ROSAT Observations of the X-ray Luminous Knots in M51
Session 31 -- Star-Forming Galaxies
Display presentation, Tuesday, 9:30-6:30, Heller Lounge Room

## [31.12] ROSAT Observations of the X-ray Luminous Knots in M51

A.P.Marston (Drake U.), K.Flanagan (SAO), D.Elmegreen (Vassar Coll.), B.Elmegreen (IBM), W.Forman, C.Jones (SAO)

We have used a 25000 second ROSAT PSPC observation of the M51 system to investigate its x-ray luminous knots. These observations provide information on the strength and distribution of emission in the 0.5 to 4.5 keV range. Photon tagging has also allowed us to produce x-ray spectra for these knots. Our observations indicate that 8 x-ray emitting knots with luminosities greater than $6\times 10^{38} ergs s^{-1}$ reside in the disk. These are significantly brighter than any galactic source. Comparison to optical images show that several of the sources coincide with HII regions. For the brighter sources, we show that they have surface brightness profiles indistinguishable from point sources majority and place upper limits on their size of 230pc. Should these be single accreting sources, we show that they would need to be black holes with masses ranging from 5 to 24 $M_\odot$. Estimates of the temperatures of such systems are consistent with bremsstrahlung fits to the x-ray spectra. These accreting black holes may be the remains of rapid stellar evolution of massive stars created in the burst of star formation induced by the interaction of M51 with NGC 5195. We also discuss other possibilities for the origin of the luminous x-ray sources, such as supernova remnants.\par Support for this project was provided by the JOVE program run by NASA and USRA.