20 research outputs found
A systematic analysis of the broad Fe Kalpha line in neutron star LMXBs with XMM-Newton
We analysed the XMM-Newton archival observations of 16 neutron star (NS)
low-mass X-ray binaries (LMXBs) to study the Fe K emission in these objects.
The sample includes all the observations of NS LMXBs performed in EPIC pn
Timing mode with XMM-Newton publicly available until September 30, 2009. We
performed a detailed data analysis considering pile-up and background effects.
The properties of the iron lines differed from previous published analyses due
to either incorrect pile-up corrections or different continuum
parameterization. 80% of the observations for which a spectrum can be extracted
showed significant Fe line emission. We found an average line centroid of 6.67
0.02 keV and a finite width, , of 0.33 0.02 keV. The
equivalent width of the lines varied between 17 and 189 eV, with an average
weighted value of 42 eV. For sources where several observations were
available the Fe line parameters changed between observations whenever the
continuum changed significantly. The line parameters did not show any
correlation with luminosity. Most important, we could fit the Fe line with a
simple Gaussian component for all the sources. The lines did not show the
asymmetric profiles that were interpreted as an indication of relativistic
effects in previous analyses of these LMXBs.Comment: Accepted for publication in A&
The Similarity of Broad Iron Lines in X-ray Binaries and Active Galactic Nuclei
We have compared the 2001 XMM-Newton spectra of the stellar mass black hole
binary XTE J1650-500 and the active galaxy MGC-6-30-15, focusing on the broad,
excess emission features at ~4--7 keV displayed by both sources. Such features
are frequently observed in both low mass X-ray binaries and active galactic
nuclei. For the former case it is generally accepted that the excess arises due
to iron emission, but there is some controversy over whether their width is
partially enhanced by instrumental processes, and hence also over the intrinsic
broadening mechanism. Meanwhile, in the latter case, the origin of this feature
is still subject to debate; physically motivated reflection and absorption
interpretations are both able to reproduce the observed spectra. In this work
we make use of the contemporaneous BeppoSAX data to demonstrate that the
breadth of the excess observed in XTE J1650-500 is astrophysical rather than
instrumental, and proceed to highlight the similarity of the excesses present
in this source and MGC-6-30-15. Both optically thick accretion discs and
optically thin coronae, which in combination naturally give rise to
relativistically-broadened iron lines when the disc extends close to the black
hole, are commonly observed in both class of object. The simplest solution is
that the broad emission features present arise from a common process, which we
argue must be reflection from the inner regions of an accretion disc around a
rapidly rotating black hole; for XTE J1650-500 we find spin constraints of 0.84
< a* < 0.98 at the 90 per cent confidence level. Other interpretations proposed
for AGN add potentially unnecessary complexities to the theoretical framework
of accretion in strong gravity.Comment: Accepted for publication in MNRAS; 22 pages, 17 figure
XMM-Newton observations reveal the disappearance of the wind in 4U1630-47
We report on XMM-Newton observations of the black hole X-ray binary 4Uâ1630â47 during its 2012â2013 outburst. The first five observations monitor the source as its luminosity increases across the highâsoft state of accretion. In the sixth observation the source has made a transition to an âanomalousâ state, characterised by a significant contribution of electron scattering. A thermally/radiatively driven disc wind is present in the first four observations, which becomes more photoionised as the luminosity increases with time. In the fifth observation, the wind is not observed any more as a consequence of strong photoionisation and the low sensitivity of this observation. This overall trend is then consistent with a fully ionised wind causing the electron scattering characteristic of the anomalous state in the sixth observation. A broad iron emission line co-exists with the absorption features from the wind in the first four observations but is not visible in the last two observations. We find that the changes in the state of the wind as measured from modelling the absorption features with a self-consistent warm absorber model are correlated to the changes in the broad iron line. When the latter is modelled with a reflection component we find that the reflection fraction decreases as the illumination increases. We propose that the changes in both the absorption and broad emission lines are caused by the increasing luminosity and temperature of the accretion disc along the soft state. Such changes ultimately enable the transition to a state where the wind is fully ionised and consequently Comptonisation plays a significant role
Influence of test parameters on in vitro fracture resistance of post-endodontic restorations: a structured review
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75093/1/j.1365-2842.2009.01940.x.pd
Discovery of strongly variable X-ray polarization in the neutron star low-mass X-ray binary transient XTE J1701-462
CONTEXT:
After about 16 years since its first outburst, the transient neutron star low-mass X-ray binary XTE J1701â462 turned on again in September 2022, allowing for the first study of its X-ray polarimetric characteristics by a dedicated observing program with the Imaging X-ray Polarimeter Explorer (IXPE).
AIMS:
Polarimetric studies of XTE J1701â462 have been expected to improve our understanding of accreting weakly magnetized neutron stars, in particular, the physics and the geometry of the hot inner regions close to the compact object.
METHOD:
The IXPE data of two triggered observations were analyzed using time-resolved spectroscopic and polarimetric techniques, following the source along its Z-track of the colorâcolor diagram.
RESULTS:
During the first pointing on 2022 September 29, an average 2â8 keV polarization degree of (4.6â
屉
0.4)% was measured, the highest value found up to now for this class of sources. Conversely, only a âŒ0.6% average degree was obtained during the second pointing ten days later.
CONCLUSIONS:
The polarimetric signal appears to be strictly related to the higher energy blackbody component associated with the boundary layer (BL) emission and its reflection from the inner accretion disk, and it is as strong as 6.1% and 1.2% (> 95% significant) above 3â4 keV for the two measurements, respectively. The variable polarimetric signal is apparently related to the spectral characteristics of XTE J1701â462, which is the strongest when the source was in the horizontal branch of its Z-track and the weakest in the normal branch. These IXPE results provide new important observational constraints on the physical models and geometry of the Z-sources. Here, we discuss the possible reasons for the presence of strong and variable polarization among these sources