Luminosity Functions and Point Source Properties from Multiple Chandra Observations of M81

TL;DR

This study analyzes multiple Chandra X-ray observations of galaxy M81 to compile a comprehensive point source catalog, examine their spectral and variability properties, and compare luminosity functions across different regions and with other galaxies.

Contribution

It provides the first extensive variability and spectral analysis of M81's X-ray sources across multiple observations, and compares its luminosity functions with those of M31 and the Milky Way.

Findings

Significant variability observed in many sources.

Snapshot observations reliably determine the X-ray luminosity function.

Luminosity functions of M81 regions are comparable to those of M31 and the Milky Way.

Abstract

We present an analysis of 15 Chandra observations of the nearby spiral galaxy M81 taken over the course of six weeks in May--July 2005. Each observation reaches a sensitivity of ~10^37 erg/s. 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 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 X-ray luminosity function of M81. We also fit the X-ray luminosity functions for multiple regions of M81 and, using common parametrizations, compare these luminosity functions to those of two other spiral galaxies, M31 and the Milky Way.