The galaxy cluster Abell 4059 was observed with the Advanced CCD Imaging Spectrometer (ACIS) on 24-Sept-2000 (22.3ksec exposure) and on 4-Jan-2001 (18.4ksec exposure). The radio nucleus of PKS 2354-35 was placed 1arcmin from the nominal aim point of the back-illuminated S3 chip, placing the bulk of the emission on chip-S3. In this Letter, we only use data collected on this chip. The data was read out at the standard 3.2 sec frame rate, telemetered using faint mode, and filtered on ASCA event grades. The energy range was restricted to the 0.3-10 keV band and corrected for exposure and vignetting, spectral fitting was restricted to 0.3-8.0 keV.
Some of the Sept-2000 data were affected by a period of relatively high background, with up to 10 counts per second per chip for the back-illuminated chips. However, most of the cluster emission is well above this rate and we decided to use the entire data set for imaging. For the spectral analysis, we filtered the data on the counts from chip-S1 to fall within a factor of 1.2 of the quiescent background rate, which rejected 33% of the observing window. We then used the quiescent background files by Markevitch1 for background subtraction. The background subtracted total count rate on chip-S3 is 5.1 counts/second.