Abstract
Only three of the dozen central compact objects (CCOs) in supernova remnants (SNRs) show thermal X-ray pulsations due to nonuniform surface temperature (hot spots). The absence of X-ray ...pulsations from several unpulsed CCOs has motivated suggestions that they have uniform-temperature carbon atmospheres (UTCAs), which adequately fit their spectra with appropriate neutron star (NS) surface areas. This is in contrast to the two-temperature blackbody or hydrogen atmospheres that also fit well. Here we investigate the applicability of UTCAs to CCOs. We show the following: (i) The phase-averaged spectra of the three pulsed CCOs can also be fitted with a UTCA of the appropriate NS area, despite pulsed CCOs manifestly having nonuniform surface temperature. A good spectral fit is therefore not strong support for the UTCA model of unpulsed CCOs. (ii) An improved spectrum of one unpulsed CCO, previously analyzed with a UTCA, does not allow an acceptable fit. (iii) For two unpulsed CCOs, the UTCA does not allow a distance compatible with the SNR distance. These results imply that, in general, CCOs must have hot, localized regions on the NS surface. We derive new X-ray pulse modulation upper limits on the unpulsed CCOs, and constrain their hot spot sizes and locations. We develop an alternative model that accounts for both the pulsed and unpulsed CCOs: a range of angles between hot spot and rotation axes consistent with an exponential distribution with scale factor
λ
∼ 20°. We discuss the physical mechanisms that could produce such small angles and small hot spots.
ABSTRACT We report on timing, flux density, and polarimetric observations of the transient magnetar and 5.54 s radio pulsar XTE J1810−197 using the Green Bank, Nançay, and Parkes radio telescopes ...beginning in early 2006, until its sudden disappearance as a radio source in late 2008. Repeated observations through 2016 have not detected radio pulsations again. The torque on the neutron star, as inferred from its rotation frequency derivative , decreased in an unsteady manner by a factor of three in the first year of radio monitoring, until approximately mid-2007. By contrast, during its final year as a detectable radio source, the torque decreased steadily by only 9%. The period-averaged flux density, after decreasing by a factor of 20 during the first 10 months of radio monitoring, remained relatively steady in the next 22 months, at an average of 0.7 0.3 mJy at 1.4 GHz, while still showing day-to-day fluctuations by factors of a few. There is evidence that during this last phase of radio activity the magnetar had a steep radio spectrum, in contrast to earlier flat-spectrum behavior. No secular decrease presaged its radio demise. During this time, the pulse profile continued to display large variations; polarimetry, including of a new profile component, indicates that the magnetic geometry remained consistent with that of earlier times. We supplement these results with X-ray timing of the pulsar from its outburst in 2003 up to 2014. For the first 4 years, XTE J1810−197 experienced non-monotonic excursions in frequency derivative by at least a factor of eight. But since 2007, its has remained relatively stable near its minimum observed value. The only apparent event in the X-ray record that is possibly contemporaneous with the radio shutdown is a decrease of 20% in the hot-spot flux in 2008-2009, to a stable, minimum value. However, the permanence of the high-amplitude, thermal X-ray pulse, even after the (unexplained) radio demise, implies continuing magnetar activity.
ABSTRACT We report on X-ray observations of the 5.54 s transient magnetar XTE J1810-197 using the XMM-Newton and Chandra observatories, analyzing new data from 2008 through 2014, and re-analyzing ...data from 2003 through 2007 with the benefit of these six years of new data. From the discovery of XTE J1810-197 during its 2003 outburst to the most recent 2014 observations, its 0.3-10 keV X-ray flux has declined by a factor of about 50 from 4.1 × 10−11 to 8.1 × 10−13 erg cm−2 s−1. Its X-ray spectrum has now reached a steady state. Pulsations continue to be detected from a 0.3 keV thermal hot spot that remains on the neutron star (NS) surface. The luminosity of this hot spot exceeds XTE J1810-197's spin-down luminosity, indicating continuing magnetar activity. We find that XTE J1810-197's X-ray spectrum is best described by a multiple component blackbody model in which the coldest 0.14 keV component likely originates from the entire NS surface, and the thermal hot-spot is, at different epochs, well described by an either one- or two-component blackbody model. A 1.2 keV absorption line, possibly due to resonant proton scattering, is detected at all epochs. The X-ray flux of the hot spot decreased by between 2008 and 2009 March, the same period during which XTE J1810-197 became radio quiet.
