A deep ( 98.2 ks ) Chandra Cycle-1 observation has revealed a wealth of discrete X-ray sources as well as diffuse emission in the nearby face-on spiral galaxy M101 .
From this rich dataset we have created a catalog of the 110 sources from the S3 chip detected with a significance of > 3 \sigma .
This detection threshold corresponds to a flux of \sim 10 ^ { -16 } ergs cm ^ { -2 } s ^ { -1 } and a luminosity of \sim 10 ^ { 36 } ergs s ^ { -1 } for a distance to M101 of 7.2 Mpc .
The sources display a distinct correlation with the spiral arms of M101 and include a variety of X-ray binaries , supersoft sources , supernova remnants , and other objects of which only \sim 27 are likely to be background sources .
There are only a few sources in the interarm regions , and most of these have X-ray colors consistent with that of background AGNs .
The derived \log N - \log S relation for the sources in M101 ( background subtracted ) has a slope of -0.80 \pm 0.05 over the range of 10 ^ { 36 } -10 ^ { 38 } ergs s ^ { -1 } .
The nucleus is resolved into 2 nearly identical X-ray sources , each with a 0.5 – 2.0 keV flux of 4 \times 10 ^ { 37 } ergs s ^ { -1 } .
One of these sources coincides with the optical nucleus , and the other coincides with a cluster of stars 110 pc to the south .
The field includes 54 optically identified SNR , of which 12 are detected by Chandra .
Two of the SNR sources are variable and hence must be compact objects .
In total , 8 of the X-ray sources show evidence for short term temporal variation during this observation .
Two of these variable sources are now brighter than the ROSAT detection threshold , but they were not detected in the previous ROSAT observations taken in 1992 and 1996 .
There are also 2 variable sources previously seen with ROSAT that apparently have faded below the Chandra detection threshold .
The brightest source in the field shows extreme long-term and short-term temporal variability .
At it ’ s peak brightness it has a super-Eddington luminosity > 10 ^ { 39 } ergs s ^ { -1 } .
There are 10 Supersoft sources ( SSS ) in the field which can be divided into 2 distinct subclasses : the brighter class ( 3 objects ) has a luminosity of \sim 10 ^ { 38 } ergs s ^ { -1 } and a blackbody temperature of \sim 70 eV whereas the other class ( 7 objects ) is an order of magnitude fainter and has a blackbody temperature of only \sim 50 eV .