2,173 research outputs found
Modeling the light curves of ultraluminous X-ray sources as precession
We present a freely available xspec model for the modulations seen in the
long-term light curves of multiple ultraluminous X-ray sources (ULXs). By
incorporating the physics of multiple electron scatterings (ray traced with a
Monte-Carlo routine), we go beyond analytical predictions and show that the
geometrical beaming of radiation in the conical outflow can be more than a
factor of 100 for opening angles smaller than . We apply our new
model to the long-term, well sampled Swift light curve of the recently
confirmed ULX pulsar NGC 5907 X-1 with an established period of 78 days. Our
results suggest that geometrical beaming together with a slight precession of
the conical wind can describe the light curve with a consistent set of
parameters for the wind. The small opening angle of roughly
implies a highly super-critical flow and boosting
factors at the order of that would yield a fairly
low surface magnetic field strength of Gauss.Comment: accepted by MNRAS for publication (7 pages, 6 figures
Adenovirus ?Hit-And-Run? Eviction From B-Cells Harboring Leukemic Runx1 Fusion Genes And Adp Controlled Latency In Lymphocytes
The common species C adenoviruses infect more than 80% of the human population early in life. The virus can establish an asymptomatic persistent infection in mucosal-associated lymphocytes. Adenovirus has long been classified as DNA tumor virus, however it still has no established associations with any specific cancer. This phenomenon may be explained by the model of hit-and-run viral oncogenesis, which proposes that a virus can infect a cell population, causing oncogenic mutations (hit) that in turn inhibit the virus from persisting in the cancerous cell progeny (run). One type of cancer in particular, childhood precursor B-cell acute lymphoblastic leukemia, is suspected of having an infectious cause, yet no viral agent has been conclusively linked to the disease. Childhood acute lymphoblastic leukemia is associated with frequently occurring chromosomal translocations that encode fusion proteins. ETV6/RUNX1 is the most commonly found translocation and the only one to be associated with the infectious etiology of the disease. We hypothesized that adenovirus may be an agent capable of initiating childhood precursor B-cell acute lymphoblastic leukemia but that the virus is evicted from cancer cells by the activities of the ETV6/RUNX1 leukemic fusion gene. We found that adenovirus retention in a B-cell model of persistence was inhibited by direct binding of the ETV6/RUNX1 fusion gene to the viral genome. This loss of virus was dependent on histone deacetylation activities, but was not impacted by NF-κB interference, selective cell death of infected cells, or known interactions of RUNX1 with viral protein. Further, epigenetic changes induced in cells following viral infection were still present after viral eviction from the cells, which demonstrates that viral retention is unnecessary for sustained repression of cellular genes. Because latency is likely related to viral retention in B-cells, we also studied how NF-κB control of the adenovirus E3 region and expression of the contained adenovirus death protein (ADP) gene could effect viral latency in lymphocytes. We failed to find specific activation of E3 region genes with NF-κB activation through PMA/Ionomycin. ADP was necessary for lytic infection in lymphocytes, but not epithelial cells, signifying differences in regulation of ADP between these cell types
Confirming the thermal Comptonization model for black hole X-ray emission in the low-hard state
Hard X-ray spectra of black hole binaries in the low/hard state are well
modeled by thermal Comptonization of soft seed photons by a corona-type region
with \thinspace{\thinspace}keV and optical depth around 1.
Previous spectral studies of 1E{\thinspace}1740.72942, including both the
soft and the hard X-ray bands, were always limited by gaps in the spectra or by
a combination of observations with imaging and non-imaging instruments. In this
study, we have used three rare nearly-simultaneous observations of
1E{\thinspace}1740.71942 by both XMM-Newton and INTEGRAL satellites to
combine spectra from four different imaging instruments with no data gaps, and
we successfully applied the Comptonization scenario to explain the broadband
X-ray spectra of this source in the low/hard state. For two of the three
observations, our analysis also shows that, models including Compton reflection
can adequately fit the data, in agreement with previous reports. We show that
the observations can also be modeled by a more detailed Comptonization scheme.
Furthermore, we find the presence of an iron K-edge absorption feature in one
occasion, which confirms what had been previously observed by Suzaku. Our
broadband analysis of this limited sample shows a rich spectral variability in
1E{\thinspace}1740.72942 at the low/hard state, and we address the possible
causes of these variations. More simultaneous soft/hard X-ray observations of
this system and other black-hole binaries would be very helpful in constraining
the Comptonization scenario and shedding more light on the physics of these
systems.Comment: 6 pages, two figures, accepted for publication in A&
Short term X-ray rms variability of Cyg X-1
A linear dependence of the amplitude of broadband noise variability on flux
for GBHC and AGN has been recently shown by Uttley & McHardy (2001). We present
the long term evolution of this rms-flux-relation for Cyg X-1 as monitored from
1998-2002 with RXTE. We confirm the linear relationship in the hard state and
analyze the evolution of the correlation for the period of 1996-2002. In the
intermediate and the soft state, we find considerable deviations from the
otherwise linear relationship. A possible explanation for the rms-flux-relation
is a superposition of local mass accretion rate variations.Comment: 3 pages, 3 figures, Proceedings of the 4th Microquasar Workshop, eds.
