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P T Boyd

Publications and source records attributed to P T Boyd.

6 recordsLinked to original sources
PubMed2006

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.

Journal Article↗
PubMed2006

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.

Journal Article↗
PubMed2005

A short gamma-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.

Journal Article↗
PubMedDate not supplied

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)

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