Session 18. Cluster Surveys/Galaxies
Oral, Tuesday, November 7, 2000, 1:00-2:30pm, Pago Pago Ballroom

## [18.06] Properties of the Chandra Sources in M81

D.A. Swartz (USRA/MSFC), A.F. Tennant (NASA/MSFC), K. Wu (Mullard Space Science Lab./Univ. College London), K.K. Ghosh (NRC/MSFC), J.J. Kolodziejczak (NASA/MSFC)

At a distance of 3.6 Mpc and an inclination of 59\circ, the nearby Sab galaxy M81 is well oriented for study of the spatial distribution of sources at high resolution (8.8 pc/ACIS-pixel). The Chandra X-ray Observatory obtained a 50-ks observation of the central region of M81 using the ACIS-S in imaging mode. We examine the global properties of the 98 x-ray sources detected in the inner ~8\arcmin \times 8\arcmin field of M81: their morphology and associations with known objects, their photometric and spectroscopic distributions, and their temporal evolution. It is found that roughly half of the sources are concentrated within the central bulge region while the remaining are distributed throughout the disk but not preferentially along the well-defined spiral arms. The majority of both bulge and disk sources exhibit hardness ratios consistent with power law spectra of index \Gamma ~1.5-1.8 as expected for a population of x-ray binaries though a group of much softer sources are present; indicative of thermal spectra such as from supernova remnants. There are also a few, weak, hard sources tenatively identified as either highly-absorbed x-ray binaries or background QSOs. The luminosity function follows a power law of index ~-1 at high luminosity but is flatter at low luminosity indicating incomplete sampling consistent with our 3\sigma detection threshold. No statistically-significant time variability was observed for these sources with one exception; a bright, soft source with a light curve declining at a 3±1 day half-life. Several interesting properties of this and other bright sources are also discussed.