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Session 20 - QSOs.
Oral session, Monday, January 13
Frontenac Ballroom,
The gravitational lens 0957+561 has been monitored with the VLA at 6 cm since 1979, and at 3.5 cm since 1990, in order to measure the time delay between the two images. Time delay analysis of the 6 cm light curves through 1994 (Haarsma et al., ApJ, 1997, in press) will be reviewed. Recently reduced 3.5 cm light curves show twice as much variability (in percentage of average flux) as the 6 cm light curves. In addition, the 3.5 cm variations precede those at 6 cm, thus the gaps in sampling have less of an impact on the time delay found. The 3.5 cm light curves will improve the accuracy of the time delay found for this lens, and joint analysis of the light curves at the two wavelengths will be presented. Recent observational and mass modeling studies of the 0957+561 system will be combined with this time delay to measure H_0, a technique that is independent of the assumptions that underlie other distance measurement methods. Finally, other scientific information in the light curves will be discussed, including interstellar scintillation, microlensing, and the size of the radio emission region of the quasar.
