1,496 research outputs found
The variable X-ray emission of PSR B0943+10
The old pulsar PSR B0943+10 (P=1.1 s, characteristic age tau=5 Myr) is the
best example of mode-switching radio pulsar. Its radio emission alternates
between a highly organized state with regular drifting subpulses (B mode) and a
chaotic emission pattern (Q mode). We present the results of XMM-Newton
observations showing that the X-ray properties of PSR B0943+10 depend on its
radio state (Hermsen et al. 2013). During the radio fainter state (Q mode) the
X-ray flux is more than a factor two larger than during the B-mode and X-ray
pulsations with about 50% pulsed fraction are detected. The X-ray emission of
PSR B0943+10 in the B-mode is well described by thermal emission with blackbody
temperature kT=0.26 keV coming from a small hot spot with luminosity of 7x10^28
erg/s, in good agreement with the prediction of the partially screened gap
model, which also explains the properties of the radio emission in this mode.
We derived an upper limit of 46% on the X-ray pulsed fraction in the B-mode,
consistent with the geometry and viewing angle of PSR B0943+10 inferred from
the radio data. The higher flux observed during the Q-mode is consistent with
the appearance of an additional component with a power-law spectrum with photon
index 2.2. We interpret it as pulsed non-thermal X-rays produced in the star
magnetosphere. A small change in the beaming pattern or in the efficiency of
acceleration of the particles responsible for the non-thermal emission can
explain the reduced flux of this component during the radio B-mode.Comment: Accepted for publication in MNRA
The spectacular X-ray echo of a magnetar burst
The Anomalous X-ray Pulsar (AXP) 1E 1547.0-5408 reactivated in 2009 January
with the emission of dozens of short bursts. Follow-up observations with
Swift/XRT and XMM-Newton showed the presence of multiple expanding rings around
the position of the AXP. These rings are due to scattering, by different layers
of interstellar dust, of a very high fluence burst emitted by 1E 1547.0-5408 on
2009 January 22. Thanks to the exceptional brightness of the X-ray rings, we
could carry out a detailed study of their spatial and spectral time evolution
until 2009 February 4. This analysis gives the possibility to estimate the
distance of 1E 1547.0-5408. We also derived constraints on the properties of
the dust and of the burst responsible for this rare phenomenon.Comment: Proceedings of the conference X-Ray Astronomy 2009, Present Status,
multiwavelength approach and future perspectives, September 7 - 11, 2009,
Bologna, Ital
XMM-Newton Slew Survey observations of the gravitational wave event GW150914
The detection of the first gravitational wave (GW) transient GW150914
prompted an extensive campaign of follow-up observations at all wavelengths.
Although no dedicated XMM-Newton observations have been performed, the
satellite passed through the GW150914 error box during normal operations. Here
we report the analysis of the data taken during these satellite slews performed
two hours and two weeks after the GW event. Our data cover 1.1 square degrees
and 4.8 square degrees of the final GW localization region. No credible X-ray
counterpart to GW150914 is found down to a sensitivity of 6E-13 erg/cm2/s in
the 0.2-2 keV band. Nevertheless, these observations show the great potential
of XMM-Newton slew observations for the search of the electromagnetic
counterparts of GW events. A series of adjacent slews performed in response to
a GW trigger would take <1.5 days to cover most of the typical GW credible
region. We discuss this scenario and its prospects for detecting the X-ray
counterpart of future GW detections.Comment: 6 pages, 3 figures, 2 tables. Accepted for publication in ApJ Letter
Three new X-ray emitting sdO stars discovered with Chandra
X-ray observations of sdO stars are a useful tool to investigate their
properties, but so far only two sdO stars were detected at X-rays. We observed
a complete flux-limited sample of 19 sdO stars with the Chandra HRC-I camera to
measure the count rate of the detected sources or to set a tight upper limit on
it for the undetected sources. We obtained a robust detection of BD+37 1977 and
Feige 34 and a marginal detection of BD+28 4211. The estimated luminosity of
BD+37 1977 is above 10^31 erg/s, which is high enough to suggest the possible
presence of an accreting compact companion. This possibility is unlikely for
all the other targets (both detected and undetected), since in their case L_X <
10^30 erg/s. On the other hand, for all 19 targets the estimated value of L_X
(or its upper limit) implies an X-ray/bolometric flux ratio that agrees with
log(L_X/L_bol) = -6.7 +/- 0.5, which is the range of values typical of
main-sequence and giant O stars. Therefore, for Feige 34 and BD+28 4211 the
observed X-ray flux is most probably due to intrinsic emission. The same is
possibile for the 16 undetected stars.Comment: 6 pages. Accepted for publication by Astronomy and Astrophysic
X-ray emission from hot subdwarfs with compact companions
We review the X-ray observations of hot subdwarf stars. While no X-ray
emission has been detected yet from binaries containing B-type subdwarfs,
interesting results have been obtained in the case of the two luminous O-type
subdwarfs HD 49798 and BD +37 442. Both of them are members of binary systems
in which the X-ray luminosity is powered by accretion onto a compact object: a
rapidly spinning (13.2 s) and massive (1.28 M_sun) white dwarf in the case of
HD 49798 and most likely a neutron star, spinning at 19.2 s, in the case of BD
+37 442. Their study can shed light on the poorly known processes taking place
during common envelope evolutionary phases and on the properties of wind mass
loss from hot subdwarfs.Comment: To be published in the proceedings of the 40th Liege International
Astrophysical Colloquium "Ageing low mass stars: from red giants to white
dwarfs
Improvement of the Rotation Arch of the Posterior Interosseous Pedicle Flap Preserving Both Reverse Posterior and Anterior Interosseous Vascular Sources.
