2,770 research outputs found
BeppoSAX observations of XTE J1946+274
We report on the BeppoSAX monitoring of a giant outburst of the transient
X-ray pulsar XTE J1946+274 in 1998. The source was detected with a flux of ~ 4
x 10^(-9) erg cm^(-2) s^(-1) (in 0.1 - 120 keV range). The broadband spectrum,
typical for accreting pulsars, is well described by a cutoff power law with a
cyclotron resonance scattering feature (CRSF) at ~ 38 keV. This value is
consistent with earlier reports based on the observations with Suzaku at factor
of ten lower luminosity, which implies that the feature is formed close to the
neutron star surface rather than in the accretion column. Pulsations with P ~
15.82 s were observed up to ~ 70 keV. The pulse profile strongly depends on
energy and is characterised by a "soft" and a "hard" peaks shifted by half
period, which suggests a strong phase dependence of the spectrum, and that two
components with roughly orthogonal beam patterns are responsible for the
observed pulse shape. This conclusion is supported by the fact that the CRSF,
despite its relatively high energy, is only detected in the spectrum of the
soft peak of the pulse profile. Along with the absence of correlation of the
line energy with luminosity, this could be explained in the framework of the
recently proposed "reflection" model for CRSF formation. However more detailed
modelling of both line and continuum formation are required to confirm this
interpretation
XMM-Newton observations of 1A 0535+262 in quiescence
Accretion onto magnetized neutron stars is expected to be centrifugally
inhibited at low accretion rates. Several sources, however, are known to
pulsate in quiescence at luminosities below the theoretical limit predicted for
the onset of the centrifugal barrier. The source 1A 0535+262 is one of them.
Here we present the results of an analysis of a ~50 ks long XMM-Newton
observation of 1A 0535+262 in quiescence. At the time of the observation, the
neutron star was close to apastron, and the source had remained quiet for two
orbital cycles. In spite of this, we detected a pulsed X-ray flux of ~3e-11
erg/cm2/s . Several observed properties, including the power spectrum, remained
similar to those observed in the outbursts. Particularly, we have found that
the frequency of the break detected in the quiescent noise power spectrum
follows the same correlation with flux observed when the source is in outburst.
This correlation has been associated with the truncation of the accretion disk
at the magnetosphere boundary. We argue that our result, along with other
arguments previously reported in the literature, suggests that the accretion in
quiescence also proceeds from an accretion disk around the neutron star. The
proposed scenario consistently explains the energy of the cyclotron line
observed in 1A 0535+262, and the timing properties of the source including the
spin frequency evolution within and between the outbursts, and the frequency of
the break in power spectrum.Comment: 7 pages, 5 figures, accepted for publication in A&
CXOU J160103.1-513353: another CCO with a carbon atmosphere?
We report on the analysis of XMM-Newton observations of the central compact
object CXOU J160103.1-513353 located in the center of the non-thermally
emitting supernova remnant (SNR) G330.2+1.0. The X-ray spectrum of the source
is well described with either single-component carbon or two-component hydrogen
atmosphere models. In the latter case, the observed spectrum is dominated by
the emission from a hot component with a temperature ~3.9MK, corresponding to
the emission from a hotspot occupying ~1% of the stellar surface (assuming a
neutron star with mass M = 1.5M, radius of 12 km, and distance of ~5
kpc as determined for the SNR). The statistics of the spectra and obtained
upper limits on the pulsation amplitude expected for a rotating neutron star
with hot spots do not allow us to unambiguously distinguish between these two
scenarios. We discuss, however, that while the non-detection of the pulsations
can be explained by the unfortunate orientation in CXOU J160103.1-513353, this
is not the case when the entire sample of similar objects is considered. We
therefore conclude that the carbon atmosphere scenario is more plausible.Comment: accepted in A&
Searching for coherent pulsations in ultraluminous X-ray sources
Luminosities of ultraluminous X-ray sources (ULXs) are uncomfortably large if
compared to the Eddington limit for isotropic accretion onto stellar-mass
object. Most often either supercritical accretion onto stellar mass black hole
or accretion onto intermediate mass black holes is invoked the high
luminosities of ULXs. However, the recent discovery of coherent pulsations from
M82 ULX with NuSTAR showed that another scenario implying accretion onto a
magnetized neutron star is possible for ULXs. Motivated by this discovery, we
re-visited the available XMM-Newton archival observations of several bright
ULXs with a targeted search for pulsations to check whether accreting neutron
stars might power other ULXs as well. We have found no evidence for significant
coherent pulsations in any of the sources including the M82 ULX. We provide
upper limits for the amplitude of possibly undetected pulsed signal for the
sources in the sample.Comment: 2 pages, 1 figure, submitted to A&
Orbit and intrinsic spin-up of the newly discovered transient X-ray pulsar Swift J0243.6+6124
We present the orbital solution for the newly discovered transient Be X-ray
binary Swift J0243.6+6124 based on the data from gamma-ray burst monitor
onboard Fermi obtained during the Oct 2017 outburst. We model the Doppler
induced and intrinsic spin variations of the neutron star assuming that the
later is driven by accretion torque and discuss the implications of the
observed spin variations for the parameters of the neutron star and the binary.
In particular we conclude that the neutron star must be strongly magnetized,
and estimate the distance to the source at 5 kpc.Comment: accepted in A&
Orbital parameters of V 0332+53 from 2015 giant outburst data
We present the updated orbital solution for the transient Be X-ray binary V
0332+53 comple- menting historical measurements with the data from the
gamma-ray burst monitor onboard Fermi obtained during the outburst in
June-October 2015. We model the observed changes in the spin- frequency of the
pulsar and deduce the orbital parameters of the system. We significantly
improve existing constrains and show that contrary to the previous findings no
change in orbital parameters is required to explain the spin evolution of the
source during the outbursts in 1983, 2005 and 2015. The reconstructed intrinsic
spin-up of the neutron star during the latest outburst is found to be
comparable with previosly observed values and predictions of the accretion
torque theory.Comment: 3 pages, 2 figures, submitted to A&
- …