The Long-term Variability of the X-ray Sources in M82

TL;DR

This study analyzes the long-term X-ray variability of sources in M82, revealing a high fraction of variable X-ray binaries with significant flux changes over years, based on multiple Chandra observations.

Contribution

It provides the first comprehensive analysis of long-term X-ray variability in M82, identifying the nature and variability patterns of its X-ray source population.

Findings

47% of sources are long-term variables with flux ratio > 3

26 sources exhibit long-term flux variability

Strong variability indicates dominance of X-ray binaries

Abstract

We investigate the long-term variability exhibited by the X-ray point sources in the starburst galaxy M82. By combining 9 Chandra observations taken between 1999 and 2007, we detect 58 X-ray point sources within the D25 isophote of M82 down to a luminosity of ~ 10^37 ergs/s. Of these 58 sources, we identify 3 supernova remnant candidates and one supersoft source. Twenty-six sources in M82 exhibit long-term (i.e., days to years) flux variability and 3 show long-term spectral variability. Furthermore, we classify 26 sources as variables and 10 as persistent sources. Among the total 26 variables, 17 varied by a flux ratio of > 3 and 6 are transient candidates. By comparing with other nearby galaxies, M82 shows extremely strong long-term X-ray variability that 47% of the X-ray sources are variables with a flux ratio of > 3. The strong X-ray variability of M82 suggests that the population is dominated by X-ray binaries.