3,295 research outputs found
RXJ0123.4-7321, a Be/X-ray binary in the wing of the SMC
To confirm faint Be/X-ray binary candidates from the XMM-Newton survey of the
Small Magellanic Cloud, we searched for X-ray outbursts in archival ROSAT
observations. We found that RXJ0123.4-7321 was much brighter when detected with
ROSAT than seen 16 years later by XMM-Newton. We analysed the ROSAT
observations and the OGLE I-band light curve of the optical counterpart to
investigate the nature of the system. High long-term variability in the X-ray
flux of a factor of ~150 was found between the ROSAT and XMM-Newton detections,
indicating strong outburst activity during the ROSAT observations. The I-band
light curve reveals long-term variability and regular outbursts with a period
of (119.9+-2.5) days indicating the orbital period of the binary system. The
large X-ray flux variations and the properties of the optical counterpart
confirm RXJ0123.4-7321 as a new Be/X-ray binary in the wing of the Small
Magellanic Cloud.Comment: 5 pages, 8 figures, accepted for publication in A&
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 source populations in the Magellanic Clouds
Early X-ray surveys of the Magellanic Clouds (MCs) were performed with the
imaging instruments of the Einstein, ASCA and ROSAT satellites revealing
discrete X-ray sources and large-scale diffuse emission. Large samples of
supernova remnants, high and low mass X-ray binaries and super-soft X-ray
sources could be studied in detail. Today, the major X-ray observatories
XMM-Newton and Chandra with their advanced angular and spectral resolution and
extended energy coverage are ideally suited for detailed population studies of
the X-ray sources in these galaxies and to draw conclusions on our own Galaxy.
We summarize our knowledge about the X-ray source populations in the MCs from
past missions and present first results from systematic studies of the Small
Magellanic Cloud (SMC) using the growing number of archival XMM-Newton
observations.Comment: 6 pages, 3 figures, Fig. 2 in low resolution, to be published in the
proceedings of the ESAC workshop "X-rays from Nearby Galaxies
Time variability of X-ray sources in the M 31 centre field
We present an extension to our XMM-Newton X-ray source catalogue of M 31,
containing 39 newly found sources. In order to classify and identify more of
the sources we search for X-ray time variability in XMM-Newton archival data of
the M 31 centre field.
As a source list we used our extended catalogue based on observations
covering the time span from June 2000 to July 2004. We then determined the flux
or at least an upper limit at the source positions for each observation.
Deriving the flux ratios for the different observations and searching for the
maximum flux difference we determined variability factors. We also calculated
the significance of the flux ratios.
Using hardness ratios, X-ray variability and cross correlations with
catalogues in the X-ray, optical, infrared and radio regimes, we detected three
super soft source candidates, one supernova remnant and six supernova remnant
candidates, one globular cluster candidate, three X-ray binaries and four X-ray
binary candidates. Additionally we identified one foreground star candidate and
classified fifteen sources with hard spectra, which may either be X-ray
binaries or Crab-like supernova remnants in M 31 or background active galactic
nuclei. The remaining five sources stay unidentified or without classification.
Based on the time variability results we suggest six sources, which were
formerly classified as "hard", to be X-ray binary candidates. The
classification of one other source (XMMM31 J004236.7+411349) as a supernova
remnant, has to be rejected due to the distinct time variability we found. We
now classify this source as a foreground star.Comment: 13 pages, 6 figures, accepted for publication in A&
Deep XMM-Newton observation of a northern LMC field: I. Selected X-ray sources
First results from a deep XMM-Newton observation of a field in the Large Magellanic Cloud (LMC) near the northern rim of the supergiant shell LMC 4 are presented. Spectral and temporal analyses of a sample of selected X-ray sources yielded two new candidates for supernova remnants, a supersoft X-ray source and a likely high mass X-ray binary (HMXB) pulsar. From the fourteen brightest sources up to ten are active galactic nuclei in the background of the galaxy which can be used as probes for the interstellar medium in the LMC. From the three previously known HMXBs the Be/X-ray binary EXO 053109-6609.2 was the brightest source in the field, allowing a more detailed analysis of its X-ray spectrum and pulse profile. During the pulse EXO 053109-6609.2 shows eclipses of the X-ray emitting areas with increased photo-electric absorption before and after the eclipse. The detection of X-ray pulsations with a period of 69.2 s is confirmed for RX J0529.8-6556 and a possible period of 272 s is discovered from XMMU J053011.2-655122. The results are discussed with respect to individual sources as well as in the view of source population studies in the vicinity of the supergiant shell LMC 4
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&
X-ray monitoring of classical novae in the central region of M 31. II. Autumn and winter 2007/2008 and 2008/2009
[Abridged] Classical novae (CNe) represent the major class of supersoft X-ray
sources (SSSs) in the central region of our neighbouring galaxy M 31. We
performed a dedicated monitoring of the M 31 central region with XMM-Newton and
Chandra between Nov 2007 and Feb 2008 and between Nov 2008 and Feb 2009
respectively, in order to find SSS counterparts of CNe, determine the duration
of their SSS phase and derive physical outburst parameters. We systematically
searched our data for X-ray counterparts of CNe and determined their X-ray
light curves and spectral properties. We detected in total 17 X-ray
counterparts of CNe in M 31, only four of which were known previously. These
latter sources are still active 12.5, 11.0, 7.4 and 4.8 years after the optical
outburst. From the 17 X-ray counterparts 13 were classified as SSSs. Four novae
displayed short SSS phases (< 100 d). Based on these results and previous
studies we compiled a catalogue of all novae with SSS counterparts in M 31
known so far. We used this catalogue to derive correlations between the
following X-ray and optical nova parameters: turn-on time, turn-off time,
effective temperature (X-ray), t2 decay time and expansion velocity of the
ejected envelope (optical). Furthermore, we found a first hint for the
existence of a difference between SSS parameters of novae associated with the
stellar populations of the M 31 bulge and disk. Additionally, we conducted a
Monte Carlo Markov Chain simulation on the intrinsic fraction of novae with SSS
phase. This simulation showed that the relatively high fraction of novae
without detected SSS emission might be explained by the inevitably incomplete
coverage with X-ray observations in combination with a large fraction of novae
with short SSS states, as expected from the WD mass distribution. In order to
verify our results with an increased sample further monitoring observations are
needed.Comment: 31 pages, 23 figures, 10 tables; submitted to A&
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