65 research outputs found
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Tc-99m labeled red blood cells scintigraphy: a diagnostic method for orbital cavernous hemangioma INTRODUCTION Tc-99m labeled red blood cells (Tc-99m RBC) is an intravascular tracer which has been used extensively in nuclear medicine (1). The main applications of the tracer are: the evaluation of the cardiovascular system (2), and the detection of gastrointestinal bleeding (3). It has also been found to be specific for diagnosing cavernous hemangioma of the liver (4). Encouraged by this high specificity of Tc-99m RBC for diagnosing cavernous hemangioma of the liver, as early as 1982 we attempted to use this intravascular tracer for diagnosing orbital cavernous hemangioma (5). We used Tc-99m RBC scintigraphy to establish the preoperative diagnosis of orbital cavernous hemangioma in 3 patients with orbital masses, in whom the diagnosis of orbital cavernous hemangioma was suspected on CT scan. The preoperative diagnosis of all 3 patients was later confirmed pathologically. From then onwards, over the past 16 years, we have used Tc-99m RBC scintigraphy routinely to confirm the diagnosis of orbital cavernous hemangioma whenever it was suspected on CT scan. Following our initial work, 3 cases of orbital cavernous hemangioma which were diagnosed by nuclear medicine techniques using red blood cells were recently published (6,7 ). The purpose of this retrospective case series was to evaluate Tc-99m RBC scintigraphy as a diagnostic method for orbital cavernous hemangioma. ABSTRACT
The 2009 outburst of magnetar 1E 1547-5408: Persistent radiative and burst properties
The magnetar 1E~15475408 recently exhibited two periods of outburst,
beginning on 2008 October 3 and 2009 January 22. Here we present an analysis of
the persistent radiative evolution and a statistical study of the burst
properties during the 2009 outburst using the {\em Swift} X-ray Telescope
(XRT). We find that the 1--10 keV flux increased by a factor of and
hardened significantly, peaking hours after the onset of the outburst.
The observed pulsed fraction exhibited an anti-correlation with phase-averaged
flux. Properties of the several hundred X-ray bursts during the 2009 outburst
were determined and compared to those from other magnetar outburst events. We
find that the peaks of the bursts occur randomly in phase but that the folded
counts that compose the bursts exhibit a pulse which is misaligned with the
persistent pulse phase. We also report a correlation between burst hardness and
flux. We compare the hardness-flux evolution of the persistent emission of both
outbursts to those from other magnetars and find that although there does exist
an overall trend, the degree of hardening for a given increase in flux is not
uniform from source to source. These results are discussed in the context of
previous results and within the magnetar model.Comment: 10 pages, 9 figures. Accepted for publication in Ap
Chandra and RXTE Observations of 1E 1547.0-5408: Comparing the 2008 and 2009 Outbursts
We present results from observations of the magnetar 1E 1547.0-5408 (SGR
J1550-5418) taken with the Chandra X-ray Observatory and the Rossi X-ray Timing
Explorer (RXTE) following the source's outbursts in 2008 October and 2009
January. During the time span of the Chandra observations, which covers days 4
through 23 and days 2 through 16 after the 2008 and 2009 events, respectively,
the source spectral shape remained stable, while the pulsar's spin-down rate in
the same span in 2008 increased by a factor of 2.2 as measured by RXTE. The
lack of spectral variation suggests decoupling between magnetar spin-down and
radiative changes, hence between the spin-down-inferred magnetic field strength
and that inferred spectrally. We also found a strong anti-correlation between
the phase-averaged flux and the pulsed fraction in the 2008 and 2009 Chandra
data, but not in the pre-2008 measurements. We discuss these results in the
context of the magnetar model.Comment: 4 figures, accepted for publication in Ap
A variable absorption feature in the X-ray spectrum of a magnetar
Soft gamma-ray repeaters (SGRs) and anomalous X-ray pulsars (AXPs) are slowly
rotating, isolated neutron stars that sporadically undergo episodes of
long-term flux enhancement (outbursts) generally accompanied by the emission of
short bursts of hard X-rays. This behaviour can be understood in the magnetar
model, according to which these sources are mainly powered by their own
magnetic energy. This is supported by the fact that the magnetic fields
inferred from several observed properties of AXPs and SGRs are greater than -
or at the high end of the range of - those of radio pulsars. In the peculiar
case of SGR 0418+5729, a weak dipole magnetic moment is derived from its timing
parameters, whereas a strong field has been proposed to reside in the stellar
interior and in multipole components on the surface. Here we show that the
X-ray spectrum of SGR 0418+5729 has an absorption line, the properties of which
depend strongly on the star's rotational phase. This line is interpreted as a
proton cyclotron feature and its energy implies a magnetic field ranging from
2E14 gauss to more than 1E15 gauss.Comment: Nature, 500, 312 (including Supplementary Information
SGR J1550-5418 bursts detected with the Fermi Gamma-ray Burst Monitor during its most prolific activity
We have performed detailed temporal and time-integrated spectral analysis of
286 bursts from SGR J1550-5418 detected with the Fermi Gamma-ray Burst Monitor
(GBM) in January 2009, resulting in the largest uniform sample of temporal and
spectral properties of SGR J1550-5418 bursts. We have used the combination of
broadband and high time-resolution data provided with GBM to perform
statistical studies for the source properties. We determine the durations,
emission times, duty cycles and rise times for all bursts, and find that they
are typical of SGR bursts. We explore various models in our spectral analysis,
and conclude that the spectra of SGR J1550-5418 bursts in the 8-200 keV band
are equally well described by optically thin thermal bremsstrahlung (OTTB), a
power law with an exponential cutoff (Comptonized model), and two black-body
functions (BB+BB). In the spectral fits with the Comptonized model we find a
mean power-law index of -0.92, close to the OTTB index of -1. We show that
there is an anti-correlation between the Comptonized Epeak and the burst
fluence and average flux. For the BB+BB fits we find that the fluences and
emission areas of the two blackbody functions are correlated. The
low-temperature BB has an emission area comparable to the neutron star surface
area, independent of the temperature, while the high-temperature blackbody has
a much smaller area and shows an anti-correlation between emission area and
temperature. We compare the properties of these bursts with bursts observed
from other SGR sources during extreme activations, and discuss the implications
of our results in the context of magnetar burst models.Comment: 13 pages, 10 figures, 2 tables; minor changes, ApJ in pres
Pulsar-wind nebulae and magnetar outflows: observations at radio, X-ray, and gamma-ray wavelengths
We review observations of several classes of neutron-star-powered outflows:
pulsar-wind nebulae (PWNe) inside shell supernova remnants (SNRs), PWNe
interacting directly with interstellar medium (ISM), and magnetar-powered
outflows. We describe radio, X-ray, and gamma-ray observations of PWNe,
focusing first on integrated spectral-energy distributions (SEDs) and global
spectral properties. High-resolution X-ray imaging of PWNe shows a bewildering
array of morphologies, with jets, trails, and other structures. Several of the
23 so far identified magnetars show evidence for continuous or sporadic
emission of material, sometimes associated with giant flares, and a few
possible "magnetar-wind nebulae" have been recently identified.Comment: 61 pages, 44 figures (reduced in quality for size reasons). Published
in Space Science Reviews, "Jets and Winds in Pulsar Wind Nebulae, Gamma-ray
Bursts and Blazars: Physics of Extreme Energy Release
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