378 research outputs found
The 14.8-h Orbital Period of GX339-4
We present the results of photometric observations of the black hole candidate GX339-4, obtained while the system was in an \u27off\u27 state. We show that a 14.8-h modulation was present, and provide evidence for a similar periodicity in the \u27high\u27 state from a reanalysis of previously published photometry and spectroscopy. The presence of the same period in both states implies that it is likely to be the orbital period of the system. The spectroscopy analysis provides evidence for an apparent change in the systemic velocity of the system. The amplitude of the observed radial velocity variations, however, permits only crude limits to be placed on the mass of the compact object. Only absorption-line spectroscopy of the secondary in the \u27off\u27 state will provide a convincing mass determination
Detection of hard X-ray pulsations and a strong iron K_beta emission line during an extended low state of GX 1+4
We present here results obtained from a detailed timing and spectral analysis
of three BeppoSAX observations of the binary X-ray pulsar GX 1+4 carried out in
August 1996, March 1997, and August 2000. In the middle of the August 2000
observation, the source was in a rare low intensity state that lasted for about
30 hours. Though the source does not show pulsations in the soft X-ray band
(1.0-5.5 keV) during the extended low state, pulsations are detected in
5.5-10.0 keV energy band of the MECS detector and in hard X-ray energy bands
(15-150 keV) of the PDS instrument. Comparing the 2-10 keV flux during this low
state with the previously reported low states in GX 1+4, we suggest that the
propeller regime in GX 1+4 occurs at a lower mass accretion rate than reported
earlier. Broad-band (1.0-150 keV) pulse averaged spectroscopy reveals that the
best-fit model comprises of a Comptonized continuum along with an iron K_alpha
emission line. A strong iron K_beta emission line is detected for the first
time in GX 1+4 during the extended low state of 2000 observation with
equivalent width of ~550 eV. The optical depth and temperature of the
Comptonizing plasma are found to be identical during the high and low intensity
states whereas the hydrogen column density and the temperature of the seed
photons are higher during the low state. We also present results from pulse
phase resolved spectroscopy during the high and low flux episodes.Comment: Accepted for publication in The Astrophysical Journa
Addendum: "The Dynamics of M15: Observations of the Velocity Dispersion Profile and Fokker-Planck Models" (ApJ, 481, 267 [1997])
It has recently come to our attention that there are axis scale errors in
three of the figures of Dull et al. (1997, hereafter D97). D97 presented
Fokker-Planck models for the collapsed-core globular cluster M15 that include a
dense, centrally concentrated population of neutron stars and massive white
dwarfs, but do not include a central black hole. In this Addendum, we present
corrected versions of Figures 9, 10, and 12, and an expanded version of Figure
6. This latter figure, which shows the full run of the velocity dispersion
profile, indicates that the D97 model predictions are in good agreement with
the moderately rising HST-STIS velocity dispersion profile for M15 reported by
Gerssen et al. (2002, astro-ph/0209315). Thus, a central black hole is not
required to fit the new STIS velocity measurements, provided that there is a
sufficient population of neutron stars and massive white dwarfs. This
conclusion is consistent with the findings of Gerssen et al. (2002,
astro-ph/0210158), based on a reapplication of their Jeans equation analysis
using the corrected mass-to-light profile (Figure 12) for the D97 models.Comment: 4 pages, 4 figures, submitted to Ap
A Sequence of Declining Outbursts from GX339-4
The flux and spectrum of the black hole candidate GX339-4 has been monitored
by the Burst and Transient Source Experiment (BATSE) on the Compton Gamma-ray
Observatory (CGRO) since the observatory became operational in May 1991.
Between the summer of 1991 and the fall of 1996, eight outbursts from GX339-4
were observed. The history of these outbursts is one of declining fluence or
total energy release, as well as a shortening of the time between outbursts. A
rough linear correlation exists between the fluence emitted during an outburst
and the time elapsed between the end of the previous outburst and the beginning
of the current one. The peak flux is also roughly linearly correlated with
outburst fluence. The lightcurves of the earlier, more intense, outbursts
(except for the second one) can be modeled by a fast exponential (time constant
~ 10 days) followed by a slower exponential (~ 100 days) on the rise and a fast
exponential decay (~ 5 days) on the fall. The later, weaker, outbursts are
modeled with a single rising time constant (~ 20 days) and a longer decay on
the fall (~ 50 days). An exponential model gives a marginally better fit than a
power law to the rise/decay profiles. GX339-4 is a unique source in having more
frequent outbursts than other low mass x-ray binary black hole candidates.
These observations can be used to constrain models of the behavior of the
accretion disk surrounding the compact object.Comment: Accepted for Publication in the Astrophysical Journal Letters, AASTE
Broad band X-ray spectrum of KS 1947+300 with BeppoSAX
We present results obtained from three BeppoSAX observations of the
accretion-powered transient X-ray pulsar KS 1947+300 carried out during the
declining phase of its 2000 November -- 2001 June outburst. A detailed spectral
study of KS 1947+300 across a wide X-ray band (0.1--100.0 keV) is attempted for
the first time here. Timing analysis of the data clearly shows a 18.7 s
pulsation in the X-ray light curves in the above energy band. The pulse profile
of KS 1947+300 is characterized by a broad peak with sharp rise followed by a
narrow dip. The dip in the pulse profile shows a very strong energy dependence.
