Deep Chandra Monitoring Observations of NGC 3379: Catalog of Source Properties

TL;DR

This study catalogs and analyzes 132 X-ray sources in NGC 3379 using deep Chandra observations, revealing their properties, variability, and potential classifications, including low-mass X-ray binaries, background AGN, and transient sources.

Contribution

It provides the first comprehensive catalog of X-ray sources in NGC 3379 with detailed spectral, variability, and optical associations, enhancing understanding of source populations in elliptical galaxies.

Findings

132 sources detected within the galaxy region

Identification of a ULX with Lx > 1E39 erg/s

64 sources show long-term variability

Abstract

We present the properties of the discrete X-ray sources detected in our monitoring program of the `typical' elliptical galaxy, NGC 3379, observed with Chandra ACIS-S in five separate pointings, resulting in a co-added exposure of 324-ks. From this deep observation, 132 sources have been detected within the region overlapped by all observations, 98 of which lie within the D25 ellipse of the galaxy. These 132 sources range in Lx from 6E35 erg/s (with 3sigma upper limit <4E36 erg/s) to ~2E39 erg/s, including one source with Lx>1E39 erg/s, which has been classified as a ULX. From optical data, 10 X-ray sources have been determined to be coincident with a globular cluster, these sources tend to have high X-ray luminosity, with three of these sources exhibiting Lx> 1E38 erg/s. From X-ray source photometry, it has been determined that the majority of the 132 sources that have well constrained colors, have values that are consistent with typical LMXB spectra. Additionally to this, a sub-population of 10 sources has been found to exhibit very hard spectra and it is expected that most of these sources are absorbed background AGN. There are 64 sources in this population that exhibit long-term variability, indicating that they are accreting compact objects. Five 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.