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Sökning: WFRF:(Wanders I.)

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1.
  • 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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2.
  • Dietrich, M., et al. (författare)
  • Monitoring of active galactic nuclei. IV. The Seyfert 1 galaxy NGC 4593
  • 1994
  • Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 284:1, s. 33-4343
  • Tidskriftsartikel (refereegranskat)abstract
    • Results of a five-month campaign of optical monitoring the Seyfert 1 galaxy NGC 4593 are presented. High resolution Halpha and Hbeta spectra and direct images in the Johnson U, B, V, R and I bands were obtained between January and June 1990. The emission lines and the continuum showed strong variations on time scales of weeks to days. The Halpha line varied by more than 30% within only 5 days. Cross-correlating the light curves of the Balmer lines with that of the optical continuum gives a lag of around 4 days. Therefore, this low luminosity Seyfert galaxy may have one of the smallest broad line regions known so far
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3.
  • Edelson, R. A., et al. (författare)
  • Multiwavelength observations of short-timescale variability in NGC 4151. IV. Analysis of multiwavelength continuum variability
  • 1996
  • Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 470:1, s. 364-377377
  • 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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4.
  • Salamanca, I., et al. (författare)
  • Spectroscopic monitoring of active galactic nuclei. III. Size of the broad line region in NGC 3227
  • 1994
  • Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 282:3, s. 742-752752
  • Tidskriftsartikel (refereegranskat)abstract
    • For pt.II see ibid., vol.269, no.1-2, p.39-53 (1993). The authors present the results of a five-month monitoring campaign of the active galactic nucleus in NGC 3227. The Hbeta and Halpha emission lines and the optical continuum have been analysed. The optical AGN continuum and the broad-line region (BLR) emission in NGC 3227 appear to vary by about 40% on a timescale of 1.5 month. The levels of the broad-line emission and the 675.0 nm continuum are well correlated, a fact consistent with the assumption that the BLR material is photoionised by the central continuum source. Cross-correlation analyses between the light curves of the 675.0 nm AGN continuum and the BLR H emission indicate that the lag of the BLR emission with respect to the continuum variations is 17plusmn7 days. This result suggests that the BLR clouds that are affected by the changes in the flux of the central ionising source lie about 17 light days away from it
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5.
  • Wanders, I., et al. (författare)
  • Spectroscopic monitoring of active galactic nuclei. II. The Seyfert-1 galaxy NGC 3516
  • 1993
  • Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 269:1-2, s. 39-5353
  • Tidskriftsartikel (refereegranskat)abstract
    • The authors present the results of a five month spectroscopic monitoring campaign of the Seyfert-1 galaxy NGC 3516. Using a new calibration method and applying a correction for seeing differences during the various observations they can scale the spectra to each other with a much higher accuracy than hitherto achieved. NGC 3516 shows large amplitude variations on a time scale of several weeks. Asymmetric profile variations occur on the same time scale as the continuum variations. The authors show the presence of a varying dip on the blue wing of the Hbeta profile, which is not present on the Halpha profile, and which corresponds to the absorption features previously seen in the UV emission lines of NGC 3516. From cross-correlation analysis they find a time lag of 14plusmn2 days for the Halpha and 7plusmn3 days for the Hbeta emission-line response to continuum variations
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6.
  • Koratkar, A, et al. (författare)
  • The disappearing broad absorption lines and variable emission lines in NGC 3516
  • 1996
  • Ingår i: ASTROPHYSICAL JOURNAL. - : UNIV CHICAGO PRESS. - 0004-637X. ; 470:1, s. 378-393
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • The Seyfert 1 galaxy NGC 3516 was monitored during 1993 February 16-May 13 by IUE every 4 days for the first month, and then every 2 days for 2 months giving a total of 40 observations. This paper gives the initial results from this campaign, (1) The broa
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7.
