TRACKING THE ANDROMEDA Z-SOURCE CANDIDATE RX J0042.6+4115

A Zsource candidate has been identified in the core of M31 using data fromexisting XMMNewton observations. Zsources are perhaps the most extreme form ofneutron star binary; powered by Roche lobe overflow from a low mass secondaryvia disc accretion, their Xray luminosities can reach 10^39 erg/s,and exhibitcomplex correlations between luminosity and Xray spectra so thatthey trace outZshapes in colourcolour diagrams over a few days. We propose a programme offour 20 ks observations over 4 days to trace the Ztrack, which willconclusively prove whether or not the candidate is a Zsource. Also, theprogramme would access for the first time variability over timescales of a fewdays in the 120 sources in the field of view. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]