| 1. |
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| 2. |
- 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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| 3. |
- Crenshaw, D. M., et al.
(författare)
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Multiwavelength observations of short-timescale variability in NGC 4151. I. Ultraviolet observations
- 1996
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 470:1, s. 322-335335
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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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| 4. |
- Clavel, J., et al.
(författare)
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Steps toward determination of the size and structure of the broad-line region in active galactic nuclei. I. An 8 month campaign of monitoring NGC 5548 with IUE
- 1991
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 366:1, s. 64-8181
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Tidskriftsartikel (refereegranskat)abstract
- The authors present emission-line and ultraviolet continuum observations of a type I Seyfert galaxy in which the time resolution is adequate for describing the character of variability. Using the IUE satellite, the nucleus of NGC 5548 was observed every 4 days for a period of 8 months. Its mean properties-continuum shape, line ratios-are not unusual for type I Seyfert galaxies, but it was found to be strongly variable. The ultraviolet continuum flux and broad emission line fluxes varied significantly, going through three large maxima and three deep minima. The great majority of all variations were well resolved in time. The data lend qualitative support to the view that photoionization by the nuclear continuum is responsible for driving the emission lines
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| 5. |
- Dominoni, Davide M., et al.
(författare)
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Why conservation biology can benefit from sensory ecology
- 2020
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Ingår i: Nature Ecology & Evolution. - : Springer Science and Business Media LLC. - 2397-334X. ; 4:4, s. 502-511
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Tidskriftsartikel (refereegranskat)abstract
- Anthropogenic sensory pollutants, such as noise, light and chemicals, are affecting biodiversity. This Perspective uses an understanding of animal sensory ecology to explore how these impacts can be mitigated. Global expansion of human activities is associated with the introduction of novel stimuli, such as anthropogenic noise, artificial lights and chemical agents. Progress in documenting the ecological effects of sensory pollutants is weakened by sparse knowledge of the mechanisms underlying these effects. This severely limits our capacity to devise mitigation measures. Here, we integrate knowledge of animal sensory ecology, physiology and life history to articulate three perceptual mechanisms-masking, distracting and misleading-that clearly explain how and why anthropogenic sensory pollutants impact organisms. We then link these three mechanisms to ecological consequences and discuss their implications for conservation. We argue that this framework can reveal the presence of 'sensory danger zones', hotspots of conservation concern where sensory pollutants overlap in space and time with an organism's activity, and foster development of strategic interventions to mitigate the impact of sensory pollutants. Future research that applies this framework will provide critical insight to preserve the natural sensory world.
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| 6. |
- Jennings, Anne, et al.
(författare)
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Modern and early Holocene ice shelf sediment facies from Petermann Fjord and northern Nares Strait, northwest Greenland
- 2022
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 283
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Tidskriftsartikel (refereegranskat)abstract
- Based on sediment cores and geophysical data collected from Petermann Fjord and northern Nares Strait, NW Greenland, an Arctic ice shelf sediment facies is presented that distinguishes sub and pro ice shelf environments. Sediment cores were collected from sites beneath the present day Petermann Ice Tongue (PIT) and in deglacial sediments of northern Nares Strait with a focus on understanding the glacial and oceanographic history over the last 11,000 cal yr BP. The modern sub ice shelf sediment facies in Petermann Fjord is laminated and devoid of coarse clasts (IRD) due to strong basal melting that releases debris (debris filtering) from the basal ice at the grounding zone driven by buoyant subglacial meltwater and entrained Atlantic Water. Laminated sediments in the deep basin proximal to the gounding zone comprise layers of fine mud formed by suspension settling from turbid meltwater plumes (plumites) interrupted by normally graded very fine sand to medium silt layers with sharp basal contacts and rip-up clasts of mud, interpreted as turbidites. An inner fjord sill limits distribution of sediment gravity flows from the grounding zone to the deep inner fjord basin, such that sites on the inner sill and beyond the ice tongue largely only comprise plumites. Bioturbation and foraminiferal abundances increase with distance from the grounding zone. The benthic foraminiferal species, Elphidium clavatum is absent beneath the ice tongue, but dominant in the turbid meltwater influenced environment beyond the ice tongue. The very sparse IRD in sediments beneath the PIT and in the fjord beyond the PIT derives mainly from englacial debris in the ice tongue, side valley glaciers, rock falls from the steep fjord walls and sea ice.We use the modern ice shelf sediment facies characteristics to infer the past presence of ice shelves in northern Nares Strait using analyses of sediment cores from several cruises (OD1507, HLY03, 2001LSSL, RYDER19). On bathymetric highs, bioturbated mud with dispersed IRD overlies a 10–15 m thick, distinctly laminated silt and clay unit with rare coarse clasts and sparse foraminifera which forms a sediment drape of nearly uniform thickness. We interpret these laminated sediments to represent glaciomarine deposition by meltwater plumes emanating from ice streams that terminated in floating ice shelves. IRD layers, shifts in sediment composition (qXRD, MS and XRF) and faunal assemblage changes in the laminated unit document periods of ice-shelf instability sometimes, but not always, coupled with grounding zone retreat. Our deglacial reconstruction, including ice shelves, begins ∼10.7 cal ka BP, with confluent ice streams grounded in Hall Basin fronted by the Robeson Channel ice shelf. Ice shelf breakup and grounding zone retreat to relatively stable grounding zones at Kennedy Channel and the mouth of Petermann Fjord was accomplished by 9.4 cal ka BP when the Hall Basin ice shelf was established. This ice shelf broke up and reformed once prior to the final break up at 8.5 to 8.4 cal ka BP marking ice stream collapse, separation of Greenland and Innuitian ice sheets, and the opening of Nares Strait for Arctic-Atlantic throughflow. The Petermann ice shelf remained in Hall Basin until the Petermann Glacier retreated from the fjord mouth ∼7.1 cal ka BP. The resilience of these northern ice streams to strong early Holocene insolation and subsurface Atlantic Water advection is attributed to their northern aspect, buttressing by narrow passages, and high ice flux from the Greenland Ice Sheet (GIS).
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