X-ray binaries in M51 I: catalog and statistics

TL;DR

This study catalogs 334 X-ray binary candidates in M51 using Chandra and HST data, analyzing their properties, variability, and optical counterparts to enhance understanding of XRB populations in interacting galaxies.

Contribution

It provides the first comprehensive catalog and statistical analysis of X-ray binaries in M51, including their X-ray luminosity function and optical counterpart identification.

Findings

X-ray luminosity function follows a power law with slope 1.65.

Approximately 80% of sources show variability over 30 days.

Nearly half of the X-ray sources have optical counterparts within 0.5 arcseconds.

Abstract

We used archival data from the \emph{Chandra X-ray Observatory} (\emph{Chandra}) and the \emph{Hubble Space Telescope}, to identify 334 candidate X-ray binary (XRB) systems and their potential optical counterparts in the interacting galaxy pair NGC 5194/5195 (M51). We present the catalog and data analysis of X-ray and optical properties for those sources, from the deep $892$ ks \emph{Chandra} observations, along with the magnitudes of candidate optical sources as measured in the $8.16$ ks \emph{HST} observations. The X-ray luminosity function of the X-ray sources above a few times $10^{36}\, {\rm erg\,s^{-1}}$ follows a power law $N(>L_{X,b})\propto L_{X,b}^{1-\alpha}$ with $\alpha=1.65\pm0.03$. Aproximately 80\% of sources are variable over a 30 day window. Nearly half of the X-ray sources (173/334) have an optical counterparts within $0{\mbox{$.\!\!^{\prime\prime}$}}5$.