TY - JOUR A1 - Puga, E. A1 - Alcalde, D. A1 - Barrena, R. A1 - Mediavilla, E. A1 - Motta, V. A1 - Munoz, J. A. A1 - Oscoz, Alejandro A1 - Serra-Ricart, M. A1 - Gil-Merino, Rodrigo A1 - Goicoechea, Luis Julian A1 - Lewis, G. f A1 - Libbrecht, C. A1 - Moreau, O. A1 - Surdej, J. A1 - Wambsganß, Joachim T1 - Daily monitoring of the gravitational lens QSO 2237+0305 at the Nordic Optical Telescope Y1 - 2001 SN - 0-7923-6974-2 ER - TY - JOUR A1 - Gil-Merino, Rodrigo A1 - Schindler, Sabine T1 - Galaxy and hot gas distributions in the z=0.52 galaxy cluster RBS380 from CHANDRA and NTT observations N2 - We present CHANDRA X-ray and NTT optical observations of the distant z=0.52 galaxy cluster RBS380 -- the most distant cluster of the ROSAT Bright Source (RBS) catalogue. We find diffuse, non-spherically symmetric X-ray emission with a X-ray luminosity of L_X(0.3-10 keV)=1.6 10^(44) erg/s, which is lower than expected from the RBS. The reason is a bright AGN in the centre of the cluster contributing considerably to the X-ray flux. This AGN could not be resolved with ROSAT. In optical wavelength we identify several galaxies belonging to the cluster. The galaxy density is at least 2 times higher than expected for such a X-ray faint cluster, which is another confirmation of the weak correlation between X-ray luminosity and optical richness. The example of the source confusion in this cluster shows how important high- resolution X-ray imaging is for cosmological research. Y1 - 2003 UR - http://xxx.uni-augsburg.de/pdf/astro-ph/0306499 ER - TY - JOUR A1 - Goicoechea, Luis Julian A1 - Gil-Merino, Rodrigo A1 - Serra-Ricart, M. A1 - Oscoz, Alejandro A1 - Alcalde, D. A1 - Mediavilla, E. T1 - IAC gravitational lenses monitoring program : difference signals from 2.5 years of QSO 0957+561 observations Y1 - 2001 SN - 0-7923-6974-2 ER - TY - JOUR A1 - Alcalde, D. A1 - Mediavilla, E. A1 - Moreau, O. A1 - De Rop, Y. A1 - Barrena, R. A1 - Gil-Merino, Rodrigo A1 - McLeod, B. A. A1 - Motta, V. A1 - Oscoz, Alejandro A1 - Serra-Ricart, M. T1 - QSO 2237+0305 VR light curves from Gravitational Lenses International Time Project optical monitoring N2 - We present VR observations of QSO 2237+0305 conducted by the Gravitational Lensing International Time Project collaboration from 1999 October 1 to 2000 February 3. The observations were made with the 2.56 m Nordic Optical Telescope at Roque de los Muchachos Observatory, La Palma (Spain). The point-spread function (PSF) fitting method and an adapted version of the ISIS subtraction method have been used to derive the VR light curves of the four components (A-D) of the quasar. The mean errors range in the intervals 0.01-0.04 mag (PSF fitting) and 0.01-0.02 mag (ISIS subtraction), with the faintest component (D) having the largest uncertainties. We address the relatively good agreement between the A and D light curves derived using different filters, photometric techniques, and telescopes. The new VR light curves of component A extend the time coverage of a high-magnification microlensing peak, which was discovered by the OGLE team. Y1 - 2002 ER - TY - JOUR A1 - Gil-Merino, Rodrigo A1 - Goicoechea, Luis Julian A1 - Serra-Ricart, M. A1 - Oscoz, Alejandro A1 - Alcalde, D. A1 - Mediavilla, E. T1 - Short time-scale fluctuations in the difference light curves of QSO 0957+561A,B: microlensing or noise? N2 - From optical R-band data of the double quasar QSO 0957+561A,B, we made two new difference light curves (with an overlap of about 330d between the time-shifted light curve for the A image and the magnitude-shifted light curve for the B image). We observed noisy behaviours around the zero line and no short time-scale events (with a duration of months), where the term `event' refers to a prominent feature that may be a result of microlensing or another source of variability. Only one