| 1. |
- Edelson, R. A., et al.
(författare)
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Multiwavelength observations of short-timescale variability in NGC 4151. IV. Analysis of multiwavelength continuum variability
- 1996
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 470:1, s. 364-377377
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Tidskriftsartikel (refereegranskat)abstract
- For pt.III see ibid., vol.470, no.1, p.349-63 (1996). Combines data from the three preceding papers in order to analyze the multi wave-band variability and spectral energy distribution of the Seyfert 1 galaxy NGC 4151 during the 1993 December monitoring campaign. The source, which was near its peak historical brightness, showed strong, correlated variability at X-ray, ultraviolet, and optical wavelengths. The strongest variations were seen in medium-energy (~1.5 keV) X-rays, with a normalized variability amplitude (NVA) of 24%. Weaker (NVA=6%) variations (uncorrelated with those at lower energies) were seen at soft gamma-ray energies of ~100 keV. No significant variability was seen in softer (0.1-1 keV) X-ray bands. In the ultraviolet/optical regime, the NVA decreased from 9% to 1% as the wavelength increased from 1275 to 6900 Aring. These data do not probe extreme ultraviolet (1200 Aring to 0.1 keV) or hard X-ray (250 keV) variability. The phase differences between variations in different bands were consistent with zero lag, with upper limits of lsim0.15 day between 1275 Aring and the other ultraviolet bands, lsim0.3 day between 1275 Aring and 1.5 keV, and lsim1 day between 1275 and 5125 Aring. These tight limits represent more than an order of magnitude improvement over those determined in previous multi-wave-band AGN monitoring campaigns. The ultraviolet fluctuation power spectra showed no evidence for periodicity, but were instead well fitted with a very steep, red power law (ales-2.5)
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| 2. |
- Crenshaw, D. M., et al.
(författare)
-
Multiwavelength observations of short-timescale variability in NGC 4151. I. Ultraviolet observations
- 1996
-
Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 470:1, s. 322-335335
-
Tidskriftsartikel (refereegranskat)abstract
- Presents the results of an intensive ultraviolet monitoring campaign on the Seyfert 1 galaxy NGC 4151, as part of an effort to study its short-timescale variability over a broad range in wavelength. The nucleus of NGC 4151 was observed continuously with the International Ultraviolet Explorer for 9.3 days, yielding a pair of LWP and SWP spectra every ~70 minutes, and during 4 hr periods for 4 days prior to and 5 days after the continuous-monitoring period. The sampling frequency of the observations is an order of magnitude higher than that of any previous UV monitoring campaign on a Seyfert galaxy. The continuum fluxes in bands from 1275 to 2688 Aring went through four significant and well-defined ldquoeventsrdquo of duration 2-3 days during the continuous-monitoring period. The authors find that the amplitudes of the continuum variations decrease with increasing wavelength, which extends a general trend for this and other Seyfert galaxies to smaller timescales (i.e., a few days). The continuum variations in all the UV bands are simultaneous to within an accuracy of ~0.15 days, providing a strict constraint on continuum models. The emission-line light curves show only one major event during the continuous monitoring (a slow rise followed by a shallow dip) and do not correlate well with continuum light curves over the short duration of the campaign, because the timescale for continuum variations is apparently smaller than the response times of the emission lines
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| 3. |
- Cutts, F T, et al.
(författare)
-
Child and Maternal Mortality during a Period of Conflict in Beira City, Mozambique
- 1996
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Ingår i: International Journal of Epidemiology. - : Oxford University Press (OUP). - 0300-5771 .- 1464-3685. ; 25:2, s. 349-356
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Tidskriftsartikel (refereegranskat)abstract
- Background Child mortality rates have been declining in most developing countries. We studied child and maternal mortality and risk factors for child mortality in Beira city in July 1993, after a decade of conflict in Mozambique. Methods A community-based cluster sample survey of 4609 women of childbearing age was conducted. Indirect techniques were used to estimate child mortality (‘children ever born’ method and Preceding Birth Techniques [PBT]), and maternal mortality sisterhood method). Deaths among the most recent born child, born since July 1990, were classified as cases (n = 106), and two controls, matched by age and cluster, were selected per case. Results Indirect estimates of the probability of dying from birth to age 5 (deaths before age 5 years, 5q0 per 1000) decreased from 246 in 1977/8 to 212 in 1988/9. The PBT estimate for 1990/91 was 154 (95% confidence interval(CI): 124–184), but recent deaths may have been underreported. Lack of beds in the household (odds ratio[OR] = 2.0, 95% CI: 1.1–3.8), absence of the father (OR = 2.4, 95% CI: 1.2–4.8), low paternal educational level (OR = 2.1, 95% CI: 0.8–5.4), young maternal age (OR = 2.0, 95% CI: 1.0–3.7), self-reported maternal illness (OR = 2.4, 95% CI: 1.2–4.9), and home delivery of the child (OR = 2.3, 95% CI: 1.2–4.5) were associated with increased mortality, but the sensitivity of risk factors was low. Estimated maternal mortality was 410/100 000 live births with a reference date of 1982. Conclusions Child mortality decreased slowly over the 1980s in Beira despite poor living conditions caused by the indirect effects of the war. Coverage of health services increased over this period. The appropriateness of a risk approach to maternal-child-health care needs further evaluation.
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| 4. |
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| 5. |
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