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

Nicola Brassington, G. Fabbiano, D.-W. Kim, A. Zezas, S. Zepf, A. Kundu, L. Angelini, R. L. Davies, J. Gallagher, V. Kalogera, T. Fragos, A.R. King, S. Pellegrini, G. Trinchieri

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    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 D 25 ellipse of the galaxy. These 236 sources range in L X from 3.5 × 1036 erg s-1 (with 3σ upper limit <=1 × 1037 erg s-1) to ~2 × 1040 erg s-1, 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 GC, these sources tend to have high X-ray luminosity, with 10 of these sources exhibiting L X > 1 × 1038 erg s-1. 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 low-mass X-ray binary spectra, with 29 of these sources expected to be background objects from the log N-log S relation. There are 103 sources in this population that exhibit long-term variability, indicating that they are accreting compact objects. Three of these sources have been identified as transient candidates, with a further three 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.
    Original languageEnglish
    Pages (from-to)605-626
    Number of pages22
    JournalAstrophysical Journal, Supplement Series
    Volume181
    DOIs
    Publication statusPublished - 1 Apr 2009

    Keywords

    • galaxies: individual: NGC 4278, X-rays: binaries, X-rays: galaxies

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