  We have measured stellar photometry with the Hubble Space Telescope (HST)
Wide Field Camera 3 (WFC3) and Advanced Camera for Surveys (ACS) in near
ultraviolet (F275W, F336W), optical (F475W, F814W), and near infrared (F110W,
F160W) bands for 117 million resolved stars in M31. As part of the Panchromatic
Hubble Andromeda Treasury (PHAT) survey, we measured photometry with
simultaneous point spread function fitting across all bands and at all source
positions after precise astrometric image alignment (<5-10 milliarcsecond
accuracy). In the outer disk, the photometry reaches a completeness-limited
depth of F475W~28, while in the crowded, high surface brightness bulge, the
photometry reaches F475W~25. We find that simultaneous photometry and optimized
measurement parameters significantly increase the detection limit of the lowest
resolution filters (WFC3/IR) providing color-magnitude diagrams that are up to
2.5 magnitudes deeper when compared with color-magnitude diagrams from WFC3/IR
photometry alone. We present extensive analysis of the data quality including
comparisons of luminosity functions and repeat measurements, and we use
artificial star tests to quantify photometric completeness, uncertainties and
biases. We find that largest sources of systematic error in the photometry are
due to spatial variations in the point spread function models and charge
transfer efficiency corrections. This stellar catalog is the largest ever
produced for equidistant sources, and is publicly available for download by the
community.