event lasting two weeks and rising -33mmag was found. Measured constraints on the possible microlensing variability can be used to obtain information on the granularity of the dark matter in the main lensing galaxy and the size of the source. In addition, one can also test the ability of the observational noise to cause the rms averages and the local features of the difference signals. We focused on this last issue. The combined photometries were related to a process consisting of an intrinsic signal plus a Gaussian observational noise. The intrinsic signal has been assumed to be either a smooth function (polynomial), a smooth function plus a stationary noise process, or a correlated stationary process. Using these three pictures without microlensing, we derived some models totally consistent with the observations. We finally discussed the sensitivity of our telescope (at Teide Observatory) to several classes of microlensing variability. Y1 - 2001 ER - TY - JOUR A1 - Gil-Merino, Rodrigo A1 - Wisotzki, Lutz A1 - Wambsganß, Joachim T1 - The Double Quasar HE 1104-1805 : a case study for time delay determination with poorly sampled lightcurves N2 - We present a new determination of the time delay of the gravitational lens system HE 1104-1805 (``Double Hamburger'') based on a previously unpublished dataset. We argue that the previously published value of Delta tA-B=0.73 years was affected by a bias of the employed method. We determine a new value of Delta tA-B=0.85+/-0.05 years (2sigma confidence level), using six different techniques based on non interpolation methods in the time domain. The result demonstrates that even in the case of poorly sampled lightcurves, useful information can be obtained with regard to the time delay. The error estimates were calculated through Monte Carlo simulations. With two already existing models for the lens and using its recently determined redshift, we infer a range of values of the Hubble parameter: H0=48+/-4 km s-1 Mpc-1 (2sigma ) for a singular isothermal ellipsoid (SIE) and H0=62+/-4 km s-1 Mpc-1 (2sigma ) for a constant mass-to-light ratio plus shear model (M/L+gamma ). The possibly much larger errors due to systematic uncertainties in modeling the lens potential are not included in this error estimate. Y1 - 2002 ER - TY - JOUR A1 - Goicoechea, Luis Julian A1 - Alcalde, D. A1 - Mediavilla, E. A1 - Munoz, J. A. A1 - Gil-Merino, Rodrigo T1 - The nature and size of the optical continuum source in QSO 2237+0305 N2 - From the peak of a gravitational microlensing high-magnification event in the A component of QSO 2237+0305, which was accurately monitored by the Gravitational Lenses International Time Project collaboration, we derived new information on the nature and size of the optical V-band and R-band sources in the distant quasar. If the microlensing peak is caused by a microcaustic crossing, we first obtain that the standard accretion disk is a scenario more reliable/ feasible than other typical axially symmetric models. Moreover, the standard scenario fits both the V-band and R-band observations with reduced ?2 values very close to 1. Taking into account all these results, a standard accretion disk around a supermassive black hole is a good candidate for the optical continuum main source in QSO 2237+0305. Second, using the standard source model and a robust upper limit on the transverse galactic velocity, we infer that 90% of the V- band and R-band luminosities are emitted from a region with a radial size less than 1.2×10-2 pc (=3.7×1016 cm, at a 2 ? confidence level). Y1 - 2002 ER - TY - JOUR A1 - Goicoechea, Luis Julian A1 - Gil-Merino, Rodrigo A1 - Serra-Ricart, M. A1 - Mediavilla, E. A1 - Oscoz, Alejandro A1 - Alcalde, D. T1 - The nature of dark matter in elliptical (cD) galaxies : main lens galaxy of Q0957+561 Y1 - 2001 SN - 1-583-81074-9 ER -