6,603 research outputs found
The Discovery of 8.7s Pulsations from the Ultrasoft X-Ray Source 4u0142+614
We discovered a periodicity at about 8.7s from the X--ray sources 4U0142+61,
previously considered a possible black hole candidate on the basis of its
ultrasoft spectrum. The pulsations are visible only in the 1--4 keV energy
range, during an observation obtained with the EXOSAT satellite in August 1984.
A search for delays in the pulse arrival times caused by orbital motion gave
negative results. In the same data, periodic oscillations at 25 minutes had
been previously found in an additional hard spectral component dominating above
4 keV which arises from the X-ray transient RX J0146.9+6121, discovered with
ROSAT and identified with a Be star. Though the very high (>10^4) X--ray to
optical flux ratio of 4U0142+61 is compatible with models based on an isolated
neutron star, the simplest explanation involves a low mass X--ray binary with a
very faint companion, similar to 4U1626--67. The discovery of periodic
pulsations from 4U0142+61 weakens the phenomenological criterion that an
ultrasoft spectral component is a signature of accreting black holes.Comment: plain LaTeX v3.1, 14 pages + 2 PostScript figures available upon
request to [email protected] . To appear on The Astrophysical Journal,
Letters. SISSA ref.: 106/94/
An unified timing and spectral model for the Anomalous X-ray Pulsars XTE J1810-197 and CXOU J164710.2-455216
Anomalous X-ray pulsars (AXPs) and soft gamma repeaters (SGRs) are two small
classes of X-ray sources strongly suspected to host a magnetar, i.e. an
ultra-magnetized neutron star with $B\approx 10^14-10^15 G. Many SGRs/AXPs are
known to be variable, and recently the existence of genuinely "transient"
magnetars was discovered. Here we present a comprehensive study of the pulse
profile and spectral evolution of the two transient AXPs (TAXPs) XTE J1810-197
and CXOU J164710.2-455216. Our analysis was carried out in the framework of the
twisted magnetosphere model for magnetar emission. Starting from 3D Monte Carlo
simulations of the emerging spectrum, we produced a large database of synthetic
pulse profiles which was fitted to observed lightcurves in different spectral
bands and at different epochs. This allowed us to derive the physical
parameters of the model and their evolution with time, together with the
geometry of the two sources, i.e. the inclination of the line-of-sight and of
the magnetic axis with respect to the rotation axis. We then fitted the
(phase-averaged) spectra of the two TAXPs at different epochs using a model
similar to that used to calculate the pulse profiles ntzang in XSPEC) freezing
all parameters to the values obtained from the timing analysis, and leaving
only the normalization free to vary. This provided acceptable fits to
XMM-Newton data in all the observations we analyzed. Our results support a
picture in which a limited portion of the star surface close to one of the
magnetic poles is heated at the outburst onset. The subsequent evolution is
driven both by the cooling/varying size of the heated cap and by a progressive
untwisting of the magnetosphere.Comment: 15 pages, 12 figures, accepted for publication in Ap
Linking the X-ray timing and spectral properties of the glitching AXP 1RXS J170849-400910
Previous studies of the X-ray flux and spectral properties of 1RXS
J170849-400910 showed hints of a possible correlation with the spin glitches
that occurred in 1999 and 2001. However, due to the sparseness of spectral
measurements and the paucity of detected glitches no firm conclusion could be
drawn. We retrieved and analysed archival XTE pointings of 1RXS J170849-400910
covering the time interval between January 2003 and June 2006 and carried out a
detailed timing analysis by means of phase fitting techniques. We detected two
relatively large glitches Delta nu / nu of 1.2 and 2.1 10^-6 occurred in
January and June 2005. Interestingly, the occurrence times of these glitches
are in agreement with the predictions made in our previous studies. This
finding strongly suggests a connection between the flux, spectral and timing
properties of 1RXS J170849-400910.Comment: Submitted to A&A, 4 pages; results presented at the INT meeting "The
Neutron Star Crust and Surface: Observations and Models" on June 27; referee
comments adde
Interior of Distorted Black Holes
We study the interior of distorted static axisymmetric black holes. We obtain
a general interior solution and study its asymptotics both near the horizon and
singularity. As a special example, we apply the obtained results to the case of
the so-called `caged' black holes.Comment: 12 pages, 16 figure
The discovery of 12min X-ray pulsations from 1WGA J1958.2+3232
During a systematic search for periodic signals in a sample of ROSAT PSPC
(0.1-2.4 keV) light curves, we discovered 12min large amplitude X-ray
pulsations in 1WGA J1958.2+3232, an X-ray source which lies close to the
galactic plane. The energy spectrum is well fit by a power law with a photon
index of 0.8, corresponding to an X-ray flux of about 10E-12 ergs cmE-2 sE-1.
The source is probably a long period, low luminosity X-ray pulsar, similar to X
Per, or an intermediate polar.Comment: 5 pages (figures included). Accepted for publication on MNRA
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