Chandra and HST Studies of the X-Ray Sources in Galactic Globular Cluster M92

Abstract

We present the analysis of two observations of M92 taken with the Chandra X-Ray Observatory. We combined the two data sets with a total exposure of ∼52 ks. With the combined observation, we detected 10 X-ray sources inside the half-mass radius (1. 02), five of which are inside the core radius (0. 26) of M92. The luminosities of the 10 sources are roughly within the range of 1030–1032 erg s−1 assuming cluster memberships. The background estimation suggests 7–8 cluster members and 2–3 background galaxies in M92. We identified the 10 sources by using Hubble Space Telescope Advanced Camera for Surveys observations of M92. Based on the X-ray and optical characteristics, we classified 4–5 possible candidates for cataclysmic variables within the half-mass radius. We discussed the possible formation mechanisms of the X-ray sources in M92 by comparing the predicted X-ray source number and observational results. Under the assumption that the number of X-ray sources scales with the encounter rate and the mass of the globular cluster, we expected eight X-ray sources formed from dynamical interactions and four from primordial binaries inside M92, which is consistent with the background estimation and comparable with the observational results. We therefore suggest that the X-ray sources in M92 may be contributed from both dynamical origin and primordial binaries.