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. My 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; from source detection, 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 quasar components. 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: dispersion estimation technique and chi-square minimization. We inferred a time delay of ~425 days, with an estimated 1-sigma formal error of about 1.2 days (which is probably too optimistic). The effects of gravitational microlensing on the measured brightness of the two quasar images were also 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

Grb 051022: Physical parameters and extinction of a prototype dark burst

GRB 051022 was undetected to deep limits in early optical observations, but precise astrometry from radio and X-rays showed that it most likely originated in a galaxy at z approximate to 0.8. We report radio, optical, near-infrared, and X-ray observations of GRB 051022. Using the available X-ray and radio data, we model the afterglow and calculate its energetics, finding it to be an order of magnitude lower than that of the prompt emission. The broadband modeling also allows us to precisely define various other physical parameters and the minimum required amount of extinction to explain the absence of an optical afterglow. Our observations suggest a high extinction, at least 2.3 mag in the infrared (J) and at least 5.4 mag in the optical (U) in the host-galaxy rest frame. Such high extinctions are unusual for GRBs and likely indicate a geometry where our line of sight to the burst passes through a dusty region in the host that is not directly colocated with the burst itself