Luminosity functions and point-source properties from multiple Chandra observations of M81

Abstract

We present an analysis of 15 Chandra observations of the nearby spiral galaxy M81 taken over the course of six weeks in 2005 May-July. Each observation reaches a sensitivity of 1037 erg s-1. With these observations and one previous deeper Chandra observation, we compile a master source list of 265 point sources, extract and fit their spectra, and differentiate basic populations of sources through their colors. We also carry out variability analyses of individual point sources and of X-ray luminosity functions (XLFs) in multiple regions of M81 on timescales of days, months, and years. We find that, despite measuring significant variability in a considerable fraction of sources, snapshot observations provide a consistent determination of the XLF of M81. We also fit the XLFs for multiple regions of M81 and, using common parameterizations, compare these luminosity functions to those of two other spiral galaxies, M31 and the Milky Way. © 2011. The American Astronomical Society. All rights reserved..