I finished my Master's (or Cand.Scient) study in astronomy in June 2002 at the Institute of Theoretical Astrophysics in Oslo. The title of my thesis was New Aperture and PSF Photometry of QSO 0957+561A,B – Application to Time Delay and Microlensing.

Five years (1992–1997; ~2650 images) of optical observations of the gravitational lens system QSO 0957+561 were analyzed using a new photometry package developed by Jan Teuber and me (photometric data table: see below). My thesis supervisor was Prof. Rolf Stabell, and the CCD images were kindly provided by Prof. Rudy Schild.

The fully automated program was written in the IDL environment and incorporated all operations needed to produce the final light curves of the quasar images: source detection and localization, field star photometry, calibration, and finally, photometry of the quasar images. We also corrected for the light-contamination by the lens galaxy and for the crosstalk between the closely juxtaposed A and B quasar components (both effects are seeing dependent). Both aperture photometry and PSF-fitting photometry were performed.

From the brightness data, the time delay between the twin images was determined utilizing two different methods: a dispersion estimation technique and chi-square minimization. We inferred a time delay of 424.9 days, with an estimated 1-sigma error of about 1.2 days.

The effects of gravitational microlensing on the measured brightness of the two quasar images were briefly investigated. Microlensing-induced variations with a time scale of a year and amplitude of ~0.05 magnitudes were observed, and a few other tentative fluctuations in the microlensing curve had shorter time scales.

We also noted several conspicuous, simultaneous fluctuations in both quasar components, which can not be attributed to microlensing (or intrinsic quasar fluctuations or program errors for that matter). The exact cause of this "zero-lag correlation" is yet unknown.

My thesis can be downloaded using the links below (144 pages, several figures are in color).

• JEO_thesis.ps (PostScript format; 20 MB)
• JEO_thesis.pdf (PDF-format; 5.7 MB)

Some of the main topics and results from my thesis are presented in a refereed paper (with the same title as my thesis) in Astronomy & Astrophysics. For this and other work, see Scientific publications.

A table containing 422 entries of brightness data for each quasar image can be found HERE.

Feel free to email me if you have any questions regarding the thesis or the QSO 0957+561A,B brightness data.