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X. Dai, G. Chartas, G. P. Garmire (Penn State U.), M. W. Bautz (Center for Space Research, MIT)
The gravitationally lensed quasars PG 1115+080 and APM 08279+5255 were observed with the Advanced CCD Imaging Spectrometer (ACIS) aboard the Chandra X-ray Observatory. PG 1115+080 was observed twice for 26.8 ks and 10 ks, respectively, and APM 08279+5255 was observed for 9.2 ks. Kolmogorov-Smirnov tests applied to the light-curves of the images indicate significant variability in selective energy bands in several of the lensed images. We find a strong correlation between the individual light-curves of images A1 and A2 of PG 1115+080 and derive a time-delay of 0.162+0.020-0.010 days with image A1 leading. This measurement demonstrates for the first time the feasibility of obtaining the time-delay of a gravitational lens system within a single X-ray observation. By combining the observed ``short-time'' delay between images A1 and A2 of PG 1115+080 with the previously observed ``long-time'' delay of ~ 24 days (Schechter et al. 1997) between images B and C we are able to narrow the allowable set of lens models for PG 1115+080 and thus place tighter limits on the Hubble constant.
We acknowledge financial support by NASA grant NAS 8-38252.
The author(s) of this abstract have provided an email address for comments about the abstract: xdai@astro.psu.edu