This paper reports the results of the analysis of the second ROSAT PSPC survey of M31 performed in summer 1992 .
We compare our results with those of the first survey , already published in Supper et al .
( [ 1997 ] ) .
Within the \sim 10.7 \mbox { deg } ^ { 2 } field of view , 396 individual X-ray sources are detected in the second survey data , of which 164 are new detections .
When combined with the first survey , this result in a total of 560 X-ray sources in the field of M31 .
Their ( 0.1 keV – 2.0 keV ) fluxes range from 7 \times 10 ^ { -15 } \mbox { erg cm } ^ { -2 } \mbox { s } ^ { -1 } to 7.6 \times 10 ^ { -12 } \mbox { erg cm } ^ { -2 } \mbox { s } ^ { -1 } , and of these 560 sources , 55 are tentatively identified with foreground stars , 33 with globular clusters , 16 with supernova remnants , and 10 with radio sources and galaxies ( including M32 ) .
A comparison with the results of the Einstein M31 survey reveals 491 newly detected sources , 11 long term variable sources , and 7 possible transient sources .
Comparing the two ROSAT surveys , we come up with 34 long term variable sources and 8 transient candidates .
For the M31 sources , the observed luminosities range from 4 \times 10 ^ { 35 } \mbox { erg s } ^ { -1 } to 4 \times 10 ^ { 38 } \mbox { erg s } ^ { -1 } .
The total ( 0.1 keV – 2.0 keV ) luminosity of M31 is ( 3.4 \pm 0.3 ) \times 10 ^ { 39 } \mbox { erg s } ^ { -1 } , distributed approximately equally between the bulge and disk .
Within the bulge region , the luminosity of a possible diffuse component combined with faint sources below the detection threshold is ( 2.0 \pm 0.5 ) \times 10 ^ { 38 } \mbox { erg s } ^ { -1 } .
An explanation in terms of hot gaseous emission leads to a maximum total gas mass of ( 1.0 \pm 0.3 ) \times 10 ^ { 6 } \mbox { M } _ { \sun } .