Broad-band pulse-phase-averaged spectroscopy obtained with three of the
BeppoSAX instruments shows that the energy spectrum in the 0.1--100 keV energy
band has three components, a Comptonized component, a ~0.6 keV blackbody
component, and a narrow and weak iron emission line at 6.7 keV with a low
column density of material in the line of sight. We place an upper limit on the
equivalent width of the iron K_\alpha line at 6.4 keV of ~13 eV (for a width of
100 eV). Assuming a spherical blackbody emitting region and the distance of the
source to be 10 kpc, the radius of the emitting region is found to be in the
range of 14--22 km, which rules out the inner accretion disk as the soft X-ray
emitting region.Comment: 17 pages, 5 figures, Accepted for publication in The Astrophysical
Journa
Unsupervised hyperspectral data mining and bioimaging by information entropy and self-modeling curve resolution
Unsupervised estimation of the dimensionality of hyperspectral
microspectroscopy datasets containing pure and mixed spectral features, and
extraction of their representative endmember spectra, remains a challenge in
biochemical data mining. We report a new versatile algorithm building on
semi-nonnegativity constrained self-modeling curve resolution and information
entropy, to estimate the quantity of separable biochemical species from
hyperspectral microspectroscopy, and extraction of their representative
spectra. The algorithm is benchmarked with established methods from satellite
remote sensing, spectral unmixing, and clustering. To demonstrate the
widespread applicability of the developed algorithm, we collected hyperspectral
datasets using spontaneous Raman, Coherent Anti-stokes Raman Scattering and
Fourier Transform IR, of seven reference compounds, an oil-in-water emulsion,
and tissue-engineered extracellular matrices on poly-L-lactic acid and porcine
jejunum-derived small intestine submucosa scaffolds seeded with bovine
chondrocytes. We show the potential of the developed algorithm by consolidating
hyperspectral molecular information with sample microstructure, pertinent to
fields ranging from gastrophysics to regenerative medicine
CXCL-8/IL8 Produced by Diffuse Large B-cell Lymphomas Recruits Neutrophils Expressing a Proliferation-Inducing Ligand APRIL.
Tumor-infiltrating neutrophils have been implicated in malignant development and progression, but mechanisms are ill defined. Neutrophils produce a proliferation-inducing ligand APRIL/TNFSF13, a factor that promotes development of tumors from diverse origins, including diffuse large B-cell lymphoma (DLBCL). High APRIL expression in DLBCL correlates with reduced patient survival, but the pathway(s) dictating APRIL expression are not known. Here, we show that all blood neutrophils constitutively secrete APRIL, and inflammation-associated stimuli, such as TNF, further upregulate APRIL. In a significant fraction of DLBCL patients, tumor cells constitutively produced the ELC-CXC chemokine CXCL-8 (IL8), enabling them to recruit APRIL-producing blood neutrophils. CXCL-8 production in DLBCL was unrelated to the cell of origin, as APRIL-producing neutrophils infiltrated CXCL-8(+) DLBCL from both germinal center (GC) and non-GC subtypes. Rather, CXCL-8 production implied events affecting DNA methylation and acetylation. Overall, our results showed that chemokine-mediated recruitment of neutrophils secreting the tumor-promoting factor APRIL mediates DLBCL progression. Cancer Res; 77(5); 1097-107. ©2016 AACR
The neuropathogenesis of feline immunodeficiency virus infection: Barriers to overcome
Feline immunodeficiency virus (FIV), like human immunodeficiency virus (HIV)-1, is a neurotropic lentivirus, and both natural and experimental infections are associated with neuropathology. FIV enters the brain early following experimental infection, most likely via the blood-brain and blood-cerebrospinal fluid barriers. The exact mechanism of entry, and the factors that influence this entry, are not fully understood. As FIV is a recognised model of HIV-1 infection, understanding such mechanisms is important, particularly as HIV enters the brain early in infection. Furthermore, the development of strategies to combat this central nervous system (CNS) infection requires an understanding of the interactions between the virus and the CNS. In this review the results of both in vitro and in vivo FIV studies are assessed in an attempt to elucidate the mechanisms of viral entry into the brain
The eclipsing supersoft X-ray binary CAL 87
We present and discuss 25 spectra obtained in November 1996, covering all
phases of the CAL 87 binary system. These spectra are superior both in
signal-to-noise and wavelength coverage to previously published data so that
additional spectral features can be measured. Photometry obtained on the same
nights is used to confirm the ephemeris and to compare with light curves from
previous years. Analysis of the color variation through the orbital cycle has
been carried out using archival MACHO data. When a barely resolved red field
star is accounted for, there is no (V-R)-color variation, even through eclipse.
There have been substantial changes in the depth of minimum light since 1988;
it has decreased more than 0.5 mag in the last several years. The spectral
features and radial velocities are also found to vary not only through the
0.44-day orbit but also over timescales of a year or more. Possible
interpretations of these long-term changes are discussed. The 1996 spectra
contain phase-modulated Balmer absorption lines not previously seen, apparently
arising in gas flowing from the region of the compact star. The changes in
emission-line strengths with orbital phase indicate there are azimuthal
variations in the accretion disk structures. Radial velocities of several lines
give different amplitudes and phasing, making determination of the stellar
masses difficult. All solutions for the stellar masses indicate that the
companion star is considerably less massive than the degenerate star. The
Balmer absorption-line velocities correspond to masses of ~1.4Msun for the
degenerate star and ~0.4Msun for the mass donor. However, the strong He II
emission lines indicate a much more massive accreting star, with Mx>4Msun.Comment: 18 pages including tables, plus10 figures. To appear in Ap
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