Using XMM-Newton and Chandra, we measure period derivatives for the second and third known pulsars in the class of central compact objects (CCOs) in supernova remnants, proving that these young ...neutron stars have exceptionally weak dipole magnetic field components. For the 112 ms PSR J0821-4300 in Puppis A, P = (9.28+ or -0.36) x 10sup -18. Its proper motion, mu = 61+ or -9 mas yrsup -1, was also measured using Chandra. Antipodal surface hot spots with different temperatures and areas are deduced from the X-ray spectrum and pulse profiles. A spectral feature, consisting of either an emission line at approximate0.75 keV or an absorption line at approximate0.46 keV, is modulated in strength with the rotation. This is also compatible with a cyclotron resonance interpretation of its prominent absorption line at 0.7 keV and its harmonics. The results deepen the mystery of the origin and evolution of CCOs.
ABSTRACT
After 15 yr, in late 2018, the magnetar XTE J1810−197 underwent a second recorded X-ray outburst event and reactivated as a radio pulsar. We initiated an X-ray monitoring campaign to follow ...the timing and spectral evolution of the magnetar as its flux decays using Swift, XMM–Newton, NuSTAR, and NICER observations. During the year-long campaign, the magnetar reproduced similar behaviour to that found for the first outburst, with a factor of 2 change in its spin-down rate from ∼7.2 × 10−12 to ∼1.5 × 10−11 s s−1 after two months. Unique to this outburst, we confirm the peculiar energy-dependent phase shift of the pulse profile. Following the initial outburst, the spectrum of XTE J1810−197 is well modelled by multiple blackbody components corresponding to a pair of non-concentric, hot thermal caps surrounded by a cooler one, superposed to the colder star surface. We model the energy-dependent pulse profile to constrain the viewing and surface emission geometry and find that the overall geometry of XTE J1810−197 has likely evolved relative to that found for the 2003 event.
To establish the diagnostic accuracy of the Montreal Cognitive Assessment (MoCA) when screening externally validated cognition in Parkinson disease (PD), by comparison with a PD-focused test (Scales ...for Outcomes in Parkinson disease-Cognition SCOPA-COG) and the standardized Mini-Mental State Examination (S-MMSE) as benchmarks.
A convenience sample of 114 patients with idiopathic PD and 47 healthy controls was examined in a movement disorders center. The 21 patients with dementia (PD-D) were diagnosed using Movement Disorders Society criteria, externally validated by detailed independent functional and neuropsychological tests. The 21 patients with mild cognitive impairment (PD-MCI) scored 1.5 SD or more below normative data in at least 2 measures in 1 of 4 cognitive domains. Other patients had normal cognition (PD-N).
Primary outcomes using receiver operating characteristic (ROC) curve analyses showed that all 3 mental status tests produced excellent discrimination of PD-D from patients without dementia (area under the curve AUC, 87%-91%) and PD-MCI from PD-N patients (AUC, 78%-90%), but the MoCA was generally better suited across both assessments. The optimal MoCA screening cutoffs were <21/30 for PD-D (sensitivity 81%; specificity 95%; negative predictive value NPV 92%) and <26/30 for PD-MCI (sensitivity 90%; specificity 75%; NPV 95%). Further support that the MoCA is at least equivalent to the SCOPA-COG, and superior to the S-MMSE, came from the simultaneous classification of the 3 PD patient groups (volumes under a 3-dimensional ROC surface, chance = 17%: MoCA 79%, confidence interval CI 70%-89%; SCOPA-COG 74%, CI 62%-86%; MMSE-Sevens item 56%, CI 44%-68%; MMSE-World item 62%, CI 50%-73%).
The MoCA is a suitably accurate, brief test when screening all levels of cognition in PD.
