688 research outputs found
XMM-Newton observations of the Small Magellanic Cloud: X-ray outburst of the 6.85 s pulsar XTE J0103-728
A bright X-ray transient was seen during an XMM-Newton observation in the
direction of the Small Magellanic Cloud (SMC) in October 2006. The EPIC data
allow us to accurately locate the source and to investigate its temporal and
spectral behaviour. X-ray spectra covering 0.2-10 keV and pulse profiles in
different energy bands were extracted from the EPIC data. The detection of 6.85
s pulsations in the EPIC-PN data unambiguously identifies the transient with
XTE J0103-728, discovered as 6.85 s pulsar by RXTE. The X-ray light curve
during the XMM-Newton observation shows flaring activity of the source with
intensity changes by a factor of two within 10 minutes. Modelling of
pulse-phase averaged spectra with a simple absorbed power-law indicates
systematic residuals which can be accounted for by a second emission component.
For models implying blackbody emission, thermal plasma emission or emission
from the accretion disk (disk-blackbody), the latter yields physically sensible
parameters. The photon index of the power-law of ~0.4 indicates a relatively
hard spectrum. The 0.2-10 keV luminosity was 2x10^{37} with a contribution of
~3% from the disk-blackbody component. A likely origin for the excess emission
is reprocessing of hard X-rays from the neutron star by optically thick
material near the inner edge of an accretion disk. From a timing analysis we
determine the pulse period to 6.85401(1) s indicating an average spin-down of
~0.0017 s per year since the discovery of XTE J0103-728 in May 2003. The X-ray
properties and the identification with a Be star confirm XTE J0103-728 as
Be/X-ray binary transient in the SMC.Comment: 5 pages, 4 figures, submitted to A&A on 21 Dec. 200
A Coherent Timing Solution for the Nearby Isolated Neutron Star RX J0720.4-3125
We present the results of a dedicated effort to measure the spin-down rate of
the nearby isolated neutron star RX J0720.4-3125. Comparing arrival times of
the 8.39-sec pulsations for data from Chandra we derive an unambiguous timing
solution for RX J0720.4-3125 that is accurate to 5 years.
Adding data from XMM and ROSAT, the final solution yields
Pdot=(6.98+/-0.02)x10^(-14) s/s; for dipole spin-down, this implies a
characteristic age of 2 Myr and a magnetic field strength of 2.4e13 G. The
phase residuals are somewhat larger than those for purely regular spin-down,
but do not show conclusive evidence for higher-order terms or a glitch. From
our timing solution as well as recent X-ray spectroscopy, we concur with recent
suggestions that RX J0720.4-3125 is most likely an off-beam radio pulsar with a
moderately high magnetic field.Comment: 5 pages, 1 figure. Accepted for publication in ApJ
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
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
On the nature of the flux variability during an expansion stage of a type I X-ray burst: Constraints on Neutron Star Parameters for 4U 1820-30
Powerful Type I X-ray burst with strong radial expansion was observed from
the low mass X-ray binary 4U 1820-30 with Rossi X-ray Timing Explorer on May 2,
1997. We investigate closely the flux profile during the burst expansion
stage. Applying a semi-analytical model we are able to uncover the behavior of
a photospheric radius and to simulate the evolution of neutron star
(NS)-accretion disk system. The bottom flux L_{bot} is a few times the
Eddington limit L_{Edd} for outer layers, because the electron cross-section is
a few times less than the Thomson cross-section at such a high temperatures.
The surplus of energy flux with respect to the Eddington, ,
goes into the potential energy of the expanded envelope. As cooling of the
burning zone starts the surplus decreases and thus the envelope shrinks while
the emergent photon flux stays the same . At a certain moment the NS
low-hemisphere, previously screened by the disk, becomes visible to the
observer. Consequently, the flux detected by the observer increases. Indeed, we
observe to the paradoxical situation when the burning zone cools, but the
apparent flux increases because of the NS-accretion disk geometry. We
demonstrate a strong observational evidence of NS-accretion disk occultation in
the behavior of the observed bolometric flux. We estimate the anisotropy due to
geometry and find that the system should have a high inclination angle.
Finally, we apply an analytical model of X-ray spectral formation in the
neutron star atmosphere during burst decay stage to infer the neutron star (NS)
mass-radius relation.Comment: 15 pages, 3 figures, accepted to ApJ
AGN in the XMM-Newton first-light image as probes for the interstellar medium in the LMC
The XMM-Newton first-light image revealed X-ray point sources which show
heavily absorbed power-law spectra. The spectral indices and the probable
identification of a radio counterpart for the brightest source suggest AGN
shining through the interstellar gas of the Large Magellanic Cloud (LMC). The
column densities derived from the X-ray spectra in combination with HI
measurements will allow to draw conclusions on HI to H_2 ratios in the LMC and
compare these with values found for the galactic plane.Comment: 4 pages, LaTex, 4 figures, Accepted for publication in A&A Letter
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
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