We report the most accurate X-ray position of the X-ray source in the giant globular cluster G1 in M31 by using the Chandra X-ray Observatory , Hubble Space Telescope ( HST ) , and Canada-France-Hawaii Telescope ( CFHT ) .
G1 is clearly detected with Chandra and by cross-registering with HST and CFHT images , we derive a 1 \sigma error radius of 0 \aas@@fstack { \prime \prime } 15 , significantly smaller than the previous measurement by XMM-Newton .
We conclude that the X-ray emission of G1 is likely to come from within the core radius of the cluster .
We have considered a number of possibilities for the origin of the X-ray emission but can rule all but two scenarios out : it could be due to either accretion onto a central intermediate-mass black hole ( IMBH ) , or an ordinary low-mass X-ray binary ( LMXB ) .
Based on the X-ray luminosity and the Bondi accretion rate , an IMBH accreting from the cluster gas seems unlikely and we suggest that the X-rays are due to accretion from a companion .
Alternatively , the probability that a 1.5 M _ { \odot } cluster LMXB lies within the 95 per cent X-ray error circle is about 0.7 .
Therefore we can not rule out a single LMXB as the origin of the X-ray emission .
While we can not distinguish between different models with current observations , future high-resolution and high-sensitivity radio imaging observations will reveal whether there is an IMBH at the centre of G1 .