Ph Durouchoux, Y. Fuchs and J. Rodriguez, published by the Center for Space
Physics: Kolkat
X-ray reflected spectra from accretion disk models. III. A complete grid of ionized reflection calculations
We present a new and complete library of synthetic spectra for modeling the
component of emission that is reflected from an illuminated accretion disk. The
spectra were computed using an updated version of our code XILLVER that
incorporates new routines and a richer atomic data base. We offer in the form
of a table model an extensive grid of reflection models that cover a wide range
of parameters. Each individual model is characterized by the photon index
\Gamma of the illuminating radiation, the ionization parameter \xi at the
surface of the disk (i.e., the ratio of the X-ray flux to the gas density), and
the iron abundance A_{Fe} relative to the solar value. The ranges of the
parameters covered are: 1.2 \leq \Gamma \leq 3.4, 1 \leq \xi \leq 10^4, and 0.5
\leq A_{Fe} \leq 10. These ranges capture the physical conditions typically
inferred from observations of active galactic nuclei, and also stellar-mass
black holes in the hard state. This library is intended for use when the
thermal disk flux is faint compared to the incident power-law flux. The models
are expected to provide an accurate description of the Fe K emission line,
which is the crucial spectral feature used to measure black hole spin. A total
of 720 reflection spectra are provided in a single FITS
file{\url{http://hea-www.cfa.harvard.edu/~javier/xillver/}} suitable for the
analysis of X-ray observations via the atable model in XSPEC. Detailed
comparisons with previous reflection models illustrate the improvements
incorporated in this version of XILLVER.Comment: 70 pages, 21 figures, submitted to Ap
Different kinds of long-term variability from Cygnus X-1
We present a study of the long-term variability of Cyg X-1 using data from
the RXTE/ASM and the RXTE/PCA during the time between the two soft states of
1996 and 2001/2002. This period has been characterized by many short ASM
flaring episodes which we have identified as "failed state transitions". The
150 d period which has been seen before and shortly after the 1996 soft state
is not obviously present in the ASM rate during most of this time. Applying
selection criteria from our pointed RXTE/PCA observations to exclude the
flaring episodes we show that the 150 d period can indeed still be
significantly detected in the hard state. Furthermore, while the ~420 d
timescale associated with the flaring is reduced in the selected hard state
count rate, it is still pronounced in the temporal evolution of the
corresponding hardness ratios. The Ryle radio flux is also consistent with the
150 d period being present but distorted during this time.Comment: 4 pages, 6 figures, to appear in Proceedings of "X-ray Timing 2003:
Rossi and Beyond", ed. P. Kaaret, F.K. Lamb, & J.H. Swan
Chandra and RXTE spectroscopy of the accreting msec pulsar IGR J00291+5934
We report on an observation of the recently discovered accreting millisecond X-ray pulsar IGR J00291+5934 performed with the RXTE-Proportional Counter Array (PCA) and Chandra-High Energy Transmission Grating Spectrometer (HETGS). The RXTE data are from a twoweek follow-up of the source, while the Chandra observation took place around the end of the follow-up, about 12 days after the discovery of
the source, when the source flux had decreased already by a factor of ten. The analysis of the Chandra data allowed us to extract the most precise X-ray position of IGR J00291+5934, RA = 00h 29m 03.08s, and Dec =+59â—¦ 34 19.2 (0.6 error), compatible with the optical and radio ones.
We find that the spectra of IGR J00291+5934 can be described by a combination of a thermal component and a power-law. Along the outburst detected by PCA, the power-law photon index showed no particular trend, while the thermal component (∼1 keV, interpreted as a hot spot on
the neutron star surface) became weaker until non-detection. In the simultaneous observation of the weak Chandra /RXTE spectrum, there was no longer any indication of the ∼1 keV thermal component, while we detected a colder thermal component (∼0.4 keV) that we interpret as the
emission from the cold disc. A hint of a 6.4 keV iron line was detected, together with an excess around 6.8 keV and absorption feature around 7.1 keV. The last two features have never been detected in the spectra of accretion-driven millisecond pulsars before and, if confirmed, would
suggest the presence of an expanding hot corona with high outflow velocities
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