TY  - JOUR
A1  - Wambsganß, Joachim
A1  - Cen, Renyue
A1  - Xu, Guohong
A1  - Ostriker, Jeremiah P.
T1  - Effects of Weak Gravitational Lensing from Large-Scale Structure of the Determination of Q 0
N2  - Weak gravitational lensing by large-scale structure affects the determination of the cosmological deceleration parameter q0. We find that the lensing induced dispersions on truly standard candles are 0.04 and 0.02 mag at redshift z = 1 and z = 0.5, respectively, in a COBE-normalized cold dark matter universe with Omega 0 = 0.40, Lamda 0 = 0.6, H = 65 km s-1 Mpc-1, and sigma 8 = 0.79. It is shown that one would observe q0 = -0.395^{+0.125}_{-0.095} and q0 = - 0.398^{+0.048}_{-0.077} (the error bars are 2 sigma limits) with standard candles with zero intrinsic dispersion at redshift z = 1 and z = 0.5, respectively, compared to the truth of q0 = -0.400. A standard COBE normalized Omega 0 = 1 CDM model would produce three times as much variance and a mixed (hot and cold) dark matter model would lead to an intermediate result. One unique signature of this dispersion effect is its non-Gaussianity. Although the lensing induced dispersion at lower redshift is still significantly smaller than the currently best observed (total) dispersion of 0.12 mag in a sample of type Ia supernovae, selected with the multicolor light curve shape method, it becomes significant at higher redshift. We show that there is an optimal redshift, in the range z ~ 0.5--2.0 depending on the amplitude of the intrinsic dispersion of the standard candles, at which q0 can be most accurately determined.
Y1  - 1997
ER  - 
TY  - THES
A1  - Wambsganß, Joachim
T1  - Gravitational lensing as a universal astrophysical tool
Y1  - 1998
ER  - 
TY  - JOUR
A1  - Wambsganß, Joachim
T1  - Gravitational Lensing as a Universal Astrophysical Tool
Y1  - 1999
ER  - 
TY  - JOUR
A1  - Wambsganß, Joachim
A1  - Brunner, H.
A1  - Schindler, Sabine
A1  - Falco, E.
T1  - The gravitationally lensed quasar Q2237+0305 in X-rays: ROSAT/HRI detection of the "Einstein Cross"
N2  - We report the first detection of the gravitationally lensed quasar Q2237+0305 in X-rays. With a ROSAT/HRI exposure of 53 ksec taken in Nov./Dec. 1997, we found a count rate of 0.006 counts per second for the combined four images. This corresponds to an X-ray flux of 2.2*E(-13) erg/cm(2) /sec and an X-ray luminosity of 4.2*E(45) erg/sec (in the ROSAT energy window 0.1-2.4 keV). The ROSAT/HRI detector is not able to resolve spatially the four quasar images (maximum separation 1.8 arcsec). The analysis is based on about 330 source photons. The signal is consistent with no variability, but with low significance. This detection is promising in view of the upcoming X-ray missions with higher spatial/spectral resolution and/or collecting power (Chandra X-ray Observatory, XMM and ASTRO-E).
Y1  - 1999
ER  - 
TY  - JOUR
A1  - Wambsganß, Joachim
A1  - Schindler, Sabine
T1  - ROSAT observations of clusters CL0500-24 & CL0939+4713
Y1  - 1999
ER  - 
TY  - JOUR
A1  - Wambsganß, Joachim
T1  - Gravitational lensing : numerical simulations with a hierarchical tree code
Y1  - 1999
ER  - 
TY  - JOUR
A1  - Wambsganß, Joachim
T1  - Gravitationslinsen - universelle Werkzeuge der Astrophysik
Y1  - 2000
ER  - 
TY  - JOUR
A1  - Wambsganß, Joachim
A1  - Schmidt, Robert W.
A1  - Colley, W.
A1  - Kundic, T.
A1  - Turner, E. L.
T1  - Microlensing results from APO monitoring of the double quasar Q0957+561A,B between 1995 and 1998
N2  - If the halo of the lensing galaxy 0957+561 is made of massive compact objects (MACHOs), they must affect the lightcurves of the quasar images Q0957+561 A and B differently. We search for this microlensing effect in the double quasar by comparing monitoring data for the two images A and B - obtained with the 3.5m Apache Point Observatory from 1995 to 1998 - with intensive numerical simulations. This way we test whether the halo of the lensing galaxy can be made of MACHOs of various masses. We can exclude a halo entirely made out of MACHOs with masses between 10-6 Msun and 10-2 Msun for quasar sizes of less than 3x 1014 h60-1/2 cm, hereby extending previous limits upwards by one order of magnitude.
Y1  - 2000
ER  - 
TY  - JOUR
A1  - Wambsganß, Joachim
A1  - Hasinger, Günther
A1  - Giacconi, R.
A1  - Gunn, J. E.
A1  - Lehmann, Ingo
A1  - Schmidt, M.
A1  - Schneider, D. P.
A1  - Stanke, Thomas
A1  - Trümper, J.
A1  - Woods, D.
A1  - Zamorani, G.
T1  - A Distant X-ray Selected, Gravitationally-Lensing Galaxy Cluster
Y1  - 2000
ER  - 
TY  - JOUR
A1  - Wambsganß, Joachim
T1  - Nützliche Illusionen : Astrophysik mit Gravitationslinsen
Y1  - 2000
ER  -