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Sökning: WFRF:(Kollatschny W.)

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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. - 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.
  • 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. - 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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3.
  • Clavel, J., et al. (författare)
  • 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
  • Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 366:1, s. 64-8181
  • 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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4.
  • Kessler, Richard (författare)
  • First-Year Sloan Digital Sky Survey-II Supernova Results : Hubble Diagram and Cosmological Parameters
  • 2009
  • Ingår i: Astrophysical Journal Supplement Series. - 0067-0049 .- 1538-4365. - 0067-0049 ; 185:1, s. 32-84
  • Tidskriftsartikel (refereegranskat)abstract
    • We present measurements of the Hubble diagram for 103 Type Ia supernovae (SNe) with redshifts 0.04 < z < 0.42, discovered during the first season (Fall 2005) of the Sloan Digital Sky Survey-II (SDSS-II) Supernova Survey. These data fill in the redshift "desert" between low- and high-redshift SN Ia surveys. Within the framework of the MLCS2K2 light-curve fitting method, we use the SDSS-II SN sample to infer the mean reddening parameter for host galaxies, RV = 2.18 ± 0.14stat ± 0.48syst, and find that the intrinsic distribution of host-galaxy extinction is well fitted by an exponential function, P(AV ) = exp(-AV /τV), with τV = 0.334 ± 0.088 mag. We combine the SDSS-II measurements with new distance estimates for published SN data from the ESSENCE survey, the Supernova Legacy Survey (SNLS), the Hubble Space Telescope (HST), and a compilation of Nearby SN Ia measurements. A new feature in our analysis is the use of detailed Monte Carlo simulations of all surveys to account for selection biases, including those from spectroscopic targeting. Combining the SN Hubble diagram with measurements of baryon acoustic oscillations from the SDSS Luminous Red Galaxy sample and with cosmic microwave background temperature anisotropy measurements from the Wilkinson Microwave Anisotropy Probe, we estimate the cosmological parameters w and ΩM, assuming a spatially flat cosmological model (FwCDM) with constant dark energy equation of state parameter, w. We also consider constraints upon ΩM and ΩΛ for a cosmological constant model (ΛCDM) with w = -1 and non-zero spatial curvature. For the FwCDM model and the combined sample of 288 SNe Ia, we find w = -0.76 ± 0.07(stat) ± 0.11(syst), ΩM = 0.307 ± 0.019(stat) ± 0.023(syst) using MLCS2K2 and w = -0.96 ± 0.06(stat) ± 0.12(syst), ΩM = 0.265 ± 0.016(stat) ± 0.025(syst) using the SALT-II fitter. We trace the discrepancy between these results to a difference in the rest-frame UV model combined with a different luminosity correction from color variations; these differences mostly affect the distance estimates for the SNLS and HST SNe. We present detailed discussions of systematic errors for both light-curve methods and find that they both show data-model discrepancies in rest-frame U band. For the SALT-II approach, we also see strong evidence for redshift-dependence of the color-luminosity parameter (β). Restricting the analysis to the 136 SNe Ia in the Nearby+SDSS-II samples, we find much better agreement between the two analysis methods but with larger uncertainties: w = -0.92 ± 0.13(stat)+0.10 -0.33(syst) for MLCS2K2 and w = -0.92 ± 0.11(stat)+0.07 -0.15 (syst) for SALT-II.
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5.
  • Sako, Masao (författare)
  • The Data Release of the Sloan Digital Sky Survey-II Supernova Survey
  • 2018
  • Ingår i: Publications of the Astronomical Society of the Pacific. - 0004-6280 .- 1538-3873. ; 130:988
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper describes the data release of the Sloan Digital Sky Survey-II (SDSS-II) Supernova Survey conducted between 2005 and 2007. Light curves, spectra, classifications, and ancillary data are presented for 10,258 variable and transient sources discovered through repeat ugriz imaging of SDSS Stripe 82, a 300 deg(2) area along the celestial equator. This data release is comprised of all transient sources brighter than r similar or equal to 22.5 mag with no history of variability prior to 2004. Dedicated spectroscopic observations were performed on a subset of 889 transients, as well as spectra for thousands of transient host galaxies using the SDSS-III BOSS spectrographs. Photometric classifications are provided for the candidates with good multi-color light curves that were not observed spectroscopically, using host galaxy redshift information when available. From these observations, 4607 transients are either spectroscopically confirmed, or likely to be, supernovae, making this the largest sample of supernova candidates ever compiled. We present a new method for SN host-galaxy identification and derive host-galaxy properties including stellar masses, star formation rates, and the average stellar population ages from our SDSS multi-band photometry. We derive SALT2 distance moduli for a total of 1364 SN. Ia with spectroscopic redshifts as well as photometric redshifts for a further 624 purely photometric SN. Ia candidates. Using the spectroscopically confirmed subset of the three-year SDSS-II SN. Ia sample and assuming a flat.CDM cosmology, we determine Omega(M) = 0.315 +/- 0.093 (statistical error only) and detect a non-zero cosmological constant at 5.7 sigma.