  • Blauhut, Veit, et al. (författare)
  • Lessons from the 2018-2019 European droughts : a collective need for unifying drought risk management
  • 2022
  • Ingår i: Natural hazards and earth system sciences. - : Copernicus Publications. - 1561-8633 .- 1684-9981. ; 22:6, s. 2201-2217
  • Tidskriftsartikel (refereegranskat)abstract
    • Drought events and their impacts vary spatially and temporally due to diverse pedo-climatic and hydrologic conditions, as well as variations in exposure and vulnerability, such as demographics and response actions. While hazard severity and frequency of past drought events have been studied in detail, little is known about the effect of drought management strategies on the actual impacts and how the hazard is perceived by relevant stakeholders. In a continental study, we characterised and assessed the impacts and the perceptions of two recent drought events (2018 and 2019) in Europe and examined the relationship between management strategies and drought perception, hazard, and impact. The study was based on a pan-European survey involving national representatives from 28 countries and relevant stakeholders responding to a standard questionnaire. The survey focused on collecting information on stakeholders' perceptions of drought, impacts on water resources and beyond, water availability, and current drought management strategies on national and regional scales. The survey results were compared with the actual drought hazard information registered by the European Drought Observatory (EDO) for 2018 and 2019. The results highlighted high diversity in drought perception across different countries and in values of the implemented drought management strategies to alleviate impacts by increasing national and sub-national awareness and resilience. The study identifies an urgent need to further reduce drought impacts by constructing and implementing a European macro-level drought governance approach, such as a directive, which would strengthen national drought management and mitigate damage to human and natural assets.
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8.
  • Blauhut, Veit, et al. (författare)
  • Lessons from the 2018–2019 European droughts: A collective need for unifying drought risk management
  • 2021
  • Ingår i: Natural hazards and earth system sciences. - : Copernicus Publications. - 1561-8633 .- 1684-9981.
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • Drought events and their impacts vary spatially and temporally due to diverse pedo-climatic and hydrologic conditions, as well as variations in exposure and vulnerability, such as demographics and response actions. While hazardous severity and frequency of past drought events have been studied in detail, little is known about the effect of drought management strategies on the actual impacts, and how the hazard is perceived by relevant stakeholders for inducing action. In a continental study, we characterised and assessed the impacts and the perceptions of two recent drought events (2018 and 2019) in Europe and examined the relationship between management strategies and drought perception, hazard and impacts. The study was based on a pan-European survey involving national representatives from 28 countries and relevant stakeholders responding to a standard questionnaire. The survey focused on collecting information on stakeholders’ perceptions of drought, impacts on water resources and beyond, water availability and current drought management strategies at national and regional scales. The survey results were compared with the actual drought hazard information registered by the European Drought Observatory (EDO) for 2018 and 2019. The results highlighted high diversity in drought perceptions across different countries and in values of implemented drought management strategies to alleviate impacts by increasing national and sub-national awareness and resilience. The study concludes with an urgent need to further reduce drought impacts by constructing and implementing a European macro-level drought governance approach, such as a directive, which would strengthen national drought management and lessen harm to human and natural potentials.
  •  
9.
  • Ciray, I., et al. (författare)
  • Effect of granulocyte colony-stimulating factor (G-CSF)-supported chemotherapy on MR imaging of normal red bone marrow in breast cancer patients with focal bone metastases
  • 2003
  • Ingår i: Acta Radiol. - 0284-1851 .- 1600-0455. ; 44:5, s. 472-84
  • Tidskriftsartikel (refereegranskat)abstract
    • PURPOSE: To investigate the effect of granulocyte colony-stimulating factor (G-CSF)-supported chemotherapy on normal red bone marrow MR imaging in breast cancer patients with focal bone metastases. MATERIAL AND METHODS: Fifteen breast cancer patients who were examined before and after chemotherapy with T1-weighted-SE and long echo-time inversion-recovery turbo-spin-echo (long TE IR-TSE) sequences in the thoracolumbar spine and pelvis were retrospectively studied. Nine of them received G-CSF therapy after the administration of each chemotherapy course. Of these 9 patients, the MR follow-ups were performed during G-CSF in 4 patients and after G-CSF therapy in 5 patients. Six patients did not receive G-CSF. Signal intensity (SI) changes in normal bone marrow were evaluated visually in all patients and quantitatively in 13 patients. RESULTS: In all 4 patients investigated during G-CSF therapy a diffuse, homogeneous SI increase on long TE IR-TSE was observed visually and quantitatively in initially normal bone marrow. This change obscured some focal lesions in 2 patients. No such SI change was visible after G-CSF therapy (p = 0.008) or in patients not receiving G-CSF. On T1-weighted images an SI decrease was found both during and after G-CSF therapy, but an increase occurred in patients not receiving G-CSF. CONCLUSION: G-CSF-supported chemotherapy can induce diffuse SI changes in normal red bone marrow on MR imaging. On long TE IR-TSE, the changes are visible during G-CSF treatment and can lead to misinterpretations in the response evaluation of bone metastases to therapy.
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10.
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  • Resultat 1-10 av 21

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