Deep Chandra Monitoring Observations of NGC 4278: Catalog of Source Properties

TL;DR

This study catalogs and analyzes 236 X-ray sources in NGC 4278 using deep Chandra observations, revealing diverse source properties, variability, and associations with globular clusters, advancing understanding of X-ray source populations in elliptical galaxies.

Contribution

First comprehensive catalog of X-ray sources in NGC 4278 with detailed spectral, variability, and globular cluster associations from deep Chandra data.

Findings

236 sources detected with luminosities up to 2E40 erg/s

39 sources coincide with globular clusters, many with high luminosity

103 sources show long-term variability, indicating accreting compact objects

Abstract

We present the properties of the discrete X-ray sources detected in our monitoring program of the globular cluster (GC) rich elliptical galaxy, NGC 4278, observed with Chandra ACIS-S in six separate pointings, resulting in a co-added exposure of 458-ks. From this deep observation, 236 sources have been detected within the region overlapped by all observations, 180 of which lie within the D25 ellipse of the galaxy. These 236 sources range in Lx from 3.5E36 erg/s (with 3sigma upper limit <1E37 erg/s) to ~2E40 erg/s, including the central nuclear source which has been classified as a LINER. From optical data, 39 X-ray sources have been determined to be coincident with a globular cluster, these sources tend to have high X-ray luminosity, with ten of these sources exhibiting Lx>1E38 erg/s. From X-ray source photometry, it has been determined that the majority of the 236 point sources that have well constrained colors, have values that are consistent with typical LMXB spectra, with 29 of these sources expected to be background objects from the logN-logS relation. There are 103 sources in this population that exhibit long-term variability, indicating that they are accreting compact objects. 3 of these sources have been identified as transient candidates, with a further 3 possible transients. Spectral variations have also been identified in the majority of the source population, where a diverse range of variability has been identified, indicating that there are many different source classes located within this galaxy.