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Abstract: We report the identification of a recurrent ultraluminous X-ray source ULX,a highly absorbed X-ray source possibly a background AGN, and a youngsupernova remnant near the center of the starburst galaxy M82. From a series ofChandra observations taken from 1999 to 2005, we found that the transient ULXfirst appeared in 1999 October. The source turned off in 2000 January, butlater reappeared and has been active since then. The X-ray luminosity of thissource varies from below the detection level ~2.5e38 erg-s to its activestate in between ~7e39 erg-s and 1.3e40 erg-s in the 0.5-10 keV energy bandand shows unusual spectral changes. The X-ray spectra of some Chandraobservations are best fitted with an absorbed power-law model with photon indexranging from 1.3 to 1.7. These spectra are similar to those of Galactic blackhole binary candidates seen in the low-hard state except that a very hardspectrum was seen in one of the observations. By comparing with near infraredimages taken with the Hubble Space Telescope, the ULX is found to be locatedwithin a young star cluster. Radio imaging indicates that it is associated witha H II region. We suggest that the ULX is likely to be a > 100 solar massintermediate-mass black hole in the low-hard state. In addition to thetransient ULX, we also found a highly absorbed hard X-ray source which islikely to be an AGN and an ultraluminous X-ray emitting young supernova remnantwhich may be related to a 100-year old gamma-ray burst event, within 2 arcsecof the transient ULX.

Autor: A.K.H. Kong MIT, Y.J. Yang, P.-Y. Hsieh ASIAA, Taiwan, D.S.Y. Mak, C.S.J. Pun University of Hong Kong



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