2004IAUC.8281....3S

L. Strolger and A. Riess, Space Telescope Science Institute, report the discovery of two apparent supernovae found in the observations of the Ultra Deep Field (UDF) and UDF Parallel fields on CCD images taken with the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope. SN 2004R, which was detected by subtracting groups of z-band (F850LP) ACS images of the same fields, is located at R.A. = 3h32m31s.30, Decl. = -27o46'13".6 (equinox 2000.0), which is 0".13 west and 0".10 south of the center of the apparent host galaxy. This new object was found in sixteen independent detection images taken during Jan. 2-11 and was not seen in images taken during 2003 Dec. 24-30 (limiting mag 28.5). The morphology of the transient is consistent with the ACS point- spread function (FWHM 0".1) and the lack of a detectable motion (< 0".05) relative to other sources over several hours of observation. Available z-band magnitude estimates: Jan. 10.44 UT, 27.2; 13.04, 26.5.