only tentatively identified as high-mass X-ray
binaries on the basis of their X-ray properties similar to the known high-mass
X-ray binaries. Further identification in other wavelength bands is needed to
finally determine the nature of these sources. In cases where there is some
doubt about the high-mass nature of the X-ray binary this is mentioned.
Literature published before 1 October 2005 has, as far as possible, been taken
into account.Comment: 25 pages, table include
Search for LBV Candidates in the M33 Galaxy
A total of 185 luminous blue variable (LBV) candidates with V < 18.5 and B-V
< 0.35 are selected based on the photometrical Survey of Local Group Galaxies
made by P. Massey et al. 2006. The candidates were selected using aperture
photometry of H-alpha images. The primary selection criterion is that the
prospective candidate should be a blue star with H-aplha emission. In order not
to miss appreciably reddened LBV candidates, we compose an additional list of
25 presumably reddened (0.35 < B-V < 1.2, V < 18.5) emission star candidates. A
comparison with the list of known variables in the M33 galaxy showed 29% of our
selected candidates to be photometrically variable. We also find our list to
agree well with the lists of emission-line objects obtained in earlier papers
using different methods.Comment: 6 figure
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