We present a detailed X-ray and optical study of a distant fossil system RX J1416.4+2315 ( z \approx 0.137 ) , combining Chandra and XMM-Newton observations , optical photometry and spectroscopy .
X-ray emitting hot gas imaged by both the Chandra and XMM-Newton shows a globally relaxed spatial distribution , supporting the idea that fossil groups are old galaxy systems with no recent mergers .
However , the diffuse X-ray emission shows signs of asymmetries in the core of the system .
With a mean gas temperature of \sim 4.0 keV and total gravitational mass of 3.1 \times 10 ^ { 14 } M _ { \odot } , within the virial radius , this is better described as a fossil galaxy cluster rather than a fossil group .
The temperature profile shows no sign of a significant cooler core despite a cooling time dropping to 5 Gyr within the resolved core .
We find a mass concentration parameter c _ { 200 } \sim 11 which is relatively high for a cluster of this mass , indicative of an early formation epoch .

Using the spectroscopically identified cluster members we present the galaxy luminosity function for this fossil system .
We measure the velocity dispersion of the galaxies to be \sim 700 km s ^ { -1 } based on 18 confirmed members .
The dynamical mass is nearly twice the total gravitational mass derived from the X-ray analysis .
The measured R-band mass-to-light ratio , within the virial radius , is \sim 440 M _ { \odot } /L _ { \odot } which is not unusual for clusters of galaxies .
The central giant elliptical galaxy has discy isophotes and spectral features typical of elliptical galaxies .