ABSTRACT

A Study of the Time Delay of the Twin Quasar Q0957+561

MAY 1996

KAREN BOURQUE WERNER, A.S., BAYPATH COLLEGE

B.A., MOUNT HOLYOKE COLLEGE

Directed by: Professor Tom R. Dennis

In 1979 astronomers discovered what appeared to be two identical quasars with an angular separation of six arc seconds in the constellation Ursa Major. Soon after their discovery, it was determined that the objects were in fact two images of a single quasar whose light was being distorted - as predicted by Einstein's general theory of relativity - by the gravitational field surrounding an intervening galaxy cluster.

Since its discovery, astronomers have observed that the brightening events of the two images (A and B) did not occur simultaneously; this is due to the differing path-lengths of the light which forms each image. Many attempts have been made to determine the time delay, both in the optical and radio bandpasses. Resolving the time delay is important because the value can be used to make an estimate of the Hubble constant and to aid in the study of the dark matter component of the intervening galaxy cluster. The most recent determination suggests a delay of 1.1 years (404 ±26 days), and that result is in need of confirmation.

If this result is correct, a well-defined brightening/dimming event in the A image should be evident in the B image 1.1 years later. CCD images of the twin quasar were taken with Mount Holyoke's 0.61 meter telescope most clear nights from October, 1995 to March, 1996. These images were compared with recently published datasets spanning the period October, 1994 to March, 1995 in an effort to find correlations between the light curves. This comparison revealed a large-scale intensity fluctuation in A that was indeed evident in B 409 ± 6 days later, a result which falls well within the predicted 404 ± 26 day period.

The method of correlating short-timescale events was then applied to previously published data, and it was found that the identifiable fluctuation events had time delays on the order of 416 days and 427 days. This discovery led to the following question: Is there only one value for the time delay, or does it vary?