Abstract
PURPOSE:
The reverse posterior interosseous artery flap has several advantages, not sacrificing any major blood vessel, but its relatively short pedicle limits the use to cover defects up to the metacarpophalangeal joint. Our purpose is to demonstrate that the ligature of the anterior interosseous artery (AIA), proximal to the communicating branch with the posterior interosseous artery, leads to an improved flap rotation arch, preserving both vascular sources.
METHODS:
Sixteen fresh cadavers with latex perfusion were analyzed before and after our technique of elongation, and the so-obtained measures were standardized in "percentage of elongation of the pedicle." Eight patient with the loss of substance at the dorsal aspect of the hand have been treated with this technique, and results were evaluated in terms of flap survival and complication rates.
RESULTS:
The medium length of the pedicle in the normal flap was 10.8\u2009cm, and after the section of the AIA, the medium length of the pedicle was 13.6\u2009cm with a medium increase of 2.8\u2009cm. It means a medium increase of 24% of the length of the pedicle. In all patients treated, full coverage of the defect was obtained, and we did not experience major complications.
CONCLUSIONS:
This anatomical study supported by our clinical experience demonstrates that the use of the variant described above permits to reach more distal part of the hand without being afraid to stretch the pedicle because of the connection with the anastomotic arcades of the AIA at the wrist reducing the risk of ischemia of the flap
Monte Carlo simulations of soft proton flares: testing the physics with XMM-Newton
Low energy protons (<100-300 keV) in the Van Allen belt and the outer regions
can enter the field of view of X-ray focusing telescopes, interact with the
Wolter-I optics, and reach the focal plane. The use of special filters protects
the XMM-Newton focal plane below an altitude of 70000 km, but above this limit
the effect of soft protons is still present in the form of sudden flares in the
count rate of the EPIC instruments, causing the loss of large amounts of
observing time. We try to characterize the input proton population and the
physics interaction by simulating, using the BoGEMMS framework, the proton
interaction with a simplified model of the X-ray mirror module and the focal
plane, and comparing the result with a real observation. The analysis of ten
orbits of observations of the EPIC/pn instrument show that the detection of
flares in regions far outside the radiation belt is largely influenced by the
different orientation of the Earth's magnetosphere respect with XMM-Newton's
orbit, confirming the solar origin of the soft proton population. The Equator-S
proton spectrum at 70000 km altitude is used for the proton population entering
the optics, where a combined multiple and Firsov scattering is used as physics
interaction. If the thick filter is used, the soft protons in the 30-70 keV
energy range are the main contributors to the simulated spectrum below 10 keV.
We are able to reproduce the proton vignetting observed in real data-sets, with
a 50\% decrease from the inner to the outer region, but a maximum flux of 0.01
counts cm-2 s-1 keV-1 is obtained below 10 keV, about 5 times lower than the
EPIC/MOS detection and 100 times lower than the EPIC/pn one. Given the high
variability of the flare intensity, we conclude that an average spectrum, based
on the analysis of a full season of soft proton events is required to compare
Monte Carlo simulations with real events
Follow-up observations of X-ray emitting hot subdwarf star: the He-rich sdO BD +37{\deg} 1977
We report on the results of the first XMM-Newton satellite observation of the
luminous and helium-rich O-type subdwarf BD +37{\deg} 1977 carried out in April
2014. X-ray emission is detected with a flux of about 4*10^(-14) erg/cm2/s
(0.2-1.5 keV), corresponding to a f_X/f_bol ratio about 10^(-7); the source
spectrum is very soft, and is well fit by the sum of two plasma components at
different temperatures. Both characteristics are in agreement with what is
observed in the main-sequence early-type stars, where the observed X-ray
emission is due to turbulence and shocks in the stellar wind. A smaller but
still significant stellar wind has been observed also in BD +37{\deg} 1977;
therefore, we suggest that also in this case the detected X-ray flux has the
same origin.Comment: 6 pages. Accepted for publication by Astronomy and Astrophysic
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