The Chaotic Long-term X-ray Variability of 4U 1705-44

The low-mass X-ray binary 4U1705-44 exhibits dramatic long-term X-ray time variability with a timescale of several hundred days. The All-Sky Monitor (ASM) aboard the Rossi X-ray Timing Explorer (RXTE) and the Japanese Monitor of All-sky X-ray Image (MAXI) aboard the International Space Station together have continuously observed the source from December 1995 through May 2014. The combined ASM-MAXI data provide a continuous time series over fifty times the length of the timescale of interest. Topological analysis can help us identify fingerprints in the phase-space of a system unique to its equations of motion. The Birman-Williams theorem postulates that if such fingerprints are the same between two systems, then their equations of motion must be closely related. The phase-space embedding of the source light curve shows a strong resemblance to the double-welled nonlinear Duffing oscillator. We explore a range of parameters for which the Duffing oscillator closely mirrors the time evolution of 4U1705-44. We extract low period, unstable periodic orbits from the 4U1705-44 and Duffing time series and compare their topological information. The Duffing and 4U1705-44 topological properties are identical, providing strong evidence that they share the same underlying template. This suggests that we can look to the Duffing equation to help guide the development of a physical model to describe the long-term X-ray variability of this and other similarly behaved X-ray binary systems.

Rheumatic heart disease in pregnancy: cardiac and obstetric outcomes

BACKGROUND

Rheumatic heart disease (RHD) remains an important health issue for indigenous women of child-bearing age in northern Australia. However, the influence of RHD on maternal outcomes with current clinical practice is unclear.

AIMS

To determine maternal cardiac complications and obstetric outcomes in patients with RHD.

METHODS

Retrospective case note analysis of women with RHD who received obstetric care between July 1999 and May 2010 at Cairns Base Hospital in north Queensland. Outcome measures were obstetric interventions and outcomes, cardiac interventions and complications, stratified according to a cardiac risk score (CRS).

RESULTS

Ninety-five confinements occurred in 54 patients, of whom 52 were Indigenous Australians. There were no maternal or neonatal deaths. With a CRS of 0, cardiac complications occurred in 0 of 70 confinements; with a CRS of 1, complications occurred in 5 of 17 confinements (29%); with a CRS of >1, complications occurred in 2 of 4 confinements (50%). Another four patients were first diagnosed with RHD after developing acute pulmonary oedema during the peripartum period.

CONCLUSIONS

  RHD has a major impact on maternal cardiac outcomes. However, with current management practices, maternal and fetal mortality are low, and the incidence of complications is predictable based on known risk factors.

The association of GRB 060218 with a supernova and the evolution of the shock wave

Although the link between long gamma-ray bursts (GRBs) and supernovae has been established, hitherto there have been no observations of the beginning of a supernova explosion and its intimate link to a GRB. In particular, we do not know how the jet that defines a gamma-ray burst emerges from the star's surface, nor how a GRB progenitor explodes. Here we report observations of the relatively nearby GRB 060218 (ref. 5) and its connection to supernova SN 2006aj (ref. 6). In addition to the classical non-thermal emission, GRB 060218 shows a thermal component in its X-ray spectrum, which cools and shifts into the optical/ultraviolet band as time passes. We interpret these features as arising from the break-out of a shock wave driven by a mildly relativistic shell into the dense wind surrounding the progenitor. We have caught a supernova in the act of exploding, directly observing the shock break-out, which indicates that the GRB progenitor was a Wolf-Rayet star.

Gamma-ray bursts: huge explosion in the early Universe

Long gamma-ray bursts (GRBs) are bright flashes of high-energy photons that can last for tens of minutes; they are generally associated with galaxies that have a high rate of star formation and probably arise from the collapsing cores of massive stars, which produce highly relativistic jets (collapsar model). Here we describe gamma- and X-ray observations of the most distant GRB ever observed (GRB 050904): its redshift (z) of 6.29 means that this explosion happened 12.8 billion years ago, corresponding to a time when the Universe was just 890 million years old, close to the reionization era. This means that not only did stars form in this short period of time after the Big Bang, but also that enough time had elapsed for them to evolve and collapse into black holes.

A short γ-ray burst apparently associated with an elliptical galaxy at redshift z = 0.225

Gamma-ray bursts (GRBs) come in two classes: long (> 2 s), soft-spectrum bursts and short, hard events. Most progress has been made on understanding the long GRBs, which are typically observed at high redshift (z approximately 1) and found in subluminous star-forming host galaxies. They are likely to be produced in core-collapse explosions of massive stars. In contrast, no short GRB had been accurately (< 10'') and rapidly (minutes) located. Here we report the detection of the X-ray afterglow from--and the localization of--the short burst GRB 050509B. Its position on the sky is near a luminous, non-star-forming elliptical galaxy at a redshift of 0.225, which is the location one would expect if the origin of this GRB is through the merger of neutron-star or black-hole binaries. The X-ray afterglow was weak and faded below the detection limit within a few hours; no optical afterglow was detected to stringent limits, explaining the past difficulty in localizing short GRBs.

The relationship between social ties and survival among black and white breast cancer patients. National Cancer Institute Black/White Cancer Survival Study Group

The relationship between social ties, stage of disease, and survival was analyzed in a population-based sample of 525 black and 486 white women with newly diagnosed breast cancer. There were significant differences between the two race groups in reported social ties. Using logistic regression to adjust for the effects of age, race, study area, education, and the presence of symptoms, there was little or no evidence for an association between individual network measures of social ties and stage of disease. However, a summary measure of social networks was found to be associated modestly with late stage disease, attributable in part to significantly more advanced disease among black, but not white, women reporting few friends and relatives [relative risk (RR) = 1.8; 95% confidence interval (CI) = 1.1-3.0]. With adjustments for differences in stage of disease and other covariates, and with the use of Cox proportional hazards modeling to estimate hazard ratios, the absence of close ties and perceived sources of emotional support were associated significantly with an increased breast cancer death rate. White women in the lowest quartile of reported close friends and relatives had twice the breast cancer death rate of white women in the highest quartile (RR = 2.1; 95% CI = 1.1-4.4). Notably, both black and white women reporting few sources of emotional support had a higher death rate from their disease during the 5-year period of follow-up (RR = 1.8; 95% CI = 1.3-2.5).(ABSTRACT TRUNCATED AT 250 WORDS)