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K O Mason

Publications and source records attributed to K O Mason.

14 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↗
PubMed2002

The signature of supernova ejecta in the X-ray afterglow of the gamma-ray burst 011211.

Now that gamma-ray bursts (GRBs) have been determined to lie at cosmological distances, their isotropic burst energies are estimated to be as high as 1054 erg (ref. 2), making them the most energetic phenomena in the Universe. The nature of the progenitors responsible for the bursts remains, however, elusive. The favoured models range from the merger of two neutron stars in a binary system to the collapse of a massive star. Spectroscopic studies of the afterglow emission could reveal details of the environment of the burst, by indicating the elements present, the speed of the outflow and an estimate of the temperature. Here we report an X-ray spectrum of the afterglow of GRB011211, which shows emission lines of magnesium, silicon, sulphur, argon, calcium and possibly nickel, arising in metal-enriched material with an outflow velocity of the order of one-tenth the speed of light. These observations strongly favour models where a supernova explosion from a massive stellar progenitor precedes the burst event and is responsible for the outflowing matter.

Journal Article↗
PubMed2000

Husbands' versus wives' fertility goals and use of contraception: the influence of gender context in five Asian countries.

Using data from Pakistan, India, Malaysia, Thailand, and the Philippines, we explore how gender context influences (1) husband-wife concordance in the demand for children and (2) the impact of each spouse's fertility preferences on contraceptive use. We also explore whether the husband's pronatalism can explain the wife's unmet need for contraception. The results suggest that gender context has little net effect on couples' concordance, but influences the relative weight of husbands' and wives' preferences in determining contraceptive use. Analysis of women's unmet need for contraception suggests that the husbands' pronatalism contributes to wives' unmet need, but only to a relatively small degree, especially in settings where unmet need is high. This is the case because the proportion of couples with differing fertility goals is small in most communities.

Asia↗
PubMed1997

Explaining fertility transitions.

In this essay, I suggest that the crisis in our understanding of fertility transitions is more apparent than real. Although most existing theories of fertility transition have been partially or wholly discredited, this reflects a tendency to assume that all fertility transitions share one or two causes, to ignore mortality decline as a precondition for fertility decline, to assume that pretransitional fertility is wholly governed by social constraints rather than by individual decision-making, and to test ideas on a decadal time scale. I end the essay by suggesting a perceptual, interactive approach to explaining fertility transitions that is closely allied to existing theories but focuses on conditions that lead couples to switch from postnatal to prenatal controls on family size.

Birth Rate↗
PubMed1994

HIV transmission and the balance of power between women and men: a global view.

This paper presents a logical analysis of the paths by which gender inequality is likely to affect the heterosexual transmission of HIV. Non-use of condoms, the combination of a sexual double standard and frequent use of female prostitutes, and a high prevalence of curable sexually transmitted diseases are considered. The 'circulation' of women as sexual and reproductive gifts, which is a near-universal feature of human societies, explains men's use of prostitutes and promiscuity, and contributes to high STD prevalence. It may also contribute to the non-use of condoms, although a separate analysis suggests this is not always the case. The empowerment of women thus might help to slow the spread of HIV/AIDS. Even more effective in countries with large commercial sex sectors would be the empowerment of female sex workers.

Condoms↗
PubMed1992

Family change and support of the elderly in Asia: what do we know?

"After outlining variations in traditional family systems in Asia, this article discusses likely impacts of urbanization, industrialization and migration on family structure and care of the elderly. Evidence about changing family support for the elderly in Asia is then reviewed. The article's main conclusion is that future changes in Asian countries and areas seem likely to erode traditional family-based systems of care for the elderly, even if the overall welfare of the elderly improves because of higher incomes. Problems faced by elderly women are likely to be especially acute and may require special policies to deal with them."

Adult↗
PubMed1992

The perceived impact of child care costs on women's labor supply and fertility.

In a sample of Detroit-area mothers of preschool-aged children interviewed in 1986, one-third reported that child care problems had constrained their employment. Such reports were relatively prevalent among poor women, those without relatives nearby, and those willing to entrust the care of their children to nonfamily members. Only one-tenth of the sample reported a similar child care constraint on fertility, a phenomenon unrelated to income but relatively prevalent among women with strong labor force attachment. The results suggest that policies to increase the supply of child care or to lower its cost could increase female labor supply by a substantial fraction, with an even greater rise among women most at risk of poverty and reliance on public assistance, but probably would not raise fertility significantly.

Adolescent↗
PubMed1981

Female employment and fertility in Peninsular Malaysia: the maternal role incompatibility hypothesis reconsidered.

Multivariate analysis of the 1974 Malaysian Fertility and Family Survey tests the hypothesis that an inverse relationship between women's work and fertility occurs only when there are serious conflicts between working and caring for children. The results are only partly consistent with the hypothesis and suggest that normative conflicts between working and mothering affect the employment-fertility relationship in Malaysia more than spacio-temporal conflicts do. The lack of consistent evidence for the hypothesis, as well as some conceptual problems, lead us to propose an alternative framework for understanding variation in the employment-fertility relationship, both in Malaysia and elsewhere. This framework incorporates ideas from the role incompatibility hypothesis but views the employment-fertility relationship as dependent not just on role conflicts but more generally on the structure of the household's socioeconomic opportunities.

Adolescent↗