1,373 research outputs found
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
X-ray and optical observations of 1RXS J154814.5-452845: a new intermediate polar with soft X-ray emission
We report the identification of the ROSAT all-sky survey source 1RXS
J154814.5-452845as new intermediate polar and present the results from
follow-up optical and X-ray observations. The source shows pulsations with a
period of 693 s both in the optical and X-ray light curves and the detection of
a synodic frequency strongly suggests that this is the rotation period of the
white dwarf. Although the one day aliasing and the sparse optical data coverage
does not allow to unambiguously identify the orbital period, the most likely
values of 9.37 h and 6.72 h add 1RXS J154814.5-452845 to the intermediate
polars with the longest orbital periods known. The optical spectrum displays
features from the late type secondary and shows the presence of broad
absorption lines at \Hbet and higher order Balmer lines which may be a
signature of the white dwarf atmosphere, very similar to V 709 Cas. The average
X-ray spectra as obtained by the EPIC instruments on board XMM-Newton show hard
emission typical for this class of objects but also the presence of soft
blackbody-like emission similar to that seen from soft intermediate polars and
thought to arise from the white dwarf surface heated by the hard X-rays. The
best fit model comprises thermal emission from multi-temperature plasma in
collisional ionization equilibrium with a continuous temperature distribution
up to a maximum of 60 keV, an Fe fluorescence line at 6.4 keV and with
equivalent width of 260 eV and a blackbody component with kT of 86 eV. The hard
X-ray emission is absorbed by matter covering 47% of the X-ray source with an
equivalent hydrogen density of \ohcm{23}. The remaining hard emission is
absorbed by a much reduced column density of 1.5\hcm{21} as is the soft
blackbody emission. (truncated)Comment: 14 pages, Latex, with 19 figures, accepted for publication in
Astronomy and Astrophysic
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
XMM-Newton observations of SNR 1987A. II. The still increasing X-ray light curve and the properties of Fe K lines
Aims. We report on the recent observations of the supernova remnant SNR 1987A
in the Large Magellanic Cloud with XMM-Newton. Carefully monitoring the
evolution of the X-ray light curve allows to probe the complex circumstellar
medium structure observed around the supernova progenitor star.
Methods. We analyse all XMM-Newton observations of SNR 1987A from January
2007 to December 2011, using data from the EPIC-pn camera. Spectra from all
epochs are extracted and analysed in a homogeneous way. Using a multi-shock
model to fit the spectra across the 0.2-10 keV band we measure soft and hard
X-ray fluxes with high accuracy. In the hard X-ray band we examine the presence
and properties of Fe K ines. Our findings are interpreted in the framework of a
hydrodynamics-based model.
Results. The soft X-ray flux of SNR 1987A continuously increased in the
recent years. Although the light curve shows a mild flattening, there is no
sudden break as reported in an earlier work, a picture echoed by a revision of
the Chandra light curve. We therefore conclude that material in the equatorial
ring and out-of-plane HII regions are still being swept-up. We estimate the
thickness of the equatorial ring to be at least 4.5x10^16 cm (0.0146 pc). This
lower limit will increase as long as the soft X-ray flux has not reached a
turn-over. We detect a broad Fe K line in all spectra from 2007 to 2011. The
widths and centroid energies of the lines indicate the presence of a collection
of iron ionisation stages. Thermal emission from the hydrodynamic model does
not reproduce the low-energy part of the line (6.4-6.5 keV), suggesting that
fluorescence from neutral and/or low ionisation Fe might be present.Comment: 4 pages, 3 figures, 2 tables. Accepted for publication in Astronomy
and Astrophysic
AXPs and X-ray dim neutron stars: Recent XMM-Newton and Chandra results
To date more than half a dozen X-ray dim isolated neutron stars are known.
Their X-ray spectra are characterized by soft blackbody-like emission (kT about
50-120 eV) without indication for harder, non-thermal components. These stars
apparently show no radio emission and no association with supernova remnants.
Four of them exhibit pulsations in their X-ray flux with periods in the range
of 8.39 s to 22.7 s. Similar pulse periods were found from AXPs, maybe
suggesting evolutionary connections. In this talk I will review the recent
observational results from X-ray dim isolated neutron obtained by the major
X-ray observatories XMM-Newton and Chandra. Spectral and temporal
characteristics, inferred luminosities and magnetic field strengths will be
compared with those of AXPs.Comment: COSPAR Symposium on High Energy Studies of Supernova Remnants and
Neutron Stars, Houston, Oct. 200
The Magnificent Seven: Nearby Isolated Neutron Stars with strong Magnetic Fields
Although the true origin of the broad absorption lines in X-ray spectra of
thermal isolated neutron stars is not clear yet, our current knowledge about
the "magnificent seven" strongly suggests that they are highly magnetized
( G), slowly rotating cooling neutron stars. Further timing
studies would be very useful to obtain more independent estimates of the
magnetic field strength (as they currently only exist from RX J0720.4-3125).Comment: Proceedings of the 2005 EPIC XMM-Newton Consortium Meeting, Ringberg
Castle, Germany, April 11-13 2005, Edt. U.G. Briel, S. Sembay and A. Read,
MPE Report 288, June 200
A Probable Optical Counterpart for the Isolated Neutron Star RX J1308.6+2127
Using a very deep observation with HST/STIS, we have searched for an optical
counterpart to the nearby radio-quiet isolated neutron star RX J1308.6+2127
(RBS 1223). We have identified a single object in the 90% Chandra error circle
that we believe to be the optical counterpart. This object has
mag, which translates approximately to an unabsorbed
flux of ergs/s/cm^2/A at 5150 A or an
X-ray-to-optical flux ratio of . This flux is a factor of
above the extrapolation of the black-body fit to the X-ray
spectrum, consistent with the optical spectra of other isolated neutron stars.
Without color information we cannot conclude that this source is indeed the
counterpart of RX J1308.6+2127. If not, then the counterpart must have
mag, corresponding to a flux that is barely consistent with
the extrapolation of the black-body fit to the X-ray spectrum.Comment: 4 pages, 2 figures. Uses emulateapj5.sty, onecolfloat5.sty. Accepted
by ApJ Letter
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