4,308 research outputs found
XMM-Newton Observations of the Be/X-ray transient A0538-66 in quiescence
We present XMM-Newton observations of the recurrent Be/X-ray transient
A0538-66, situated in the Large Magellanic Cloud, in the quiescent state.
Despite a very low luminosity state of (5-8)E33 ergs/s in the range 0.3-10 keV,
the source is clearly detected up to ~8 keV. and can be fitted using either a
power law with photon index alpha=1.9+-0.3 or a bremsstrahlung spectrum with
kT=3.9+3.9-1.7 keV. The spectral analysis confirms that the off-state spectrum
is hard without requiring any soft component, contrary to the majority of
neutron stars observed in quiescence up to now.Comment: Accepted for proceedings of 5th INTEGRAL Worksho
Extended Emission from Cygnus X-3 Detected with Chandra
We have discovered extended X-ray emission from the microquasar Cyg X-3 in
archival Chandra X-ray Observatory observations. A 5" wide structure lies
approximately 16" to the NE from the core point source and may be extended in
that direction. This angular scale corresponds to a physical extent of roughly
0.8 lyr, at a distance of 2.5 lyr from Cyg X-3 (assuming a 10 kpc distance).
The flux varied by a factor of 2.5 during the four months separating two of the
observations, indicating significant substructure. The peak 2-10 keV luminosity
was about 5e34 ergs/s. There may also be weaker, extended emission of similar
scale oppositely directed from the core, suggesting a bipolar outflow. This
structure is not part of the dust scattering halo, nor is it caused by the
Chandra point spread function. In this Letter we describe the observations and
discuss possible origins of the extension.Comment: Submitted to ApJ Letters. 5 pages, 2 figures (1 color). Uses
emulateap
Multiple Cyclotron Lines in the Spectrum of 4U 0115+63
We report phase resolved spectroscopy of the transient accreting pulsar,
4U0115+63. For the first time, more than two cylotron resonance scattering
features are detected in the spectrum of an X-ray pulsar. The shape of the
fundamental line appears to be complex, and this is in agreement with
predictions of Monte-Carlo models. As in other pulsars, the line energies and
optical depths are strong functions of pulse phase. One possible model for this
is an offset of the dipole of the neutron star magnetic field.Comment: 5 pages. To appear in "Proceedings of the 5th Compton Symposium
Disappearing Pulses in Vela X-1
We present results from a 20 h RXTE observation of Vela X-1, ncluding a
peculiar low state of a few hours duration, during which the pulsation of the
X-ray emission ceased, while significant non-pulsed emission remained. This
``quiescent state'' was preceded by a ``normal state'' without any unusual
signs and followed by a ``high state'' of several hours of increased activity
with strong, flaring pulsations. while there is clear spectral evolution from
the normal state to the low state, the spectra of the following high state are
surprisingly similar to those of the low state.Comment: 5 pages, 5 figures, Proceedings of the 5th Compton Symposium, AIP, in
pres
RXTE Observations of LMC X-1 and LMC X-3
Of all known persistent stellar-mass black hole candidates, only LMC X-1 and
LMC X-3 consistently show spectra that are dominated by a soft, thermal
component. We present results from long (170ksec) Rossi X-ray Timing Explorer
(RXTE) observations of LMC X-1 and LMC X-3 made in 1996 December. The spectra
can be described by a multicolor disk blackbody plus an additional high-energy
power-law. Even though the spectra are very soft (Gamma is about 2.5), RXTE
detected a significant signal from LMC X-3 up to energies of 50keV, the hardest
energy at which the object was ever detected.
Focusing on LMC X-3, we present results from the first year of an ongoing
monitoring campaign with RXTE which started in 1997 January. We show that the
appearance of the object changes considerably over its ~200d long cycle. This
variability can either be explained by periodic changes in the mass transfer
rate or by a precessing accretion disk analogous to Her X-1.Comment: 4 pages, 5 figures, also available at
http://aitzu3.ait.physik.uni-tuebingen.de/publications/preprints1998.html to
be published in "Highlights of X-Ray Astronomy, a symposium in honour of
Joachim Truemper" (B. Aschenbach et al., eds.), MPE Repor
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