3,578 research outputs found
Spectroscopy of the bright optical counterparts of X-ray sources in the direction of M 31. II
A recent survey of the Local Group spiral galaxy M 31 with XMM-Newton yielded
a large number of X-ray sources. This is the second in a series of papers with
the aim of identifying the optical counterparts of these X-ray sources. We have
obtained optical spectra for 21 bright optical counterparts of 20 X-ray sources
in the direction of M 31, using the 1.3-m Skinakas telescope in Crete, Greece.
For 17 of the 20 X-ray sources, we have identified the optical counterpart as a
normal late type star (of type F or later) in the foreground (i.e. in the Milky
Way). For two more sources there were two possible optical counterparts in each
case, while two more objects have X-ray properties that are not compatible with
the spectral characteristics of late type non-flaring stars.Comment: Accepted for publication by Astronomy & Astrophysics (7 pages, 8
figures, and 2 tables
A ROSAT PSPC X-Ray Survey of the Small Magellanic Cloud
We present the results of a systematic search for point-like and moderately
extended soft (0.1-2.4 keV) X-ray sources in a raster of nine pointings
covering a field of 8.95 deg^2 and performed with the ROSAT PSPC between
October 1991 and October 1993 in the direction of the Small Magellanic Cloud.
We detect 248 objects which we include in the first version of our SMC
catalogue of soft X-ray sources. We set up seven source classes defined by
selections in the count rate, hardness ratio and source extent. We find five
high luminosity super-soft sources (1E 0035.4-7230, 1E 0056.8-7146, RX
J0048.4-7332, RX J0058.6-7146 and RX J0103-7254), one low-luminosity super-soft
source RX J0059.6-7138 correlating with the planetary nebula L357, 51 candidate
hard X-ray binaries including eight bright hard X-ray binary candidates, 19
supernova remnants, 19 candidate foreground stars and 53 candidate background
active galactic nuclei (and quasars). We give a likely classification for ~60%
of the catalogued sources. The total count rate of the detected point-like and
moderately extended sources in our catalogue is 6.9+/-0.3 s^-1, comparable to
the background subtracted total rate from the integrated field of ~6.1+/-0.1
s^-1.Comment: Accepted by A&AS, 13 pages, 2 Postscript figure
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&
X-Ray Binary Systems in the Small Magellanic Cloud
We present the result of a systematic search for spectrally hard and soft
X-ray binary systems in the Small Magellanic Cloud (SMC). This search has been
applied to ROSAT PSPC data (0.1-2.4 keV) collected during 9 pointed
observations towards this galaxy covering a time span of 2 years from October
91 till October 93. Selection criteria have been defined in order to confine
the sample of candidates. Finally 7 spectrally hard and 4 spectrally soft
sources were selected from the list as candidates for binaries in the SMC. The
sample is luminosity limited (>3.10**35 erg/s). SMC X-1 has been observed
during a full binary orbit starting with a low-state covering an X-ray eclipse
and emerging into a bright long-duration flare with two short-duration flares
separated by 10 hours. The Be type transient SMC X-2 has been redetected with
ROSAT. Variability has been found in the sources RX J0051.8-7231 and RX
J0052.1-731 already discovered with Einstein. RX J0101.0-7206 has been
discovered at the north-eastern boundary of the giant SMC HII region N66 during
an X-ray outburst and half a year later during a quiescent phase. A variable
source, RX J0049.1-7250, located north-east of the SMC supernova remnant N19
and which may either be an X-ray binary or an AGN turns out to be strongly
absorbed. It may be located behind the SMC. If it is an X-ray binary then it
radiates at the Eddington limit in the X-ray bright state. Another variable and
hard X-ray source RX J0032.9-7348 has been discovered at the south-eastern
border of the body of the SMC. A high mass X-ray binary nature is favored for
this source. We searched for CAL87 like systems in the SMC catalog and found
none. A new candidate supersoft source RX J0103.8-7254 has been detected. We
cannot exclude that it is a foreground object.Comment: 22 pages, Late
Swift J053041.9-665426, a new Be/X-ray binary pulsar in the Large Magellanic Cloud
We observed the newly discovered X-ray source Swift J053041.9-665426 in the
X-ray and optical regime to confirm its proposed nature as a high mass X-ray
binary. We obtained XMM-Newton and Swift X-ray data, along with optical
observations with the ESO Faint Object Spectrograph, to investigate the
spectral and temporal characteristics of Swift J053041.9-665426. The XMM-Newton
data show coherent X-ray pulsations with a period of 28.77521(10) s (1 sigma).
The X-ray spectrum can be modelled by an absorbed power law with photon index
within the range 0.76 to 0.87. The addition of a black body component increases
the quality of the fit but also leads to strong dependences of the photon
index, black-body temperature and absorption column density. We identified the
only optical counterpart within the error circle of XMM-Newton at an angular
distance of ~0.8 arcsec, which is 2MASS J05304215-6654303. We performed optical
spectroscopy from which we classify the companion as a B0-1.5Ve star. The X-ray
pulsations and long-term variability, as well as the properties of the optical
counterpart, confirm that Swift J053041.9-665426 is a new Be/X-ray binary
pulsar in the Large Magellanic Cloud.Comment: 10 pages, 8 figures, accepted for publication in A&
Discovery of a 168.8 s X-ray pulsar transiting in front of its Be companion star in the Large Magellanic Cloud
We report the discovery of LXP169, a new high-mass X-ray binary (XRB) in the
LMC. The optical counterpart has been identified and appears to exhibit an
eclipsing light curve. We performed follow-up observations to clarify the
eclipsing nature of the system. Energy spectra and time series were extracted
from two XMM-Newton observations to search for pulsations, characterise the
spectrum, and measure spectral and timing changes. Long-term X-ray variability
was studied using archival ROSAT data. The XMM positions were used to identify
the optical counterpart. We obtained UV to NIR photometry to characterise the
companion, along with its 4000 d long I-band light curve. We observed LXP169
with Swift at two predicted eclipse times. We found a spin period of 168.8 s
that did not change between two XMM observations. The X-ray spectrum, well
characterised by a power law, was harder when the source was brighter. The
X-ray flux of LXP169 is found to be variable by a factor of at least 10. The
counterpart is highly variable on short and long timescales, and its photometry
is that of an early-type star with a NIR excess. This classifies the source as
a BeXRB pulsar. We observed a transit in the UV, thereby confirming that the
companion star itself is eclipsed. We give an ephemeris for the transit of MJD
56203.877 + N*24.329. We propose and discuss the scenario where the matter
captured from the companion's equatorial disc creates an extended region of
high density around the neutron star (NS), which partially eclipses the
companion as the NS transits in front of it. This is most likely the first time
the compact object in an XRB is observed to eclipse its companion star. LXP169
would be the first eclipsing BeXRB, and a wealth of important information might
be gained from additional observations, such as a measure of the possible Be
disc/orbital plane misalignment, or the mass of the NS.Comment: Updated version of arXiv 1302.4665v1, accepted for publication in
Astronomy and Astrophysics. 11 pages, 8 figures, 3 table
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