Classical novae (CNe) have been found to represent the major class of
supersoft X-ray sources (SSS) in our neighbour galaxy M 31. We determine
properties and evolution of the two first SSSs ever discovered in the M 31
globular cluster (GC) system. We have used XMM-Newton, Chandra and Swift
observations of the centre region of M 31 to discover both SSS and to determine
their X-ray light curves and spectra. We performed detailed analysis of
XMM-Newton EPIC PN spectra of the source in Bol 111 (SS1) using blackbody and
NLTE white dwarf (WD) atmosphere models. For the SSS in Bol 194 (SS2) we used
optical monitoring data to search for an optical counterpart. Both GC X-ray
sources were classified as SSS. We identify SS1 with the CN M31N 2007-06b
recently discovered in the M 31 GC Bol 111. For SS2 we did not find evidence
for a recent nova outburst and can only provide useful constraints on the time
of the outburst of a hypothetical nova. The only known CN in a M 31 GC can be
identified with the first SSS found in a M31 GC. We discuss the impact of our
observations on the nova rate for the M 31 GC system.Comment: 11 pages, 9 figures, 4 tables, submitted to A&A; v2: accepted versio