共查询到20条相似文献，搜索用时 78 毫秒
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L. Christensen S.F. Snchez K. Jahnke T. Becker A. Kelz L. Wisotzki M.M. Roth 《Astronomische Nachrichten》2004,325(2):124-127
We report preliminary results from a targeted investigation on quasars containing damped Lyman‐α absorption (DLA) lines as well strong metal absorption lines, carried out with the Potsdam Multi Aperture Spectrophotometer (PMAS). We search for line‐emitting objects at the same redshift as the absorption lines and close to the line of sight of the QSOs. We have observed and detected the already confirmed absorbing galaxies in Q2233+131 (zabs = 3.15) and Q0151+045 (zabs=0.168), while failing to find spectral signatures for the z = 0.091 absorber in Q0738+313. From the Q2233+131 DLA galaxy, we have detected extended Lyα emission from an area of 3″ ×5″. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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E. Koptelova E. Shimanovskaya B. Artamonov A. Yagola 《Monthly notices of the Royal Astronomical Society》2007,381(4):1655-1662
The microlensing high-amplification events in the light curves of the gravitationally lensed quasar Q2237+0305 observed by the OGLE group and GLITP collaboration are analysed. The significant brightness amplification in the A and C components in 1999 observational season are considered under the assumption of the fold caustic crossing. Under this assumption we applied the model-independent method based on regularization technique for one-dimensional profile restoration of the quasar accretion disc brightness distribution. The recovered brightness distribution of the source seems to obey the standard model for the accretion disc. The estimated effective radius of the quasar emitting region is in agreement with the previous studies. 相似文献
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Olaf Wucknitz 《Monthly notices of the Royal Astronomical Society》2002,332(4):951-961
The time-delay in gravitational lenses can be used to derive the Hubble constant in a relatively simple way. The results of this method are less dependent on astrophysical assumptions than in many other methods. For systems with accurately measured positions and time-delays, the most important uncertainty is related to the mass model used. Simple parametric models like isothermal ellipsoidal mass distributions seem to provide consistent results with a reasonably small scatter when applied to several lens systems. We discuss a family of models with a separable radial power law and an arbitrary angular dependence for the potential ψ = r β F ( θ ) . Isothermal potentials are a special case of these models with β =1 . An additional external shear is used to take into account perturbations from other galaxies. Using a simple linear formalism for quadruple lenses, we can derive H 0 as a function of the observables and the shear. If the latter is fixed, the result depends on the assumed power-law exponent according to H 0 ∝(2- β )/ β . The effect of external shear is quantified by introducing a 'critical shear' γ c as a measure for the amount of shear that changes the result significantly. The analysis shows that in the general case H 0 and γ c do not depend on the position of the lens galaxy. Spherical lens models with images close to the Einstein radius with fitted external shear differ by a factor of β /2 from shearless models, leading to H 0 ∝2- β in this case. We discuss these results and compare them with numerical models for a number of real lens systems. 相似文献
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J. S. B. Wyithe R. L. Webster E. L. Turner 《Monthly notices of the Royal Astronomical Society》2000,318(3):762-768
Microlensing in Q2237+0305 between 1985 and 1995 has been interpreted in two different ways. First, the observed variations can be explained through microlensing by stellar mass objects of a continuum source with dimensions significantly smaller than the microlens Einstein Radius ( 0 ), but consistent with that expected for thermal accretion discs . However, other studies have shown that models having sources as large as 5 0 can reproduce the observed variation . In this paper we present evidence in favour of a small source. Our approach uses the distribution of microlensed light-curve derivatives to place statistical limits (as a function of source size) on the number of microlens Einstein radii crossed by the source during the monitoring period. In contrast with previous analyses, our results are therefore not dependent on an assumed time-scale. Limits on the source size are obtained from two separate light-curve features. First, recently published monitoring data show large variations (0.81.5 mag) between image brightnesses over a period of 700 d or 15 per cent of the monitoring period. Secondly, the 1988 peak in the image A light curve had a duration that is a small fraction (0.02) of the monitoring period. Such rapid microlensing rises and short microlensing peaks only occur for small sources. We find that the observed large, rapid variation limits the source size to be <0.2 0 (95 per cent confidence). The width of the light-curve peak provides a stronger constraint of <0.025 0 (99 per cent confidence). The Einstein radius (projected into the source plane) of the average microlens mass m in Q2237+0305 is The interpretation that stars are responsible for microlensing in Q2237+0305 therefore results in limits on the continuum source size that are consistent with current accretion disc theory. 相似文献