We present the earliest X-ray observations of the 2018 outburst of XTE J1810−197, the first outburst since its 2003 discovery as the prototypical transient and radio-emitting anomalous X-ray pulsar ...(AXP). The Monitor of All-sky X-ray Image (MAXI) detected XTE J1810−197 immediately after a November 20-26 visibility gap, contemporaneous with its reactivation as a radio pulsar, first observed on December 8. On December 13 the Nuclear Spectroscopic Telescope Array (NuSTAR) detected X-ray emission up to at least 30 keV, with a spectrum well-characterized by a blackbody plus power-law model with temperature kT = 0.74 0.02 keV and photon index Γ = 4.4 0.2 or by a two-blackbody model with kT = 0.59 0.04 keV and kT = 1.0 0.1 keV, both including an additional power-law component to account for emission above 10 keV, with Γh = −0.2 1.5 and Γh = 1.5 0.5, respectively. The latter index is consistent with hard X-ray flux reported for the nontransient magnetars. In the 2-10 keV bandpass, the absorbed flux is 2 × 10−10 erg s−1 cm−2, a factor of 2 greater than the maximum flux extrapolated for the 2003 outburst. The peak of the sinusoidal X-ray pulse lags the radio pulse by 0.13 cycles, consistent with their phase relationship during the 2003 outburst. This suggests a stable geometry in which radio emission originates on magnetic field lines containing currents that heat a spot on the neutron star surface. However, a measured energy-dependent phase shift of the pulsed X-rays suggests that all X-ray emitting regions are not precisely coaligned.
Cartilage Restoration, Part 1 Alford, J. Winslow; Cole, Brian J.
The American journal of sports medicine,
02/2005, Letnik:
33, Številka:
2
Journal Article
Recenzirano
Surgical procedures designed to treat focal chondral lesions are evolving and are supported by basic science principles of cartilage physiology and known responses to injury. Selecting the proper ...treatment algorithm for a particular patient depends on careful patient evaluation, including the recognition of comorbidities such as ligamentous instability, deficient menisci, or malalignment of the mechanical limb axis or extensor mechanism. These comorbidities may need to be treated in conjunction with symptomatic chondral injuries to provide a mutually beneficial effect. A central tenet of cartilage restoration is to leave future treatment options available should they become necessary. In this article (part 1), the authors review the basic science of chondral injuries, the historical perspective of the available surgical options, and present guidelines for patient evaluation and treatment.
Abstract
The surface temperature distributions of central compact objects (CCOs) are powerful probes of their crustal magnetic field strengths and geometries. Here we model the surface temperature ...distribution of RX J0822−4300, the CCO in the Puppis A supernova remnant, using 471 ks of XMM-Newton data. We compute the energy-dependent pulse profiles in 16 energy bands, fully including the general relativistic effects of gravitational redshift and light bending, to accurately model the two heated surface regions of different temperatures and areas, in addition to constraining the viewing geometry. This results in precise measurements of the two temperatures:
kT
warm
=
(
1
+
z
)
×
0.222
−
0.019
+
0.018
keV and
kT
hot
= (1 +
z
) × 0.411 ± 0.011 keV. The two heated surface regions are likely located very close to the rotational poles, with the most probable position of the hotter component ≈ 6° from the rotational pole. For the first time, we are able to measure a deviation from a pure antipodal hot-spot geometry, with a longitudinal offset
δ
γ
=
11
.°
7
−
2
.°
5
+
2
.°
6
. The discovery of this asymmetry, along with the factor of ≈2 temperature difference between the two emitting regions, may indicate that RX J0822−4300 was born with a strong, tangled crustal magnetic field.
In part 1 of this 2-part Current Concepts article, the authors reviewed the basic science of normal articular and meniscal cartilage and its response to injury. They reviewed the historical ...perspectives and basic science behind these various methods and presented a rationale for patient evaluation, treatment selection, and timing. In part 2, the authors review the specific indications for the treatment of chondral injuries and describe the techniques and outcomes of the various treatment options, including palliative, reparative, and restorative procedures. In addition, they will examine specific complex clinical scenarios emphasizing treatment options of comorbid conditions including ligament instability, meniscal deficiency, and malalignment. A limited review of the application of these techniques in joints other than the knee will also be presented. A conceptual algorithm is developed to assist in clinical decision making.
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