Diving into the Inner Disk of Black Holes with HST

I will present accretion-disk structure measurements for eight quasars selected from the Sloan Digital Sky Survey Reverberation Mapping project sample. Reverberation mapping measures disk size using time lag between variability in the inner/hotter and outer/cooler disk emission. We use Hubble Space Telescope ultraviolet coordinated with optical observations from the Liverpool Telescope and Las Cumbres Observatory g, r, i, z bands. Over our first cycle of HST UV monitoring, we used the proximity of the set of five targets in the sky to perform the observations in the “drift-and-shift” observing mode, dropping to gyro guiding after the first target to avoid guide-star acquisition time and fit 5 quasars per orbit. While this is a clever observation design, it results in higher background and lower SNR since the targets shift positions across the detector and may be smeared across several pixels in each subexposure. I will present our data reduction methods including identification of targets in images mottled with cosmic rays and determination of the correct aperture to use for photometry measurements of the irregularly shaped, smeared targets.