科研之友
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摘要
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 x 10(36) erg s(-1) ( with 3 sigma upper limit <= 1 x 10(37) erg s(-1)) to similar to 2 x 10(40) 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 x 10(38) 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.
- 出版日期2009-4
- 单位西北大学