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A recently taken WHT optical spectrum of the BAL QSO Q1303+308 shows interesting changes in the spectral characteristics of the absorption systems. In particular, the equivalent widths of many of the broad absorption lines have markedly increased with respect to observations taken 15 yr earlier by Foltz et al., with the more blueshifted components showing the greatest increase by a factor of ≈5 in optical depth. Perhaps the most remarkable feature of the data is that, in the rest frame of the quasar, the line-of-sight outflow velocity of the clouds has only increased by ≈55 km s−1 in a rest-frame time interval of 5–6 yr. Various examples of doublet line locking are still visible in the system, and we present a provisional model analysis of the spectrum showing that theories based on small cloud velocity interactions via line locking can successfully explain the general appearance of the spectrum and its variability. Finally we highlight the need for further ongoing monitoring of this fascinating object. 相似文献
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Isobel M. Hook & Richard G. McMahon 《Monthly notices of the Royal Astronomical Society》1998,294(1):L7-L12
We report the discovery of two radio-loud quasars with redshifts greater than 4: GB1428+4217, with z =4.72, and GB1713+2148 with z =4.01. This doubles the number of published radio-selected quasars with z >4, bringing the total to 4. GB1428+4217 is the third most distant quasar known and the highest redshift radio and X-ray source currently known. It has a radio flux density at 5 GHz of 259±31 mJy and an optical magnitude of R ∼20.9. The rest frame absolute UV magnitude, Mv (1450 Å), is −26.7, similar to that of the archetypal radio-selected quasar 3C273 [ z =0.158; Mv (1450 Å)=−26.4]. GB1428+4217 is tentatively detected in ROSAT PSPC observations, which has been confirmed by more recent ROSAT observations described in a companion paper by Fabian et al. Both quasars were discovered during the CCD imaging phase of an investigation into the evolution of the space density of radio-loud quasars at high redshift. Combined with our earlier survey results, these objects give a lower limit on the space density of quasars with radio power P 5 GHz >5.8×1026 W Hz−1 sr−1 between z =4 and z =5 of 1.4±0.9×10−10 Mpc−3 . This can be compared to 2.9±0.2×10−10 Mpc−3 at z =2 from Dunlop & Peacock for flat-spectrum sources of the same luminosity. 相似文献
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J. S. B. Wyithe R. L. Webster E. L. Turner 《Monthly notices of the Royal Astronomical Society》1999,309(1):261-272
Determination of microlensing parameters in the gravitationally lensed quasar Q2237+0305 from the statistics of high-magnification events will require monitoring for more than 100 years (Wambsganss, Paczynski & Schneider). However, we show that the effective transverse velocity of the lensing galaxy can be determined on a more realistic time-scale through consideration of the distribution of light-curve derivatives. The 10 years of existing monitoring data for Q2237+0305 are analysed. These data display strong evidence for microlensing that is not associated with a high-magnification event. An upper limit of v t <500 km s−1 is obtained for the galactic transverse velocity, which is smaller than previously assumed values. The analysis suggests that the observed microlensing variation may be predominantly due to stellar proper motions. The statistical significance of the results obtained from our method will be increased by the addition of data points from current and future monitoring campaigns. However, reduced photometric errors will be more valuable than an increased sampling rate. 相似文献
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We present the results of microlens ray-tracing simulations showing the effect of absorbing material between a source quasar and a lensing galaxy in a gravitational lens system. We find that, in addition to brightness fluctuations due to microlensing, the strength of the absorption line relative to the continuum varies with time, with the properties of the variations depending on the structure of the absorbing material. We conclude that such variations will be measurable via ultraviolet spectroscopy of image A of the gravitationally lensed quasar Q2237+0305 if the Lyman α clouds between the quasar and the lensing galaxy possess structure on scales smaller than ∼0.1 pc. The time-scale for the variations is on the order of years to decades, although very short-term variability can occur. While the Lyman α lines may not be accessible at all wavelengths, this approach is applicable to any absorption system, including metal lines. 相似文献
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