We report the identification of a recurrent ultraluminous X-ray source ( ULX ) , a highly absorbed X-ray source ( possibly a background AGN ) , and a young supernova remnant near the center of the starburst galaxy M82 .
From a series of Chandra observations taken from 1999 to 2005 , we found that the transient ULX first appeared in 1999 October .
The source turned off in 2000 January , but later reappeared and has been active since then .
The X-ray luminosity of this source varies from below the detection level ( \sim 2.5 \times 10 ^ { 38 } \hbox { ergs } \thinspace \hbox { s } ^ { -1 } ) to its active state in between \sim 7 \times 10 ^ { 39 } ergs s ^ { -1 } and 1.3 \times 10 ^ { 40 } ergs s ^ { -1 } ( in the 0.5-10 keV energy band ) and shows unusual spectral changes .
The X-ray spectra of some Chandra observations are best fitted with an absorbed power-law model with photon index ranging from 1.3 to 1.7 .
These spectra are similar to those of Galactic black hole binary candidates seen in the low/hard state except that a very hard spectrum was seen in one of the observations .
By comparing with near infrared images taken with the Hubble Space Telescope , the ULX is found to be located within a young star cluster .
Radio imaging indicates that it is associated with a H ii region .
We suggest that the ULX is likely to be a > 100 M _ { \odot } intermediate-mass black hole in the low/hard state .
In addition to the transient ULX , we also found a highly absorbed hard X-ray source which is likely to be an AGN and an ultraluminous X-ray emitting young supernova remnant which may be related to a 100-year old gamma-ray burst event , within 2 arcsec of the transient ULX .