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6.
  • Stirpe, G. M., et al. (författare)
  • Monitoring of active galactic nuclei. V. The Seyfert 1 galaxy Markarian 279
  • 1994
  • Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 285:3, s. 857-867867
  • Tidskriftsartikel (refereegranskat)abstract
    • For pt. IV see ibid., vol.284, no.1, p.33-43 (1994). Reports on the Lovers of Active Galaxies' (LAG) monitoring of the Seyfert 1 galaxy Markarian 279 from January to June 1990. The source, which was in a very bright state, gradually weakened after the first month of monitoring: the Halpha and Hbeta flux decreased by 20% and 35% respectively, and the continuum under Halpha by 30%. The luminosity-weighted radius of the broad line region (BLR), as derived from the cross-correlation function, is of the order of 10 light days. This result is very uncertain because the features in the light curves are very shallow, but it is unlikely that the radius of the BLR is more than 1 light month. The profile variations of Halpha confirm that the prevailing motions are not radial. The data of the present campaign and those obtained in previous years, when the source was in a much weaker state, show that the red asymmetry of the Balmer lines correlates positively with the broad line flux. This new effect is briefly discussed
  •  
7.
  • 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
  •  
8.
  • ERKENS, U, et al. (författare)
  • MONITORING OF ACTIVE GALACTIC NUCLEI .6. THE QUASAR MKN-876
  • 1995
  • Ingår i: ASTRONOMY AND ASTROPHYSICS. - : SPRINGER VERLAG. - 0004-6361. ; 296:1, s. 90-98
  • Tidskriftsartikel (övrigt vetenskapligt)abstract
    • We present the results of a 6 month monitoring campaign of Mkn 876, a low luminosity quasar with M(abs) approximate to -24. High resolution spectroscopy and direct imaging in the Johnson filters B, V, R, I was carried out in the first half of 1990. Line a
  •  
9.
  • Erkens, U., et al. (författare)
  • Monitoring of active galactic nuclei. VI. The quasar Mrk 876
  • 1995
  • Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 296:1, s. 90-9898
  • Tidskriftsartikel (refereegranskat)abstract
    • For pt. V see ibid., vol. 285, no. 3, p. 857-67 (1994). We present the results of a 6 month monitoring campaign of Mrk 876, a low luminosity quasar with M absap-24. High resolution spectroscopy and direct imaging in the Johnson filters B, V, R, I was carried out in the first half of 1990. Line and continuum light curves are presented. Mrk 876 showed a decrease of 17% in the continuum over the whole observing period whereas the line flux of Hbeta and Halpha stayed constant. This implies, that the radius of the broad line region is larger than 6 light months. Coadded spectra of Hbeta and Halpha are presented which confirm an extreme asymmetry of the line profiles to the red. With respect to much earlier spectra the line profiles changed considerably
  •  
10.
  • Jackson, N., et al. (författare)
  • Monitoring of active galactic nuclei. I. The quasars 1302-102 and 1217+023
  • 1992
  • Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 262:1, s. 17-2525
  • Tidskriftsartikel (refereegranskat)abstract
    • Presents the results of a five-month spectroscopic monitoring campaign of two radio-loud quasars PKS 1217+023 and PKS 1302-102. There is a pronounced lack of variability in 1302-102 apart from a possible small change in the continuum level near the end of the monitoring period, but 1217+023 underwent a 20% continuum decrease in the middle of the campaign. No line variability at all was observed. The co-added data represent two of the best spectra yet obtained of any radio-loud quasar other than 3C 273, and the shape of the Hbeta line and the presence underneath it of other contaminating lines are well determined. The Hbeta broad line in 1302-102 is redshifted by 3 Aring with respect to the narrow line region and there is evidence for a separate broad Hbeta feature on top of the main Hbeta emission in both quasars. This feature is stronger in 1217+023 than in 1302-102
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  • Resultat 1-10 av 14
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