A link between prompt optical and prompt gamma-ray emission in gamma-ray bursts.

The prompt optical emission that arrives with the gamma-rays from a cosmic gamma-ray burst (GRB) is a signature of the engine powering the burst, the properties of the ultra-relativistic ejecta of the explosion, and the ejecta's interactions with the surroundings. Until now, only GRB 990123 had been detected at optical wavelengths during the burst phase. Its prompt optical emission was variable and uncorrelated with the prompt gamma-ray emission, suggesting that the optical emission was generated by a reverse shock arising from the ejecta's collision with surrounding material. Here we report prompt optical emission from GRB 041219a. It is variable and correlated with the prompt gamma-rays, indicating a common origin for the optical light and the gamma-rays. Within the context of the standard fireball model of GRBs, we attribute this new optical component to internal shocks driven into the burst ejecta by variations of the inner engine. The correlated optical emission is a direct probe of the jet isolated from the medium. The timing of the uncorrelated optical emission is strongly dependent on the nature of the medium.

An infrared flash contemporaneous with the gamma-rays of GRB 041219a.

The explosion that results in a cosmic gamma-ray burst (GRB) is thought to produce emission from two physical processes: the central engine gives rise to the high-energy emission of the burst through internal shocking, and the subsequent interaction of the flow with the external environment produces long-wavelength afterglows. Although observations of afterglows continue to refine our understanding of GRB progenitors and relativistic shocks, gamma-ray observations alone have not yielded a clear picture of the origin of the prompt emission nor details of the central engine. Only one concurrent visible-light transient has been found and it was associated with emission from an external shock. Here we report the discovery of infrared emission contemporaneous with a GRB, beginning 7.2 minutes after the onset of GRB 041219a (ref. 8). We acquired 21 images during the active phase of the burst, yielding early multi-colour observations. Our analysis of the initial infrared pulse suggests an origin consistent with internal shocks.

A giant gamma-ray flare from the magnetar SGR 1806-20.

Two classes of rotating neutron stars-soft gamma-ray repeaters (SGRs) and anomalous X-ray pulsars-are magnetars, whose X-ray emission is powered by a very strong magnetic field (B approximately 10(15) G). SGRs occasionally become 'active', producing many short X-ray bursts. Extremely rarely, an SGR emits a giant flare with a total energy about a thousand times higher than in a typical burst. Here we report that SGR 1806-20 emitted a giant flare on 27 December 2004. The total (isotropic) flare energy is 2 x 10(46) erg, which is about a hundred times higher than the other two previously observed giant flares. The energy release probably occurred during a catastrophic reconfiguration of the neutron star's magnetic field. If the event had occurred at a larger distance, but within 40 megaparsecs, it would have resembled a short, hard gamma-ray burst, suggesting that flares from extragalactic SGRs may form a subclass of such bursts.

The risk of measles, mumps, and varicella among young adults: a serosurvey of US Navy and Marine Corps recruits.

OBJECTIVES: To assess the risk of epidemic transmission and to guide immunization policy, the seroprevalence of antibody to measles, mumps, and varicella was determined in a group of young adults. METHODS: A cross-sectional study of 1533 US Navy and Marine Corps recruits was conducted in June 1989. Antibody status was determined with commercially available enzyme-linked immunosorbent assays. RESULTS: Direct sex and race adjustment to the 15- to 29-year-old US population resulted in seronegativity rates of 17.8% for measles, 12.3% for mumps, and 6.7% for varicella. Measles and mumps seronegativity rates were higher among Whites whereas varicella seronegativity was higher among non-Whites. Recruits enlisting from outside the 50 US states, especially those from island territories, were more likely to lack varicella antibody. The sensitivity of a positive history of vaccination or disease in predicting antibody status was less than 90% for all diseases. CONCLUSIONS: These results suggest a continued potential for epidemics, especially of measles, and the need for mandatory immunization policies. Immigrants to the United States, especially those from island territories, may be a high-risk group that could benefit from varicella vaccination.

Pneumonia hospitalizations in the US Navy and Marine Corps: rates and risk factors for 6,522 admissions, 1981-1991.

The authors identified hospitalizations for pneumonia (n = 6,522) in active-duty Navy and Marine Corps personnel during 1981-1991 from computerized inpatient records. The crude mean annual rate of pneumonia hospitalization was 77.6 per 100,000 active-duty personnel; 65% of pneumonia hospitalizations had no etiologic agent identified. The most commonly reported agents to cause pneumonia hospitalization were Streptococcus pneumoniae (12.3%), Mycoplasma pneumoniae (10.8%), other streptococcal species (2.1%), and Haemophilus influenzae (1.9%). The median age at hospitalization was 22 years. The median duration of hospital stay was 4 days and the case fatality rate was 0.4%. The authors used a 2% sample of the entire population and by means of stepwise unconditional multivariate logistic regression modeling for pneumonia found that, independent of age, the most junior Navy and Marine Corps personnel were at highest risk. Whites were at higher risk than blacks, Hispanics, or Filipinos. These results indicate that among this generally healthy US young adult military population, pneumonia hospitalization is common, often brief, and frequently without specifically identified pathogens.

Systemic reactions in U.S. Marine Corps personnel who received Japanese encephalitis vaccine.

The overall hypersensitivity reaction rate among 14,249 U.S. Marine Corps personnel who received 36,850 doses of an investigational Japanese encephalitis vaccine was 10.3 per 10,000 doses; reaction rates were 16.1 and 10.3 per 10,000 doses for the first two doses, and 2.0 per 10,000 doses for the third. The reaction rate was 26.7 per 10,000 vaccinees. Of 38 reactors, 26 had urticaria and/or angioedema, and 11 had pruritus. Vaccine reaction intervals clustered within 48 hours for dose 1, but the median reaction interval for dose 2 was 96 hours. A history of urticaria or allergic rhinitis was associated with an increased probability of a vaccine reaction.

Supermirror hard-x-ray telescope.

The practical use of a grazing x-ray telescope is demonstrated for hard-x-ray imaging as hard as 40 keV by means of a depth-graded d-spacing multilayer, a so-called supermirror. Platinum-carbon multilayers of 26 layer pairs in three blocks with a different periodic length d of 3-5 nm were designed to enhance the reflectivity in the energy range from 24 to 36 keV at a grazing angle of 0.3 deg. The multilayers were deposited on thin-replica-foil mirrors by a magnetron dc sputtering system. The reflectivity was measured to be 25%-30% in this energy range; 20 mirror shells thus deposited were assembled into the tightly nested grazing-incidence telescope. The focused hard-x-ray image was observed with a newly developed position-sensitive CdZnTe solid-state detector. The angular resolution of this telescope was found to be 2.4 arc min in the half-power diameter.