ИСТИНА

The most well-known application of gravitational lensing research is an estimation of the Hubble constant – the expansion rate of the Universe - through time delays. When light travels from distant source to an observer in GLS, it passes different paths for different images of the source. So, if the source is variable with some observable amplitude, the variability manifests itself in different images with some delays. Light travel time consists of geometrical time and potential time which is subject to Fermat theorem. We can switch to dimensionless times and distances and get that Hubble constant is inversely proportional to the time delay. Time delays are also important for estimating the mass distribution of the lensing galaxy. We analysed all publically available long-term optical observations data of PG1115+080 with our modification of cross-correlation method to estimate time delays. We conclude that Maidanak data are most homogeneous and quality data available for PG1115+080. But 2006 observational term should be excluded from the analysis because the lightcurves show almost linear trend with some fast variations seen only in the A1 and C components. This can be as due to microlensing or observational errors. These fast variations can decrease statistical significance of the time delay estimates or even produce misleading results. We obtained time delay values tBC=22+2-3, tAC=12+2-1 and tBA = 10+2-3. Time delays found are in agreement with previous results by Schechter et al (tBC=23.7 and tAC=9.4) and Barkana (tBC=25. and tAC=13.3) obtained for 1995-1996 lightcurves with two different methods based on chi-square minimization, but differ from results of Vakulik et al (tBC=16.4 and tAC=12). Hubble constant estimations based on graviational lens time delays are generally smaller than of other methods (Cepheids, CMB): HST Key Project provides 73.8±2.4 км/с/Мпк (Riess et al 2011), WMAP7 provides 71.0±2.5 км/с/Мпк . Our results "vote" for smaller value of Hubble constant than results of Vakulik et al (Tsvetkova 2010) for the same GL. Note that the estimations based on Sunyaev-Zeldovich effect and recent Plank results are also smaller: H_0=66±11 км/с/Мпк (Jones et al 2005) and H_0=67.3±1.2 км/с/Мпк (Planck Collaboration, arXiv:1303.5076). The ratio tAC/tBA of our intermediate delays is ~1.2 that is close to the value reported by Barkana (~1.13) and predicted by lens models (~1.4) unlike the Schechter et al. and Vakulik et al. values (~ 0.7 and ~2.7).